GRB 110312A

S. R. Oates (UCL-MSSL), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
M. M. Chester (PSU), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), C. B. Markwardt (NASA/GSFC),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), M. H. Siegel (PSU),
M. Stamatikos (OSU/NASA/GSFC), R. L. C. Starling (U Leicester),
E. Troja (NASA/GSFC/ORAU) and T. N. Ukwatta (MSU) report on behalf of
the Swift Team:

At 17:55:37 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110312A (trigger=449074).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 157.479, -5.255 which is 
   RA(J2000)  =  10h 29m 55s
   Dec(J2000) = -05d 15' 18"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is typical for image triggers, the BAT lightcurve
does not show anything significant. 

The XRT began observing the field at 17:58:16.3 UT, 159.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
157.4813, -5.2628 which is equivalent to:
   RA(J2000)  = 10h 29m 55.50s
   Dec(J2000) = -05d 15' 46.0"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 28 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 3.72
x 10^20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 4.19e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 167 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
0.04. 

Burst Advocate for this burst is S. R. Oates (sro AT mssl.ucl.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.)

S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC),
S. R. Oates (UCL-MSSL), 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 110312A (trigger #449074)
(Oates, et al., GCN Circ. 11782
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 ).  The BAT ground-calculated position is
RA, Dec = 157.500, -5.259 deg, which is 
   RA(J2000)  =  10h 30m 00.0s 
   Dec(J2000) = -05d 15' 32.6" 
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 26%.
 
The mask-weighted light curve shows a single start at ~T+25 sec, peaking
around T+45 sec, and ending at ~T+65 sec.  T90 (15-350 keV) is 28.7 +- 7.6 sec
(estimated error including systematics).
 
The time-averaged spectrum from T+24.1 to T+64.9 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.32 +- 0.26.  The fluence in the 15-150 keV band is 8.2 +- 1.3 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+44.08 sec in the 15-150 keV band
is 1.2 +- 0.3 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/449074/BA/

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

Using 1937 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 110312A, 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 = 157.48111, -5.26262 which is equivalent
to:

RA (J2000): 10h 29m 55.47s
Dec (J2000): -05d 15' 45.4"

with an uncertainty of 1.7 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. Nicuesa Guelbenzu (TLS Tautenburg), F. Olivares E., and J. Greiner
(MPE Garching) report on behalf of the GROND team:

 We observed the field of GRB 110312A (Swift trigger 449074; Oates et
 al., GCN #11782
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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 MPI/ESO telescope at La
 Silla Observatory (Chile).

 Observations started at 23:57 UT on March 11, 2011, 6 hours after the
 GRB trigger, and continued for 2.6 hours. They were performed at an
 average seeing of 1.3" and at an average airmass of 1.5.

 We find no sources within the the 1.7" enhanced XRT error circle
 (Osborne et al.; GCN #11783
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 ). Co-added images of 64.5 min of
 integration time in g'r'i'z' and 56 min in JHK yield the following
 3-sigma upper limits (all in the AB system):

 g' > 24.3,
 r' > 24.1,
 i' > 23.0,
 z' > 23.1,
 J  > 22.0,
 H  > 21.4, and
 K  > 19.3


calibrated against GROND zeropoints and 2MASS field stars. No
corrections for the expected Galactic foreground extinction were made,
which correspond to a reddening of E(B-V)=0.04 mag in the direction of
the burst (Schlegel et al. 1998).

P.A. Evans (U. Leicester) and S. R. Oates (UCL-MSSL) report on behalf
of the Swift-XRT team:

We have analysed 2.9 ks of XRT data for GRB 110312A (Oates  et al. GCN
Circ. 11782
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 ), from 147 s to 18.1 ks after the  BAT trigger. The data
comprise 82 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Osborne et
al. (GCN. Circ 11784).

The light curve can be modelled with an initial power-law decay with an
index of alpha=3.8 (+0.8, -1.1), followed by a break at T+356 s to an
alpha of 0.55 (+0.10, -0.12).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.36 (+0.22, -0.21). The
best-fitting absorption column is  4.3 (+/-0.8) x 10^21 cm^-2, in
excess of the Galactic value of 3.7 x 10^20 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.0 x 10^-11 (8.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.3 (+/-0.8) x 10^21 cm^-2
Galactic foreground: 3.7 x 10^20 cm^-2
Excess significance: 9.5 sigma
Photon index:	     2.36 (+0.22, -0.21)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00449074.

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

S. R Oates (UCL-MSSL) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 110312A
168 s after the BAT trigger (Oates et al., GCN Circ. 11782
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 ).
No optical afterglow consistent with the XRT position
(Evans et al., GCN Circ. 11784
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 ) is detected in the initial UVOT  
exposures.

Preliminary 3-sigma upper limits using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC)
exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag
----------------------------------------------------------------
white_FC           168          318          147         >21.8
u_FC               327          577          246         >20.1
white              168         1896          429         >21.3
v                  657         1946          156         >19.2
b                  582         6063          315         >20.6
u                  327         2020          382         >20.1
w1                 706         1995          136         >19.6
m2                 682         1970          156         >19.6
w2                1036         1402           39         >18.8

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.04 in the direction of the burst
(Schlegel et al. 1998).

I. Bikmaev, R. Zhuchkov, R. Gumerov, A. Nemtinov, N. Sakhibullin 
(Kazan University),
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI),
Z. Eker, I. Khamitov (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.)

report:

The field of GRB 110312A (Oates et al., GCN 11782
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 ) was observed with
Russian-Turkish 1.5-m telescope (RTT150,Bakirlitepe, TUBITAK National
Observatory, Turkey) in March 12, 2011, during UT 20:00 - 21:40,
i.e. starting approximately 2 hours after the burst. 

We obtained serie of 16 exposures by 300 sec each in Rc filter.

We found no optical source within the 1.7" enhanced XRT error circle
(Osborne et al.; GCN 11784
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 ) in co-added image with frame limit of 
Rc ~ 23.5 mag

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 110312A (Oates et al., GCN 11782
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 )
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 2011-03-12 18:35:03 UT (~39 mins
after the burst). We did not find any new point source within the
enhanced XRT circle (Osborne et al., GCNC 11784) in all the
three bands.

Three sigma upper limits of the OT are listed below. We used
GSC2.3 catalog for flux calibration.


T0+[day]   MID-UT   T-EXP[sec]    g'     Rc     Ic
------------------------------------------------------
0.02269    18:28:18    1020.0    >17.8  >18.0  >17.4
------------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]