[vsnet-grb-info 16864] GRB 150817A: Continued RATIR Observations, Revised Candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18145
SUBJECT: GRB 150817A: Continued RATIR Observations, Revised Candidate
DATE:    15/08/17 06:16:09 GMT
FROM:    Nat Butler at UC berkeley  <natxbutler at gmail.com>

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

We continue to observe the field of GRB 150817A (V. D'Elia, et al., GCN 18143) 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 2015/08 17.14 to 2015/08 17.25 UTC (1.29 to 3.93 hours after the BAT trigger), obtaining a total of 2.13 hours exposure in the r, i, and z bands.

We note that the source reported in Butler et al. (GCN 18144) appears to have remained constant in flux over the time period quoted above, while an uncatalogued source just west of the XRT error circle has faded strongly as t^(-0.8+/-0.1).  This second source is located at RA, Dec = 16:38:31.51, -12:03:9.6 (J2000, +/-0.5").

In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following detections and upper limit (3-sigma):

   r = 22.06 +/- 0.09
   i = 21.49 +/- 0.07
   z > 20.33

These magnitudes, corresponding to the midpoint of our observation, are in the AB system and are not corrected for Galactic extinction in the direction of the GRB.

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