[vsnet-grb-info 14130] GRB 131030A: Continued RATIR Optical and NIR Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15444
SUBJECT: GRB 131030A: Continued RATIR Optical and NIR Observations
DATE:    13/11/04 20:01:34 GMT
FROM:    Owen Littlejohns at Az State U  <olittlej at asu.edu>

Owen Littlejohns (ASU), 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), 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 again observed the field of GRB 131030A (Troja, et al., GCN Circ. 15402)
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 2013/11 4.10 to 2013/11 4.17 UTC (101.35
to 103.16 hours after the BAT trigger), obtaining a total of 1.04 hours
exposure in the r and i bands and 0.29 hours exposure in the Z, Y, J, and
H bands.

We continue to detect the uncatalogued source reported by UVOT (Troja et
al., GCN Circ. 15414) in the r, i and Z bands, at fainter magnitudes than
the previous epochs of RATIR observations (Littlejohns et al., GCN Circ.
15436; Littlejohns et al., GCN Circ. 15420). For a source within the
Swift-XRT error circle, in comparison with the SDSS DR9 and 2MASS, we
obtain the following detections and upper limits (3-sigma):

  r     22.48 +/- 0.13
  i     22.71 +/- 0.30
  Z     21.70 +/- 0.34
  Y     > 21.28
  J     > 21.05
  H     > 20.49

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. In comparison with the second epoch
of RATIR observations the source has faded by an average of 1.8 magnitudes
in the r, i and Z bands. The upper limits all indicate that the source has
faded by a minimum of approximately 1 magnitude in the Y, J and H bands.
Our observations in the Z, Y, J and H bands are consistent with the
previously reported power-law decay indices (Littlejohns et al., GCN Circ.
15436), however, there is indication of a steeper decay in both the r and
i bands. Between this and the second epoch of RATIR observations we find
power-laws of t^-1.33 for the r band and t^-1.72 for the i band.

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