GRB 120403B

V. D'Elia (ASDC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
S. Campana (INAF-OAB), M. M. Chester (PSU), J. A. Kennea (PSU),
C. B. Markwardt (NASA/GSFC), A. Maselli (INAF-IASFPA),
A. Melandri (INAF-OAB), P. T. O'Brien (U Leicester),
T. Sakamoto (NASA/UMBC), C. J. Saxton (UCL-MSSL),
B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU), G. Stratta (ASDC),
C. A. Swenson (PSU), T. N. Ukwatta (MSU) and B.-B. Zhang (PSU) report
on behalf of the Swift Team:

At 20:33:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120403B (trigger=519256).  Because of an observing constraint,
the slew to the burst was delayed by 12.9 minutes. 
The BAT on-board calculated location is 
RA, Dec 54.809, -89.037, which is 
   RA(J2000)  =  03h 39m 14s
   Dec(J2000) = -89d 02' 12"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows several spikes
with a total duration of about 10 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 20:49:04.0 UT, 907.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 55.33838, -89.00933 which is equivalent
to:
   RA(J2000)  = 03h 41m 21.21s
   Dec(J2000) = -89d 00' 33.6"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 104 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 9.52
x 10^20 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 910 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
0.13. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.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 1035 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 120403B, 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 = 55.27631, -89.00862 which is equivalent
to:

RA (J2000): 03h 41m 6.31s
Dec (J2000): -89d 00' 31.0"

with an uncertainty of 2.3 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. A. Breeveld (MSSL-UCL) and V. D'Elia (ASDC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120403B
911s after the BAT trigger (D'Elia et al., GCN Circ. 13203
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 ).
No optical afterglow consistent with the XRT position
(Goad et al., GCN Circ. 13205
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 ) is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC           911         1061          147         >21.7
white             1190         7931          568         >22.0
v                 1068         8342          588         >20.7
b                 1166         7726          568         >21.3
u                 1141        12488          404         >21.1
w1                1117         9020          851         >21.1
m2                1092         8547          568         >20.8
w2                1216         8137          485         >21.0

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.13 in the direction of the 
burst (Schlegel et al. 1998).

M. Stamatikos (OSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), V. D'Elia (ASDC), E. E. Fenimore (LANL),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC),
G. Sato (ISAS), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+70 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120403B (trigger #519256)
(D'Elia, et al., GCN Circ. 13203
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 ).  The BAT ground-calculated position is
RA, Dec = 54.302, -89.029 deg, which is 
   RA(J2000)  =  03h 37m 12.6s 
   Dec(J2000) = -89d 01' 45.1" 
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 47%.
 
The mask-weighted light curve shows several overlapping peaks starting 
at ~T-5 sec and ending at ~T+10 sec.  T90 (15-350 keV) is 7.3 +- 1.9 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-3.0 to T+5.3 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.79 +- 0.31.  The fluence in the 15-150 keV band is 2.1 +- 0.4 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+0.92 sec in the 15-150 keV band
is 0.9 +- 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/519256/BA/

Rhaana Starling, Klaas Wiersema (U. Leicester), Stuart Ryder (AAO), Peter Barnes (U. Florida) and Christopher Stockdale (Marquette Univ.) report:

We began observations of the field of GRB 120403B with IRIS2 on the 4m Anglo-Australian Telescope on 2012-04-04 at 08:34:00 UT, 
12 hours after the BAT trigger (D'Elia et al., GCN Circ. 13203
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 ). We performed near-infrared photometry in the Ks, H and J bands, 
totalling 2x9 minutes in each filter. 

We do not detect any source within the UVOT-enhanced XRT error circle (Goad et al., GCN Circ. 13205
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 ) down to limiting magnitudes of
Ks > 19.4 mag
H  > 20.0 mag
J  > 20.9 mag.
Calibration was carried out using 8 2MASS field stars. No correction for Galactic extinction has been applied.


These observations were obtained under programme AAT/11B/21.

George Younes (USRA)
reports on behalf of the Fermi GBM Team:

"At 20:33:58.49 UT on April 03, 2012, the Fermi Gamma-ray Burst
Monitor (GBM) triggered and located GRB 120403B (trigger 355178040 /
120403857) which was triggered and detected by Swift (D'Elia et al.,
GCN 13203
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 ). The on-ground calculated location, using the Fermi GBM
trigger data is consistent with the Swift location.

The GBM light curve shows a single event with a duration (T90) of
about 4 s (50-300 keV).

The time-averaged spectrum from T0-1.792 s to T0 is well fit
by a power law with index -1.51 +/- 0.08.
A power law with an exponential high-energy cutoff fits the
spectrum equally well. The power law index is  -0.9 +/- 0.3
and the cutoff energy, parameterized as Epeak, is 182 +/- 74 keV.

The event fluence (10-1000 kev) in this time interval is
(4.6 +/- 0.6)E-07 erg/s-cm^2. The 1-s peak photon flux starting at
T0-0.896 s in the 10-1000 keV range is 1.7 +/- 0.2 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

Klotz A. (IRAP-CNRS-OMP), Gendre B. (ASDC/INAF-OAR),
Boer M. (UNS-CNRS-OCA), Atteia J.L. (IRAP-CNRS-OMP) report:

We imaged the field of GRB 120403B detected by SWIFT
(trigger 519256) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 2.8h after the GRB trigger
(the burst occured during the afternoon).
The elevation of the field was 29 degrees above
horizon and weather conditions were good.

We co-added a series of exposures. No optical
counterpart was found. The limiting magnitude
of the image is R=19.5 but the burst occured
close to a R=17.2 star. So we prefer to
publish a conservative value of 18.2 as the
upper limit of the afterglow:

start   stop
2.95h   4.82h   R > 18.2

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.

This message may be cited.

O.M. Littlejohns (U. Leicester), A. Melandri (INAF-OAB), B. Sbarufatti
(INAF-OAB/PSU), G. Stratta (ASDC), D.N. Burrows (PSU), J.A. Kennea
(PSU), M.C. Stroh (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester) and V.D'Elia report on behalf of the Swift-XRT team:

We have analysed 4.5 ks of XRT data for GRB 120403B (D'Elia  et al. GCN
Circ. 13203
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 ), from 920 s to 8.9 ks after the  BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Goad et al. (GCN. Circ 13205).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.80 (+0.15, -0.14).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.2 (+/-0.3). The
best-fitting absorption column is  2.2 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 9.5 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 3.5 x 10^-11 (5.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.2 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 9.5 x 10^20 cm^-2
Excess significance: 2.5 sigma
Photon index:	     2.2 (+/-0.3)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00519256.

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