AstroSat/LAXPC observed 4U 1630-472 on very first day of a new outburst

ATel #9515; J S Yadav, Jai Verdhan Chauhan, P C Agrawal, H M Antia, Mayukh Pahari, V R Chitnis, Ranjeev Misra, Dhiraj Dedhia, Tilak Katoch, P. Madhwani, R K Manchanda, B Paul, Parag Shah, Diego Altamirano, P Gandhi, K H Navalgund, K S Sarma, S Seetha, and K Subbarao
on 20 Sep 2016; 13:38 UT
Credential Certification: J S Yadav (jsyadav@tifr.res.in)

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We have observed 4U 1630-472 on 1st day of outburst during 01:07(UT) 27th August to 01.20(UT) 28 August, 2016 with AstroSat/LAXPC. 4U 1630-472 is a transient black hole X-ray binary. MAXI/GSC has reported start of a new outburst on 2016 August 27 (MJD57627) with detection at ~23 mCrab and one day averaged 4-10 keV flux increases by a factor of 10 in a day (ATel#9462). The AstroSat/LAXPC photon flux in 3-80 keV energy range has increased by a factor of 6 during this observation. A preliminary spectral analysis shows that the energy spectrum is hard with gamma 1.47 +/- 0.04 at the start of the observation. The energy spectrum softens with flux and Gamma changes to 1.82 (+0.07-0.076) at the end of the observation. The thermal flux is increased by a factor of ~13 while non thermal flux is increased by a factor of ~2. The non thermal contribution to total flux is decreased from ~ 90% to ~ 65%. Absorption column density is taken to be fixed at 6*10^22 during this analysis. We plan to follow this source with AstroSat/LAXPC on 28th September 2016 and multi wavelength observations are encouraged.