GRB 110319A

A. Melandri (INAF-OAB), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), P. D'Avanzo (INAF-OAB),
J. M. Gelbord (PSU), C. Gronwall (PSU),
S. T. Holland (CRESST/USRA/GSFC), N. P. M. Kuin (UCL-MSSL),
R. Margutti (INAF-OAB), C. B. Markwardt (NASA/GSFC),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL),
B. Sbarufatti (INAF-OAB/IASFPA) and M. H. Siegel (PSU) report on
behalf of the Swift Team:

At 02:16:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110319A (trigger=449578).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is RA, Dec 356.401, -66.017 which is 
   RA(J2000) = 23h 45m 36s
   Dec(J2000) = -66d 01' 01"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about ~30 sec.  The peak count rate
was ~3800 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 02:17:37.5 UT, 55.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
356.5017, -66.0114 which is equivalent to:
   RA(J2000)  = 23h 46m 0.40s
   Dec(J2000) = -66d 00' 40.9"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 148 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 2.62
x 10^20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 1.10e-09 erg cm^-2 s^-1 (0.2-10
keV). 

     UVOT took a finding chart exposure of 150 seconds with the White
filter starting 66 seconds after the BAT trigger.  No credible
afterglow candidate has been found in the initial data products.  The
2.7' x 2.7' 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 0.03. 

Burst Advocate for this burst is A. Melandri (andrea.melandri 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.)

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

Using 285 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 110319A, 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 = 356.50181, -66.01113 which is equivalent
to:

RA (J2000): 23h 46m 0.43s
Dec (J2000): -66d 00' 40.1"

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, B. Sbarufatti and R. Margutti (INAF-OAB) reports on behalf
of the Swift-XRT team:

We have analysed 9.9 ks of XRT data for GRB 110319A (Melandri  et al.
GCN Circ. 11807
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 ), from 47 s to 23.4 ks after the  BAT trigger. The data
comprise 33 s in Windowed Timing (WT) mode (the first 7 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 Goad et al.
(GCN. Circ 11808).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=3.7 (+0.6, -0.3). At T+151 s  the decay
flattens to an alpha of -0.63 (+0.07, -0.65). The light curve breaks
again at T+4335 s to a decay with alpha=0.98(+0.11, -0.10).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 3.4 (+0.4, -0.3). The
best-fitting absorption column is  2.4 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 2.6 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.33 (+0.13, -0.14)
and a best-fitting absorption column of 1.16 (+0.32, -0.18) x 10^21
cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.3 x 10^-11 (5.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.16 (+0.32, -0.18) x 10^21 cm^-2
Galactic foreground: 2.6 x 10^20 cm^-2
Excess significance: 10.8 sigma
Photon index:	     2.33 (+0.13, -0.14)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00449578.

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

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),
A. Melandri (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-239 to T+963 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 110319A (trigger #449578)
(Melandri, et al., GCN Circ. 11807
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 ).  The BAT ground-calculated position is
RA, Dec = 356.510, -66.008 deg, which is 
   RA(J2000)  =  23h 46m 02.4s 
   Dec(J2000) = -66d 00' 28.7" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows two overlapping peaks starting
at ~T_zero, peaking at ~T+5 and ~T+13 sec, and ending at ~T+30 sec.
T90 (15-350 keV) is 19.3 +- 1.6 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.3 to T+31.3 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.31 +- 0.43, 
and Epeak of 21.9 +- 7.0 keV (chi squared 54.2 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.4 +- 0.1 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+13.10 sec in the 15-150 keV band is
2.2 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 2.55 +- 0.08 (chi squared 86.5 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/449578/BA/

M. H. Siegel (PSU), S. T. Holland (CRESST/USRA/GSFC) and A. Melandri  
(INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 110319A
65s after the BAT trigger (Melandri et al, GCN Circ 11807
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 ). We identify
an optical afterglow near the enchanced XRT position given by Melandri
et al. (GCN Circ. 11810
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 ).  The transient is only detected in the optical
filters and shows fading between the first and second orbits.

The preliminary UVOT position is:

     RA (J2000)  23:46:00.69  =  356.50287 (deg)
    Dec (J2000) -66:00:40.4   =  -66.01122 (deg)

with an estimated uncertainty of 0.44 arcsec (radius, 90% confidence,
statistical + systematic).  Preliminary 3-sigma upper limits and  
magnitudes
using the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627)  
for the
exposures are:

Filter    T_start(s) T_stop(s)  Exp(s)   Mag
white (fc)      65      215    147     18.36+-0.07
white         3924     5560    393     20.32+-0.22
v             4336     5971    393    >19.56
b             3719     5355    393     19.51+-0.21
b            11317    11950    615    >20.63
u              277      395    115     18.13+-0.13
u             4950    11310   1081     19.76+-0.18
uvw1          4745     4945    196    >19.72
uvw1          9497    10397    885    >20.58
uvm2          4540     4740    196    >19.64
uvm2          5976     6172    193    >19.69
uvw2          4131     4330    196    >19.91
uvw2          5566     5766    196    >19.91

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).