[vsnet-grb-info 18372] GRB 160816A: RATIR Optical and NIR Afterglow Confirmation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19820
SUBJECT: GRB 160816A: RATIR Optical and NIR Afterglow Confirmation
DATE:    16/08/18 12:35:04 GMT
FROM:    Eleonora Troja at GSFC  <eleonora.troja at nasa.gov>

Eleonora Troja (GSFC), Nat Butler (ASU), Alan M. Watson (UNAM),
Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G.
Richer (UNAM), Ori Fox (STScI), J. Xavier Prochaska (UCSC),
Josh Bloom (UCB), Antonino Cucchiara (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), Harvey Moseley (GSFC), John
Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report:

We observed the field of GRB 160816A (Mailyan, et al., GCN 19804;
Racusin, et al., GCN 19802) 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 2016/08 18.17 to 2016/08 18.47 UTC (1.44 to
1.72 days after the GBM trigger), obtaining a total of 2.47 hours
exposure in the r and i bands and 1.03 hours exposure in the Z,
Y, J, and H bands.

For the source reported in Troja, et al. (GCN 19809), in comparison
with the USNO-B1 and 2MASS catalogs, we obtain the following
detections and upper limit (3-sigma):


    r    22.74 +/- 0.15
    i    22.40 +/- 0.12
    Z    22.19 +/- 0.19
    Y    22.18 +/- 0.25
    J    > 22.32
    H    21.20 +/- 0.18

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

The source intensity decreased significantly between our two epochs,
corresponding to fading with power-law index alpha~-1.3 referenced to
the burst trigger. This confirms that the candidate reported by
Guidorzi, et al. (GCN 19808) and Troja et al. (GCN 19809) is the GRB
afterglow.

Deep imaging of the GRB location reveals additional optical sources
within the XRT localization (Kennea et al., GCN 19806), however none of
them have faded.

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