Swift/BAT detection of a 13 crab hard X-ray flare from the FSRQ SDSS J002829.81+200026.7

ATel #12120; Shangyu Sun, Dongming Mao, Jie Lin and Wenfei Yu (Shanghai Astronomical Observatory)
on 17 Oct 2018; 20:33 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Wenfei Yu (wenfei@shao.ac.cn)

Tweet

With the All Sky Automated Survey for SuperNovae (ASAS-SN), the flat-spectrum radio quasar (FSRQ) SDSSJ002829.81+200026.7 (z=1.552007; Alam et al. 2015) was optically detected on 2018 October 3-6 in a rapid, unprecedented factor ~100 outburst (Stanek et al. ATel #12082). Fermi-LAT reported that this source was in a gamma-ray high state during October 3-5, 2018 (Buson et al. ATel #12084), with a peak gamma-ray flux on October 4. Swift/XRT observations in October 8-9 have shown the source was under a decay in soft X-rays(Komossa et al. ATel #12094). We have investigated the observations in the same period by the Burst Alert Telescope (BAT) on board Neil Gehrels Swift observatory. We found BAT had also observed a extreme hard X-ray (15-150 keV) flare from a source coincident with the position of SDSS J002829.81+200026.7 at (R.A., Dec) = (7.124 deg, -20.007 deg)(J2000). The BAT peak flux of the flare was 13.3 +- 0.2 Crab (14.0-194.9 keV, 1 sigma error) on 2018-10-05.59265 UT. The rise of the bright hard X-ray flare was extremely rapid. The flux increased by a factor of 9.7 in about 280 seconds, and then decreased by a factor of 31 in < 4300 seconds. In the period between the BAT observation of the apparent flare peak and the following BAT survey observations, the source was outside the field of view of BAT. The entire duration of the hard X-ray flare is thus estimated shorter than about 76 minutes. Such a bright hard X-ray flare and its fast rise and rapid decay, are very rare for flares seen in quasars. The hard X-ray flare is probably associated with some violent jet activities, which deserves further multi-wavelength and multi-messenger investigations.

We would like to mention that the source is also known as TXS 0025+197 (Douglas et al. 1996 AJ, 111.1945D). We thank the Neil Gehrels Swift observatory for kindly providing the data to the public.