GCN Circular 26062
Subject
GRB 191019A: NOT optical afterglow and host association confirmation
Date
2019-10-23T21:55:37Z (6 years ago)
From
Daniel Perley at Liverpool JMU <d.a.perley@ljmu.ac.uk>
D. A. Perley (LJMU), D. B. Malesani (DTU Space), A. J. Levan (Radboud
Univ.), J. P. U. Fynbo (DAWN/NBI), and A. A. Djupvik (NOT) report on
behalf of a larger collaboration:
We obtained additional observations of the optical counterpart (Reva et
al., GCN 26036; LaPorte & Simpson, GCN 26053; Zhu et al., GCN 26059) of
GRB 191019A (Simpson et al., GCN 26031), using the Nordic Optical
Telescope (NOT) equipped with the ALFOSC camera. A total of 25 minutes
exposure was secured with mid time Oct 22.875 UT (77.8 hr after the GRB).
The archival object consistent with the XRT error circle is well
detected, with a magnitude of i = 18.71 +/- 0.02 AB, consistent with the
Pan-STARRS tabulated value of i = 18.71 +/- 0.01 and slightly fainter
than our earlier observation (Perley et al., GCN 26039), for which the
mid time was 4.60 hr after the GRB.
Digital image subtraction was carried out with ISIS (Alard 2000, A&AS,
144, 363) between the two epochs. A clear point-like residual is
detected, for which we measure a magnitude i = 21.78 +/- 0.05 AB
(assuming no residual flux in our second epoch). Its position calibrated
against the Gaia catalog is:
RA(J2000) = 22:40:05.89
Dec(J2000) = -17:19:42.6
(+/- 0.3")
An image showing the subtraction result is available here:
http://outer.space.dtu.dk/~dmales/GRB/191019A/subtraction.jpg
The transient location is 0.07" east of the galaxy nucleus,
strengthening the case for a physical association between the two
objects. The offset is within the margin of error, although the NOT
spectroscopy (Fynbo et al., GCN 26041) does not suggest that the source
is an AGN.
Our observations thus confirm the presence of a transient optical source
at a position consistent with the X-ray afterglow, located to within the
errors on top of the nucleus of the candidate host. The lack of any
non-obscured star formation makes this system unique among long-duration
GRBs.
We encourage observations of this puzzling source at all wavelengths.
DisclaimerNone