GRB 120521A

M. M. Chester (PSU), J. R. Cummings (NASA/UMBC), V. D'Elia (ASDC),
B. Gendre (ASDC), D. M. Palmer (LANL) and G. Stratta (ASDC) report on
behalf of the Swift Team:

At 05:59:42 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120521A (trigger=522578).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 148.693, -49.419 which is 
   RA(J2000) = 09h 54m 46s
   Dec(J2000) = -49d 25' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single short FRED
structure with a duration of about 0.7 sec.  The peak count rate
was ~5000 counts/sec (15-350 keV), at ~0.25 sec after the trigger. 

The XRT began observing the field at 06:00:56.6 UT, 73.8 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 148.72544, -49.41760 which
is equivalent to:
   RA(J2000)  = 09h 54m 54.11s
   Dec(J2000) = -49d 25' 03.4"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 76 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 2.08
x 10^21 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 77 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the large, but uncertain extinction expected.

Klotz A. (IRAP-CNRS-OMP), Gendre B. (ASDC/INAF-OAR),
Boer M. (UNS-CNRS-OCA), Atteia J.L. (IRAP-CNRS-OMP) report:

We imaged the field of GRB 120521A detected by SWIFT
(trigger 522578) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 35.2s after the GRB trigger
(15.1s after the notice). The elevation of the field decreased from
10 degrees above horizon and weather conditions
were good.

The first image is trailed with a duration of 60.0s
(see the description in Klotz et al., 2006, A&A 451, L39).
We do not detect any OT in the XRT position (Chester et al.
GCNC 13302) with a limiting magnitude of:
t0+35.2s to t0+95.2s : R > 15.8

The second image is 30.0s exposure in tracking mode:
t0+108.9s to t0+138.9s : R > 16.5

We co-added a series of exposures:
t0+109s to t0+533s : R > 17.4

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

M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 508 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 120521A, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 148.72462, -49.41733 which is equivalent
to:

RA (J2000): 09h 54m 53.91s
Dec (J2000): -49d 25' 02.4"

with an uncertainty of 1.9 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
M. M. Chester (PSU), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+363 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120521A (trigger #522578)
(Chester, et al., GCN Circ. 13302
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 ).  The BAT ground-calculated position is
RA, Dec = 148.692, -49.422 deg, which is 
   RA(J2000)  =  09h 54m 46.1s 
   Dec(J2000) = -49d 25' 17.8" 
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows FRED pulse starting at ~T+0.0, peaking
at ~T+0.1, and ending at ~T+1.0 sec.  T90 (15-350 keV) is 0.45 +- 0.08 sec
(estimated error including systematics).
 
The time-averaged spectrum from T+0.02 to T+0.56 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
0.98 +- 0.22.  The fluence in the 15-150 keV band is 7.8 +- 1.1 x 10^-8 erg/cm2.
The 1-sec peak photon flux measured from T-0.21 sec in the 15-150 keV band
is 0.9 +- 0.1 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/522578/BA/

S. R. Oates (MSSL-UCL) and M. M. Chester (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120521A
77 s after the BAT trigger (Chester et al., GCN Circ. 13302
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 ).
No optical afterglow consistent with the XRT position
(Goad et al., GCN Circ. 13304
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 ) is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC            77          227          147         >21.4
u_FC               289          539          246         >20.9
white               77         5491          363         >21.9
v                 4266         5901          393         >19.7
b                  545        11343          766         >21.9
u                  289        10775         1386         >21.6
w1                4676         6312          393         >20.4
m2                4470         6106          393         >20.6
w2                4061         5697          393         >20.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.43 in the direction of the burst
(Schlegel et al. 1998).

J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows (PSU), A.P. Beardmore
(U. Leicester), P.A. Evans (U. Leicester), O.M. Littlejohns (U.
Leicester), V. D'Elia (ASDC), A. Maselli  (INAF-IASFPA), V. Mangano
(INAF-IASFPA) and M.M. Chester report on behalf of the Swift-XRT team:

We have analysed 4.3 ks of XRT data for GRB 120521A (Chester  et al.
GCN Circ. 13302
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 ), from 83 s to 11.3 ks after the  BAT trigger. The data
are entirely in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Goad et al. (GCN. Circ 13304).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=anf (+/anf).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.81 (+0.36, -0.29). The
best-fitting absorption column is  2.6 (+1.4, -0.5) x 10^21 cm^-2,
consistent with the Galactic value of 2.1 x 10^21 cm^-2 (Kalberla et
al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 4.6 x 10^-11 (6.3 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.6 (+1.4, -0.5) x 10^21 cm^-2
Galactic foreground: 2.1 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.81 (+0.36, -0.29)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00522578.

This circular is an official product of the Swift-XRT team.

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

There was an error in GCN 13326
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 : the light curve decay slope was
reported as infinity.

The XRT light curve in fact shows a plateau (alpha=0.2 +/-0.4) until
T0+270 seconds. After this it undergoes an extremely sharp decay
(alpha~10) and is not detected in X-rays after T0+1ks.

A. Rossi (TLS Tautenburg), M. Nardini (Universita' degli Studi
Milano-Bicocca), S. Klose (TLS Tautenburg), and J. Greiner (MPE
Garching) report on behalf of the GROND team:

We observed the field of GRB 120521A (Swift trigger 522578; Chester
et al., GCN 13302
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 ) simultaneously in g'r'i'z'JHKs with GROND (Greiner
et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at
La Silla Observatory (Chile).

Observations started at 22:53 UT on 2012-05-21, 16.9 h after the GRB
  trigger, and lasted for 100 minutes.  They were performed under good
  sky conditions at an average seeing of 0.9 and at an average airmass
  of 1.1.

Using an exposure of 50 minutes in the optical and 40 minutes in the
NIR we do not detect any source within the Swift-XRT error circle
reported by Goad et al. (GCN 13304
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 ).  Preliminary observed upper
limits (AB mags) are:

g' > 25.5
r' > 25.0
i' > 24.0
z' > 23.7
J > 20.9
H > 20.3
K > 19.1

The given limits are derived based on calibrating the images against
GROND zeropoints (g'r'i'z') and 2MASS stars (JHK).  We note that the
Galactic reddening along the line of sight is E_(B-V)= 0.43 mag
(Schlegel et al. 1998).

P. Hancock, T. Murphy, B. Gaensler, M. Bell, D. Burlon (University of 
Sydney/CAASTRO), A. de Ugarte Postigo (Dark Cosmology / IAA)

We observed GRB120521A (GCN13302
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 ) with the Australia Telescope Compact 
Array at 34GHz for 112 mins centered on 07:55UT May 22 2012 (T0+1.08days).

We detect no radio source at the location of the GRB (GCN13304
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 ) and 
place a 3sigma upper limit of 95uJy on the flux of an afterglow.

These observations were obtained as part of ATCA project C2689. We thank 
the observatory staff for their support and scheduling the observations. 
The Australia Telescope is funded by the Commonwealth of Australia for 
operation as a National Facility managed by CSIRO.