Hard X-ray polarimetry with Astrosat-CZTI

Vadawale, S.; Chattopadhyay, Tanmoy; Rao, A. R.; Bhattacharya, Dipankar; Bhalerao, V.; Vagshette, N. D.; Pawar, Pramod; Sreekumar, S.

doi:10.1051/0004-6361/201525686

Cited by 62 publications

(57 citation statements)

References 33 publications

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“…The most exciting feature of this new instrument is its capability to measure the polarisation signals above 100 keV (Chattopadhyay et al 2014;Vadawale et al 2015). One good feature of the CZT Imager is the continuous availability of the time-tagged data so that no additional modes are required to be activated to measure the polarisation signature.…”

Section: Discussionmentioning

confidence: 99%

Astrosat CZT Imager Observations of GRB 151006a: Timing, Spectroscopy, and Polarization Study

Rao

Chand

Hingar

et al. 2016

ApJ

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AstroSat is a multi-wavelength satellite launched on 2015 September 28. The CZT Imager of AstroSat on its very first day of operation detected a long duration gamma-ray burst (GRB) namely GRB 151006A. Using the off-axis imaging and spectral response of the instrument, we demonstrate that CZT Imager can localise this GRB correct to about a few degrees and it can provide, in conjunction with Swift, spectral parameters similar to that obtained from Fermi /GBM. Hence CZT Imager would be a useful addition to the currently operating GRB instruments (Swift and Fermi ). Specifically, we argue that the CZT Imager will be most useful for the short hard GRBs by providing localisation for those detected by Fermi and spectral information for those detected only by Swift. We also provide preliminary results on a new exciting capability of this instrument: CZT Imager is able to identify Compton scattered events thereby providing polarisation information for bright GRBs. GRB 151006A, in spite of being relatively faint, shows hints of a polarisation signal at 100-300 keV (though at a low significance level). We point out that CZT Imager should provide significant time resolved polarisation measurements for GRBs that have fluence 3 times higher than that of GRB 151006A. We estimate that the number of such bright GRBs detectable by CZT Imager is 5 -6 per year. CZT Imager can also act as a good hard X-ray monitoring device for possible electromagnetic counterparts of Gravitational Wave events.

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Section: Discussionmentioning

confidence: 99%

Astrosat CZT Imager Observations of GRB 151006a: Timing, Spectroscopy, and Polarization Study

Rao

Chand

Hingar

et al. 2016

ApJ

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“…It was also experimentally verified before launch using polarized X-rays and more importantly, using unpolarized X-rays 8 . Thus CZTI is the first hard X-ray polarimeter in recent times having ground calibration with unpolarized X-rays.…”

Section: Hard X-ray Polarizationmentioning

confidence: 93%

Cadmium-Zinc-Telluride Imager On-Board Astrosat:A Multi-Faceted Hard X-Ray Instrument

Rao¹,

Bhattacharya²,

Bhalerao³

et al. 2017

Current Science

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The AstroSat satellite is designed to make multiwaveband observations of astronomical sources and the Cadmium-Zinc-Telluride Imager (CZTI) instrument of AstroSat covers the hard X-ray band. CZTI has a large area position-sensitive hard X-ray detector equipped with a coded aperture mask, thus enabling simultaneous background measurements. Ability to record simultaneous detection of ionizing interactions in multiple detector elements is a special feature of the instrument, and this is exploited to provide polarization information in the 100-380 keV region. CZTI provides sensitive spectroscopic measurements in the 20-100 keV region, and acts as an all-sky hard X-ray monitor and polarimeter above 100 keV. During the first year of operation, CZTI has recorded several gamma-ray bursts, measured the phase-resolved hard X-ray polarization of the Crab pulsar, and the hard X-ray spectra of many bright galactic X-ray binaries. The excellent timing capability of the instrument has been demonstrated with simultaneous observation of the Crab pulsar with radio telescopes like Gaint Metrewave Radio Telescope and Ooty Radio Telescope.

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“…The double pixel events within the photon tagging time window of 40 µs which satisfy the Compton kinematics are identified as valid Compton events. The validity of the Compton event selection and the polarization measurement capability of CZTI have been established by detailed simulation and experimental studies during ground calibration of CZTI (Chattopadhyay et al 2014;Vadawale et al 2015). The first onboard validation of CZTI polarimetry was obtained with the detection of polarization of GRB 160131A (Vadawale et al 2016) and GRB 151006A .…”

Section: Polarization Measurement -Further Evidence For the Second Pumentioning

confidence: 99%

Surprise in simplicity: an unusual spectral evolution of a single pulse GRB 151006A

Basak

Iyyani

Chand

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present a detailed analysis of GRB 151006A, the first GRB detected by Astrosat CZT Imager (CZTI). We study the long term spectral evolution by exploiting the capabilities of Fermi and Swift satellites at different phases, which is complemented by the polarization measurement with the CZTI. While the light curve of the GRB in different energy bands show a simple pulse profile, the spectrum shows an unusual evolution. The first phase exhibits a hard-to-soft (HTS) evolution until ∼ 16 − 20 s, followed by a sudden increase in the spectral peak reaching a few MeV. Such a dramatic change in the spectral evolution in case of a single pulse burst is reported for the first time. This is captured by all models we used namely, Band function, Blackbody+Band and two blackbodies+power law. Interestingly, the Fermi Large Area Telescope (LAT) also detects its first photon (> 100 MeV) during this time. This new injection of energy may be associated with either the beginning of afterglow phase, or a second hard pulse of the prompt emission itself which, however, is not seen in the otherwise smooth pulse profile. By constructing Bayesian blocks and studying the hardness evolution we find a good evidence for a second hard pulse. The Swift data at late epochs (> T 90 of the GRB) also shows a significant spectral evolution consistent with the early second phase. The CZTI data (100-350 keV), though having low significance (1σ), show high values of polarization in the two epochs (77% to 94%), in agreement with our interpretation.

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Hard X-ray polarimetry with Astrosat-CZTI

Cited by 62 publications

References 33 publications

Astrosat CZT Imager Observations of GRB 151006a: Timing, Spectroscopy, and Polarization Study

Astrosat CZT Imager Observations of GRB 151006a: Timing, Spectroscopy, and Polarization Study

Cadmium-Zinc-Telluride Imager On-Board Astrosat:A Multi-Faceted Hard X-Ray Instrument

Surprise in simplicity: an unusual spectral evolution of a single pulse GRB 151006A

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