TITLE:   GCN CIRCULAR
NUMBER:  24690
SUBJECT: GRB 190530A: COATLI Optical Detection of the Fading Afterglow
DATE:    19/05/31 06:41:22 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:

We observed the field of Fermi GBM/LAT GRB 190530A (Fermi GBM Team, GCN
Circ. 24676; Longo et al., GCN Circ. 24679) 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
2019-05-31 03:33 to 06:27 (from 17.2 to 20.1 hours after the trigger),
obtaining a total of 8190 seconds of exposure in the w filter.

We detect the afterglow (Lipunov et al., GCN Circ. 24680; Melandri et
al., GCN Circ. 24689) at

  w = 18.18 +/- 0.01

During our observations, the afterglow fades with a power-law index of
-1.05 +/ 0.25.

Our w magnitudes are calibrated against the Pan-STARRS1 catalog, are on
an approximate AB system, and are not corrected for Galactic extinction
in the direction of the GRB.

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