Swift detection of an outburst from SGR Swift J1555.2-5402
Abstract
At 06:53:27 UT, the Swift Burst Alert Telescope (BAT) triggered on a burst from the Soft Gamma-ray Repeater Swift J1555.2-5402 (trigger=1070298). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 238.836, -54.070 which is RA(J2000) = 15h 55m 21s Dec(J2000) = -54d 04' 12" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single structure with a duration of about 0.1 sec. The peak count rate was ~2700 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 06:54:47.7 UT, 80.4 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source with an enhanced position: RA, Dec 238.7859, -54.0617 which is equivalent to: RA(J2000) = 15h 55m 08.61s Dec(J2000) = -54d 03' 42.2" with an uncertainty of 1.9 arcseconds (radius, 90% containment). This location is 109 arcseconds from the BAT onboard position, within the BAT error circle. This position is consistent with the previously-reported position of Swift J1555.2-5402 (GCN 30122). This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. We cannot determine whether the source is fading at the present time. A power-law fit to a spectrum formed from promptly downlinked event data does not constrain the column density. UVOT took a finding chart exposure of 150 seconds with the White filter starting 85 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain, extinction expected.
- Publication:
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GRB Coordinates Network
- Pub Date:
- August 2021
- Bibcode:
- 2021GCN.30711....1B