[vsnet-grb-info 21721] GRB 190129B: DDOTI Detection of the Possible Afterglow and Suggestion of Fading

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23820
SUBJECT: GRB 190129B: DDOTI Detection of the Possible Afterglow and Suggestion of Fading 
DATE:    19/01/30 20:32:24 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan at astro.unam.mx>

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

We observed the entire IPN error box of GRB 190129B (Hurley et al., GCN
Circ. 23808) with the DDOTI/OAN wide-field imager at the Observatorio
Astronómico Nacional on Sierra San Pedro Mártir
(http://ddoti.astroscu.unam.mx) from 2019-01-30 02:15 UTC to 12:48 UTC
(14.0 to 24.5 hours after burst) obtaining a total of 4.4 hours exposure
in the w filter.

If we split our exposures roughly in two, in the first half from 02:15
to 05:40 UTC we clearly detect a faint source close to the error region
for the candidate XRT afterglow (LaPorte et al., GCN Circ. 23813) at

  07:49:50.82 +00:56:06.1 J2000 (+/- 0.5 arcsec). 

In the second half from 05:41 to 12:48 UTC, this source is not visible.

The presence of a nearby bright star complicates photometry. However, in
the difference image we measure a magnitude and 1-sigma error of

  w = 22.7 +/- 1.0.

Our w magnitudes are calibrated against the USNO-B1 catalog (adjusted to
an approximate AB system) and are not corrected for Galactic extinction
in the direction of the GRB.

We assume this source corresponds to the sources reported previously by
Bolmer & Steinle (GCN Circ. 23814) and Piranomonte et al. (GCN Circ.
23818) at a similar position and magnitude. However, our observations
are the first to suggest fading, albeit at low significance.

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