[vsnet-grb-info 20364] GRB 180305A: RATIR Optical Afterglow Candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22460
SUBJECT: GRB 180305A: RATIR Optical Afterglow Candidate
DATE:    18/03/06 11:24:41 GMT
FROM:    Eleonora Troja at GSFC  <eleonora.troja at nasa.gov>

Eleonora Troja (GSFC), Nat Butler (ASU), Alan M. Watson (UNAM),
Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM),
Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB),
Antonino Cucchiara (UVI), Owen Littlejohns (ASU), Enrico
Ramirez-Ruiz (UCSC), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM),
Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and
Vicki Toy (UMD) report:

We observed the field of the LAT GRB 180305A (Axelsson, et al., GCN 22457)
with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org)
on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico
Nacional on Sierra San Pedro Mártir from 2018/03 6.11 to 2018/03 6.20 UTC
(17.28 to 19.45 hours after the burst), obtaining a total of 1.36 hours
exposure in the r and i bands.

At the position of source #2 found by Swift-XRT  (Evans, et al., GCN 
22459),
we detect a faint uncatalogued optical source. In comparison with the
USNO-B1 catalog, we obtain the following detections:

   r    = 21.95 +/- 0.12
   i    = 21.48 +/- 0.08

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.
The source is located at RA,Dec = 03:18:28.33,+32:06:36.2 (J2000, +/-0.5").

Further observations to establish fading of the optical source are planned.

We thank the staff of the Observatorio Astronómico Nacional in San Pedro
Mártir.