GRB 110315A

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

At 23:57:04 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110315A (trigger=449399).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 279.191, +17.532 which is 
   RA(J2000)  =  18h 36m 46s
   Dec(J2000) = +17d 31' 56"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows 3 or 4 peaks
with a total duration of about 20 sec.  The peak count rate
was ~1200 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 23:58:49.1 UT, 104.6 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 279.1928, +17.5388 which is equivalent to:
   RA(J2000)  = 18h 36m 46.27s
   Dec(J2000) = +17d 32' 19.6"
with an uncertainty of 5.8 arcseconds (radius, 90% containment). This
location is 25 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 112 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 coverage of the XRT error circle by the 8'x8' region for the list of
sources generated on-board is uncertain because the large number of sources
filled the available telemetry. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.25. 

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.)

E. Gorbovskoy, V. Lipunov, V.Kornilov, A.Belinski, N.Shatskiy, N.Tyurina,
D.Kuvshinov, P.Balanutsa, V.V.Chazov, P.V.Kortunov, A.Kuznetsov,
D.Zimnukhov, M. Kornilov, A.V.Krylov, V.Shumkov, S.Shurpakov
Sternberg Astronomical Institute, Moscow State University


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


V.Yurkov, Yu.Sergienko, D.Varda, I.Kudelina
Blagoveschensk Educational State University, Blagoveschensk

V.Krushinski, I.Zalozhnich, A. Popov
Ural State University, Kourovka

K.Ivanov, O.Chuvalaev, V.Poleschuk, E.Konstantinov, V.Lenok, O.Gres,
S.Yazev, N.M.Budnev,
Irkutsk State University


MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Kislovodsk was pointed to the GRB110315A (Melandri et al., GCN 
11790
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 ) 44 sec s 
after notice time and 89 sec after GRB time at 2011-03-15 23:58:33.212 UT.
On our first (20s exposure) set we haven`t found optical transient  within 
SWIFT BAT error-box (ra=18 36 45 dec=+17 31 48 ).
The 3-sigma upper limit has been about 17.3 mag
The upper limit for 25 coadded images is 20.0 started 23:58:33.212 UT 
(mean time after trigger is 3240 sec ). 
The Galactic absroption in this direction is about 1 mag (Kalbela et al., 
2005, A&A,440,775).

The message may be cited.


mailto: lipunov@sai.msu.ru

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

Using 8887 s of XRT Photon Counting mode data and 15 UVOT
images for GRB 110315A, 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 = 279.19531, +17.53899 which is equivalent
to:

RA (J2000): 18h 36m 46.87s
Dec (J2000): +17d 32' 20.4"

with an uncertainty of 1.4 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.

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), 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 the recent telemetry downlink,
we report further analysis of BAT GRB 110315A (trigger #449399)
(Melandri, et al., GCN Circ. 11790
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 ).  The BAT ground-calculated position is
RA, Dec = 279.205, 17.537 deg which is 
   RA(J2000)  =  18h 36m 49.2s 
   Dec(J2000) = +17d 32' 13.9" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 57%.
 
The mask-weighted light curve shows a multi-peak structure starting 
at ~T-70 sec, with several peaks of approximate equal brightness
at T-21, T-3, T+3, and T+17 sec, and then returning to background
at ~T+90 sec.  There is weak emission (~2 sigma) in the BAT 15-25 keV band
starting at ~T+440 out to ~T+580 sec.  This is likley associated with the flare
in the XRT lightcurve at ~T+500 sec.  T90 (15-350 keV) is 77 +- 12 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-66.8 to T+38.8 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.77 +- 0.08.  The fluence in the 15-150 keV band is 4.1 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+3.13 sec in the 15-150 keV band
is 1.7 +- 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/449399/BA/

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

We have analysed 14 ks of XRT data for GRB 110315A (Melandri  et al.
GCN Circ. 11790
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 ), from 94 s to 34.8 ks after the  BAT trigger. The data
comprise 97 s in Windowed Timing (WT) mode (the first 8 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 Beardmore
et al. (GCN. Circ 11792).

The light curve can be modelled with an initial power-law decay with an
index of alpha=2.48 (+0.64, -0.53), followed by a break at T+150 s to
an alpha of 1.03 (+0.03, -0.03). Flaring activity is detected around
T+500 s.

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.14 (+0.26, -0.24). The
best-fitting absorption column is  2.5 (+0.8, -0.7) x 10^21 cm^-2, in
excess of the Galactic value of 1.8 x 10^21 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.19 (+0.15, -0.12)
and a best-fitting absorption column of 2.7 (+/-0.4) 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:	     2.7 (+/-0.4) x 10^21 cm^-2
Galactic foreground: 1.8 x 10^21 cm^-2
Excess significance: 10.0 sigma
Photon index:	     2.19 (+0.15, -0.12)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00449399.

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

E. A. Hoversten (PSU) and A. Melandri (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 110315A
113 s after the BAT trigger (Melandri et al., GCN Circ. 11790
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 ).
No optical afterglow consistent with the enhanced XRT position
(Beardmore et al., GCN Circ. 11792
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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           113          263          147         >20.5
u_FC               325          559          230         >19.7
white              113        12119         1275         >21.8

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.25 in the direction of the burst
(Schlegel et al. 1998).

I. Bikmaev, R. Zhuchkov, 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 110315A (Melandri et al., GCN 11790
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 ) was observed
with Russian-Turkish 1.5-m telescope (RTT150, Bakirlitepe, TUBITAK
National Observatory, Turkey) in March 16, 2011, during UT 01:05 -
03:15, i.e. starting approximately 1 hour after the burst. A serie of
21 exposures by 300 sec each in Rc filter was obtained.

We found no optical source within the 1.4'' enhanced XRT error circle
(Beardmore et al., GCN 11792
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 ) in our combined image at a limiting
magnitude of Rc =~ 23.6 mag.