[vsnet-grb-info 23963] GRB 191019A: NOT optical afterglow and host association confirmation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26062
SUBJECT: GRB 191019A: NOT optical afterglow and host association confirmation
DATE:    19/10/23 21:55:37 GMT
FROM:    Daniel Perley at Liverpool JMU  <d.a.perley at 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