GRB 130521A

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
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 , 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
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 ) 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:
http://skynet.unc.edu/grb/grb130521a_finder.png

A preliminary light curve is at:
http://skynet.unc.edu/grb/grb130521a_2.png

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.

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
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 , 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. We did not detect a fading afterglow within 
the 3 arcmin radius of the Swift/BAT error circle, which was centered on 
RA 05h50m14.2s, Dec +14d27m08.6s (J2000.0).

A plot of the 3-sigma limiting magnitudes in each exposure, calibrated 
to six USNO-B1/NOMAD stars in the field, is here:
http://skynet.unc.edu/grb/grb130521a.png

We stacked all the images in each band and obtained 3-sigma limiting 
magnitudes on any afterglow of:
Filter       B       V       R       I
Mag       >18.29  >18.53  >18.13  >17.07

Magnitudes are Vega magnitudes, and have not been corrected for the 
expected line-of-sight Milky Way dust extinction E(B-V)=0.38 (Schlegel 
et al. 1998).

No further Skynet observations are scheduled.

S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (GSFC), C. Pagani (U Leicester),
D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU),
T. N. Ukwatta (MSU) (i.e. the Swift-BAT team):

Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 130521A (trigger #556344)
(Pagani, et al., GCN Circ. 14691
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 ).  The BAT ground-calculated position is
RA, Dec = 87.568, 14.470 deg which is
    RA(J2000)  =  05h 50m 16.3s
    Dec(J2000) = +14d 28' 10.8"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 67%.

The mask-weighted light curve shows a single peak starting at T-2 sec, peaking
at T+0 sec and falling to near background by T+4 sec, followed by a weak tail
out to approximately T+12 sec.  At around T+120 sec, the source moved out of the 
field of view due to a pre-planned slew to another target. T90 (15-350 keV) is 
11.0 +- 2.4 sec (estimated error including systematics).

The time-averaged spectrum from T-0.64 to T+12.64 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.11 +- 0.20.  The fluence in the 15-150 keV band is 4.2 +- 0.5 x 10^-07 
erg/cm2. The 1-sec peak photon flux measured from T-0.14 sec in the 15-150 keV 
band is 1.9 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/556344/BA/

Klotz A. (IRAP-CNRS-OMP), Gendre B. (IRAP-CNRS-OMP),
Boer M., Siellez K., Dereli H., Bardho O. (UNS-CNRS-OCA),
Atteia J.L. (IRAP-CNRS-OMP) report:

We imaged the field of GRB 130521A detected by SWIFT
(trigger 556344) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 33.0s after the GRB trigger
(13.7s after the notice). The elevation of the field decreased from
14 degrees above horizon and weather conditions
were good but the event occured during the dusk
at 28 degrees from the Sun. Due to the twilight the
first image of 60s is saturated.

The second image is 30.0s exposure in tracking mode.
We do not detect any OT in the Swift BAT error box
with a limiting magnitude of:
t0+106.3s to t0+136.3s : Rlim = 15.5

We co-added a series of exposures:
t0+106.3s to t0+1795s : Rlim = 17.3

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.

N.B. Galactic coordinates are lon=193.0037 lat= -6.5236
and the galactic extinction in R band is about 1.6 magnitude
estimated from D. Schlegel et al. 1998ApJ...500..525S.

This message may be cited.

C. Pagani (U Leicester), N. Gehrels (NASA/GSFC),
H. A. Krimm (CRESST/GSFC/USRA), C. J. Mountford (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sakamoto (AGU) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 22:49:16 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130521A (trigger=556344).  Swift could not slew to the
burst due to the Sun constraint.  The BAT on-board calculated location is 
RA, Dec 87.559, +14.452 which is 
   RA(J2000) = 05h 50m 14s
   Dec(J2000) = +14d 27' 09"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak
structure with a duration of about 6 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

Due to a Sun observing constraint, Swift cannot slew to the BAT
position until 05:50 UT on 2013 August 06. There will thus be no XRT or
UVOT data for this trigger before this time. 

Burst Advocate for this burst is C. Pagani (cp232 AT star.le.ac.uk). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)