D. James, C. Foster, P. Taylor, M. Carroll, A. Trotter, D. Reichart, A.
LaCluyze, J. Haislip, T. Berger, H. T. Cromartie, R. Egger, A. Foster,
N. Frank, K. Ivarsen, M. Maples, J. Moore, M. Nysewander, E. Speckhard,
and J. A. Crain report
Skynet observed the Swift/BAT localization of GRB 130521A (Pagani et
al., GCN 14691, Swift trigger #556344) with four 16" telescopes of the
PROMPT array at CTIO, Chile. Starting at 2013-05-21, 22:49:16 UT and
continuing until 23:01:04 UT (t=49.2s-11.8m post-trigger), it took 66
exposures in the BVRI bands. The field was 28.5 degrees from the sun at
this time, so the duration of the observation was limited by sky
brightness and high airmass.
In James et al. (GCN 14697) we reported that we did not detect an
afterglow. We conducted follow-up observations two nights later, and on
reexamination discovered that an extremely red afterglow was in fact
detected in our first night�s I and R band exposures.
The position of the afterglow is (J2000.0):
RA = 05h 50m 10.55s
Dec = 14d 27m 26.8s
A finder chart is at:
A preliminary light curve is at:
Magnitudes are in the Vega system and are calibrated to 19 APASS stars
in the field. We regard the V band detection to be questionable, but the
R and I band detections are solid.
The galactic coordinates of the afterglow are l=193.3312, b=-5.9321. The
dust emission maps of Schlegel et al. (1998) indicate E(B-V)=0.381 along
this line of sight; the predicted extinction in each of the bands that
we observed is:
Filter B V R I
A_lambda 1.65 1.24 1.00 0.75
The observed R band brightness is 1.5 magnitudes fainter than in the I
band. Correcting for galactic dust extinction, the R band is still 1.25
magnitudes fainter than in the I band. Such an extremely red afterglow
could be due to an unusually large amount of dust extinction in the host
galaxy or to the burst being at a redshift z-5. Follow-up observations
are encouraged when the source is again visible in early August.
We encourage anyone who may have observed this field, particularly in
the near infrared, to reexamine their images to see if this afterglow
was detected in them.
No further Skynet observations are scheduled.