Big Bang Cosmic Microwave Background (~ 400 K years) Dark Ages - before the stars. First stars & galaxies - Epoch of Reionization (~ 400 M years)

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1 The Square Kilometer Array Radio Astronomy HST Dayton Jones, K6DJ Principal Scientist (Retired), Jet Propulsion Laboratory, California Institute of Technology Senior Research Scientist, Space Science Institute, Boulder Provides unique information about the Universe from the Big Bang to the Solar System non-thermal processes highest angular resolution unaffected by dust 1 2 Why is Radio Astronomy important? A Universe of stars A Universe of hydrogen gas Epoch of Reionization (and before) Big Bang Cosmic Microwave Background (~ 400 K years) Dark Ages - before the stars? radio COBE, WMAP, & Planck satellites Square-Kilometer Array First stars & galaxies - Epoch of Reionization (~ 400 M years) light A very different view -- but signal is very weak! Present (~ 13.7 B years) HST, JWST 4 SKA will be able to image, not just detect, the EoR Distribution of first sources of ionizing radiation Tomography of intergalactic medium Incredibly rich data set 5

2 Strong-Field Gravity PRL 116, (2016) Selected for a Viewpoint in Physics PHYSICAL REVIEW LETTERS week ending 12 FEBRUARY 2016 Observation of Gravitational Waves from a Binary Black Hole Merger B. P. Abbott et al.* (LIGO Scientific Collaboration and Virgo Collaboration) (Received 21 January 2016; published 11 February 2016) On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per years, equivalent to a significance greater þ0.03 than 5.1σ. The source lies at a luminosity distance of 410þ Mpc corresponding to a redshift z ¼ þ4 In the source frame, the initial black hole masses are 36þ5 4 M and 29 4 M, and the final black hole mass is þ4 þ M, with M c radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger. DOI: /PhysRevLett December 2004 Square Kilometer Array 7 8 I. INTRODUCTION In 1916, the year after the final formulation of the field equations of general relativity, Albert Einstein predicted the existence of gravitational waves. He found that the linearized weak-field equations had wave solutions: transverse waves of spatial strain that travel at the speed of light, generated by time variations of the mass quadrupole moment of the source [1,2]. Einstein understood that gravitational-wave amplitudes would be remarkably small; moreover, until the Chapel Hill conference in 1957 there was significant debate about the physical reality of gravitational waves [3]. Also in 1916, Schwarzschild published a solution for the field a P H Y S I Cequations A L R[4]E that V Iwas E Wlater Lunderstood E T T EtoRdescribe S PRL 116, (2016) black hole [5,6], and in 1963 Kerr generalized the solution to rotating black holes [7]. Starting in the 1970s theoretical work signal-toled to the understanding of black hole quasinormal propagation time, the events have a combined modes [8 10], and in the 1990s higher-order postnoise ratio (SNR) of 24 [45]. Newtonian calculations [11] preceded extensive analytical Only the LIGO detectors were observing studies at the oftime of two-body dynamics [12,13]. These relativistic advances, together with numerical relativity breakthroughs GW The Virgo detector was being upgraded, in the past decade and GEO 600, though not sufficiently sensitive to detect [14 16], have enabled modeling of binary black hole mergers and accurate predictions of this event, was operating but not in their observational gravitational waveforms. While numerous black hole mode. With only two detectors the source position candidates haveisnow been identified through electromagnetic observations primarily determined by the relative arrival time and [17 19], black hole mergers have not previously 2 been observed. Laser Interferometer Gravitationalwave Observatory (LIGO) The discovery of the binary pulsar system PSR B1913þ16 by Hulse and Taylor [20] and subsequent observations of its energy loss by Taylor and Weisberg [21] demonstrated the existence of gravitational waves. This discovery, along with emerging astrophysical understanding [22], led to the recognition that direct observations of the amplitude and phase of gravitational waves would enable studies of additional relativistic systems and provide new tests of general relativity, especially in the dynamic strong-field regime. Experiments to detect gravitational waves began with Weber and his resonant mass detectors in the 1960s [23], followed by an international network of cryogenic resonant detectors [24]. Interferometric detectors were first week ending suggested in the 1960s [25] and the 1970s [26]. A 12 early FEBRUARY 2016 study of the noise and performance of such detectors [27], and further concepts to improve them [28], led to proposals for long-baseline broadband laser interferometers with the potential for significantly increased sensitivity [29 32]. By the early 2000s, a set of initial detectors was completed, including TAMA 300 in Japan, GEO 600 in Germany, the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States, and Virgo in Italy. Combinations of these detectors made joint observations from 2002 through 2011, setting upper limits on a variety of gravitational-wave sources while evolving into a global network. In 2015, Advanced LIGO became the first of a significantly more sensitive network of advanced detectors to begin observations [33 36]. A century after the fundamental predictions of Einstein and Schwarzschild, we report the first direct detection of gravitational waves and the first direct observation of a binary black hole system merging to form a single black hole. Our observations provide unique access to the Strong-Field Gravity localized to an area of approximately 600 deg (90% credible region) [39,46]. * Full author list given at the end of the article. The basic features of GW point to it being Published by the American Physical Society under the terms of produced by the coalescence of two blackthe holes i.e., Creative Commons Attribution 3.0 License. Further distribution of thisblack work must maintain attribution to the author(s) and their orbital inspiral and merger, and subsequent final the published article s title, journal citation, and DOI. hole ringdown. Over 0.2 s, the signal increases in frequency and amplitude in about 8 cycles from 35 to 150 Hz, where =16=116(6)=061102(16) the amplitude reaches a maximum. The most plausible explanation for this evolution is the inspiral of two orbiting masses, m1 and m2, due to gravitational-wave emission. At the lower frequencies, such evolution is characterized by 9 the chirp mass [11] M¼! ðm1 m2 Þ c 5 8=3 11=3 _ π ¼ f f ðm1 þ m2 Þ1=5 G 96 3=5 3 "3=5 ; Published by the American Physical Society 10 FIG. 2. Top: Estimated gravitational-wave strain amplitude from GW projected onto H1. This shows the full bandwidth of the waveforms, without the filtering used for Fig. 1. The inset images show numerical relativity models of the black hole horizons as the black holes coalesce. Bottom: The Keplerian effective black hole separation in units of Schwarzschild radii (RS ¼ 2GM=c2 ) and the effective relative velocity given by the post-newtonian parameter v=c ¼ ðgmπf=c3 Þ1=3, where f is the gravitational-wave frequency calculated with numerical relativity and M is the total mass (value from Table I). where f and f_ are the observed frequency and its time derivative and G and c are the gravitational constant and speed of light. Estimating f and f_ from the data in Fig. 1, we obtain a chirp mass of M 30M, implying that the total mass M ¼ m1 þ m2 is 70M in the detector frame. This bounds the sum of the Schwarzschild radii of the binary components to 2GM=c2 210 km. To reach an detector [33], a modified Michelson interferometer (see orbital frequency of 75 Hz (half the gravitational-wave Fig. 3) that measures gravitational-wave strain as a differfrequency) the objects must have been very close and very ence in length of its orthogonal arms. Each arm is formed compact; equal Newtonian point masses orbiting at this by two mirrors, acting as test masses, separated by frequency would be only 350 km apart. A pair of Lx ¼ Ly ¼ L ¼ 4 km. A passing gravitational wave effecneutron stars, while compact, would not have the required tively alters the arm lengths such that the measured mass, while a black hole neutron star binary with the Complete survey difference is ΔLðtÞ ¼ δlx δly ¼ hðtþl, where h is the deduced chirp mass would have a very large total mass, of pulsars in our gravitational-wave strain amplitude projected onto the and would thus merge at much lower frequency. This detector. This differential length variation alters the phase leaves black holes as the only known objects compact galaxy difference between the two light fields returning to the enough to reach an orbital frequency of 75 Hz without beam transmitting an optical signal proportional to Find largesplitter, number contact. Furthermore, the decay of the waveform after it the gravitational-wave strain to the output photodetector. peaks is consistent with the damped oscillations of a black of millisecond To achieve sufficient sensitivity to measure gravitational hole relaxing to a final stationary Kerr configuration. waves, detectors include several enhancements to the forthetiming Below, we present a general-relativistic analysis pulsars of basic Michelson interferometer. First, each arm contains a GW150914; Fig. 2 shows the calculated waveform using Find resonant rare pulsaroptical cavity, formed by its two test mass mirrors, the resulting source parameters. multiplies the effect of a gravitational wave on the light blackthat hole binary phase by a factor of 300 [48]. Second, a partially transiii. DETECTORS systems missive power-recycling mirror at the input provides addi1.4 GHz/400 MHz/1024 T/G = 0.25 Jy 600 s Gravitational-wave astronomy exploits multiple, widely tional resonant buildup of theska: laser light in the interferometer separated detectors to distinguish gravitational waves from as a whole [49,50]: 20 W of laser input is increased to 700 W 11 local instrumental and environmental noise, to provide incident on the beam splitter, which is further increased to source sky localization, and to measure wave polarizations. 100 kw circulating in each arm cavity. Third, a partially The LIGO sites each operate a single Advanced LIGO transmissive signal-recycling mirror at the output optimizes Pulsar Timing Array Galactic Census of Pulsars

3 The importance of sensitivity Arecibo 3 December Square Kilometer 13 SKA Sensitivity Reaches New Classes of Objects SKA s large field-of-view for surveys and transient events in 10 9 galaxies! HST VLA SKA Mpc at z = 2 SKA 6cm HST SKA 20 cm ALMA 15 ~ 1 deg. 16 SKA Technology Overview Three Antenna Types Needed The SKA is the next generation radio telescope at meter/centimeter wavelengths ~ $3B project, construction start ~ countries, 55 institutions involved US deeply involved in planning SKA, but not currently a member > $500M already committed to tech. tech. development and development and prototypes Sparse dipole array at low frequencies: GHz Dense aperture array at medium frequencies: GHz Parabolic dishes at high frequencies: 1.0 GHz to ~10-20 GHz 17 18

4 SKA Animation Terrestrial Interference Drives Site Selection Forte satellite: 131MHz O " O" South Africa Western Australia 19 FORTÉ satellite: 131 MHz 20 Possible SKA configuration in Africa SKA Prototype in South Africa SKA Core Site in the Karoo desert region of South Africa m composite antenna for MeerKAT prototype array Antenna construction building Antenna mounts arriving at site 22 SKA combines many small antennas over a large area Dense Core + Remote Stations Wide range of baseline lengths 200km 23 24

5 SKA Prototype in Australia SKA Core Site in Australia 12-m antennas for Australian SKA Pathfinder (ASKAP) array SKA Engineering Challenge: Lower cost through mass-produced antennas and receivers Example: Allen Telescope Array 6.1 m offset parabolas GHz (simultaneously) 42 antennas installed so far One-piece 15 x 18 m composite reflector developed by China Lower cost through simple mechanical & electrical systems Example: SKA Low Freq Antennas and Receivers LOFAR, MWA, and LWA (shown) serve as SKA prototypes for low frequency Uncooled LNAs, simple antenna kits 29 Fig. 7. Feeding of current antenna including the LNA boards. 30

6 SKA LF Antenna Impedance Imaginary part (measured) Imaginary part (simulated) Real part (measured) Real part (simulated) 200 real part Z /Ohm imaginary part Freq /GHz High Frequency Receivers MMIC Technology to Array Receiver Cost Multifunction MMIC packaging of Ka band dual-downconverter for the DSN array reduces size and replication cost by an order of magnitude IF Assembly of Connectorized, Single-Function Parts IF 50 cm Multi-Function MMIC Module IF 11 cm IF RF LO LO RF RF RF Enables high survey speed and extreme flexibility Uncooled LNA are OK Digital signal processing is challenging Lower cost through massproduced wideband feeds

7 Multiple Simultaneous Beams SKA Poster Low-Frequency Prime Focus Feed Options for US SKA 12/16m Reflector Decade Bandwidth Single Dual-Polarized Feed for 0.1 Feeds to 1.5 GHz Feed is 0.46 λ MAX Square. Reflector Beamwidths are 2.2 O at 700 MHz, 1.1 O at 1420 MHz 37-Element Focal Plane Array of 0.7 to 1.4 GHz Kildal-Type Feeds FOV 173 deg 2 Feed is 1.38m Square at 700 MHz Chalmers Log-Periodic Feed Single Polarized 1-6 GHz Test Model Dual-Polarized 1.2 to 11 GHz Under Construction 2m Diameter Gregorian Subreflector Locus for 1dB Gain Loss at 1420 MHz for F/D= m Diameter Gregorian Subreflector NTENNA Decade Bandwidth Feeds SKA computing challenges oss-polar far-field patterns in the 45 plane of the ponents only. UMERICAL DESIGN ering a simple feed consisting of two s separated by a half wavelength and lone. This is as explained in the introducves a pattern with equal E- and H-planes the ground plane [3]. Our idea was then pole by log-periodic series-fed dipoles, rying dipole length, spacing and height see Fig. 2. The initial studies were made e soon found out that the dipoles needed ed together in such a way that the feed le is connected to a gap in the normally f the previous dipole. The studies were on strip models of the dipoles to enable lectric circuit board. ce characteristics and radiation patterns ly used the method of moments (MoM) ommercial code WIPL-D [29], but we MoM code described in [30] for some tion. numerical results obtained for the feed 0.15 to 1.5 GHz, thereby covering a that we believe that, in principle, there it to the bandwidth of the log-periodic objective in the SKA application is to h feeds. In practice the bandwidth is nate of the feed at low frequencies and by ing cables at higher frequencies. Fig. 2 t longest dimensions of the feed. These rms of the wavelength at 100 MHz. All ipoles such as length L, separation D, ane h, and strip width, are scaled with log-periodic shape. The scaling factor excited with a delta voltage source behe split transmission line originating in ctric support is neglected. Furthermore ere done for one linear polarization to fort. The finite ground plane is included ows typical far-field patterns in the GHz similar to the patterns shown Fig. 4. Computed directivity of the antenna in Fig. 2. Fig. 5. Computed return loss of the antenna in Fig. 2. Fig. 6. Computed phase center location of the antenna in Fig. 2. in [22] for an eleven antenna covering 1 to 12 GHz. Fig. 4 shows the directivity of the feed as a function of frequency. In Fig. 5 we see the return loss of the feed at the feed point. This constitutes the main drawback of the feed. The return loss is not better than 5.0 db at the worst frequencies, but we are confident it can be improved. One of the major advantages of the feed is shown in Fig. 6 which presents the phase center location as a function 39 Parallel processing 1 EFlop ~ 1 billion cores How do we program these? Computing power requirements 1Eflop = 350MW at IBM Blue Gene efficiency Need one to two orders of magnitude improvement Data flow Data rate ~ 1 EB/day Computing Potentially Possible 41 42

8 SKA Member Countries SKA Timeline 2000 Initial SKA Concept Developed 2005 International Agreement on Sites 2014 Prototype Design, PDR Detailed Design SKA1 Construction 2020 SKA1 Early Science SKA2 Design 45