TITLE:   GCN CIRCULAR
NUMBER:  17343
SUBJECT: GRB 150120B: RATIR Optical and NIR Observations
DATE:    15/01/21 21:24:35 GMT
FROM:    Nat Butler at Az State U  <natbutler@asu.edu>

Nat Butler (ASU), Alan M. Watson (UNAM), 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), Jos� A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes�s
Gonz�lez (UNAM), Carlos Rom�n-Z��iga (UNAM), Neil Gehrels (GSFC), and
Harvey Moseley (GSFC) report:

We observed the field of GRB 150120B (D'Elia, et al., GCN 17314) 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 2015/01 21.09 to 2015/01 21.29 UTC (18.73 to
23.64 hours after the BAT trigger), obtaining a total of 3.91 hours
exposure in the r, i, and z bands.

For a source coincident with the GROND optical transient (Wiseman et al.,
GCN 17336), in comparison with 2MASS, we obtain the following detections
and upper limit (3-sigma):

  r = 23.4 +/- 0.2
  i = 22.6 +/- 0.1
  z > 20.72

These magnitudes 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 Astron�mico Nacional in San Pedro
M�rtir.