Insight-HXMT detection of a bright short x-ray counterpart of the Fast Radio Burst from SGR 1935+2154

ATel #13687; Zhang S.-N., Tuo Y.-L, Xiong S.-L., Li C.-K, Xiao, S., Jia S.-M., Li, X. B., Ge M.-Y., Luo, Q., Li, B., Cai C., Tan Y., Xue W.-C., Lu F.-J., Song L.-M, Liu C.-Z, Chen, Y., Cao X.-L., Xu, Y.-P., Li, T.-P. (IHEP), Lin L. (BNU), Zhang B. (UNLV), on behalf of the Insight-HXMT team
on 29 Apr 2020; 19:05 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Yu-Peng Chen ([email protected])

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During the ToO observation of SGR 1935+2154 (GCN# 27662), Insight-HXMT detected a very bright short x-ray burst peaking at 14:34:24.5 UT of April 28 (denoted as T0). This burst lasted for about 1 s in 1-150 keV and was seen clearly in all three telescopes (HE: 20-250 keV, ME: 5-30 keV and LE: 1-10 keV) of Insight-HXMT, whose light curves, without correcting for significant data saturation for HE and moderate deadtime effects for LE and ME caused by its extreme brightness, can be found at: http://newshxmt.ihep.ac.cn/images/grb/SGR1935.png The timing of the light curve is consistent with INTEGRAL (Atel #13685), AGILE (Atel #13686) and Konus-Wind (GCN #27669) observations. A preliminary joint spectral fitting using HE, ME and LE data has been implemented, after correcting approximately for the total data saturation and deadtime effects. The best fit model (reduced chisq of 0.97, with DOF of 475) is cutoff power-law with nH=(2.60+/-0.17) E22/cm2, photon index=1.44+/-0.07, and cutoff energy=69.8+/-6.7 keV, and the unabsorbed total fluence from T0-0.5 s to T0+0.5 s is (6.8+/-0.1)E-07 erg/cm2 in 1-150 keV range. Either power-law or double blackbody model provides significantly worse fit. Considering that this burst is one of a series of 9 short bursts in a total exposure time of about 6 hours targeted on this active SGR source, and it has a typical SGR spectrum and duration, we confirm that this bright short burst originated from SGR 1935+2154. This burst occurred about 8.5 s before and is the closest one in Insight-HXMT data in time with the fast radio burst (14:34:33 UTC, topocentric arrival time at 400 MHz) reported by CHIME/FRB and STARE2 (Atel #13681 & 13684). This time delay is roughly consistent with the dispersion between x-ray and radio (as pointed out in Atel #13686), but nevertheless by about 4-5 seconds more, suggesting a possible intrinsic delay of the radio bursts with respect to the X-ray burst. In addition, the location of radio burst is consistent with the SGR within systematic error (Atel #13681). We therefore conclude that this bright short burst is the first confirmed X-ray counterpart of the Fast Radio Burst from SGR 1935+2154. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org.