TITLE:   GCN CIRCULAR
NUMBER:  21742
SUBJECT: LIGO/Virgo G299232: COATLI Observations of MASTER OT J033744.97+723159.0
DATE:    17/08/29 05:53:46 GMT
FROM:    Alan M Watson at UNAM  <alan@astro.unam.mx>

Nat Butler (ASU), Alan M. Watson (UNAM), V. Zach Golkhou (University of
Washington), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Eleonora
Troja (GSFC), and Carlos Rom��n-Z����iga (UNAM) report:

We observed the field of MASTER OT J033744.97+723159.0 (Lipunov et al.,
GCN Circ. 21719) with the COATLI 50-cm telescope and interim imager
(Watson et al. 2016, Proc. SPIE, 9908, 50) at the Observatorio
Astron��mico Nacional on the Sierra de San Pedro M��rtir from 2017-08-28
03:13 to 12:05 obtaining a total of 2.21 hours of observation in the
Bessell B and 1.79 hours in Bessell R.

We detect the OT. Calibrating with respect to the USNO-B1 catalog, we
estimate a preliminary magnitude of

B = 17.21 +/- 0.01
R = 16.15 +/- 0.01

These magnitudes are in the USNO-B1 Vega system and are not corrected for
Galactic extinction in the direction of the OT.

Using the Lupton (2005) conversion from B-R to g-r, we find good agreement between our B-R = 1.06 color and the g-r color reported by Im et al. (GCN 21738). However, our color is much bluer than the B-R = 2.06 color of Lipunov et al. (GCN 21736).

We thank the COATLI technical team (Fernando ��ngeles, Rosa Becerra,
Oscar Chapa, Salvador Cuevas, Alejandro Farah, Jorge Fuentes, Rosal��a
Langarica, Fernando Quir��s, and Carlos Tejada) and the staff of the
Observatorio Astron��mico Nacional.
-- 
Dr. Alan M. Watson
Instituto de Astronom��a
Universidad Nacional Aut��noma de M��xico