GRB 130315A

P. A. Evans (U Leicester), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
B.P. Gompertz (U Leicester), J. A. Kennea (PSU),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
M. H. Siegel (PSU), R. L. C. Starling (U Leicester) and
E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift Team:

At 12:45:32 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130315A (trigger=551126).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 157.542, -51.810 which is 
   RA(J2000)  =  10h 30m 10s
   Dec(J2000) = -51d 48' 36"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple peaks
with a total duration of about 40 sec.  The peak count rate
was ~1100 counts/sec (15-350 keV), at ~10 sec after the trigger. 
There is a possible flare at T+160 sec. 

The XRT began observing the field at 12:48:13.7 UT, 160.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 157.54648, -51.79244 which
is equivalent to:
   RA(J2000)  = 10h 30m 11.16s
   Dec(J2000) = -51d 47' 32.8"
with an uncertainty of 5.0 arcseconds (radius, 90% containment). This
location is 63 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 2.27
x 10^21 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 1.10e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 171 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
0.36. 

Burst Advocate for this burst is P. A. Evans (pae9 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.)

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 130315A (Evans et al., GCNC 14311),
detected by Swift/BAT, with the 0.6m Yock-Allen robotic telescope
(BOOTES-3) located in Blenheim, New Zealand. Unfiltered images were
obtained starting 13:21:02UT (35m after the burst, limited by clouds). An
exposure of 30 seconds revealed no uncatalogued sources down to a magnitude
of RMag~16.5 when compared to the USNO-B1 catalogue."

S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), P. A. Evans (U Leicester) 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), 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 130315A (trigger #551126)
(Evans, et al., GCN Circ. 14311
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 ).  The BAT ground-calculated position is
RA, Dec = 157.541, -51.794 deg which is
    RA(J2000)  =  10h 30m 09.9s
    Dec(J2000) = -51d 47' 37.4"
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 42%.

The mask-weighted light curve shows two broad peaks, the first starting at
~T-10 sec, peaking at T+10 sec and then slowly declining until ~T+70 sec.  The
rise to the second peak begins almost immediately, with a broad peak around
T+160 sec and falling to background by T+240 sec. Note that a slew took the
source out of the field of view at ~T+650 sec. T90 (15-350 keV) is
233.4 +- 17.5 sec (estimated error including systematics).

The time-averaged spectrum from T-3.30 to T+268.00 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.81 +- 0.08.  The fluence in the 15-150 keV band is 4.9 +- 0.2 x 10^-6 erg/cm2. 
The 1-sec peak photon flux measured from T+8.41 sec in the 15-150 keV band is 
1.0 +- 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/551126/BA/

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

We have analysed 10 ks of XRT data for GRB 130315A (Evans  et al. GCN
Circ. 14311
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 ),  from 167 s to 29.4 ks after the	BAT trigger. The data
comprise 337 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The refined XRT position is RA, Dec =
157.54687, -51.79362 which is equivalent to:

RA (J2000): 10 30 11.25
Dec(J2000): -51 47 37.0

with an uncertainty of 3.6 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=.

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.49 (+/-0.04). The
best-fitting absorption column is  2.88 (+0.19, -0.18) x 10^21 cm^-2,
in excess of the Galactic value of 2.3 x 10^21 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.1 (+/-0.3) and a
best-fitting absorption column of 3.1 (+1.2, -0.8) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.9 x 10^-11 (6.7 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.1 (+1.2, -0.8) x 10^21 cm^-2
Galactic foreground: 2.3 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.1 (+/-0.3)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00551126.

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

T. E. Pickering, P. Vaisanen, V. van Wyk report on behalf of SALT:

We have observed the field of GRB 130315A (Evans et al. GCN 14311
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 ) using the RSS imager/spectrograph at the Southern African Large Telescope (SALT).  The observations began at 17:40 UT, just under 5 hours after the initial Swift trigger.  Imaging was performed using a broadband filter with a blue cutoff at 4600 A and three narrow-band filters centered at 4820 A, 6530 A, and 8175 A. The data were somewhat hampered by scattered clouds and mediocre seeing.  Comparison to a DSS2 red image finds no evidence of a new source within the error circle of the refined XRT position (3.6"; Page et al. GCN 14317
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 ).  The limiting magnitude of our best images is roughly ~0.5 mag deeper than the DSS2 image which gives a detection upper limit of r ~ 21 based on comparison with nearby stars in the GSC 2.3.  

This message may be cited.

S. T. Holland (STScI) and P. A. Evans (U Leicester)
report on behalf of the Swift/UVOT team:

     Swift/UVOT began settled observations of the field of GRB 130315A
starting 171 s after the BAT trigger (Evans et al., 2013, GCNC 14311).
We do not detect any new source within the XRT error circle (Page et al.,
2013, GCNC 14317).  Preliminary UVOT 3-sigma upper limits at this
position are presented below.

------------------------------------------------
Filter      TSTART     TSTOP    Exposure     Mag
------------------------------------------------
white (FC)     171       321         147   >21.1 
    u (FC)     330       580         246   >20.3 
------------------------------------------------
    v         4476    23,657        1136   >20.7 
    b         3860    28,925        1685   >21.7 
    u          330    17,889        1443   >21.4 
 uvw1         4887    17,764        1995   >21.3 
 uvm2         4681    16,857        1277   >21.0 
 uvw2         4271    22,898        1279   >21.2 
white          171    29.424        1022   >22.2 
------------------------------------------------

    The quoted upper limits have not been corrected for the Galactic
extinction along the line of sight to this burst of E_{B-V} = 0.32 mag
(Schlafly et al. 2011, ApJS, 737, 103).  The photometry is in the UVOT
photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373).
The photometry is affected by the presence of a J = 15.4 mag 2MASS
source 10301128-5147395 located 2.3 arcsec south of the XRT position.

S. Schmidl (TLS Tautenburg), J. Elliott (MPE Garching), A. Nicuesa
Guelbenzu (TLS Tautenburg), S. Klose (TLS Tautenburg), and J. Greiner
(MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 130315A (Swift trigger 551126; Evans et
al., GCN 14311
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla
Observatory (Chile).

First-epoch observations started on March 15, 2013, at 23:51 UT, 11.1
hrs after the GRB trigger. They were performed at an average seeing of
0."7 and at an average airmass of 1.18. No evidence for a fading
afterglow was found.

Second-epoch observations were executed the following night (38.4 hr
after the trigger) under slightly worse observing conditions. A
comparison with the first-epoch images reveales a fading source at the
south-east border of the Swift/XRT error circle (Page et al., GCN 14317
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 )
at coordinates

RA (J2000.0)  =  10:30:11.54
Dec (J2000.0) = -51:47:39.8

with an uncertainty of 0."5 in each coordinate.

Based on a total exposure time of 1500 s in r'i'z' at a midtime of
12.8 hrs after the burst, for this source we measure the following
preliminary AB magnitudes:

r' = 22.0 +/- 0.1,
i' = 21.5 +/- 0.1,
z' = 21.1 +/- 0.1.

Between both epochs this object faded by more than 1 magnitude, implying
a decay with alpha > 0.75.

The given magnitudes are calibrated against GROND zeropoints. The
Galactic reddening along the line of sight is E(B-V)= 0.36 mag (Schlegel
et al. 1998).

GRB 130315A: Zadko observatory - Gingin optical observations
------------------------------**------------------------------**----------
H. Dereli (UNS-CNRS-OCA), A. Klotz (IRAP-CNRS-OMP),
D. Macpherson (UWA/ICRAR), D. Coward (UWA),
B. Gendre (IRAP-CNRS-OMP), M. Boer, K. Siellez, O. Bardho (UNS-CNRS-OCA),
A. Williams (PO-UWA), R. Martin (PO-UWA)
report:

We imaged the field of GRB 130315A detected by SWIFT
(trigger 551126) with the Zadko robotic telescope (D=100cm)
located at the observatory - Gingin, Australia.

The observations started 1.22h after the GRB trigger.
The elevation of the field increased from
65 degrees above horizon and weather conditions
were good.

We co-added a series of unfiltered exposures and we
substracted images taken with the same telescope
4h to 8h later to eliminate contaminations by
foreground stars. We did not detect any optical
transient at the position provided by Schmidl
et al. (GCNC 14325):

t0+1.22h to t0+1.54h : Rlim = 20.4

This limiting magnitude and the detection
of Schmidl et al. (GCNC 14325) implies a
decay with alpha < 0.67. As Schmidl et al.
(GCNC 14325) announced alpha > 0.75 after 12h
we suspect a late rising of a faint afterglow
or a break of the decay.

Magnitudes were estimated with the nearby NOMAD1
stars and are not corrected for galactic
dust extinction.