GRB 110318B

R. Margutti (INAF-OAB), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
S. Campana (INAF-OAB), P. D'Avanzo (INAF-OAB),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
J. M. Gelbord (PSU), C. Gronwall (PSU), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), O. M. Littlejohns (U Leicester),
V. Mangano (INAF-IASFPA), C. B. Markwardt (NASA/GSFC),
F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB),
P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
P. Romano (INAF-IASFPA), B. Sbarufatti (INAF-OAB/IASFPA),
M. H. Siegel (PSU), E. Sonbas (GSFC/USRA/Adiyaman Univ.) and
C. A. Swenson (PSU) report on behalf of the Swift Team:

At 15:27:09 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110318B (trigger=449549).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 211.695, -51.559, which is 
   RA(J2000)  =  14h 06m 47s
   Dec(J2000) = -51d 33' 31"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a couple peaks
with a total duration of about 10 sec.  The peak count rate
was ~1100 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 15:28:22.5 UT, 72.8 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 211.67805, -51.57933 which
is equivalent to:
   RA(J2000)  = 14h 06m 42.73s
   Dec(J2000) = -51d 34' 45.6"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 82 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 2.42
x 10^21 cm^-2 (Kalberla et al. 2005). 

The UVOT processed images are delayed and will be analyzed as soon as
possible. 

Burst Advocate for this burst is R. Margutti (raffaella.margutti AT brera.inaf.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.)

S. T. Holland (CRESST/USRA/GSFC) &
R. Margutti (INAF-OAB)
report on behalf of the Swift/UVOT team:

     UVOT took a finding chart exposure of the field of GRB 110318B
(Margutti et al. 2011, GCNC 11800) 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. No correction has been
made for the expected extinction corresponding to E(B-V) of 0.46.

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

Using 1818 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 110318B, 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 = 211.67808, -51.57883 which is equivalent
to:

RA (J2000): 14h 06m 42.74s
Dec (J2000): -51d 34' 43.8"

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.

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
R. Margutti (INAF-OAB), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
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 110318B (trigger #449549)
(Margutti, et al., GCN Circ. 11799
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 ).  The BAT ground-calculated position is
RA, Dec = 211.691, -51.577 deg, which is 
   RA(J2000)  =  14h 06m 45.9s 
   Dec(J2000) = -51d 34' 35.7" 
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 85%.
 
The mask-weighted light curve shows a single peak starting at ~T-2 sec,
peaking at ~T+1 sec, and ending at ~T+5 sec.  T90 (15-350 keV) is
4.8 +- 0.6 sec (estimated error including systematics).
 
The time-averaged spectrum from T-1.7 to T+3.7 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.09 +- 0.17.  The fluence in the 15-150 keV band is 2.9 +- 0.3 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.76 sec in the 15-150 keV band
is 0.7 +- 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/449549/BA/

R. Margutti, B. Sbarufatti, A. Melandri (INAF-OAB) report on behalf of
the Swift-XRT team:

We have analysed 4.9 ks of XRT data for GRB 110318B (Margutti  et al.
GCN Circ. 11799
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 ), from 83 s to 13.4 ks after the  BAT trigger. The data
are entirely in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Evans et al. (GCN. Circ 11803).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.10 (+0.10, -0.09).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.3 (+/-0.3). The
best-fitting absorption column is  5.2 (+1.5, -1.3) x 10^21 cm^-2, in
excess of the Galactic value of 2.4 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 4.3 x 10^-11 (9.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.2 (+1.5, -1.3) x 10^21 cm^-2
Galactic foreground: 2.4 x 10^21 cm^-2
Excess significance: 6.5 sigma
Photon index:	     2.3 (+/-0.3)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00449549.

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

T. Kruehler, J. Greiner, F. Schrey (all MPE Garching), and S. Klose (TLS
Tautenburg) report on behalf of the GROND team.

We observed the field of GRB 110318B (Swift trigger 449549; Margutti et
al., GCN #11800
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  simultaneously in g'r'i'z' with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2 m MPI/ESO telescope at La Silla
Observatory (Chile).

Observation started at 07:40 UT, which is 16.2 h after the trigger, and
were obtained under clear skies with an airmass of around 1.1 and seeing
of 1"

In stacked images with a total integration time of 25 min, we do not
detect a source in the refined XRT error circle (Evans et al., GCN #11803
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 )
to the following upper limits (AB system):

g' > 23.7
r' > 23.6
i' > 23.6
z' > 23.4

Given magnitudes are calibrated against GROND zeropoints and are not
corrected for the expected Galactic foreground extinction corresponding to
a reddening of E_(B-V)=0.46 mag in the direction of the burst (Schlegel et
al. 1998).

GROND is currently undergoing hardware maintenance, and hence no NIR data
are available for this burst.

S. T. Holland (CRESST/USRA/GSFC) and
R. Margutti (INAF-OAB)
report on behalf of the Swift/UVOT team:

      The Swift/UVOT observed the field of GRB 110318B starting 58 s
after the BAT trigger (Margutti, et al., 2011, GCN Circ. 11799
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 ).
Settled observations started at 76 s.  We do not detect an optical
afterglow at the UVOT-enhanced XRT position (Evans, et al., 2011, GCN
Circ. 11803
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 ) in any of the UVOT filters.  Preliminary 3-sigma upper
limits for detecting a source in the finding charts and in the
co-added images, are

Filter      T_start   T_stop    Exp(s)      Mag
-----------------------------------------------
white (fc)       76      226       147    >21.5
                868     1018       147    >21.5

    v           619     7035       529    >20.6
    b           545     7693       370    >21.2
    u           289     7649       756    >21.2
 uvw1           668     7445       529    >20.8
 uvm2          5602     7239       393    >20.5
 uvw2          1024     6829       236    >20.3
white            76     6623       626    >22.2
-----------------------------------------------

     The quoted magnitudes and upper limits have not been corrected
for the expected Galactic extinction along the line of sight
corresponding to a reddening of E_{B-V} = 0.46 mag (Schlegel, et al.,
1998, ApJS, 500, 525).

D. Suzuki (STE Lab. Nagoya Univ.), P.J. Tristram (Mt. John University
Observatory),
S. Kobara, K. Omori, H. Naito and T. Sako (STE Lab. Nagoya Univ.)
on behalf of the MOA Collaboration report :

We searched for an optical afterglow of GRB110318B (GCN 11799
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 , R. Margutti
et al.)
starting from 15:40 UT on 2011 March 18 (13 minutes after the burst)
with the MOA-II 1.8m telescope at Mt.John observatory in New Zealand.
In a single image of a 60 sec exposure with a wideband Red filter (center
wavelength ~ 750nm and FWHM ~ 250nm), we did not find any object
within the error circle of the Swift XRT source position (GCN 11803
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 , P.A.
Evans et al.).
A 3 sigma upper limit is set in the I magnitude at 20.7 mag.

This photometry was done by using the DoPhot and calibrated against
the USNO-B1.0 catalog stars, and not corrected for the Galactic extinction.