[vsnet-grb-info 15529] GRB 140907A: Continued DCT Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16818
SUBJECT: GRB 140907A: Continued DCT Observations
DATE:    14/09/13 15:49:21 GMT
FROM:    S. Bradley Cenko at NASA/GSFC  <brad.cenko at nasa.gov>

S. B. Cenko, A. Cucchiara (NASA-GSFC), J. Capone, V. Toy (UMD), E. Troja, A. Kutyrev (NASA-GSFC), S. Veilleux, and S. Gezari (UMD) report on behalf of a larger collaboration:

We re-observed the field of the Swift GRB 140907A (Krimm et al., GCN 16788) with the Large Monolithic Imager on the 4.3m Discovery Channel Telescope (DCT).  Observations were obtained in the r' filter beginning at 11:28 UT on 2014 Sep 10 (~ 2.8 d after the Swift trigger) for a total exposure time of 720 s. 

Using nearby point sources from the APASS catalog for calibration, we measure a magnitude of r' = 22.79 +/- 0.07 mag for the optical afterglow (Xu et al., GCN 16789; Kuin et al., GCN 16791).  Compared with our previous epoch of DCT imaging, we infer a corresponding power-law decay index of alpha = 1.2 +/- 0.1.