GRB 130508A

S. T. Holland (STScI), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
J. R. Cummings (NASA/UMBC), V. D'Elia (ASDC), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), D. Malesani (DARK/NBI),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU),
E. Troja (NASA/GSFC/UMCP) and B.-B. Zhang (PSU) report on behalf of
the Swift Team:

At 17:08:53 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a probable GRB 130508A (trigger=555413).  Swift slewed immediately to the 
source location. 
The BAT on-board calculated location is 
RA, Dec 305.312, +34.949 which is 
   RA(J2000)  =  20h 21m 15s
   Dec(J2000) = +34d 56' 58"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The real-time lightcurve shows a weak peak
with a duration of about 40 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~18 sec after the trigger. 

The XRT began observing the field at 17:11:03.9 UT, 130.5 seconds after
the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued
X-ray source with an enhanced position: RA, Dec 305.3217, 34.9583 which
is equivalent to:
   RA(J2000)  = 20h 21m 17.20s
   Dec(J2000) = +34d 57' 29.9"
with an uncertainty of 2.5 arcseconds (radius, 90% containment). This
location is 44 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.  We
cannot determine whether the source is fading at the present time. 

The on-board calculated light curve shows evidence for a strong flare in 
Windowed Timing mode data at about 145-150 s after the BAT trigger. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (7.72 x
10^21 cm^-2, Kalberla et al. 2005), with an excess column of 1
(+1.60/-1.01) x 10^22 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 135 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. 

Even though this is a weak detection and it is on the Galactic Plane
(lon,lat= 74,-1), we determine that this is probably a GRB, but can not rule out
some other type of astrophysical source.  We will need the full data set 
to make the determination. 

Burst Advocate for this burst is S. T. Holland (sholland AT stsci.edu). 
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.)

J.C. Tello, R. S�nchez-Ramirez, M. Jelinek (IAA-CSIC Granada), J. Gorosabel
(UPV/EHU-IAA/CSIC), W. Allen (Vintage Lane Obs.), Ph. Yock (Auckland
Univ.), P. Kubanek (IP AS CR & IAA-CSIC), and A. J. Castro-Tirado
(IAA-CSIC) report on behalf of a larger collaboration:

"We observed the field of GRB 130508A (Holland et al., GCNC 14607),
detected by Swift/BAT, with the 0.6m Yock-Allen robotic telescope
(BOOTES-3) located in Blenheim, New Zealand. Unfiltered images were
obtained starting 17:10:28UT (94 seconds after the burst, 17.65s after
receiving the first GCN packet). The combined exposure of 120 images of 0.5
seconds each revealed no uncatalogued sources within the XRT uncertainty
circle down to a magnitude of R Mag~15 when compared to the USNO-B1
catalogue. Further images of longer exposure revealed no other sources and
did not provide a significantly better limit."

D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ),
S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto)
and N. Kawai(Tokyo Tech)
report on behalf of the MITSuME collaboration:

We observed the field of GRB 130508A (Holland et al., GCNC 14607)
with the optical three color (g', Rc and Ic) CCD camera attached
to the MITSuME 50cm telescope of Okayama Astrophysical Observatory.

The observation started on 2013-05-08 17:10:40 UT (~1.8 min after the burst).
We did not find any new point source within the XRT error circle
(Holland et al., GCNC 14607) in all the three bands.

Photometric results of the OT are listed below.
We used GSC2.3 catalog for flux calibration.

#T0+[day]  MID-UT    T-EXP[sec]   g'     Rc     Ic
-----------------------------------------------------
0.04312    18:10:59    6360.0   >20.5  >20.4  >19.1
-----------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]

T. Sakamoto (AGU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
S. T. Holland (STScI), H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), 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 the recent telemetry downlink,
we report further analysis of BAT GRB 130508A (trigger #555413) (Holland, et al.,
GCN Circ. 14607
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 ).
The BAT ground-calculated position is RA, Dec = 305.351, 34.966 deg which is
    RA(J2000)  =  20h 21m 24.2s
    Dec(J2000) = +34d 57' 57.6"
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment).  The
partial coding was 60%.
  
The mask-weighted light curve shows a single peak from about T+9 to T+55 sec.
T90 (15-350 keV) is 42 +- 11 sec (estimated error including systematics).
  
The time-averaged spectrum from T+9.62 to T+56.75 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.80 +- 0.23.  The fluence in the 15-150 keV band is 6.6 +- 1.0 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+11.07 sec in the 15-150 keV band
is 0.7 +- 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/555413/BA/

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

GCN 14126
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  was sent in error, with several pieces of information missing, 
as new data were being processed as the circular was sent.

The corrected refined XRT analysis is as follows:


We have analysed 10 ks of XRT data for GRB 130508A (Holland  et al. GCN 
Circ. 14607
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 ),  from 134 s to 45.8 ks after the  BAT trigger. The data 
comprise 53 s in Windowed Timing (WT) mode with the remainder in Photon 
Counting (PC) mode. The best available XRT position  (using the promptly 
downlinked event data, the XRT-UVOT alignment and matching UVOT field 
sources to the USNO-B1 catalogue) is RA, Dec = 305.3218, 34.9583 which 
is equivalent to:

RA (J2000): 20 21 17.22
Dec(J2000): +34 57 29.9

with an uncertainty of 2.5 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay 
index of alpha=1.98 (+0.39, -0.28).

A spectrum formed from the PC mode data can be fitted with an absorbed 
power-law with a photon spectral index of 1.0 (+0.6, -0.5). The 
best-fitting absorption column is  1.6 (+1.0, -0.8) x 10^22 cm^-2, in 
excess of the Galactic value of 7.7 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 1.0 x 10^-10 (1.3 x 10^-10) erg 
cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
Total column:        1.6 (+1.0, -0.8) x 10^22 cm^-2
Galactic foreground: 7.7 x 10^21 cm^-2
Excess significance: 1.7 sigma
Photon index:        1.0 (+0.6, -0.5)

If the light curve continues to decay with a power-law decay index of 
1.98, the count rate at T+24 hours will be 6.0 x 10^-6 count s^-1, 
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.1 x 
10^-16 (7.8 x 10^-16) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at 
http://www.swift.ac.uk/xrt_products/00555413.

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

Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB)
J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UCSC),
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC),
José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM),
Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC)
report:

We observed the field of GRB 130508A (Holland, et al., GCN 14607
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 ) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on
Sierra San Pedro Mártir from 2013/05 9.36 to 2013/05 9.45 UTC (15.45 to
17.54 hours after the BAT trigger), obtaining a total of 1.42 hours
exposure in the r' and i' bands and 0.60 hours exposure in the Z, Y, J, and
H bands.

For a source within the Swift-XRT error circle (Evans et al., GCN 14614
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 ),
in comparison with USNO-B1 and 2MASS, we obtain the following upper limits
(3-sigma):

  r' > 23.81
  i' > 23.53
  Z  > 21.95
  Y  > 21.66
  J  > 21.00
  H  > 20.42

These magnitudes are in the AB system and not corrected for Galactic
extinction in the direction of the GRB.

We thank the staff of the Observatorio Astronómico Nacional in San Pedro
Mártir.

Y. Saito, Y. Yano, R. Usui, Y. Tachibana, K. Ito, T. Yoshii,
S. Kurita, Y. Yatsu, and N. Kawai (Tokyo Tech)
report on behalf of the MITSuME collaboration:

We observed the field of GRB 130508A (Holland et al., GCNC 14607) with the
optical
three color (g, Rc, and Ic) CCD cameras attached to the MITSuME 50 cm
telescope of Akeno Observatory, Yamanashi, Japan.

The observation started on 2013-05-08 17:10:32 UT ( ~99 sec after
the burst). And we could not find any new point source within the XRT
error circle (Holland et al., GCNC 14607) in all the three bands.

The results of photometry (3 sigma upper limits) are listed below.
We used GSC2.3 catalog for flux calibration.


T0+[sec]   MID-UT   T-EXP[sec]    g'           Rc          Ic
------------------------------------------------------------
-------------------------------
    283      17:13:30      240      >19.4   >19.1   >18.0
   2803      17:55:30     4320      >20.7   >20.4   >19.1
------------------------------------------------------------
-------------------------------
T0+ : Elapsed time after the burst [sec]
T-EXP: Total Exposure time [sec]

S. T. Holland (STScI) reports on behalf of the Swift/UVOT team:

     The Swift/UVOT began settled observations of the field of GRB
130508A starting 136 s after the BAT trigger (Holland et al. 2013,
GCNC 14607).  We do not detect any new source consistent with the
UVOT-enhanced XRT position (Evans 2013, GCNC 14614) in any of the UVOT
exposures.  Preliminary 3-sigma upper limits using the UVOT
photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373)
for the finding chart (FC) exposures and initial summed exposures are
presented below.

Filter       TSTART     TSTOP   Exposure      Mag
-------------------------------------------------
white (FC)      136       285        147    >20.8
u (FC)          296       545        246    >19.8
-------------------------------------------------
v              4416      5642        393    >20.0
b               551      6336        288    >20.5
u               296      6257        639    >20.5
uvw1           4417      6052        393    >20.3
uvm2           4212      5847        393    >20.3
uvw2           3801      5437        393    >20.5
white           136      5231        344    >21.5
-------------------------------------------------

     The quoted upper limits have not been corrected for the expected
extinction due to the Galactic reddening along the line of sight to
this burst of E(B-V) = 2.54 mag (Schlafly et al. 2011, ApJS, 737,
103).

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

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

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

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

V.Krushinski, I.Zalozhnih,  A. Popov
Ural Federal University, Kourovka

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)

MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Tunka was pointed to the  GRB130508A 37 sec after notice time 
and 119 sec after GRB time at 2013-05-08 17:10:52.959 UT. On our first 
(20s exposure) set we haven`t found optical transients within SWIFT 
error-box (Holland et al. GCN14607
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 ).
The 5-sigma upper limit has been about 17.3 mag
The message may be cited.