The Search for Fast Transients with CZTI

Sharma, Y.; Marathe, Aboli; Bhalerao, V.; Shenoy, V.; Waratkar, G.; Nadella, D.; Page, Pranav S.; Hebbar, Pavan R.; Vibhute, A.; Bhattacharya, Dipankar; Rao, A. R.; Vadawale, S.

doi:10.48550/arxiv.2011.07067

Cited by 4 publications

(5 citation statements)

References 4 publications

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“…AstroSat Cadmium Zinc Telluride Imager (CZTI; Bhalerao et al 2017) detected the second and third pulse of GRB 210204A, with a total of 18141 photons: 94% of which came from the brighter third pulse (Waratkar et al 2021;Sharma et al 2020). These two pulses were also clearly seen in the veto detectors.…”

Section: Astrosat Cztimentioning

confidence: 99%

The long-active afterglow of GRB 210204A: Detection of the most delayed flares in a Gamma-Ray Burst

Kumar,

Gupta,

Saraogi

et al. 2022

Preprint

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We present results from extensive broadband follow-up of GRB 210204A over the period of thirty days. We detect optical flares in the afterglow at 7.6 × 10 5 s and 1.1 × 10 6 s after the burst: the most delayed flaring ever detected in a GRB afterglow. At the source redshift of 0.876, the rest-frame delay is 5.8 × 10 5 s (6.71 d). We investigate possible causes for this flaring and conclude that the most likely cause is a refreshed shock in the jet. The prompt emission of the GRB is within the range of typical long bursts: it shows three disjoint emission episodes, which all follow the typical GRB correlations. This suggests that GRB 210204A might not have any special properties that caused late-time flaring, and the lack of such detections for other afterglows might be resulting from the paucity of late-time observations. Systematic late-time follow-up of a larger sample of GRBs can shed more light on such afterglow behaviour. Further analysis of the GRB 210204A shows that the late time bump in the light curve is highly unlikely due to underlying SNe at redshift (z) = 0.876 and is more likely due to the late time flaring activity. The cause of this variability is not clearly quantifiable due to the lack of multi-band data at late time constraints by bad weather conditions. The flare of GRB 210204A is the latest flare detected to date.

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Section: Astrosat Cztimentioning

confidence: 99%

The long-active afterglow of GRB 210204A: Detection of the most delayed flares in a Gamma-Ray Burst

Kumar,

Gupta,

Saraogi

et al. 2022

Preprint

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“…All light curves show a single pulse, with hints of sub-structure in during the rise in the smaller time bins (see Extended Data Figure 1). We process the 0.05 s light curves with the CIFT pipeline 103 , which incorporates better data analysis as compared to the quick-look pipeline and produces more robust results. Our reanalysis yields a peak time of UT 04:29:52.95 -consistent with the Fermi peak.…”

Section: Grbmentioning

confidence: 99%

Discovery and confirmation of the shortest gamma ray burst from a collapsar

Ahumada,

Singer,

Anand

et al. 2021

Preprint

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Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the universe.The duration and hardness distribution of GRBs has two clusters 1 , now understood to reflect (at least) two different progenitors 2 . Short-hard GRBs (SGRBs; T 90 <2 s) arise from compact binary mergers, while long-soft GRBs (LGRBs; T 90 >2 s) have been attributed to the collapse of peculiar massive stars (collapsars) 3 . The discovery of SN 1998bw/GRB 980425 4 marked the first association of a LGRB with a collapsar and AT 2017gfo 5 /GRB 170817A/GW170817 6 marked the first association of a SGRB with a binary neutron star merger, producing also gravitational wave (GW). Here, we present the discovery of ZTF20abwysqy (AT2020scz), a fast-fading optical transient in the Fermi Satellite and the InterPlanetary Network (IPN) localization regions of GRB 200826A; X-ray and radio emission further confirm that this is the afterglow. Follow-up imaging (at rest-frame 16.5 days) reveals excess emission above the afterglow that cannot be explained as an underlying kilonova (KN), but is consistent with being the supernova (SN). Despite the GRB duration being short (rest-frame T 90 of 0.65 s), our panchromatic follow-up data confirms a collapsar origin. GRB 200826A is the shortestLGRB found with an associated collapsar; it appears to sit on the brink between a successful and a failed collapsar. Our discovery is consistent with the hypothesis that most collapsars fail to produce ultra-relativistic jets.On August 26, 2020, at 04:29:52 UT, the Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope detected GRB 200826A with duration (T 90 ) of 1.14 ± 0.13 seconds in the 50-300 keV energy rangeIn addition to Fermi (GBM trigger 620108997), GRB 200826A was detected by four other Interplanetary Network (IPN) instruments (see Methods).The gamma-ray properties alone do not always yield an unambiguous classification. Some SGRBs show afterglow and host properties akin to LGRBs, e.g. Ref. 7 ; some LGRBs show no evidence for collapsars to deep limits akin to SGRBs, e.g. Ref. 8 . Based solely on T 90 9 , GRB 200826A has a SGRB probability of 65% +12 −11 . Also taking into consideration the E peak parameter of a Comptonized model fit to the single spectrum over the duration of the burst (see

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“…The background level is not constant: it varies slowly through the orbit (dominated by proximity to the South Atlantic Anomaly), and also shows variations across orbits (dominated by orbital precession and solar activity). It is known that these background variations for CZTI occur on timescales of several hundreds to thousands of seconds, and is wellapproximated by a quadratic function (Sharma et al, 2020) (Anumarlapudi et al, 2020). Hence we too model background as a quadratic function, b g (t) = a(t…”

Section: Background and Observed Fluxmentioning

confidence: 99%

“…At energies above ∼ 100 keV, the instrument and satellite structures become transparent to radiation, giving CZTI sensitivity to sources well outside the primary field of view. CZTI data have been used to detect over 400 Gamma Ray Bursts (GRBs) in the 5 years since launch (Sharma et al, 2020), and even study the Crab pulsar at angles from 5 • to 70 • from the principal axis (Anusree et al, 2021). However, CZTI faces the same limitations as other all-sky monitors for studying persistent astrophysical sources.…”

Section: Introductionmentioning

confidence: 99%

Using collimated CZTI as all sky X-ray detector based on Earth Occultation Technique

Singhal,

Srinivasan,

Bhalerao

et al. 2021

Preprint

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All-sky monitors can measure the fluxes of astrophysical sources by measuring the changes in observed counts as the source is occulted by the Earth. Such measurements have typically been carried out by all-sky monitors like CGRO-BATSE and Fermi-GBM. We demonstrate for the first time the application of this technique to measure fluxes of sources using a collimated instrument: the Cadmium Zinc Telluride detector on AstroSat. Reliable flux measurements are obtained for the Crab nebula and pulsar, and for Cyg X-1 by carefully selecting the best occultation data sets. We demonstrate that CZTI can obtain such measurements for hard sources with intensities 1Crab.Keywords. X-ray telescopes (1825) -Occultation (1148) -Astronomical techniques (1684).

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The Search for Fast Transients with CZTI

Cited by 4 publications

References 4 publications

The long-active afterglow of GRB 210204A: Detection of the most delayed flares in a Gamma-Ray Burst

The long-active afterglow of GRB 210204A: Detection of the most delayed flares in a Gamma-Ray Burst

Discovery and confirmation of the shortest gamma ray burst from a collapsar

Using collimated CZTI as all sky X-ray detector based on Earth Occultation Technique

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