TITLE:   GCN CIRCULAR
NUMBER:  16165
SUBJECT: GRB 140423A pODI/WIYN afterglow photometry
DATE:    14/04/24 11:00:08 GMT
FROM:    Dieter Hartmann at Clemson.U  <hdieter@clemson.edu>

D. Harbeck (WIYN Observatory), A. Kaur (Clemson U.), A. Delgado-Navarro
(Clemson U.), M. Orio (INAF, UW Madison), D. H. Hartmann (Clemson U.)
report on behalf of a larger collaboration:



We imaged the location of the Swift detected GRB 140423A (Sonbas et al.,
GCN 16142) at two epochs with the pODI instrument on the 3.5 m WIYN
telescope at KPNO (http://www.wiyn.org/ODI/About/wiynpODI.html).



Observations in the sdss r' band on 23 April 2014 consist of a single 300s
exposure, and on 24 April 2014 we performed two 600s exposures. The optical
counterpart of the burst (Elenin et al., GCN 16143; Kaur et al., GCN 16144;
Ferrante et al., GCN 16145; Chester et al., GCN 16147) was detected under
fair seeing conditions (~ 1 arcsec) in all single exposures.



Date            Exp. Start Time        Magnitude



2014-04-23 UT 09:52:50.400         r' = 18.85



2014-04-24 UT 08:29:12.393         r' = 21.90



2014-04-24 UT 08:41:12.901         r' = 21.85



The photometric error is dominated by calibration and is 0.07 mag (in r')
rms for a secondary reference star ensemble (but not accounting for color
terms or galactic foreground extinction).



The photometric calibration is based on

(i) cross-correlating with the sdss dr9 star catalog in the r' band over
the entire field of view (24' X 24')

(ii) consistency check on exemplary star  SDSS J130915.57+494948.5 at sdss
r' = 19.98. The photometric error based on this reference star is < 0.02
mag rms.