[vsnet-grb-info 14825] GRB 140419A: Continued RATIR Optical and NIR Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16139
SUBJECT: GRB 140419A: Continued RATIR Optical and NIR Observations
DATE:    14/04/21 19:19:13 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 observed the field of GRB 140419A (Marshall, et al., GCN 16118) 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 2014/04 21.14 to 2014/04 21.29 UTC (47.30
to 50.93 hours after the BAT trigger), obtaining a total of 2.49 hours
exposure in the r and i bands and 1.04 hours exposure in the Z, Y, J, and
H bands.

We continue to detect the UVOT optical transient (Zheng, et al., GCN 16116;
Guver et al., GCN 16120). For a source located at the position of the KAIT
optical counterpart candidate (Zheng, et al., GCN 16119), in comparison with
the SDSS DR9 and 2MASS, we obtain the following detections and upper limit
(3-sigma):

  r     21.92 +/- 0.07
  i     21.77 +/- 0.07
  Z     21.74 +/- 0.13
  Y     21.58 +/- 0.19
  J     21.54 +/- 0.21
  H     > 21.66

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. In comparison to the first two
epochs of RATIR observations (Littlejohns, et al., GCN 16136; Butler, et
al., GCN 16121) we note that the decay in the NIR bands appears steeper,
now consistent with 1.4 < alpha < 1.6 in the i, Z, Y, J and H bands (see
also; Xu et al., GCN 16138). The XRT data for this GRB
(http://www.swift.ac.uk/xrt_curves/00596426/) may support a temporal break
at low significance after 100 ks. Further XRTdata can constrain this
possibility.

Conversely, the decay observed in the r band has become shallower, with
alpha = 0.8. This shallow decay in the r band could be attributed to the
presence of an underlying host galaxy or contamination from the nearby
bright star.

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