GRB 111121A

V. D'Elia (ASDC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
S. Campana (INAF-OAB), M. M. Chester (PSU), N. Gehrels (NASA/GSFC),
B. Gendre (ASDC), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL),
V. Mangano (INAF-IASFPA), C. B. Markwardt (NASA/GSFC),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
J. P. Osborne (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (INAF-IASFPA), T. Sakamoto (NASA/UMBC),
B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU),
M. Stamatikos (OSU/NASA/GSFC), R. L. C. Starling (U Leicester),
G. Stratta (ASDC), C. A. Swenson (PSU), E. Troja (NASA/GSFC/ORAU),
T. N. Ukwatta (MSU) and B.-B. Zhang (PSU) report on behalf of the
Swift Team:

At 16:26:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 111121A (trigger=508161).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 154.751, -46.637 which is 
   RA(J2000)  =  10h 19m 00s
   Dec(J2000) = -46d 38' 13"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single spike
with a duration of about 1 sec.  The peak count rate
was ~38000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 16:27:41.3 UT, 76.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
154.7612, -46.6709 which is equivalent to:
   RA(J2000)  = 10h 19m 2.68s
   Dec(J2000) = -46d 40' 15.1"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 124 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 in excess of the Galactic value (1.20 x
10^21 cm^-2, Kalberla et al. 2005), with an excess column of 4
(+2.62/-2.25) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 4.58e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White 
filter  starting 85 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  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
18.0 mag.No  correction has been made  for the expected extinction
corresponding to  E(B-V) of 0.26. We note that the XRT centroid is
close to a known 14th  magnitude star, which may complicate the
analysis. 

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

Using 2196 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 111121A, 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 = 154.76137, -46.67064 which is equivalent
to:

RA (J2000): 10h 19m 2.73s
Dec (J2000): -46d 40' 14.3"

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.

J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
V. D'Elia (ASDC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC), J. Norris (BSU), 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 recent telemetry downlinks,
we report further analysis of BAT GRB 111121A (trigger #508161)
(D'Elia, et al., GCN Circ. 12578
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 ).  The BAT ground-calculated position is
RA, Dec = 154.746, -46.670 deg, which is 
   RA(J2000)  =  10h 18m 59.1s 
   Dec(J2000) = -46d 40' 10.7" 
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 64%.
 
The mask-weighted light curve shows an inital strong pulse composed 
of two overlapping peaks, the first starting at ~T-0.3 sec and 
peaking at ~T+0.17 sec (at 2.6 cnts/det/sec). The second peaks
at ~T+0.3 sec and is done by ~T+0.6 sec.  This is followed by
two episodes of extended emission.  The first is roughly constant
(~0.02 to 0.03 cnts/det/sec) out to ~T+65sec.  The second episode
is ~0.006 cnts/det/sec out to ~T+130 sec.  T90 (15-350 keV)
is 119 +- 16 sec (estimated error including systematics).
This T90 includes the extended emission.

The spectral lag is 10.2 ms +2.6-1.8 ms (for the 100-350 to 25-50 keV band)
and 12.7 ms +6.8-8.7 ms (for the 50-100 to 15-25 keV band).  This puts it
on the long end of the distribution for spectral lag for short GRBs.
 
The time-averaged spectrum from T-0.34 to T+141.08 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.66 +- 0.12.  The fluence in the 15-150 keV band is 2.2 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.26 sec in the 15-150 keV band
is 7.1 +- 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/508161/BA/

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

We have analysed 10 ks of XRT data for GRB 111121A (D'Elia  et al. GCN
Circ. 12578
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 ), from 66 s to 24.1 ks after the  BAT trigger. The data
comprise 180 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 Evans et
al. (GCN. Circ 12579).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=1.85 (+/-0.09). At T+217 s  the decay
steepens to an alpha of 3.7 (+1.2, -0.7). The light curve breaks again
at T+378 s to a decay with alpha=0.93 (+0.07, -0.08),  before a final
break at T+9772 s s after which the decay index is 2.1 (+0.5, -0.4).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.71 (+/-0.08). The
best-fitting absorption column is  4.2 (+/-0.4) x 10^21 cm^-2, in
excess of the Galactic value of 1.2 x 10^21 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.88 (+0.15, -0.17)
and a best-fitting absorption column of 3.4 (+/-0.7) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.6 x 10^-11 (6.9 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.4 (+/-0.7) x 10^21 cm^-2
Galactic foreground: 1.2 x 10^21 cm^-2
Excess significance: 8.0 sigma
Photon index:	     1.88 (+0.15, -0.17)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00508161.

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

W. Fong (Harvard), A. Seth (U. Utah), R. Chornock and E. Berger (Harvard)
report:

"We imaged the field of the short GRB 111121A (GCN 12578
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 ) with Megacam on
the Magellan/Clay 6.5-m telescope at a mid-time of 2011 November 22.27 UT
(13.9 hours post-burst).  We obtained 25x30-sec exposures in r-band at an
airmass of 1.7 in ~0.7" seeing.

The location of the latest enhanced XRT error circle (improved from GCN
12579
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  at http://www.swift.ac.uk/xrt_positions/ with RA(J2000) =
10:19:02.71, Dec(J2000) = -46:40:14.5, 1.4" uncertainty) is contaminated by
emission from a nearby bright (R~12.5) star.  However, we find a faint
source on the southern edge of the XRT circle at (J2000):

RA = 10:19:02.7
Dec = -46:40:15.6,

with an uncertainty of ~0.5" in each coordinate that includes contributions
from the centroiding error of the source and a 0.27" rms uncertainty from
the astrometric tie to USNO-B.

Due to the location of the source near a diffraction spike from the bright
star, it is unclear at present whether it is extended or point-like.
Additional analysis to extract a magnitude for the source is on-going, and
additional observations to check for variability are planned."

N.P.M. Kuin, S. 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 111121A
86 s after the BAT trigger (D'Elia et al., GCN Circ. 12578
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 ).
No optical afterglow consistent with the XRT position
(Evans et al, GCN Circ. 12579
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 ) is detected in the initial UVOT exposures.

The XRT enhanced position falls within the PSF wings of a B~13.6
magnitude star. Inspection of the event mode data after correction
for a slight wander in attitude shows no evidence for any transient
source.

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 dominated
by the nearly star and are:

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

white_FC            86          235          147         >14.8
u_FC               298          548          246         >15.5
white               86          990          296         >14.7
v                  629          822           39         >13.1
b                  554          748           39         >14.2
u                  298          723          265         >15.5
w1                 678          873           39         >16.5
m2                 653          847           39         >18.5
w2                 604          797           39         >17.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.26 in the direction of the burst
(Schlegel et al. 1998).

S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:

The short hard intense GRB 111121A (Swift-BAT trigger #508161:
D'Elia et al., GCN 12578
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 ; Cummings et al., GCN 12581
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 )
triggered Konus-Wind at T0=59182.640s UT (16:26:22.640)

The light curve shows of a hard bright pulse with
a total duration of ~600 ms followed by a tail
of a weak soft extended emission for at 20 s.
The emission is seen up to ~10 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB111121_T59182/

As observed by Konus-Wind the burst
had a fluence of (2.3 � 0.3)x10-5 erg/cm2,
and a 16-ms peak flux, measured from T0+0.160 s,
of (8.4 � 1.5)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The spectrum of the burst (measured from T0 to T0+0.256 s)
is best fitted in the 20 keV - 10 MeV range
with the GRB (Band) model, for which:
the low-energy photon index alpha = -0.44 (-0.07, +0.07),
the high energy photon index beta = -3.0 (<-2.4),
the peak energy Ep = 1780(-290, +310) keV,
chi2 = 59.7/51 dof.

All the quoted results are preliminary.
All the quoted errors are at the 90% confidence level.

C-J. Chuang, Y. Urata, P. Tsai (NCU), Y. Hanabata, T. Uehara,
T. Takahashi, M. Mizuno, M. Ohno, Y. Fukazawa (Hiroshima U.),
T. Yasuda, Y. Terada, M. Tashiro, W. Iwakiri, K. Takahara, M. Asahina,
S. Kobayashi, A. Sakamoto (Saitama U.), S. Sugita (Nagoya U.),
K. Yamaoka (Aoyama Gakuin U.), M. Kokubun, T. Takahashi (ISAS/JAXA),
Y. E. Nakagawa (Waseda U.), N. Ohmori, M. Akiyama, M. Yamauchi
(Univ. of Miyazaki), K. Nakazawa, K. Makishima (Univ. of Tokyo),
on behalf of the Suzaku WAM team, report:

The bright short GRB 111121A (Swift/BAT trigger 508161 ; D'Elia et
al., GCN 12578
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 ) was detected by the the Suzaku Wide-band All-sky
Monitor (WAM) which covers an energy range of 50 keV - 5 MeV at
16:26:24.488 UT (=T0).

The observed light curve shows a single peak structure starting at T0,
ending at T0+1 s with a duration (T90) of about 0.45 seconds. The
fluence in 100 - 1000 keV was 4.29(-0.41, 0.23) x 10^-6 erg/cm^2. The
1-s peak flux measured from T0+1 s was 20.26 photons/cm^2/s in the
same energy range.

Preliminary result shows that the time-averaged spectrum from T0 to
T0+1 s is well fitted by a power-law with exponential cutoff model:

  dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
  alpha   0.58 (-0.19, 0.18), and
  Epeak   1678.97 (-210.66, 300.31) keV (chi^2/d.o.f. = 60.1/47).

The light curves for this burst are available at:
 http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html