TITLE:   GCN CIRCULAR
NUMBER:  25918
SUBJECT: GRB 191001A: RATIR Optical and NIR Observations
DATE:    19/10/02 04:57:45 GMT
FROM:    Emma Margarita Pereyra Talamantes at IA-UNAM Ensenada  <mpereyra@astro.unam.mx>

Margarita Pereyra (UNAM), Alan M. Watson (UNAM), Eleonora Troja (GSFC), Nat
Butler (ASU),  Alexander Kutyrev (GSFC), William H. Lee (UNAM), Diego
Gonzalez (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier
Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), 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 the candidate afterglow of GRB 191001A (trigger
591604915, Fermi GBM Team, GCN Circ. 25893, Pereyra et al. GCN Circ.
25911), centered at 20:20:47.65 +15:05:03.4,  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 2019/10 2.12 to 2019/10 2.17 UTC (20.08 to 21.45 hours
after the Fermi trigger), obtaining a total of 0.34 hours exposure in the g
and r bands, 0.67 hours exposure in the i band and 0.37 hours exposure in
the i, Z, Y, J, and H bands.

At the position of the transient source AT2019rog discovered independently
by ATLAS and DDOTI, in comparison with the USNO-B1, PS1 and 2MASS catalogs,
we obtain the following upper limits (3-sigma):

  g > 23.20
  r > 23.01
  i > 23.26
  Z > 21.40
  Y > 21.49
  J > 21.22
  H > 20.92

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

The non-detection implies that the source has faded by about 6 magnitudes
in 20 hours. This is consistent with it being the afterglow of GRB 191001A.

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