Julia Saleh-Natur, Ehud Behar, Omer Reich, Shlomit Tarem, Zvika Tarem, Alex Vdovin, Amir Feigenboim, Roi Rahin, Avner Kaidar, Hovannes Agalarian, Alon Osovizky, Max Ghelman
We present a full-size engineering model of GALI - The GAmma-ray burst Localizing Instrument, composed of 362 CsI(Tl) small cubic scintillators, distributed within a small volume of ∼ 2l, and read out by silicon photomultipliers. GALI can provide directional information about GRBs with high angular accuracy from angledependent mutual obstruction between its scintillators. Here, we demonstrate GALI’s laboratory experiments with an 241Am source, which achieved directional reconstruction of <3° accuracy, in agreement with our Monte- Carlo simulations. GALI has a wide field view of the unobstructed sky. With its current cubic configuration, GALI’s effective area varies between 97 cm2 (face on) and 138 cm2 (from the corners at 45°), which is verified in the current experiment.
The detection of astrophysical Gamma-Ray Bursts (GRBs) has always been intertwined with the challenge of identifying the direction of the source. Accurate angular localization of better than a degree has been achieved to date only with heavy instruments on large satellites, and a limited field of view. The recent discovery of the association of GRBs with neutron star mergers gives new motivation for observing the entire γ-ray sky at once with high sensitivity and accurate directional capability. We present a novel γ-ray detector concept, which utilizes the mutual occultation between many small scintillators to reconstruct the GRB direction. We built an instrument with 90 (9 mm)3 CsI(Tl) scintillator cubes attached to silicon photomultipliers. Our laboratory prototype tested with a 60 keV source demonstrates an angular accuracy of a few degrees for ∼25 ph cm−2 bursts. Simulations of realistic GRBs and background show that the achievable angular localization accuracy with a similar instrument occupying 1l volume is < 2° . The proposed concept can be easily scaled to fit into small satellites, as well as large missions.
ISS-TAO is a mission selected for a concept study by NASA, and proposed by GSFC for launch to the International Space Station (ISS) in order to observe transient high-energy astrophysical sources. It is composed of an X-ray Wide-Field Imager (WFI), and a multi-directional Gamma-ray Transient Monitor (GTM). WFI will be built by NASA/GSFC while the secondary GTM, described in this article is contributed by the Israel Space Agency (ISA) and developed at the Technion, Israel Institute of Technology, in collaboration with Israel space industries. ISS-TAO's main science goal is to detect electromagnetic (EM) counterparts to gravitational waves (GW) detected by GW observatories, such as the Laser Interferometer GW Observatory (LIGO). Observations of simultaneous GW and EM counterparts will address fundamental questions on the nature of coalescing neutron stars and black holes as astrophysical GW sources. An EM detection will also increase LIGO’s sensitivity to detecting these events above the GW background. Promising candidates for LIGO GW sources and EM counterparts are coalescing neutron star binaries, which are now known to also emit a short Gamma-Ray Burst (sGRB). The GTM will measure these GRBs and other transient gamma-ray events, and will trigger the WFI, with or without a GW trigger. The concept of the GTM detector consists of a compact configuration of 4 segments, which will allow a fair angular resolution of a few hundred square degrees, which will facilitate a prompt follow up. Each of the GTM segments consists of a crystal scintillator, a photo-multiplier tube (PMT), followed by analog and digital electronics designed to reconstruct the energy of each incoming photon, and to yield the light-curve and spectrum of any gamma-ray transient. A central CPU then calculates the ratio of the signal of each one of the segments, and deduced the transient position relative to the GTM.
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