AstroNote 2023-238

We report the discovery of a fast-evolving red transient by the Zwicky Transient Facility (ZTF). The transient has a coincident Fermi GRB counterpart [1].

AT 2023qxj (ZTF23abaanxz) was discovered at the position (J2000) of:

RA = 19:58:33.55 (299.6397739 deg)

Dec = +54:27:48.02 (54.4633396 deg)

on 2023-08-27 07:10:10.94 UT by ZTF at r = 17.11 +/- 0.04 mag (MJD=60183.26872). ZTF obtained a non-detection 1 day prior (MJD=60182.26553) at r > 20.18 mag, indicating a fast rise rate of >3 mag/day in r. ZTF also obtained detections later that night at r = 18.88 +/- 0.08 mag (MJD=60183.33919) and g = 19.27 +/- 0.16 mag (MJD=60183.40719), implying that the transient was red and fading quickly.

The Galactic latitude of AT 2023qxj is 12.8 degrees, and the Galactic reddening toward the direction of AT 2023qxj is: E_(g-r) = 0.227 from Schlafly & Finkbeiner (2011).

The fast rise, fast decay, red color, and lack of archival optical counterpart of AT 2023qxj make it a strong candidate afterglow. We identify the coincident GRB 230827256 discovered by Fermi at the position (J2000) of:

RA = 19:57:16.8 

Dec = +56:28:12

with an error radius of 2.17 deg. The time of the GRB trigger was 2023-08-27 06:08:31 UT (MJD=60183.25591), 18.45 minutes prior to the first ZTF detection of AT 2023qxj.

ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW.

[1] https://heasarc.gsfc.nasa.gov/db-perl/W3Browse/w3hdprods.pl?files=P&Tar…