{
  "bibcode": "2016GCN.19011....1V",
  "body": "S. V. Vadawale (PRL), T. Chattopadhyay  (PRL),  N. P. S. Mithun (PRL),\nA. R. Rao (TIFR),  D. Bhattacharya (IUCAA), Varun Bhalerao (IUCAA)\nreport on behalf of the Astrosat CZTI collaboration:\n\nAstrosat CZT Imager detected GRB 160131A (Page and Barthelmy, GCN 18951)\nat an incident angle of 63 degrees from the telescope pointing axis.\nThe T90 was measured to be 106 s and 97 s in 30 - 100 keV and 100 - 300\nkeV respectively. CZTI being sensitive to polarimetry [Chattopadhyay et\nal, 2014, EXPA, Vadawale et al 2015, A&A], we have analysed the double\nevents due to Compton scattering and detect a clear azimuthal modulation\nof 0.30 +/- 0.12 %, with a detection significance of 2.5 sigma. Based on a\npreliminary mass modelling, we estimate that the source polarisation\nfraction lies between ~ 50 - 60 % in 100-300 keV band.  A detailed mass \nmodeling to refine this measurement and its estimated uncertainty is in \nprogress.  In an earlier event, GRB 151006A (Bhalerao et al. GCN 18422) \nCZT Imager data showed a marginal evidence for polarisation signal.  From \nthe higher detection confidence for this brighter GRB160131A, we estimate \nthat CZT Imager can provide time resolved spectro-polarimetry for GRBs \nwith fluence larger than 10^-4 erg per cm^2.\n\nThis message may be cited.",
  "circularId": 19011,
  "createdOn": 1455283386000,
  "email": "dipankar@iucaa.in",
  "subject": "GRB160131A: detection of polarisation by Astrosat CZTI",
  "submitter": "Dipankar Bhattacharya at IUCAA  <dipankar@iucaa.in>",
  "eventId": "GRB 160131A"
}