TITLE:   GCN CIRCULAR
NUMBER:  24650
SUBJECT: LIGO/Virgo S190521r: RATIR Optical and NIR Observations of the CNEOST Transient 
DATE:    19/05/22 06:20:23 GMT
FROM:    Alan M Watson at UNAM  <alan@astro.unam.mx>

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

We observed the field of the optical transient observed by CNEOST (Li et
al., GCN Circ. 24647) 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
2019/05 22.22 to 2019/05 22.23 UTC, obtaining a total of 0.18 hours
exposure in the r and i bands and 0.07 hours exposure in the Z, Y, J,
and H bands.

The source is located at RA, Dec = 17:19:41.79, +01:04:44.9 (J2000,
+/-0.5"). In comparison with the SDSS DR9 and 2MASS catalogs, we obtain
the following detections:

  r	= 17.88 +/- 0.01
  i	= 17.93 +/- 0.02
  Z	= 18.08 +/- 0.06
  Y	= 18.15 +/- 0.08
  J	= 18.27 +/- 0.14
  H	= 18.61 +/- 0.24

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

We note that the spectrum is not especially red and can be well-fitted by a
power law with F_\nu \proportional to \nu. The source does not appear to
have faded dramatically since the CNEOST observations about 13 hours
previously.

Further observations are planned.

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