The Fermi Large Area Telescope Towards the (first) years in orbit Luca Baldini Università di Pisa and INFN Sezione di Pisa luca.baldini@pi.infn.it Pisa, September 5, 014
Prelude: the Fermi Observatory Large Area Telescope (LAT) I Pair conversion telescope. I Energy range: 0 MeV > 300 GeV I Large field of view (.4 sr): 0% of the sky at any time, all parts of the sky for 30 minutes every 3 hours. I Long observation time: 5 years minimum lifetime, years planned, 85% duty cycle. Gamma-ray Burst Monitor (GBM) I 1 NaI and BGO detectors. I Energy range: 8 kev 40 MeV. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 / 19
Fermi status and timeline SR 01 SR 014 Prime phase Extended phase 008 009 0 011 01 013 014 015 016 017 018 Year 0 000 0000 30000 # orbits 0 500 00 6 Distance traveled [km] 0 50 0 150 00 50 300 350 9 0 0 30 40 50 60 70 6 0 500 00 1500 000 6 0 50 0 150 00 50 300 0 0 5 50 0 75 0 15 150 30 175 40 00 5 50 50 60 70 80 75 9 # triggers # events downlinked # events @ FSSC # γ-ray candidates # ATELs # GCNs Baseline: operate through FY 018 (i.e., years) TBR in 016. Full SR reports @ http://science.nasa.gov/astrophysics/documents/ Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 3 / 19
The Fermi science menu in a nutshell A remarkably wide dynamic range SNR CRE EGB GRB - TGF Pulsar substr. -1 1 Pulsar periods GRB prompt 3 GRB extended Solar flares AGN flares 4 5 Binary systems Energy [MeV] 6-5 -4-3 - -1 1 3 4 5 6 8 7 Time [s] Earth limb TGF Moon Sun Galactic CRE AGN GRB 6 8 1 14 16 18 0 6 4 Distance [m] Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 4 / 19
Dark matter constraints from dsph Ackermann et al., PRD 89, 4001 (014) Dwarf Spheroidal Galaxies among the cleanest targets for indirect DM searches: largely DM-dominated objects; do not expect significant γ-ray emission through conventional channels. Stringent DM limits based on a combined analysis of 5 dsph. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 5 / 19
The Fermi bubbles Ackermann et al., ApJ 793, 64 (014) First discovered by Su, Finkbeiner & Slatyer in 0. First Fermi-LAT publication on the topic. Based on 50 months of data. Modeling of the diffuse emission is the foremost challenge. Hard spectrum with cutoff at 1 GeV. No spectral variations in latitude stripes. No energy dependence of the overall morphology. Excess emission in the the South-East; no evidence for a jet. Leptonic and hadronic interpretation of gamma-ray data possible. Assuming association with microwave haze prefers leptonic models. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 6 / 19
The IGRB and EGB (Re)Submitted to ApJ Updated LAT measurement of IGRB spectrum. 50 months of data, dedicated event selection(s). Extended energy range: 00 MeV 0 GeV 0 MeV 80 GeV. Roughly 1/ of total EGB intensity above 0 GeV now resolved into individual sources. Significant high-energy cutoff feature around 50 GeV. Consistent with simple source populations attenuated by EBL. Reality might be more complex, with multiple populations contributing. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 7 / 19
The 3FGL Coming soon, and heading toward 3000 sources 4 years of reprocessed LAT data above 0 MeV: vs. years of (un-reprocessed) data for the FGL. Front/Back handled separately (different isotropic and Earth limb). More data and improved performance (due to reprocessing): Better localization on average (error radius 15% smaller outside the Galactic plane). Improved interstellar model of Galactic diffuse (e.g., Fermi bubbles): Lower overall detection threshold. Association process improved. Dedicated multiwavelength follow-up, new surveys. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 8 / 19
Prospects for the extended mission Beating the square root of time Time-domain astronomy (GRB, AGN, Solar Flares, TGFs, novæ). Large acceptance and FOV, all-sky coverage and long integration time are key. Fermi plays a prominent role, in synergy with other instruments and observatories. Steady sources. High-energy limiting sensitivity comes from photon counting statistics (rather than the background). Many specific LAT analyses rely on external inputs: radio timing solutions for pulsar searches; targets for indirect DM searches (e.g., dwarf spheroidal galaxies); maps for modeling the gamma-ray diffuse emission (e.g., Planck). Long-baseline measurements. And Pass 8 (see next slides). Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 9 / 19
Pass 8 Cover image: a 540 GeV simulated gamma ray z x Long-term effort aimed at a comprehensive revision of the entire LAT event-level analysis. Simulation, reconstruction, background rejection, analysis methods. Goals: extending the energy reach, maximizing the S/N, reducing the systematic uncertainties. Basic analysis components ready, now entering science validation. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 / 19
IRFs: Future vs. present sr] Acceptance [m Ratio (P8/P7) 3.5 1.5 1 0.5 0 1 Preliminary 3 P8_SOURCE prototype P7REP_SOURCE_V15 4 5 Energy [MeV] Containment angle [ ] Ratio (P7/P8) 1-1 1.5 1 0.5 Preliminary 3 P7REP_SOURCE_V15 (on-axis 95%) P8_SOURCE prototype (on-axis 95%) P7REP_SOURCE_V15 (on-axis 68%) P8_SOURCE prototype (on-axis 68%) 4 5 Energy [MeV] Larger acceptance (effective area and field of view) at all energies. Most notably below 0 MeV ( at 0 MeV and at 30 MeV) Performing spectral analysis down to such low energies presents significant challenges (e.g., energy dispersion). Pass 8 will double the number of photons detected by the LAT above 30 MeV. For both archival data and future observations. Narrower PSF at moderate-to-high energies, with reduced tails. Can improve PSF further by tightening event selections. Preliminary indications that an in-flight correction is not needed. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 11 / 19
Pass 8 at high energy New high-energy photons from GRBs Energy [GeV] BLLacs FSRQs GRBs (Pass 6 and Pass 8) GRBs (new in Pass 8) Predicted optical depth (τ = 1) for various EBL models 0.5 1 1.5.5 3 3.5 4 4.5 5 Redshift 0% acceptance increase at high energy. And relatively (much) larger at large off-axis angles. Re-analysis of the prompt phase of GRBs with measured redshift in the first LAT GRB catalog. Really testing the new event reconstruction. 4 photons above GeV (previously discarded) recovered in Pass 8. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 1 / 19
Pass 8 at low energy Periodic and transient sources Counts/bin Counts/bin Counts/bin Counts/bin 450 400 350 300 50 00 50 00 150 0 50 0 800 700 600 500 400 300 00 600 500 400 300 00 0 0 Crab (30-60 MeV) Preliminary Crab (60-0 MeV) Preliminary P8_SOURCE prototype n source = 3480, H = 6097 P7REP_SOURCE_V15 n source = 4049, H = 1489 P8_SOURCE Pulse prototype phase = 7941, H = 18444 n source P7REP_SOURCE_V15 Pulse phase n source = 8961, H = 6307 0 0. 0.4 0.6 0.8 1 1. 1.4 1.6 1.8 Pulse phase Counts/bin Counts/bin 15 5 0 5 4 3 1 GRB086A (30-60 MeV) Preliminary GRB086A (60-0 MeV) Preliminary P8_TRANSIENT prototype n evts = 81 P7REP_TRANSIENT_V15 n evts = 16 P8_TRANSIENT Time since prototype trigger [s] = 18 0-300 -00-0 0 0 00 300 Time since trigger [s] n evts P7REP_TRANSIENT_V15 n evts = 9 Substantially improved sensitivity for pulsar searches: blind and epoch-folding pulsar searches. Substantially improved sensitivity for time-domain astronomy: transient searches (e.g., GRB). Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 13 / 19
More Pass 8 at low energy Solar flares Counts/bin 8 SFR0 06 1 P8_SFR prototype P7_REP_TRANSIENT_V15 Preliminary 6 4 0 0 80 60 40 0 0 0 40 60 80 0 Time since flare (sec) Dedicated event selection for Solar Flares: alleviate the effect of X-ray pile up in the impulsive phase; increase the number of flare for localization studies. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 14 / 19
Looking after Fermi Spaced-based gamma-ray astronomy The Fermi LAT has its sweet spot between 1 and GeV. Hard to do significantly better there without an instrument significantly bigger. The high-energy frontier: several projects being actively developed: CALET, DAMPE, Gamma-400, HERD (in order of appearance); all of them are gamma-ray and cosmic-ray instruments. Here we should keep in mind our ground-based big cousins! Both the current generation of IACTs and the forthcoming CTA. The low-energy frontier: several concepts, both in the Compton and in the pair-production regime: AdEPT, COMPAIR, GammaCube, GAMMA-LIGHT, HARPO, LArGO, PANGU (in alphabetical order). Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 15 / 19
High energy: acceptance s -1 sr -1 ) - Integral flux above a given energy (m 4 3 1-1 - -3-4 -5-6 Gamma-ray all-sky intensity Fermi LAT (unpublished) Gamma-ray extragalactic diffuse Fermi LAT (Abdo et al. 0) -1 1 Primary protons AMS01 (Aguilar et al. 00) Pamela (Adriani et al. 011) ATIC- (Panov et al. 006) CREAM (Yoon et al. 011) Primary electrons AMS01 (Aguilar et al. 00) Pamela (Adriani et al. 011) Fermi LAT (Abdo et al. 0) H.E.S.S. (Aharonian et al. 008) Primary positrons Pamela (Adriani et al. 008) 1 particle/day 1 particle/hour 5 4 3-1 - -3-4 -5 1 particle/month -6 3 Rigidity (GV) or Energy (GeV) Statistics is the main limiting factor! Is high-energy gamma-ray astronomy really IACT playground? Possibly not, e.g., wide FOV sky monitoring and diffuse emission. Most future instruments putting emphasis on the energy resolution, instead. (And most of them smaller than the Fermi LAT.) Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 16 / 19 1 Integral rate of particles crossing the LAT (Hz)
An example: Line-search sensitivity Energy resolution [%] 0.5 0.50 1.00 LAT 1 CALET DAMPE.00 Gamma-400 4.00 8.00 Gamma-400 (CC) HERD The basic figure of merit Q is 1 Exposure factor [m sr year] Q = n s nb E σ E /E. Better energy resolution is obviously beneficial. But the sensitivity is really a trade-off between exposure and energy resolution. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 17 / 19
Low energy: point-spread function PSF 68% containmnent [ ] Fermi-LAT (back) Fermi-LAT (total) Fermi-LAT (front) Kinematic limit 1-1 - -1 1 Energy [GeV] Can we get closer to the limit dictated by nuclear recoil? Silicon only, no converters (GAMMA-LIGHT, COMPAIR). Go to gas/liquid (AdEPT, HARPO, LArGO). Measure single-track energies (PANGU). What about 1 m 3 of scintillator (GammaCube)? At low energy statistics is not so much of an issue. Trading acceptance for PSF can be advantageous. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 18 / 19
Conclusions Fermi has been operating in space flawlessly for more than six years. No sign of performance degradation. On track for the original goal of a ten year mission. More results to come in the next few years. And more than one would expect just based on the deeper exposure. Path forward for space-based gamma-ray astronomy not as clear as for the ground-based instruments...... but definitely a lot of margin for improvements and many clever ideas around. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 19 / 19
Spare slides Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 Spare slides
Faster than the t: steady sources Low energy Bkg. dominated t High energy Photon counting nearly t Envelope of the minimum detectable power-law spectra over the full band, varying the spectral index. (i.e, not a differential sensitivity plot.) High-energy limiting sensitivity comes from photon counting statistics (rather than the background). Increase nearly linear with time, rather than t. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 Spare slides
Something fading out... The 130 GeV line, see arxiv:1303.1798 Expected for signal (1 σ) Data Expected for pure noise (1 σ) Fix signal hypothesis Weniger s updated results are consistent with the results from the recent LAT line-search paper. Likely that the original putative line signal was a statistical fluctuation. More data and Pass 8 will hopefully give the final word. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 Spare slides
And a continuing challenge DM from the Galactic center? arxiv:140.6703 The Characterization of the Gamma-Ray Signal from the Central Milky Way: A Compelling Case for Annihilating Dark Matter Example of a clever analysis of public LAT data performed outside the collaboration. The Inner Galaxy is notoriously a very complicated region. Modeling the diffuse emission is the foremost challenge. The LAT collaboration is targeting a presentation (and paper) for the Fermi Symposium in October. Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 Spare slides
DGE: interplay between aeff and PSF Latitude [ ] 80 60 40 0 0-0 -40-60 -80 = 0.15 θ 68-150 -0-50 0 50 0 150 Longitude [ ] 1 year -1 ] - -1 [m Integral flux > GeV within θ 68 PSF 68% containment [ ] 1-1 = years T obs = 0 GeV E 0 = GeV E 0 Statistics-limited PSF-limited LAT -1 1 Acceptance [m sr] Luca Baldini (UNIPI and INFN Pisa) Pisa, September 5, 014 Spare slides