GRB 121031A

V. D'Elia (ASDC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
M. M. Chester (PSU), J. R. Cummings (NASA/UMBC),
N. Gehrels (NASA/GSFC), S. T. Holland (STScI), J. A. Kennea (PSU),
F. E. Marshall (NASA/GSFC) and D. M. Palmer (LANL) report on behalf of
the Swift Team:

At 22:50:30 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 121031A (trigger=537195).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 170.771, -3.511 which is 
   RA(J2000)  =  11h 23m 05s
   Dec(J2000) = -03d 30' 37"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a large peak
with several smaller peaks riding on top with a total duration
of about 50 sec.  The peak count rate was ~4000 counts/sec (15-350 keV),
at ~4 sec after the trigger. 

The XRT began observing the field at 22:51:32.6 UT, 61.9 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 170.7694, -3.5153 which is equivalent to:
   RA(J2000)  = +11h 23m 4.66s
   Dec(J2000) = -03d 30' 55.1"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 17 arcseconds from the BAT onboard position, within the BAT
error circle. Despite the onboard localisation, no X-ray source was
detected in 732 s of promptly-downlinked data, suggesting that the
initial centroid may equally have been a cosmic ray. This position
should	therefore be treated with caution. 

The initial flux in the 2.5 s image was 5.90e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White 
filter starting 70 seconds after the BAT trigger. No aspect solution
is available for the 2.7'x2.7' sub-image; results from the list of 
sources  generated on-board are not available at this time. The 
expected extinction corresponding to E(B-V) of 0.05. 

We note that the XRT position is 1.4 arcminutes from the galaxy 
2MASX J11225935-0331287, at redshift 0.1126, which has a nominal 
radius of 0.3 arcminutes according to NED. 

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.)

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Using  promptly downlinked XRT event data for GRB 121031A, we find an
enhanced XRT position of the afterglow: RA, Dec: 170.7705, -3.5172
which is equivalent to:
   RA (J2000)  = 11 23 04.91
   Dec (J2000) = -03 31 01.9
with an uncertainty of 2.0 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/537195.

Position enhancement is is described by Goad et al. (2007, A&A, 476,
1401) and Evans et al. (2009, MNRAS, 397, 1177).

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

GRB 121031A: Swift-BAT refined analysis
 
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),
T. Sakamoto (AGU), G. Sato (ISAS), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-61 to T+243 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 121031A (trigger #537195)
(D'Elia, et al., GCN Circ. 13934
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 170.772, -3.513 deg, which is 
   RA(J2000)  =  11h 23m 05.2s 
   Dec(J2000) = -03d 30' 47.7" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows a FRED-like peak with a couple smaller peaks
superposed.  It starts at ~T-10 sec, peaks at ~T+4 sec, and ends at ~T+100 sec.
T90 (15-350 keV) is 62.5 +- 25.1 sec (estimated error including systematics).
 
The time-averaged spectrum from T-2.64 to T+98.31 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.59 +- 0.07.  The fluence in the 15-150 keV band is 3.1 +- 0.1 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+4.10 sec in the 15-150 keV band
is 2.2 +- 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/537195/BA/

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

Using 4059 s of XRT Photon Counting mode data and 5 UVOT
images for GRB 121031A, 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 = 170.77019, -3.51704 which is equivalent
to:

RA (J2000): 11h 23m 4.85s
Dec (J2000): -03d 31' 01.3"

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.

V. D'Elia (ASDC) reports on behalf of the Swift-XRT team:

We have analysed 9.2 ks of XRT data for GRB 121031A (D'Elia  et al. GCN
Circ. 13934
Loading...
 
 ), from 68 s to 22.6 ks after the  BAT trigger. The data
comprise 276 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Goad et al. (GCN. Circ 13935, 13944).

The late-time light curve (from T0+4.7 ks) can be modelled with  a
power-law decay with a decay index of alpha=0.86 (+/-0.07).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.03 (+/-0.08). The
best-fitting absorption column is  4.6 (+0.4, -0.3) x 10^21 cm^-2, in
excess of the Galactic value of 4.0 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.33 (+/-0.10) and a
best-fitting absorption column of 5.2 (+/-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 (9.1 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.2 (+/-0.4) x 10^21 cm^-2
Galactic foreground: 4.0 x 10^20 cm^-2
Excess significance: 18.5 sigma
Photon index:	     2.33 (+/-0.10)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00537195.

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

S. R. Oates (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 121031A
70 s after the BAT trigger (D'Elia et al., GCN Circ. 13934
Loading...
 
 ).
No optical afterglow consistent with the enhanced XRT position
(Goad et al., GCN Circ. 13944
Loading...
 
 ) 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            70          220          147         >19.9
white             5366         7002          393         >20.5
v                 5776        11730          787         >19.4
b                 5161        18152          492         >20.0
u                16939        17239          295         >19.5
w1                4751        16932         1279         >20.5
m2                4545        22572         1870         >21.1
w2                5572        11120         1082         >20.8

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst
(Schlegel et al. 1998).

GRB 121031A, Early peak observed with Swift-BAT
  
J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL),
A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):


With an additional data set from T-240 to T-61 sec, we report further
analysis of BAT GRB 121031 (trigger #537195) (D'Elia, et al., GCN Circ.
13934
Loading...
 
 ).  In an earlier circular (Barthelmy, et al., GCN Circ. 13936
Loading...
 
 ) we
described the second of two equal-sized peaks from this burst.  BAT
triggered on that second peak.  The earlier peak occurred during a pre-
planned slew maneuver, and its time interval was not covered by the data
available at the time the circular was produced.

The entire burst had two large peaks at T-190 and T0 that were about the
same in flux, duration, and shape.  Each was a FRED about 60 seconds long as
seen in BAT.  There was a small peak at T-50 sec of about 5 seconds duration.
For the entire burst, T90 (15-350 keV) was 226 +- 19 sec (estimated error
including systematics).
  
The time-averaged spectrum from T-209.0 to T+98.3 sec is best fit by a
simple power-law model.  The power law index of the time-averaged spectrum
is 1.50 +- 0.05.  The fluence in the 15-150 keV band is
7.8 +- 0.2 x 10^-06 erg/cm2.  The 1-sec peak photon flux measured from
T-190.72 sec in the 15-150 keV band is 2.4 +- 0.2 ph/cm2/sec.  All the
quoted errors are at the 90% confidence level.

A. Goldstein (UAH) and C.A. Meegan (USRA) report on behalf of the Fermi GBM Team:

"At 22:47:15.27 UT on 31 October 2012, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 121031A (trigger 373416438 / 121031949).
which was also detected by the Swift/BAT (V. D'Elia et al. 2012, GCN 13934
Loading...
 
 ).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 85 degrees.
This burst was also independently detected by INTEGRAL SPI-ACS.

The GBM light curve consists of two main pulses separated by a
long quiescent period with a total burst duration (T90) of about 
242 s (50-300 keV) with a possible soft tail out to about T0+500 s. 
The time-averaged spectrum from T0=-47 s to T0+297 s is adequately fit 
by a power law function with an exponential high-energy cutoff.  The 
power law index is -0.87 +/- 0.07 and the cutoff energy, parameterized a
as Epeak, is 142.3 +/- 10.8 keV

The event fluence (10-1000 keV) in this time interval is 
(1.99 +/- 0.09)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.6 s in the 8-1000 keV band is 7.4 +/- 0.7 ph/s/cm^2.

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