GRB 180620A: Swift detection of a burst with an optical counterpart
Abstract
At 08:34:58 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180620A (trigger=843122). Swift slewed to the burst with a 3 min delay. The BAT on-board calculated location is RA, Dec 279.883, +23.265, which is RA(J2000) = 18h 39m 32s Dec(J2000) = +23d 15' 55" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows several overlapping peaks with a total duration of about 25 sec. The peak count rate was ~8000 counts/sec (15-350 keV), at ~12 sec after the trigger. The XRT began observing the field at 08:39:25.1 UT, 267.1 seconds after the BAT trigger. Using promptly downlinked data we find an uncatalogued X-ray source located at RA, Dec 279.89575, 23.24373 which is equivalent to: RA(J2000) = 18h 39m 34.98s Dec(J2000) = +23d 14' 37.4" with an uncertainty of 3.6 arcseconds (radius, 90% containment). This location is 87 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 1.60 x 10^21 cm^-2 (Willingale et al. 2013). UVOT took a finding chart exposure of nominal 150.000 seconds with the White filter starting 270 seconds after the BAT trigger. There is a candidate afterglow in the list of sources generated on-board at RA(J2000) = 18:39:35.08 = 279.89618 DEC(J2000) = +23:14:39.7 = 23.24437 with a 90%-confidence error radius of about 1.10 arc sec. This position is 1.7 arc sec. from the center of the XRT error circle. The estimated magnitude is 18.24. No correction has been made for the expected extinction corresponding to E(B-V) of 0.13. Burst Advocate for this burst is P. A. Evans (pae9 AT star.le.ac.uk). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.)
- Publication:
-
GRB Coordinates Network
- Pub Date:
- June 2018
- Bibcode:
- 2018GCN.22798....1E