GRB 130528A

V. D'Elia (ASDC), D. N. Burrows (PSU), C. Gronwall (PSU),
J. A. Kennea (PSU), A. Y. Lien (NASA/GSFC/ORAU),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester) and
D. M. Palmer (LANL) report on behalf of the Swift Team:

At 16:41:23 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130528A (trigger=556870).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 138.911, +87.276 which is 
   RA(J2000) = 09h 15m 39s
   Dec(J2000) = +87d 16' 33"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiple-peaked
structure with a duration of about 85 sec.  The peak count rate
was ~5500 counts/sec (15-350 keV), at ~8 sec after the trigger. 

The XRT began observing the field at 16:42:28.7 UT, 64.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 139.51074,
87.30239 which is equivalent to:
   RA(J2000)  = 09h 18m 02.58s
   Dec(J2000) = +87d 18' 08.6"
with an uncertainty of 4.1 arcseconds (radius, 90% containment). This
location is 139 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 (5.18 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 1.9
(+2.14/-1.88) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 0.1 s image was 1.20e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 75 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
0.16. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.it). 
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.)

A. Volnova (IKI), E. Litvinenko (UBAI), I. Molotov (KIAM), A. Pozanenko 
(IKI) report on behalf of  larger GRB  follow-up collaboration:

We observed the field of  GRB 130528A (D'Elia et al., GCN  14711
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 ) with 
0.4-m telescope of ISON-Kitab observatory  starting on  May 28 (UT) 
17:01:13, i.e. 20 minutes after burst trigger.  We took  several 
unfiltered images of 30 s exposure. In the first image we do not detect 
any source in XRT error circle (D'Elia et al., GCN  14711
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 ). A photometry 
   is based  on nearby USNO-B1.0 stars:

T_start,     T0+,      Exposure,  OT,    UL (3sigma)
(UT)         mid, d    (s)

17:01:13    0.01395    1x30       n/d    17.3


A finding chart can be found at 
http://grb.rssi.ru/GRB130528A/GRB130528A_Kitab_fc.png

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

Using 842 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 130528A, 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 = 139.50051, +87.30103 which is equivalent
to:

RA (J2000): 09h 18m 0.12s
Dec (J2000): +87d 18' 03.7"

with an uncertainty of 1.8 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.

A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), M.C. Stroh (PSU),
D.N. Burrows (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), C.
Pagani (U. Leicester), A.P. Beardmore (U. Leicester), G. Stratta (ASDC)
and V. D'Elia report on behalf of the Swift-XRT team:

We have analysed 9.0 ks of XRT data for GRB 130528A (D'Elia  et al. GCN
Circ. 14711
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 ),  from 68 s to 22.8 ks after the  BAT trigger. The data
comprise 842 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Goad et al. (GCN. Circ 14714).

The late-time light curve (from T0+4.9 ks) can be modelled with  a
power-law decay with a decay index of alpha=1.06 (+/-0.12).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.69 (+/-0.07). The
best-fitting absorption column is  3.6 (+/-0.3) x 10^21 cm^-2, in
excess of the Galactic value of 5.2 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.92 (+/-0.15) and a
best-fitting absorption column of 3.6 (+/-0.6) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.4 x 10^-11 (6.9 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.6 (+/-0.6) x 10^21 cm^-2
Galactic foreground: 5.2 x 10^20 cm^-2
Excess significance: 8.5 sigma
Photon index:	     1.92 (+/-0.15)

If the light curve continues to decay with a power-law decay index of
1.06, the count rate at T+24 hours will be 0.013 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.7 x
10^-13 (8.9 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00556870.

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

J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
V. D'Elia (ASDC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU), 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-61 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 130528A (trigger #556870)
(D'Elia, et al., GCN Circ. 14711
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 ).  The BAT ground-calculated position is
RA, Dec = 139.405, 87.300 deg, which is 
   RA(J2000)  =  09h 17m 37.2s 
   Dec(J2000) = +87d 18' 01.5" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows several overlapping peaks starting
at ~T+0, peaking at ~T+4 sec, and ending at ~T+80 sec.
T90 (15-350 keV) is 59.4 +- 3.6 sec (estimated error including systematics).
 
The time-averaged spectrum from T+0.12 to T+79.34 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.39 +- 0.19, 
and Epeak of 118.3 +- 79.7 keV (chi squared 42.3 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 5.1 +- 0.2 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+6.06 sec in the 15-150 keV band is
3.0 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.67 +- 0.05 (chi squared 48.6 for 57 d.o.f.).  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/556870/BA/

M. De Pasquale (MSSL-UCL) and V. D'Elia (ASDC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB
130528A 75 s after the BAT trigger (D'Elia et al., GCN Circ. 14711
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 ).
No optical afterglow consistent with the enhanced XRT position
(Goad et al. GCN Circ. 14714
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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            75          225          147         >20.3
u_FC               287          537          246         >19.5
white               75        18737         1239         >21.7
v                  617        11553         1245         >19.9
b                  543        18247         1356         >20.8
u                  287        17334         1583         >21.0
w1                 667        22765         1443         >20.7
m2                 641        12459         1179         >20.7
w2                 592         7143          491         >20.5

The magnitudes in the table are not corrected for the Galactic
extinction due to the reddening of E(B-V) = 0.16 in the direction
of the burst (Schlegel et al. 1998).

S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:

The long-duration GRB 130528A
(Swift-BAT trigger 556870: D'Elia et al., GCN 14711
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 ;
Cummings et al., GCN 14718
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 )
triggered Konus-Wind at T0=60085.301s UT (16:41:25.301).

The light curve shows a pulse from ~T0-5 s to ~T0+10s,
followed by weaker and softer emission out to ~T0+60s.

The emission is seen up to 7 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB130528_T60085/

As observed by Konus-Wind, the burst
had a fluence of (8.0 � 0.7)x10-6 erg/cm2,
and a 64-ms peak flux, measured from T0+0.640s,
of (1.7 � 0.2)x10-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+57.600 s)
is best fit in the 20 keV - 15 MeV range
by the cutoff power law model with the following parameters:
the photon index alpha = -1.30 � 0.15,
the peak energy Ep = 93 � 9 keV,
chi2 = 90/98 dof.

The spectrum at the maximum count rate
(measured from T0+0.256 to T0+5.888 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.21 � 0.23,
the high energy photon index beta = -2.6 � 0.3,
the peak energy Ep = 142 � 14 keV,
chi2 = 70/97 dof.

All the quoted results are preliminary.

P. Jenke (UAH) reports on behalf of the Fermi GBM Team:

"At 16:41:21.41 UT on May 28 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 130528A (trigger 391452087 / 130528695),
which was also detected by the Swift/BAT (D'Elia et al., GCN  14711
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 ).
The GBM on-ground location is consistent with the Swift position.

The angle of the Fermi LAT boresight is 60 degrees from the Swift location.

The GBM light curve consists of at least three peaks
with a duration (T90) of about 55 s (50-300 keV).
The time-averaged spectrum from T0-0.9 s to T0+58.5 s is
well fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.12 +/- 0.04 and
the cutoff energy, parameterized as Epeak, is 130 +/- 7 keV.

The event fluence (10-1000 keV) in this time interval is
(9.5 +/- 0.3)E-06 erg/cm^2. The 1.0-sec peak photon flux measured
starting from T0+3.2 s in the 10-1000 keV band
is 5.5 +/- 0.2 ph/s/cm^2.

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