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 (GSFC/STScI), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jos� A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes�s Gonz�lez (UNAM), Carlos Rom�n-Z��iga (UNAM), Neil Gehrels (GSFC), Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report:
We observed the field of GRB 150910A (Pagani et al., GCN 18264) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astron�mico Nacional on Sierra San Pedro M�rtir from 2015/09 14.17 to 2015/09 14.46 UTC (90.88 to 98.01 hours after the BAT trigger), obtaining a total of 1.71 hours exposure in the r, i, and z bands.
The optical afterglow (Pagani et al.; Zheng and Filippenko, GCN 18265) is well detected. In comparison with the SDSS DR9 catalog, we obtain:
r = 22.23 +/- 0.09
i = 22.44 +/- 0.10
z > 19.89 (3-sigma)
These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. Compared to our previous night of observations (Butler et al., GCN 18302), the source flux is consistent with remaining constant at the ~1-sigma level. Also, the source appears to be extended in our images, suggesting that the flux may be dominated by the GRB host galaxy.
We thank the staff of the Observatorio Astron�mico Nacional in San Pedro