GRB 120521B

J. R. Cummings (NASA/UMBC), S. D. Barthelmy (GSFC),
M. M. Chester (PSU), V. D'Elia (ASDC), N. Gehrels (NASA/GSFC),
B. Gendre (ASDC), D. M. Palmer (LANL),
E. Sonbas (NASA/GSFC/Adiyaman Univ.) and G. Stratta (ASDC) report on
behalf of the Swift Team:

At 09:07:48 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120521B (trigger=522586).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 197.014, -52.746 which is 
   RA(J2000)  =  13h 08m 03s
   Dec(J2000) = -52d 44' 45"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple overlapping peaks
with a duration of about 40 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~6 sec after the trigger. 

The XRT began observing the field at 09:09:47.6 UT, 118.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
197.0100, -52.7548 which is equivalent to:
   RA(J2000)  = 13h 08m 02.41s
   Dec(J2000) = -52d 45' 17.4"
with an uncertainty of 2.5 arcseconds (radius, 90% containment). This
location is 32 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 in excess of the Galactic value (2.27 x
10^21 cm^-2, Kalberla et al. 2005), with an excess column of 2.2
(+1.94/-1.36) x 10^22 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.42e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 127 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 expected extinction corresponding to E(B-V) of
0.45. 

Burst Advocate for this burst is J. R. Cummings (jayc AT milkyway.gsfc.nasa.gov). 
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.)

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

We imaged the field of GRB 120521B detected by SWIFT
(trigger 522586) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 88.8s after the GRB trigger
(25.6s after the notice). The elevation of the field decreased from
12 degrees above horizon and weather conditions
were poor.

In a clean exposure, taken between T0 + 473.1s and T0 + 563.1s,
we do not detect any afterglow with a limiting magnitude of R > 17.2.


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

N.B. Galactic coordinates are lon=305.4846 lat=+10.0434
and the galactic extinction in R band is 1.2 magnitudes
estimated from D. Schlegel et al. 1998ApJ...500..525S.

This message may be cited.

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D Bersier, C. Guidorzi, A. Melandri, J. Jalpelj report:

The Faulkes Telescope South robotically observed GRB120521B (Swift trigger 
522586, Cumming et al, GCN 13305
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 ). The first exposure started approximately 240 
seconds after the trigger time.
Digital image subtraction does not reveal any variable source inside the XRT 
error circle. We find upper limits in R ~ 22.0 (40 minutes after the burst).

[GCN OPS NOTE(21may12): Corrected per Circular 13308.]

D. Bersier wishes to apologise for any confusion related to the wrong title of 
GCN  13307
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 . The GCN Circular reports observations of GRB120521B, not GRB120521A. 
The title should read: "GRB120521B: Faulkes Telescope South observations".

I thank C. Guidorzi for drawing my attention to this mistake.

Hugo Levato and Carlos Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

Claudio Mallamaci, Carlos Lopez and Federico Podest
Observatorio Astronomico Felix Aguilar (OAFA)

E. Gorbovskoy, V. Lipunov, V.Kornilov, D.Kuvshinov, D.Denisenko, A.Belinski,
N.Tyurina, N.Shatskiy, P.Balanutsa, D.Zimnukhov, A.Kuznetsov,  V.V.Chazov, 
A.Kuznetsov
Moscow Lomonosov State University, Sternberg Astronomical Institute,

A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik
Kislovodsk Solar Station of the Pulkovo Observatory

K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk
Irkutsk State University

V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov
Blagoveschensk Educational State University, Blagoveschensk

V.Krushinski, I.Zalozhnich,  A. Popov, A. Bourdanov, A. Punanova
Ural Federal University

MASTER VWF   robotic cameras (400 square degrees, 1 pix = 22 
arcsec,  http://observ.pereplet.ru) 
located in  Argentina (Observatorio Astronomico Felix Aguilar) was pointed 
to the Fermi Trigger 359284074 12 sec before Swift notice time and 65 
sec after Swift trigger (Cummings et al., GCN Circ 13305
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 )  time at 
2012-05-21 09:08:53 UT.

On our first image  (5 sec exposure)  we 
have not found any OT.


T_start(UT)  T - T_trig  MeanTime     Exp   Limit  Coadd?   Filter
----------------------------------------------------------------------
09 08 53       65 s       67.5s        5s    11.5    No     Unfiltered
09 08 53       65 s       77.5s       25s    12.4    Yes    Unfiltered

The message may be cited.

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

Using 809 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 120521B, 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 = 197.00990, -52.75479 which is equivalent
to:

RA (J2000): 13h 08m 2.38s
Dec (J2000): -52d 45' 17.2"

with an uncertainty of 2.0 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.

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

We have analysed 9.1 ks of XRT data for GRB 120521B (Cummings  et al.
GCN Circ. 13305
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 ), from 125 s to 19.4 ks after the  BAT trigger. The
data comprise 28 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Osborne et al. (GCN. Circ 13311).

The light curve can be modelled with an initial power-law decay with an
index of alpha=5.0 (+0.7, -0.6), followed by a break at T+267 s to an
alpha of 0.69 (+/-0.07).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.9 (+0.4, -0.3). The
best-fitting absorption column is  1.5 (+0.4, -0.3) x 10^22 cm^-2, in
excess of the Galactic value of 2.3 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 6.6 x 10^-11 (1.4 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.5 (+0.4, -0.3) x 10^22 cm^-2
Galactic foreground: 2.3 x 10^21 cm^-2
Excess significance: 6.2 sigma
Photon index:	     1.9 (+0.4, -0.3)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00522586.

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

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
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-60 to T+243 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120521B (trigger #522586)
(Cummngs, et al., GCN Circ. 13305
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 ).  The BAT ground-calculated position is
RA, Dec = 197.016, -52.742 deg, which is 
   RA(J2000)  =  13h 08m 03.9s 
   Dec(J2000) = -52d 44' 31.9" 
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 35%.
 
The mask-weighted light curve shows several overlapping peaks starting
at ~T-1 sec, with equal-amplitude maximum peaks at ~T+6 and ~T+32 sec,
and ending at around T+180 sec.  There is a possibility (at the 2-sigma level)
that emission continues out past the T+243sec end of the downlinked data.
T90 (15-350 keV) is 31.4 +- 4.0 sec (estimated error including systematics).
 
The time-averaged spectrum from T-1.39 to T+35.58 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
0.97 +- 0.15.  The fluence in the 15-150 keV band is 1.5 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+31.04 sec in the 15-150 keV band
is 0.9 +- 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/522586/BA/

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 120521B (Swift trigger 522586; Cummings et 
al., GCN 13305
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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 00:35 UT on 2012-05-22, 15.3 h after the GRB 
trigger, and lasted for 140 minutes. They were performed with good sky 
conditions at an average seeing of 0.8" and at an average airmass of 1.05. 
(At the time of the GRB trigger the field was already too close to the 
telescope's horizon distance limit in order to observe it with GROND.)

Based on an exposure of 37 minutes in the optical and 30 minutes in the 
NIR we do not detect any source within the Swift-XRT error circle reported 
by Osborne et al. (GCN 13311
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 ). Preliminary observed upper limits (AB mags) 
are:

  g' > 24.5
  r' > 24.2
  i' > 23.9
  z' > 23.9
  J  > 21.3
  H  > 20.3
  Ks > 19.3.

These limits are derived based on 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)= 0.45 mag (Schlegel et al. 1998).

S. R. Oates (MSSL-UCL) and J. R. Cummings (NASA/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120521B
127 s after the BAT trigger (Cummings et al., GCN Circ. 13305
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 ).
No optical afterglow consistent with the XRT position (Osborne et al., GCN Circ. 13311
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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           127          277          147         >19.4
u_FC               286          535          246         >19.4
white              127        30912         2930         >19.8
v                  615        23584         2045         >18.7
b                  541        36686         2819         >19.7
u                  286        36128         2526         >20.2
w1                 665        35215         2046         >20.7
m2                5582        24489         1279         >21.0
w2                 765        19363         1746         >21.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.45 in the direction of the burst
(Schlegel et al. 1998).

David Gruber (MPE) reports on behalf of the Fermi GBM Team:

"At 09:07:52.39 UT on 21 May 2012, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 120521B (trigger 359284074 / 120521380).
which was also detected by the Swift/BAT
(Krimm et al. 2012, GCN 13317
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 )
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight is 84 degrees.

The GBM light curve consists of a single pulse
with a duration (T90) of about 91 s (50-300 keV).
The time-averaged spectrum from T0-5 s to T0+29 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.34 +/- 0.20 and
the cutoff energy, parameterized as Epeak, is 213 +/- 29 keV

The event fluence (10-1000 keV) over the T90 time interval is
(3.11 +/- 0.07)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+2.4 s in the 10-1000 keV band
is 1.55 +/- 0.23 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

S. Rapoport, S. Sweet, J. Scharwachter, B. Schmidt, M. Childress

report observations of GRB120521B taken on 2012-05-21.42 UTC (2.7
hours post-alert) using the Wide Field Spectrograph (WiFeS) on the ANU
2.3m, obtaining 3x900s integration at resolution R=3000.  

Spectral summation of the sky-subtracted data cube in a 3" radius centered at
the GRB location shows no detectable optical counterpart to the GRB
and no detectable host galaxy. Based on measurement of a nearby field
star in the data cube (m_B=18.4, m_R=17.2 -- USNO) we estimate a
non-detection upper limit of m_R=20.5 and m_B=20.0 at 5 sigma for the
GRB or its host galaxy.