[vsnet-grb-info 16797] GRB 140724A: Continued RATIR Optical Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18078
SUBJECT: GRB 140724A: Continued RATIR Optical Observations
DATE:    15/07/27 21:00:53 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan at astro.unam.mx>

Alan M. Watson (UNAM), Nat Butler (ASU), Alexander Kutyrev (GSFC), William 
H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), 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), 
and Harvey Moseley (GSFC) report:

We reobserved the field of the LAT GRB 150724B (Bissaldi et al., GCN 
18065) 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 2015/07 27.24 to 
2015/07 27.47 UTC (8819.11 to 8824.45 hours after the Fermi trigger), 
obtaining a total of 4.01 hours exposure in the r and i bands.

We detect the source we previously reported (Butler et al. GCN 18072) at 
23:27:33.82 +3:49:06.8 (J2000, ±0.5"). In comparison with the SDSS DR9, we 
obtain the following detections:

   r	23.50 ± 0.19
   i	23.99 ± 0.27

These magnitudes are in the AB system and are not corrected for Galactic 
extinction in the direction of the GRB.

A naive comparison to our observations from the previous night would 
suggest that the source has not faded in r but has faded in i. However, 
examining the images in detail, we suspect that our photometry in i from 
the first night might be influenced by a spuriously bright pixel. We 
therefore discount the apparent fading in i.

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