[vsnet-grb-info 20418] GRB 180316A: RATIR Optical Observations, Possible Re-brightening

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22514
SUBJECT: GRB 180316A: RATIR Optical Observations, Possible Re-brightening
DATE:    18/03/17 15:19:48 GMT
FROM:    Nat Butler at Az State U  <natbutler at asu.edu>

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 (UVI), Eleonora
Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jesús
González (UNAM), Carlos Román-Zúñiga (UNAM), Harvey Moseley (GSFC), John
Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki Toy (UMD) report:

We observed the field of GRB 180316A (Melandri,, et al., GCN 22500) 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 2018/03 17.39 to 2018/03 17.52 UTC (28.35
to 31.55 hours after the BAT trigger), obtaining a total of 2.36 hours
exposure in the r and i bands.

The optical afterglow (e.g., Lipunov, et al., GCN 22502) is again cleanly
detected.  In comparison with the USNO-B1 catalog, we obtain:

  r = 20.23 +/- 0.02
  i = 19.93 +/- 0.01

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  These magnitudes are comparable to
those reported for RATIR for 2018/03.16 (Butler, et al., GCN 22509).
During that observation, the afterglow was fading strongly.  We again
observe the afterglow to be fading, as t^(-0.7+/-0.3), and we infer that
the afterglow may have brightened between our epochs, at a time around 1
day after the GRB.

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