TITLE:   GCN CIRCULAR
NUMBER:  22935
SUBJECT: GRB 180709A: Optical limits
DATE:    18/07/09 16:36:22 GMT
FROM:    Jules Halpern at Columbia U.  <jph1@columbia.edu>

J. P. Halpern (Columbia U.) reports:

I observed the field of Swift GRB 180709A (Marshall et al., GCN 22930)
with an SDSS r filter using the 1.3m McGraw Hill telescope of the
MDM Observatory, beginning 17.6 minutes after the trigger.
Four 5-minute exposures were obtained in morning twilight.
Upper limits at the enhanced Swift-XRT position of Beardmore et al.
(GCN 22933) are listed below, as calibrated to Pan-STARRS1 photometry.

       ---------------------------------------------
        Date(UT)  Start(UT)  Mid-time T-T0   r(mag)
       ---------------------------------------------
        July 9     11:09:34      1194 s      > 22.0
        July 9     11:14:41      1501 s      > 21.8
        July 9     11:19:47      1807 s      > 21.4
        July 9     11:24:54      2114 s      > 21.1
       ---------------------------------------------

These magnitudes are not corrected for Galactic extinction, which is
considerable at this Galactic latitude of -0.1 deg.  According to the
NED implementation of Schlafly & Finkbeiner (2011), A_r = 6.1 mag.