Swift detection of a new transient Swift J1728.9-3613

ATel #12436; S. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester), D. M. Palmer (LANL) and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift Observatory Team:
on 28 Jan 2019; 01:54 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)

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At 01:22:25 UT, the Swift Burst Alert Telescope (BAT) triggered and located a new transient which we name Swift J1728.9-3613 (trigger=886157, GCN #23800). The BAT on-board calculated location is RA, Dec 262.232, -36.237 which is

RA(J2000) = 17h 28m 56s,
Dec(J2000) = -36d 14' 13",

with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As is normal for an image trigger, the onboard light-curve showed no significant structure.

Due to a Sun observing constraint, Swift cannot slew to the BAT position until 09:11 UT on 2019 January 29. There will thus be no XRT or UVOT data for this trigger before this time.

The rise of this transient was seen by the BAT transient monitor (Krimm et al., 2013), with the first detection on 2019 January 25. The BAT light-curve can found at the link below.

We note that this transient has also been reported as being detected by MAXI.

BAT Transient Monitor lightcurve of Swift J1728.9-3613