ERC Advanced Grant 2013 Research proposal [Part B2)] Luminous Supernovae. LBVs

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1 1. State of the art ERC Advanced Grant 2013 Research proposal [Part B2)] The sky is intrinsically variable. Variable and transient objects encompass all astronomical distances ranging from comets and asteroids, exo-planets, stars (normal and compact), novae, supernovae, blazars, tidal disruption events and gamma-ray bursts (GRBs). Now the first surveys start probing the transient sky especially at optical (Palomar Transient Factory PTF, PanSTARRS, and in the future Large Synoptic Survey Telescope LSST). Radio surveys are starting nowadays (Low Frequency ARray LOFAR, and later on Square Kilometer Array SKA). The discovery space in this field is immense (Figure 1). M R (mag) Fallback Supernovae Macro Novae Long GRB Orphan Afterglows.Ia Short GRB Orphan Afterglows Classical Novae CCSNe SNe Ia Luminous Red Novae Decay Time (days) Luminous Supernovae Tidal Disruption Flares LBVs Figure 1: Left: R band magnitude as a function of characteristic decay/variability timescale for luminous optical transients and variables (from Rau et al. 2009). Right: A compilation of high-energy transients that are known (solid) and/or predicted (hatched) in the local (d<200 Mpc) Universe (from Soderberg et al. 2009). The entire parameter space will be accessible to the EVENT survey, except transients with a very short variability timescale less than ~30 s (greyed out region). These large area chronoptic surveys (from the Greek words chronos personification of time and opsis view ) are however almost uniquely United States based, with proprietary data. In addition, these surveys are carried out with single telescopes, monitoring the sky in just one optical band (typically red) thus loosing the possibility of directly characterize the variable sources. In addition, many of these surveys (cf. PTF) do not have the possibility to follow-up the discovered transients and must rely (if any) on external facilities. More importantly, soon we shall see the advent of High Energy Neutrino (HEN) detectors able to localise events only to degree-scale accuracy and new TeV Čerenkov telescopes much larger area able to detected thousand of TeV emitter at arcmin resolution. Likewise, Advanced-VIRGO and Advanced-LIGO are expected to localise degenerate object merger events through gravitational waves (GW) with, typically, one to ten degree scale uncertainties. Much of the science extracted from these new windows on the Universe will require the identification of electromagnetic counterparts, which would yield the redshift of the object. For these transients one would need a rapid, large-area follow-up that is not guaranteed by existing facilities. 2. Scientific objectives and requirements These above represent great opportunities for discoveries, which can be grasped with the timely realisation of an unprecedented European experiment: a versatile instrument able to carry out surveys in multiple optical bands, in order to directly obtain a broad-band spectral energy distribution for new transient/variable sources, and to follow-up discovered transients or to quickly respond to external transients. To cope with these needs we designed our experiment: the European VErsatile Northern Telescope EVENT. EVENT will consist of three robotic telescopes. Each telescope will cover 1 deg 2 and will be equipped with a set of dichroics and filters in order to cover 6 bands (g, r, i, z, J and H) simultaneously. Two telescopes will have a primary mirror of 1 m, called Niña and Pinta telescopes (NT and PT). The large field of view will be 1

2 covered in the optical by single 4096x4096 pixels CCDs in order to achieve a pixel scale of ~0.9 arcsec/pixel. We will limit the coverage in J and H bands to the central part. One of the telescopes is larger with a 1.2 m diameter and it will be equipped also with a low-resolution spectrometer. This telescope will be named Santa Maria (SMT) and it will guarantee us the follow-up of the brightest transients. A 1.5 m telescope will be purchased if lower quotations than the present ones will be found. EVENT will operate in four different observing modes: - triggered mode: EVENT will respond to external triggers automatically (without human intervention), observing with a pre-planned strategy (e.g. the large error boxes of gravitational wave alerts will be covered with raster scan observations; GRBs will be observed in photometric mode and if a bright transient is discovered in real-time, EVENT-SMT will switch to spectroscopic mode, etc.); - survey mode: during which the three telescopes will survey pre-defined contiguous (but different) regions of the sky; - photometric mode: during which the telescopes will observe single objects obtaining six contemporaneous light curves; - spectroscopic mode: during which the largest telescope will take spectra of the target and the other two telescopes will take photometric data of the same target. 2.1 EVENT triggered mode This mode provides the fastest response to external triggers (<1 min). We envisage responding to triggers of different kinds. Gravitational Wave sources. The detection of Gravitational Waves (GWs) would be a momentous discovery in science. It is most likely to be a very faint signal with low statistical significance. Therefore, finding an electromagnetic counterpart would massively increase the confidence in the GW detection. EVENT will be in the best position to do this. In the next few years the A-LIGO and A-VIRGO experiments will be able to provide GW (best) triggers with uncertainties of several degrees (also in different regions of the sky). EVENT will be able to cover quickly these regions, searching for an electromagnetic counterpart. The LIGO Scientific Collaboration and the Virgo Collaboration have expressed their strong interest in distributing GW events and quasi-real time alerts to our experiment. EVENT would be particularly useful in this respect since it can simultaneously scan the spatially disconnected error boxes provided by GW experiments. Up to 50 triggers yr -1 are expected. Neutrino sources. Core-Collapse SNe are known to produce a burst of HENs well in advance of the appearance of an optical supernova. In the next few years triggers from enhanced neutrino experiments will become available (e.g. ANTARES, IceCube). This will provide positions with uncertainties of a few degrees. A scanning machine allowing for a wide field of view to be covered in a short time like EVENT will be quite unique in searching for an electromagnetic counterpart in the several contemporaneous bands. The ANTARES collaboration has expressed strong interest in our experiment and will distribute to us their alerts. Gamma-ray bursts. Swift is the main provider of well localized GRBs. Rapid follow up will be guaranteed for any Swift trigger (including Soft Gamma-ray repeaters). This will give us the possibility to exploit observation from UV (made by UVOT on-board Swift) to the near IR band. In case of a bright afterglow (r~16) the SMT telescope will provide spectroscopic observations soon after the repointing, allowing for an early GRB redshift determination. Swift is not the only GRB detector. The Gamma-ray Burst Monitor (GBM) on board the Fermi satellite is providing real-time alerts for GRBs. These GRBs are however characterized by a large error box (several degrees). The size of the error boxes is dominated by systematic effects. We plan to reply to these alerts scanning the error box with the three telescopes. Comparison with SDSS survey data or DSS data will reveal any bright afterglow in real time. We expect to find an optical/nir afterglow for a large number (>60%) of the observable GBM GRBs. In all cases the possibility of having GRB afterglow observations in six bands will provide us with a reliable photometric redshift for those GRBs with a redshift z>3 (via the Lyman limit detection). It is interesting to recall that one of the farthest GRBs ever observed, GRB at z=6.3, was detected within 1 min from its discovery by a 25 cm telescope. GW and HEN triggers are of paramount importance and call for an immediate follow-up all over the world. Facilities exist in the US but none is foreseen in the European time zone. EVENT will cover this gap. 2.2 EVENT survey mode A figure of merit for surveys EVENT will be in survey mode for at least 50% of the observing time. Our goal is to have a survey, 2

3 competitive with existing surveys (but with multi-band capabilities), leaving the other observing time for external triggers, follow up of discovered transients or monitoring of interesting sources. It has become customary to compare surveys using the so-called etendue, a product of the telescope collecting area, A, and the instrument field of view, Ω, as a figure of merit (FoM). However, the etendue simply characterises the instrument and says nothing about how the survey is carried out, e.g., the depth, coverage rate, cadence, etc. Djorgovski proposed as an indicator of a survey s discovery potential, a product of its spatio-temporal coverage rate, C, and the estimate of the depth, D, which may be reasonably expressed as proportional to the S/N ratio of the individual exposures. The coverage rate C can be expressed as C=R N p f eff where R is the area coverage in deg 2 /night (not counting repeated exposures), N p is the number of passes per field in a given night, f eff is the fraction of the effective observing time averaged over the year (including the weather losses, engineering time). The depth D can be expressed as D=[A t exp ε] 1/2 /FWHM ( S/N), where A is the effective collecting area of the telescope, t exp is the average exposure time, ε is the overall efficiency (throughput) of the instrument, and FWHM is the typical image resolution. The product C D=DRE represents a Figure of Merit (FoM) for a Discovery Rate of Events (DRE), and net discovery potential of a given survey. Therefore, the DRE is a more relevant measure (than the etendue) to characterise planned and future surveys. Table 1: ongoing and planned surveys Figure of Merit parameters (from Djorgovski et al. 2012). The two lines for EVENT (3 telescopes) refer for half or full use of the three telescopes in survey mode. LSST is still to be built (foreseen for 2020). Survey R (deg 2 /n) N p f eff Area (m 2 ) In Table 1 we report the parameters for on-going and planned surveys; the two rows for EVENT correspond to lower and upper bound (50% or 100%) of the total observing time dedicated to the survey. These numbers allow us to put into a wider context the capabilities of our survey. Based on the respectively DRE, we see that the EVENT survey is highly competitive with current large area surveys, like Skymapper1 and PTF. The peculiarity of the EVENT survey is that it will be carried out contemporaneously in four multiple optical bands (plus two nir for the central part of the field of view, 8 arcmin square), allowing for an unprecedented source characterization, as well as a better control on spurious events. This is unique to our survey Survey strategy The survey will consist of 60 s exposures in all the bands. With this exposure we will reach a limiting magnitude g~20.5 with a signal to noise ratio S/N~13. This exposure time is a good compromise between the survey depth (going deeper will just provide fainter transients that are more difficult to follow-up and identify) and sky coverage. In the other bands (r, i, z) we reach the same magnitude with a S/N~9, 6 and 3, respectively, allowing for strong detections. In the nir we reach at S/N=10 a limiting magnitude of J~19 and H~18 in 60 s 2. A detection with S/N=5 is reached for g~21.3, r~21.3, i~20.8, z~20, J~19.6 and H~19.2. Clearly different science topics require different kind of surveys. The basic survey will consist of two exposures per night with the field covered with logarithmically increasing delays each month (observations on day 1,2,3,5,7,10,13,16,19,23,27,31,32,33, ). The field will be covered across its visibility window, up to 6 months. This will guarantee a sufficiently deep sampling for a number of scientific themes. Bright moon will disturb observations, so we will concentrate during these times on intensive monitoring programs, particularly useful for planetary transits and star variability below 1 d. These programs will t exp (s) ε FWHM (arcsec) C D DRE CRST PTF Skymapper PanSTARR EVENT EVENT LSST The telescopes area was obtained by multiplying the mirror area by the sum of the CCD quantum efficiencies in the 2 These magnitudes were estimated using the Advanced Exposure Time Calculator suited to our specifications at 3

4 consist of monitoring the same field 10 times per night for a few days in a row. Open clusters will be one of the targets of these investigations, representing a coeval population of stars. The Andromeda galaxy (M31) will also be the target of a high cadence survey to reveal fast galactic phenomena (cataclysmic variables, novae, variable stars, planetary disruptions, etc). On the longer side we will monitor the Virgo cluster on a 5 d basis in order to complete a census of SNe in the ~1,300 galaxies. In addition, this will give HEN and GW experiments an approximate time for searching relevant events. Extensive discussions will be carried out within the EVENT survey network (see below) to find out the best survey strategy and to propose innovative survey programs EVENT survey: science themes One important part of the EVENT experiment is to provide a chronoptic large area survey of the sky in at least 4 optical filters contemporaneously. The emphasis of the survey is in the detection of transient events of any kind, light curve monitoring (and low amplitude variability) of sources and, at the end of the experiment, a deep four bands survey, summing up all the exposures. Figure 1 shows a variability timescale diagram (0.1 s 50 d) for several classes of sources. In addition this figure just highlights single astrophysical events (flare stars, SNe, etc.) and does not include the variability of existing sources with different timescales (blazars, persistent high energy sources, etc.). This indicates that the discovery space of the EVENT survey is decidedly large. EVENT will cover an impressive number of science themes. In the following we briefly outline a few of them. In Table 2 we report a summary of the predicted EVENT rate detection for a few class of sources. EVENT will result in a survey across the Universe: Near-Earth objects. Near-Earth Objects (NEOs) are a subgroup of asteroids and comets whose orbits enter the Earth s neighbourhood. NEOs are very interesting both because they sample the left over material from the Solar System formation and they represent a potential risk of impact. New NEOs, as well as asteroids, will be easily detected in the high cadence survey (> 10 observations per night), allowing us to construct their light curves, measure their rotation periods, having clues of the shape and, thanks to colours, leading to a taxonomic classification. Table 2: Summary of event rates for a few classes of sources in the EVENT survey (*Neutrino and gravitational wave sources have not been observed yet: we prefer not to give a rate). Discovery of transient events Rate (yr -1 ) PI (Institute ) New Asteroids & NEOs ~50 F. Bernardi (Spacedys I) G. Hahn (DRL D) Tidal Disruption Events super- Eddington (sub-eddington) ~300 (3) S. Campana (Oss. Brera I) E. M. Rossi (Leiden Univ. NL) Type Ia Supernovae ~500 F. Mannucci (Oss. Arcetri I) P. Astier (CNRS/IN2P3 F) Core-collapse Supernovae ~200 M. Della Valle (Oss. Napoli I) S. Taubenberger (MPA Garching D) GRBs (and orphans GRBs) >1 S. Covino (Oss. Brera I) A. Gomboc (Ljubljana Univ. SI) Variability in light curves Rate (yr -1 ) PI (Institute ) Stellar flares >40 I. Pagano (Oss. Catania I) J. Schmitt (Hamburger Sternwarte D) Cataclysmic Variables ~100 S. Shore (Pisa Univ. I) J. Osborne (Leicester Univ. UK) Variable stars and population ~20,000 E. Poretti (Oss. Brera I) synthesis J.-F. Le Borgne (IRAP Toulouse F) Blazars flares and AGN variability ~100 G. Tagliaferri (Oss. Brera I) A. Sillanpää (Turku Univ. SF) Planetary transits. White dwarfs (WDs) are small, dense cores that remain after a star has gone through its red giant phase. WDs make an attractive target for transit hunters because they are so small. Even an Earthsize planet would eclipse it deeply or totally, causing its brightness to drop periodically by up to 100% (~50% for terrestrial planets). WDs are quite common in the Galaxy and more than 10,000 will be monitored on timescales from fractions of a day to ~30 d to search for variability. The same principle will be applied to 4

5 dim dwarf M stars were planets are found in increasing number. Stellar flares. Stellar flares are unpredictable phenomena due to the sudden transformation of energy stored in the magnetic field into thermal and kinetic energy. Flares are observed on all the stars that show coronal type emission, brown dwarfs, active binaries and T Tauri stars. Energy of stellar flares ranges from the erg s -1 for nanoflares to even erg s -1 for very large flares in RS CVn-type binaries. Microflares potentially account for the coronal heating. EVENT can play an important role in assessing statistics of microflares. At the other extreme, superflares occur on normal main-sequence stars in spectral classes F8- G8 with energy ranges from to erg s -1. The Kepler satellite assessed that only 0.2% of Sun-like stars experience monster flares. We recall that a superflare on our Sun would strip away the Earth s ozone layer, leading to increased radiation at ground level. Widespread extinctions could result. On the other hand, superflares might actually be life-enabling by providing sufficient energy in the atmospheres of other worlds to initiate the chemistry necessary for biology to get going. EVENT can simultaneously probe the rotational modulation variability due to chromospheric and transition region active regions, hence allowing the measurement of stellar rotation, and the superflare occurrence. We expect to detect ~40 events per year. In such a way, conclusive statistics on the possibility of superflare occurrence in truly solar-type stars can be derived. More in general, the characterization of flares made by EVENT (e.g., energetics, time scales, relation with other stellar parameters) is mandatory to assess the habitability of planets. Variable stars. Stellar variability encompasses both intrinsically variable stars (notably those exhibiting pulsations) and extrinsically variable stars (including both eclipsing binaries and single or double stars displaying rotational modulation of their light due to star spots or ellipsoidal shapes). There are now several wide-area photometric surveys in the optical part of the spectrum, such as SuperWASP, OGLE and ASAS, which return single-color visible light curves of hundreds of thousands of variable stars. However, a single color photometric light curve is often of limited use in modeling systems, because many of the parameters are degenerate without spectral information. All the types of variable stars, displaying periods from hours to months, will benefit from the multi-band photometric survey provided by EVENT. The modeling of their light curves will disclose the possibility to determine stellar parameters in a number of eclipsing, pulsating, and rotational variables without the extensive use of spectroscopic monitoring. The wide field survey will allow us to start their systematic use as stellar population tracers by means of period-luminosity relations and spectral indices. Microlensing. Microlensing events occur when a stellar mass object passes in front of a foreground star, amplifying through gravitational focusing, its luminosity. The duration and light curve of the event depends on the mass of the lensing object and on the impact parameter of the encounter. Particularly interesting is the possibility of detecting planets around the lensing star (short duration events) or isolated compact objects (neutron stars or black holes characterised by long duration timescales) or even lone planets (short events). Based on simulations of the event rate in large area surveys, we can expect ~5 events yr -1 (with magnifications A>1.34) for a limiting magnitude of g~20. Multi-band observations will clearly pinpoint them as achromatic variables. Cataclysmic variables. Cataclysmic variables (CVs) are binary systems comprising a WD and a low mass donor. Particularly interesting are dwarf novae (DNe) showing periodic and frequent outbursts with amplitudes of 3 8 mag and durations of 3 20 d. These systems are important to shed light on accretion disk theory, including quiescence. Given their space density we could expect to detect a ~300 DN outbursts during the entire survey. An important class of CVs is composed of two WDs (AM CVn systems). These systems are rare but very important being the dominant population of GW sources detectable with the New Gravitational Observatory (NGO). A few new systems can be discovered during the EVENT survey. Classical Novae. In CVs if the accreted matter experiences a thermonuclear runaway we have a nova star. These novae reach bright peak luminosities and can be easily observed in nearby galaxies. We can expect to detect a hundred per year, mainly in nearby, large galaxies. Nova studies will be important for binary systems evolution theory and to secure the true nova rate. X ray binaries. Multi-band photometry of X ray binaries can, as in the case of CVs, shed light on disk emission. This is particularly important for transient sources where, during quiescence, the presence and the state of the accretion disk is uncertain. Type Ia SuperNovae. Observations of Type Ia SNe provided the best evidence to date that the Universe is accelerating powered by dark energy. To discriminate among different models of dark energy and to unravel subtle and systematic effects connected to dust reddening multi-band observations are mandatory. Recently, unusually sub-luminous and blue SN Ia has been discovered (e.g. PTF 09dav), opening an unexplored territory. In the EVENT survey we expect to detect more than a thousand Type Ia SNe during the entire 5

6 survey and follow a fraction of them. We expect to detect ~500/yr SN Ia and ~10/yr in also the nir. Core-collapse SuperNovae. Core-collapse SNe represent the final stages of massive star evolution. These are important for neutron star and black hole formation, as well as tracing star formation and producing dust and heavy elements. CCSNe are very luminous and we expect to detect more than a thousand during the entire survey and follow a fraction of them. Being a galaxy-impartial survey EVENT will be able to detect CCSNe without biases. A correlation with nearby (z<0.1) galaxies will provide constraints on the theory of massive star formation and explosion, in different environments, both of high and low metallicity as well as a correlation of SNe occurrence with the brightest parts of their galaxies. For a few CCSNe we will also be able to detect shock breakouts. Shock breakouts last ~ hr, based on the progenitor s star radius. If an envelope around the progenitor exists, times are much longer up to 5 hrs. The use of SN breakout can provide a precise and unique time-stamp for the gravitational collapse of the star (accurate to within minutes), enabling searches for coincident GW and HEN experiments. We would expect to detect 3-10 /yr. Gamma Ray Bursts and orphan GRB afterglows. Gamma ray bursts (GRBs) represent the most violent events in the Universe after the Big Bang. The long duration GRBs (duration >2 s) are associated with the death of massive stars. The probability of directly observing a GRB during the prompt phase is slim, but we expect to serendipitously detect GRB afterglows at a rate of a tens yr -1, limited to about z<1.5. Orphan afterglows (i.e. those generate by GRBs not pointing towards us) will largely increase this budget. The detection rate will also provide information on the collimation angle of GRB beams as well as jet structure. The detection of just one orphan GRB will be of paramount importance enable us to constrain the jet structure. Short GRBs (duration <2 s) will probably not be detected by the EVENT survey due to the faintness of their afterglows. UltraLuminous X ray Sources. UltraLuminous X ray (ULX) sources are one of the main high-energy emitters of local galaxies. ULXs are probably an ensemble of different class of sources. Main constituents are however expected to be massive (~ M ) black holes. These objects shine in X rays through the emission from an accretion disk with copious emission (peak) in the UV band. Variability studies of ULXs in external galaxies can reveal similarities with X ray binaries in our Galaxy and multi-band photometry can assess disk properties. Planetary tidal disruption on stars in nearby galaxies. In recent years it became apparent that a large number of heavy planets (hot Jupiters) are very close to their star (<0.5 AU). This would result in a large number of mergers due to tidal dissipation (0.1 1 yr -1 galaxy -1 ). Optical/UV transients can arise from direct-impact merger or tidal-disruption events. The most promising search strategy is with combined surveys of nearby massive galaxies (e.g. M31) at optical and X ray wavelengths with cadences from days to months. Tidal disruption events. Once a star in a galaxy will pass within the tidal disruption radius of the central black hole (BH) it will be torn apart by tidal forces. Nearly half of the debris is ejected from the system, while the remaining half remains bound to the BH and accreted. The fall-back of debris onto the BH produces a luminous electromagnetic flare that is expected to exhibit typical peak energies in the UV/X-rays and to radiate close to the Eddington luminosity. Super-Eddington events can also be expected depending on the dynamics of the encounter. The detection of a tidal disruption event (TDE) is unambiguous evidence for the presence of a central BH, and enables the detection of any kind of SMBHs, even those not accreting. TDEs also provide a unique cosmic laboratory for studying the physics of accretion onto BHs, with the build up of an accretion disk. The properties of the flare from the accreting stellar debris (luminosity, light curve, and spectral energy distribution) are dependent on the mass and spin of the BH. Detailed observations of TDE can provide an independent means of measuring the masses and spins of dormant BHs in distant galaxies. A further peculiarity of TDEs is that for the most massive BHs (> 10 8 M ), a solar-type star is swallowed directly without disruption. This limits the observations of very massive BHs but, at the same time, opens the possibility to study in detail the most elusive and numerous populations of M BHs. It appears clear that gaining an unbiased understanding of the population of BHs in galactic centres as a function of cosmic time is crucial for understanding the growth of structure in the Universe. Active Galactic Nuclei. Variability is a very valuable tool in Active Galactic Nuclei (AGN). Monitoring the emission in several optical bands contemporaneously can probe the dynamics of the putative accretion disk and through correlation (time lag analysis) with optical or X-ray (if available) light curves, the structure of the emitting region. Blazars. Blazars are AGN with a jet pointed toward the observer. Blazars are dominated by Doppler-boosted instabilities in the jet and are extremely variable objects at all wavelengths. Multi-band observations can help in constraining the overall spectral energy distribution during these wild variations deriving the jet properties and, possibly revealing signs for the presence of an accretion disk. 6

7 The unexpected. EVENT will disclose an unexplored discovery space. Unforeseen and exciting discoveries might be expected. 2.3 EVENT photometric mode Photometric mode will be the used in case of external triggers. In addition, a number of sources will be monitored on a fixed basis (daily, weekly, etc.) in order to provide long-term multi-band light curves. These will include low mass and high mass X-ray binaries, Active Galactic Nuclei, blazars. These multi-band light curves will provide a legacy for detailed studies of variability. In X-ray binary transients this will allow us to characterise the beginning of outbursts, shedding light on its onset that is currently unknown. EVENT will reach in 600 s exposure, at S/N=5 a limiting magnitude of g~22.7, r~22.6, i~22.1, z~21.3, J~21, and H~ EVENT spectroscopic mode Spectroscopic mode by the SMT will be used in case an external trigger counterpart is identified in real time. In addition, this mode will be used to follow-up the brightest transients discovered during the survey for a spectral characterization. Spectroscopic mode will also be used for a spectro-photometric monitoring of bright sources. In order to guarantee a further spectroscopic follow-up of the discovered transients, we will apply for a 2 (+1) yr Large Program at the Telescopio Nazionale Galileo (TNG) and at the European Southern Observatory (ESO, for transients visible also from the southern hemisphere) for transient follow-up. We will also apply for observing time at other international like the Large Binocular Telescope (LBT), Gemini and national facilities (Asiago 1.8m telescope). An informal agreement for follow-up of transients with the Liverpool and Faulkes telescopes is in place, pending a UK funding revision. A polarimetric follow-up with the PAOLO instrument at TNG can also be envisaged, as the instrument PI is at OAB. 3. Methodology 3.1 Exploiting EVENT science EVENT will provide different kind of data. - Trigger data. We will exploit triggered mode data. This will require scientists and an organization in charge of analysing data and send out reports in near-real time (see below). This is done routinely with the GRBs detected by the Swift satellite (the PI has a wide experience on this) and by the optical follow-up GRB community. Multi-messenger astronomy (including GW and HEN candidates) will be one the prime targets of EVENT. - Survey data. EVENT will provide a huge amount of high-quality astronomical data. Several survey experiments can detect a comparable number of transient sources like EVENT (see Table 1), but they lack a clear characterisation. To circumvent this problem, we designed EVENT following a different approach: we conceive three different telescopes covering a smaller field of view but allowing for 4 (up to 6) different optical filters contemporaneously in order to provide a first (broad-band) spectral characterisation. This will sort out different classes of transient sources from the beginning. In order to maximise the science returns of EVENT, we will immediately distribute the alerts for all transients discovered during the survey soon after the discovery (i.e. within one day, and often much less). The best mechanism to do this is to use VOEvents, a community-endorsed protocol for the distribution of alerts. This already happens for GRBs and for on-going surveys such as the Catalina Real-Time Survey. This being said, we are not proposing this experiment only as a service to the community. We want to be at the forefront of the follow-up and exploitation of the EVENT data, characterising the most important events spectroscopically and photometrically. We will focus on a few selected topics of high interest, including tidal disruption events, very bright core-collapsed Supernovae (possibly connected to GRBs). The discovery space is still very large. A scientific network has been appointed to cover all the survey results and to assure their (first) scientific exploitation (see Table 2). In particular, we identified two highly representative scientists, one in Italy and one in another European country, who will exploit together the data based on their expertise in close connection to the PI. These people will form the EVENT science network. This will assure a timely look at the survey data, at no cost for the project. At variance with other surveys, we plan to make public all the survey data on a six months basis. At the end of the survey all the data will be summed, reaching limiting magnitudes of g~23.5, r~23.4, i~22.9, and z~22 (S/N=5). This deep survey will be useful to future mission such as EUCLID, providing the needed 7

8 multi-band optical coverage for photometric redshift. - Pointing mode data. In addition, the experience of the NASA-ASI-UKSA Swift satellite is inspiring. Swift is a fast-slewing high-energy mission (initially) dedicated to the study of GRBs. Since the beginning of the mission Target of Opportunity were allowed to the community. We plan to repeat this productive experience allowing EU scientists for the trigger of ToO on a short notice basis. Up to 20% of the time every night might be dedicated to triggered ToO or interesting source monitoring. These data will be made public to the entire community on a short track basis. For example we will respond to selected Gaia alerts. Finally we emphasize that this project builds on the heritage of the Rapid Eye Mount (REM) robotic telescope in La Silla. If supported, it will generate a large science return at a crucial time for the European research at large. 3.2 Building the EVENT telescopes For the building of the telescopes we adopted an off-the-shelf approach. In recent years a reduction in the cost of 1-2 m telescopes took place as well as the production of low-cost high-quality CCDs. These improvements made possible a quick and cheap procurement of the instruments needed to build EVENT Telescope characteristics The telescopes should be relatively easy to build. They are modified Ritchey-Chrétien telescopes with 1 deg 2 field of view. The primary mirror (M1) diameter is 1 m for NT and PT and 1.2 m (1.5 m goal) for SMT. Given the CCD plate scale of 0.9 arcsec/pixel there is ample margin for the mirror optical quality. For the focal plane of SMT the proposed configuration foresee a 3 rd mirror (M3) mounted on a rotating device than can feed the two main instruments: the multi-band imaging camera and the low-resolution spectrograph. The focal plane of the telescope will be collimated and a 90 pick off mirror (M3) will bend the light into a plane normal to the telescope axis. The multi-band photometer will consist in a dichroic tree-like configuration that will split the light in the wavelength domain towards the dedicated cameras (based on the experience of the GROND instrument at the ESO/MPI 2.2 m in La Silla). The same collimated beam will also feed a dispersing system that projects the spectra into the dedicated camera. The collimated beam allows the adoption of identical focal reducers for each channel (photometric and spectrograph) with evident reduction of optical manufacturing costs. In Figure 2 a sketch of one telescope is shown and in Table 3 its main characteristics are reported. Table 3: Telescope characteristics. Telescope Values characteristics M1 diameter 1000 mm M2 diameter 200 mm Field of view 1 deg 2 Pixel scale 100 arcsec/mm Focal ratio 1.8 Pointing speed 2 deg/s Pointing accuracy 3 arcsec rms Tracking error 0.2 arcsec/10min Figure 2: Telescopes assembly. The Gruppo di Ottiche e LEnti a Merate (GOLEM) group at the Osservatorio di Brera (OAB) worked out the telescope optical design. The mechanical structure designs will be finalized after approval within 3 months. The telescope is already provided with fast moving capabilities and it is fully planned for a robotic control. The mechanical layout will be an alt-az, guarantying a cost minimization considering its scalability with respect to existing solutions. State of the art telescope technology guarantee fast pointing characteristics both in terms of structural stiffness thanks to the increasing of use of new materials (Carbon Fiber Reinforced Plastic), and rapid and precise motions (direct drive motors). Telescope quotations are reported below (Section 5). As a general rule we obtained a quotation for all the prices we included in the proposal 3. 3 Supporting material (all quotations, endorsements, instrumental characteristics, etc.) is not inserted in the proposal but is available at the site 8

9 3.2.2 CCD characteristics For the optical CCDs we use 4kx4k front illuminated CCDs. These provide quantum efficiencies up to 70% in the r band and result in a cost-effective solution to our needs. The reported quotation is for an Apogee F16M using a Kodak KAF16803 chip with 9 µm pixel size. NIR CCDs are very expensive and we are forced to limit the CCD size to 0.5kx0.5k. These will cover only a limited part of the field of view in survey mode (8 arcmin square) but will allow a detailed study of pointed sources. We select an InGaAs array that guarantees quantum efficiencies larger than 70% in the H and J bands. The quoted array is the Anacapa SWIR 640A by Teledyne. For spectroscopy we used a smaller 1kx0.1k back-illuminated CCD which guarantees a larger quantum efficiency (>90%) in the wavelength range µm. This is the Andor with IDUS DV401A-BV model (pixel size 26 µm) Dome and telescope mechanics The domes, made in thick glass polyester laminate, are fully manoeuvrable and remotely controlled. The GOLEM group projected the CCDs assembly and will take care of it under the PI responsibility. This will allow us for a strong cost cutting. A sketch is shown Figure 3. Filters and optical material (lenses and dichroics) will be easily acquired or manufactured in house, including the prism for the spectrograph. Figure 3: Left: Overall focal plane assembly with all the channels indicated. Right: Example of dichroic beam splitting Spectrograph characteristics The spectrograph will be similar to the 300V grism mounted on the ESO/FORS instrument. It is centred at 590 µm, covering the range µm. The resolution is 300. The slit width is fixed to 2 arcsec. 3.3 Installing and operating the EVENT telescopes EVENT site We have selected two possible sites for hosting EVENT. One Valle d Aosta (OAVdA 4 ). The site is placed in Lignan (Nus, AO) at an altitude of 1,630 m on the Italian Alps. The site is already working and hosts several small telescopes including a 0.8 m main telescope. The site is scientifically active with a program searching for planetary transits in dm stars. It also hosts a planetarium and has a vigorous exhibition activity. The site is good with a large number of clear nights (~50%), a sky as dark as m V ~21.3 mag/arcsec 2, a median seeing of 1.5 arcsec, matching our pixel scale. OAVdA is willing to host EVENT. The other site is in the Parco astronomico delle Madonie (PAM) on the top of mount Mufara (1,865 m) in Sicily (Isnello, PA). This site was studied extensively during the site searching for the Telescopio Nazionale Galileo. The site is good with a high number of clear nights (~60%), m V ~21.3 mag/arcsec 2, and a seeing as good as 1 arcsec. The PAM site has no facilities, yet, but it received a large grant to build an astronomical park for the public (planetarium, small telescopes), as well as for starting a research program. The works to prepare the site will start in early PAM has agreed to host EVENT and to cover the installation costs

10 S. Campana Part B2 We would need a 12mx12m area over which to mount all the three telescopes. We need obviously power and a meteo station to remotely control the dome s aperture. A set of webcams will also provide a real-time monitoring. The selected site will provide these logistic facilities at no cost to the project. Both sites are operated by in-situ astronomers and, despite the fact that the EVENT telescopes are fully robotic, they can intervene on a short track in case of need. Figure 4: Left: OADVA (Lignan, Nus (AO), I) at night. The site is already operational. Right: Top of mount Mufara (Isnello (PA), I) where the PAM will be based. An additional important cost of a telescope would be the dismantling cost. For this reason we did not choose the Canary Islands (clear night at ~70%) as our preferred site. At the end of the project the EVENT telescopes will become part of the site foundation and will be used in part for educational purposes and in part for scientific purposes if alternative funding will be raised. Further possible site are the Fracastoro station at Serra la Nava on the mountainside of Etna (at 1,735 m) of the INAF Osservatorio astronomico di Catania where the prototype ASTRI of the CTA will be based, or the top of mount Toppo (1,250 m) in Castelgrande (PZ) of the INAF Osservatorio astronomico di Capodimonte, or at the Hotel Kulm on top of the Gornergrat (3,135 m) near Zermatt (CH), where the TIRGO telescope of the INAF Osservatorio astrofisico di Arcetri was based. The site will then be selected based on readiness and best hosting conditions and infrastructure costs Installing EVENT Our timeline is relatively straightforward. Taking T0 the time of approval, we will finalize the site selection signing a memorandum of understanding. Soon after, the needed licence to install the telescopes will be requested (both sites are in regional parks) and at T0+6 months (as guaranteed by both sites) we should start to build the terrace (duration 1 month). Meanwhile we will start with the procurement of the telescopes and CCDs. For the telescopes we will set-up a competitive, transparent, open call for a fixed maximal price: the telescopes will be assigned based on best value for money. Based on the quotations we already have, all the material will be ready in 6-8 months. Computers and hard disks will also be purchased in this period. With the GOLEM group, we will work at the mechanical interface to mount CCDs and filters on the telescope. '()*#!"#!$#!%#!&#!"#"$%&'"$( Figure 5: Timeline of the EVENT project. In green there is the procurement of material. In brown there is the preparation of the site and in orange the instruments calibration. Finally, in blue science related events are described. ))>$( >&8"( >+%?-&+%$("2%( 0+2"( #*.&/( )*#+,-*. &/( 0%+"/%"(12-+33"-$4$5-6"748&/+2&-+/39( >*2*(*-%?+6+/3( >*2*('5,#+%( :7-( =7-( <7-( ;7-( Telescopes and CCDs will be directly shipped to the selected site. We plan to have at T0+10 months all the material in place. We then start the installation of the telescopes and of the optical system on site. This phase will last approximately 4 months. 10

11 This schedule is also based on the extensive experience we made with the building and installation of the REM robotic telescope (PI Dr. F. Zerbi) in La Silla (Chile). After T months (including contingency) we plan to completely finish the installation phase and enter the commissioning phase. This phase is dedicated to tests and calibrations. We will fully calibrate the telescope, CCDs, filters and prisms. We will calibrate and test the motion of the telescopes and the response to external alerts. We will test data acquisition and data transmission. We will test our algorithms for source detection and source characterization and refine the identification of spurious sources (cosmic rays, airplanes, satellites, meteors, etc.). This extensive phase will last 6 months, ending at T months (including contingency). The commissioning phase will end with a dedicated external review (appointed by the PI). The following three years will be dedicated completely to science (up to T months) Operating EVENT We, at the OAB, have a long tradition of robotic telescopes, since we are successfully operating the REM robotic telescope since The REM telescope is operating in pointing mode, observing pre-planned sources and it responds to Swift GRB alerts automatically. An automatic scheduler has been implemented allowing for target priorities. This software dynamically optimizes the observing nights, scheduling observations at their best observing conditions. This testifies that the needed expertise and the relevant software are already available to the EVENT project. Each telescope will be equipped with two computers, one controlling and operating the 4 optical cameras and one dedicated to the 2 nir cameras. This is necessary due to the way in which nir images are acquired (i.e. moving the image on the camera every 10 s). The nir computer will then sum the short exposures (10 s) into a single 60 s image. Images will then be stored on an 8 TB disk. Given the image production rate, this disk space is enough for more than 40 d (12 hr per night fully dedicated to the survey). Given the huge amount of data, these will not be transferred directly to the data analysis centre located at the OAB. The data will be preliminarily analysed on site by a high-level computer to find new transient sources. In case of new transients only small images centred on the source will be transferred to the data centre. This architecture will be duplicated for each telescope. To complete the set there will be a computer (and its back-up) dedicated to the telescope pointings and dome movements (connected to a meteo station). One back-up computer for the optical and nir camera each are also foreseen. An UPS will take care of closing the domes in case of power outage. All the telescopes will be connected with an internal (optical fiber) line. A fast (10 MB/s) link with the data centre will guarantee the rapid dissemination of new transient alerts and the timely data analysis of triggered events. Finally every 2 weeks hard disks will be shipped to the OAB and replaced on site. Maintenance of the telescopes is foreseen with visits at least every 6 months. *$ +,-.$!"#$ %$ )$ &$ '$ ($ +,/0$ 1'23$ ",+$ *$ +,-.$ 4#$ %$ )$ &$ '$ ($ +,/0$ 1'23$ ",+$ Figure 6: Scheme of the hardware around the telescopes (only two shown). Small squares connected to circles indicate the CCDs. Larger squares indicate the computers (C-ott, C-IR and Main computer M-C). Outside there is Control computer and back-ups. +,/0$ 56$ "898/$ +,-.$ 56$ +/7 56$!"# $%"&' ;1!<$ 5&8&:$ At the EVENT data centre (EDC) a 250 TB disk unit will archive all the EVENT data in a searchable database. Light curve and spectral energy distribution generation will take place at the EDC as well as the real time exploitation of triggered mode data (which will be transferred in real time). 11

12 3.4 Analysing EVENT data Analysis of survey mode data The analysing scheme is depicted in Figure 7. Each frame in each band will be first calibrated (bias, dark, flat) and then astrometrized (e.g. matching the USNO astrometric catalog). The image is then ready for source detection. We split this task into two parts. First we detect sources with standard programs (e.g SExtractor). For each source we will derive an instrumental magnitude and then a physical magnitude after correcting for zero-points. For each detected source we will provide a light curve, which will grow as the survey proceeds and flag new and variable source. A further search for new transients is carried out. This is done matching the scientific image with a template image (obtained with the sum of EVENT images of the same fields or from other surveys like the Sloan SDSS). The image template image is blurred to match the seeing of the image under analysis and then an image subtraction tool is applied (several astronomical packages already perform this task, like ISIS). This allows to detect source positive and negative variations as well as the appearance or disappearance of sources, at a given confidence level. This procedure provides transient candidates. A Figure of Merit (FoM) algorithm is then applied to these candidates, selecting the highly significant ones. This can be done requiring the detection into, at least, two bands or/and applying a morphological criterion (to discard cosmic rays, meteors, satellites, airplanes, etc.). These transients will then be matched with detected sources for their final magnitudes. A small portion of the images around each transient will be extracted and data transferred to the EVENT data centre (EDC). Transients will then be flagged and inspected visually, before sending the alert to the '()*+,-$."*%(/$ 69)-*:;9$<1"3-$ '.)"(=%"1>=?"&/$ 0(&123-&14$ '5678/$ 1-2"+') *'('+,-$) H*(&1I3-*&",$ BE2&23-&14$ 69)-*:;9$ BE2&23-&14$ Figure 7: Scheme of data analysis steps. In red are the raw data passages to derive a scientific image. Then two different paths are envisaged to search for new transients and to derive source light curves (photometry).!"#$%&'$() (-,-9:2*$./0) '321BE2,2+4F$G$ ;,&-1(F$-&9D/$ Analysis triggered mode data Triggered mode data will require a special procedure to be analysed in real time. Depending on the error box of the trigger (known a priori) all the data or a reduced part of the images will be transferred to the EDC through the fast ADSL link. This will supersede any other task. People on duty will be paged by an alert and will analyse the data in (near) real time, producing an appropriate message to the community (GCN, ATel, IAUC, CBET, MPEC, etc.). This is set-up similar to what we are already using for Swift alerts. 4. Communication and outreach A Science Communication and Public Outreach Office (SC&PO), led by the EVENT PI, will be set up. The SC&PO will develop an outreach and science communication plan in collaboration with the OAB and INAF outreach division, which will be regularly updated as the project progresses. Docs and Post-docs will dedicate part of their time to present to the public and schools in a proper form the research carried out under this proposal. We feel this is also a duty we have toward the layman and the youngest. At the OAVdA site scientists, in addition to research activities, exploit a vigorous outreach program and are interested in these EVENT-related activities. Also at the PAM site, extensive outreach activities are planned. During the development phase, the EVENT SC&PO will set up and maintain web pages for the general public and the media. These web pages will be enriched with more material and features related to EVENT with the progress of the project. The EVENT web pages will be the prime tool for communicating scientific 12

13 and project-related content to the science community and the general public. With the final aim to communicate the making of science and attract young people to a career in science and technology, the web page will have live information, showing the public who the EVENT scientists and engineers are, showing the mission faces and names, telling a story on the technical and scientific challenges about the mission preparations and operations. Blogs, social network pages, twitter or smart-phone apps, depending on, and adapted to up-to-date communication-tool preferences of the public will be part of the outreach and science communication plan. The results of the EVENT survey will have a deep cultural impact, not just in the scientific community but also on the broader public, as topics like black holes, stellar explosions, exo-planets and near-earth asteroids are among the themes that mostly excite the imagination of the public. We will set-up a dedicated web page where, for every class of objects observed by EVENT, there will be a brief general explanation and a weekly-updated counter and sky-map that will set the number and the position of the new objects discovered as the survey is on going. Dedicated press releases will be issued for every new high impact discovery while periodical updates on the status of the survey will be released, including statistics, sky-maps, plots and artist's impressions. We plan to organize two international conferences, addressed to scientists working on the thematic areas of the project. We will hold one of these conferences at the beginning of the project, to set the state of the art in the field, and one at the end of the project, to check, within an international environment, the progress that have been obtained also with the contribution of our team members. Finally, bright transient phenomena (like novae and supernovae) and asteroids are also among the main interest of the world-wide growing community of amateur astronomers, always looking for chances to interact with the scientific community of professional astronomers. On our web page we will provide for every newly discovered object all the useful information for the ground-based follow-up like finding charts, visibility plots and light curve generators. A section for the Object of the month will be created dedicated to the most interesting object (for every class) according to its brightness, visibility and peculiarity. All these easily available information will also encourage follow-up projects in the schools, with the students having the possibility to Catch a Supernova or Follow the asteroid's path. 5. Resources (including project costs) The EVENT group will comprise of a PI, 2 staff collaborators, 2 post-docs, 2 PhD students, 1 optical engineer and 1 archival manager (see below). We expect to host (at no cost for the project) additional PhD and BS students from local Universities in Milano and surroundings (Pavia and Insubria). Our group and the EVENT science data center will be based at OAB in Merate. In parallel, we will have a distributed scientific network made by European scientists in charge of exploiting EVENT survey data in close collaboration with us and at no costs for the project. This will improve EU excellence at large. The majority of the requested funds will be dedicated to the equipment (55%). The second voice in order of importance in the budget is used to hire young researchers (23%). A relatively large amount of money is required for travels (2%). This is needed to support the installation of the EVENT telescopes and their calibration on-site. This is mainly concentrated in the first period. Subcontracts refer to Certificates on Financial Statements only. 5.1 Man-power The managing and operations of the EVENT project requires a number of collaborators. The first phase (see Figure 5) requires the acquisition of the instruments and set up of the observing site. The PI with the administrative help of the OAB staff will do this. The PI will dedicate at least half of his working time to the project (maintaining the Swift XRT calibration lead responsibility). Dr. Filippo Zerbi (OAB staff) will provide advice for the optical infrastructure. Dr. Dino Fugazza (OAB staff) will provide advice for CCD related issues, scheduling and data managing. A summary of the people to be hired is presented in Figure 8. An optical engineer (OE) will be hired at the beginning of the project for two years (assegno di ricerca 5 category B, 40.3 k /yr). The OE, together with the PI and Dr. Zerbi and the GOLEM group, will take care of the building of the EVENT experiment. 5 Assegno di ricerca is a particular form of an Italian research fellowship, which allows a low taxation rate. 13

14 Table 4: Summary of instrumental costs. Item Number Total cost In house (quotation, ) Robotic 1m telescope 2 900,000 Robotic 1.2m telescope 1 680,000 Optical CCD 4kx4k camera (+ optical ,000 spectroscopy CCD) nir CCD 0.5kx0.5k array 6 147,000 Dome Site preparation ,000 50,000 Telescope mechanics 3 300,000 Optical material (filters, dichroics, prism, 20,000 etc.) Total 1,997, ,000 An archival manager and observation scheduler (AMS) is foreseen to take care of the acquisition and data storage (together with Dr. Fugazza). The ASM will be hired 1.5 yr after the start of the project up to its end (assegno di ricerca category A, 35.6 k /yr). These positions will cover the technical part of the project. For the science part we need a relatively larger number of scientists to assure a fast exploitation of triggered mode data and to work directly on survey data. One post-doc (PhD1) will be hired after one year from the start and up to the end of the project, to start working on the instruments and to help in the calibration of the instruments (assegno di ricerca category B, 40.3 k /yr). During the first year their main task will be to develop the software for the transients detection and for the light curve accumulation together with ASM, the PI and Dr. Fugazza. PhD1 will also aid the PI, acting as his scientific deputy (e.g. in the approval of external Target of Opportunity observations). Once in the scientific phase (2 yr after the start) we will hire the large majority of scientists. We foresee another post-doc (PhD2) for 3 yr (assegno di ricerca category A, 38 k /yr each) and two PhD students (Doc1&2, 23 k /yr each). The two PhD students will be based at the University of Insubria (Como), with which the OAB has an agreement for joined PhDs. These scientists will provide the core team to fully exploit the EVENT science. The entire group will secure a full scientific coverage for triggered events. We will develop methods for classifying sources based on multi-band photometry. We will also pursue our own research. One post-doc and one PhD student will focus on GRBs observed in triggered mode (we expect to observe ~20 GRB/yr from Swift and ~60 GRB/yr from Fermi/GBM). This post-doc will work on supernovae (~500/yr type Ia and ~200/yr core collapse), focusing on shock breakout events. This PhD student will exploit super-eddington tidal disruption events (~300/yr) with a main emphasis on their physics. Such young man-power not only is essential in helping the on-going research since we are competing with public data at the frontier of science but it is needed to educate the youngest to move at the cutting edge of science and technology in a highly competitive world. Table 5: Summary of computing costs (these will be acquired using the PI overhead). Item Number Total cost (quotation, ) Hardware for each telescope 3 40,000 Hardware for the site 1 40,000 Optical fiber to connect the telescopes 1 10,000 ADSL internet connection (4 yr) 1 10,000 EDC hardware 1 90,000 Total 190,000 The EVENT scientific network (see Table 2), in close relationship with the core team, will then assure not to leave aside any major discovery. This is composed by Italian scientists as well as by scientists from other European countries (D, F, NL, SF, SL, UK). 14

15 Figure 8: Scheme of the men-power foreseen for the EVENT project. Green refers to the instrumental part, orange to the science part and red to the database part. '()*#!"#!$#!%#!&#!"#$%&'()*(()(+,)*' -./0'1.$' -./0'1.$' -21'/034()0' -21'/034()0' 5+$2,6('7%)%*(+89$2(43&(+' :;+' >;+' =;+' <;+' Summary of costs: Cost Category Month 1-18 P1 Month P2 Month P3 Month P4 Total (Month 1-60) Direct Costs: Personnel: PI 56,000 56,000 56,000 20, ,000 Senior Staff 15,000 15,000 4, ,000 Post docs 81, , ,000 57, ,000 Students 0 46,000 69,000 23, ,000 Other Total Personnel: 152, , , , ,000 Other Direct Costs: Equipment 599, , , ,000 1,997,000 Consumables Travel 40,000 17,000 17,000 5,000 79,000 Publications, etc Other Total Other Direct Costs: 639, , , ,000 2,076,000 Indirect Costs (overheads): Subcontracting Costs: Total Costs of project: Requested Grant: Total Direct Costs: 791, , , ,000 2,897,000 Max 20% of 158, , ,000 61, ,000 Direct Costs (No overheads) 6,000 7,000 7, ,000 (by reporting period and total) (by reporting period and total) 955,000 1,069,000 1,106, ,000 3,496, ,000 1,069,000 1,106, ,000 3,496,000 For the above cost table, please indicate the % of working time the PI (at least) dedicates to the project over the period of the grant: 50% 15