Difference: GCNCIRCULAR21742 ( vs. 1)

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 Román-Zúñiga (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
Astronómico Nacional on the Sierra de San Pedro Mártir 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 Ángeles, Rosa Becerra,
Oscar Chapa, Salvador Cuevas, Alejandro Farah, Jorge Fuentes, Rosalía
Langarica, Fernando Quirós, and Carlos Tejada) and the staff of the
Observatorio Astronómico Nacional.
-- Dr. Alan M. Watson
Instituto de Astronomía
Universidad Nacional Autónoma de México

-- ShaonGhosh - 29 Aug 2017