| 1. |
- Chattopadhyay, Tanmoy, et al.
(author)
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Sub-MeV spectroscopy with AstroSat-CZT imager for gamma ray bursts
- 2021
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In: Journal of astrophysics and astronomy. - : Springer Nature. - 0250-6335 .- 0973-7758. ; 42:2
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Journal article (peer-reviewed)abstract
- Cadmium-Zinc-Telluride Imager (CZTI) onboard AstroSat has been a prolific Gamma-Ray Burst (GRB) monitor. While the 2-pixel Compton scattered events (100-300 keV) are used to extract sensitive spectroscopic information, the inclusion of the low-gain pixels (similar to 20% of the detector plane) after careful calibration extends the energy range of Compton energy spectra to 600 keV. The new feature also allows single-pixel spectroscopy of the GRBs to the sub-MeV range which is otherwise limited to 150 keV. We also introduced a new noise rejection algorithm in the analysis ('Compton noise'). These new additions not only enhances the spectroscopic sensitivity of CZTI, but the sub-MeV spectroscopy will also allow proper characterization of the GRBs not detected by Fermi. This article describes the methodology of single, Compton event and veto spectroscopy in 100-900 keV combined for the GRBs detected in the first year of operation. CZTI in last five years has detected similar to 20 bright GRBs. The new methodologies, when applied on the spectral analysis for this large sample of GRBs, has the potential to improve the results significantly and help in better understanding the prompt emission mechanism.
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| 2. |
- Iyyani, Shabnam, et al.
(author)
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Study of the Prompt Emission of Short Gamma-Ray Bursts Using a Multicolor Blackbody : A Clue to the Viewing Angle
- 2021
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In: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 255:2
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Journal article (peer-reviewed)abstract
- The prompt emission of short gamma-ray bursts (sGRBs) with known redshifts is analyzed using the model of a multicolor blackbody, which is interpreted as the emission from a nondissipative photosphere taking into account a power-law jet structure and the viewing geometry of the jet. We find nearly 69% and 26% of the sample is consistent with a multicolor blackbody and a pure blackbody model, respectively. Using this interpretation, we infer that nearly 57% (18%) of the sGRBs in our sample are observed within (or along the edge of) the jet core. The sGRB jets are deduced to possess a narrow core with a median theta ( c ) similar to 3 degrees. This suggests the rate of sGRBs that would be viewed within the jet core to be 1.8-26 Gpc(-3) yr(-1). The power-law index of the decreasing Lorentz factor profile of the jet structure is deduced to be 1.3-2.2. The intrinsic luminosity is found to range between 10(48)-10(53) erg s(-1). The average values of the Lorentz factor and nozzle radius of the sGRB jets are inferred to be 210 (85) and 10(7.7) (10(9.6)) cm for the cases when the photosphere forms in the coasting (accelerating) phase, respectively. The viability of the inferred values of the different parameters of the GRB outflow and viewing geometry within this physical interpretation enhances the prospect of the photospheric emission model explaining the observed GRB spectrum.
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