TITLE:   GCN CIRCULAR
NUMBER:  26010
SUBJECT: GRB 191016A: COATLI Optical Observations and Detection of the Afterglow
DATE:    19/10/16 05:03:38 GMT
FROM:    Alan M Watson at UNAM  <alan@astro.unam.mx>

Alan M. Watson (UNAM),  Nat Butler (ASU), Rosa L. Becerra (UNAM), Diego González
(UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Margarita Pereyra
(UNAM), and Eleonora Troja (GSFC) report:

Alan M. Watson (UNAM),  Nat Butler (ASU), Rosa L. Becerra (UNAM), Diego González
(UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Margarita Pereyra
(UNAM), and Eleonora Troja (GSFC) report:

We observed the field of GRB 191016A (Gropp et al., GCN Circ. Gropp) with the
COATLI 50-cm telescope and interim imager at the Observatorio Astronómico
Nacional on the Sierra de San Pedro Mártir (http://coatli.astroscu.unam.mx) from
2019-10-16 04:40:19 (378.7 seconds after the trigger and 21.8 seconds after the
alert) to 04:49, obtaining a total of 1200 seconds of exposure in the w filter.

We detect a bright uncataloged source at 02:01:04.75 +24:30:36.8 J2000 (+/- 0.5
arcsec), about 91 arcsec from the BAT position. The source rises from w = 16.5
to w = 15.0 before fading. We suggest this is the afterglow.

Our w magnitudes are calibrated against the Pan-STARRS1 catalog, are on an
approximate AB system (Becerra et al., 2019, ApJ, 872, 118), and are not
corrected for Galactic extinction in the direction of the GRB.

Observations are continuing.

We thank the COATLI technical team and the staff of the Observatorio Astronómico
Nacional.