GCN Circular 25144
Subject
GRB 190719C: optical afterglow confirmation
Date
2019-07-24T08:31:42Z (5 years ago)
From
Kasper Elm Heintz at Univ. of Iceland and DAWN/NBI <keh14@hi.is>
Kasper E. Heintz (Univ. Iceland), Daniele B. Malesani (DTU Space), Daniel A. Perley (LJMU), Shane Moran (NOT and Univ. Turku), report on behalf of a larger collaboration:
We observed again the field of GRB 190719C (Ambrosi et al., GCN 25106; Poolakkil & Meegan, GCN 25130) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A coadded exposure of 3000 s was collected in the SDSS r filter, starting on July 21.125 UT (1.501 days after the GRB).
The source first noticed in our previous observation (Malesani et al., GCN 25110) visually faded and is no longer clearly detected. This was quantitatively confirmed by carrying out image subtraction between the two epochs. A clear residual is visible at coordinates (J2000):
RA = 16:00:49.58
Dec = 13:00:04.5
This is approximately 0.7" west of the object visible in the archival Pan-STARRS images.
Photometry of the transient computed on the subtraction image (calibrated against nearby stars from the Pan-STARRS catalog) yields r = 23.03 +- 0.12 AB at epoch July 19.88 UT (Malesani et al., GCN 25110). We caution that the actual brightness would be higher if significant residual light were present in our second epoch of observation (this would be ~20% for a t^-1 decay).
The consistency with the X-ray afterglow position (Beardmore et al., GCN 25125) and the optical fading confirm that the source above is the afterglow of GRB 190719C. The close angular proximity with the object seen in the Pan-STARRS images suggests it to be the GRB host galaxy.