GRB 130427A

I imaged the GRB from 20.58UT to 22.43UT (April 27)  until conditions deteriorated to the point that the data was too noisy to be useful. Equipment was a 0.35-m SCT and SXVR-H9 CCD camera with an Astrodon V filter.

 Using Astrometrica and the UCAC4 catalogue, I derived its mean position from 5 images with between 7 and 10 reference stars per image as RA 11h 32m 32.81s, Dec 27d 41' 56.3".

 I measured the V magnitude of the GRB with reference to two nearby stars from the 2MASS catalogue: 2MASS 1085717559 and 2MASS 1085717584. Magnitudes of these comparison stars were derived from the CMC14 r' and 2MASS J and K mags as V=15.76 and V=15.69 respectively.

 Over this period of 1.75 hrs the GRB faded at an average rate of 2.811 mags/day. There was a short-lived apparent brightening of the GRB by about 0.2 mag around JD 2456410.425 for which there is no obvious explanation such as an uncorrected hot pixel in the images. The comparison stars remained constant with std devs of 0.03 mag throughout.

David Boyd