GRB 120922A

F. Knust (MPE Garching), T. Kruehler (DARK/NBI), S. Klose (TLS Tautenburg) and J. Greiner (MPE Garching) report on behalf of the GROND team:

We report on further analysis of the GROND (Greiner et al. 2008, PASP 120, 405) optical/NIR imaging of the afterglow (Knust et al. GCN 13795
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 , Klotz et al., GCN 13799
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 , Yershov et al., GCN 13803
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 , Kuin et al., GCN 13808
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 ) of GRB 120922A (Yershov et al., GCN 13793
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 ). Tying our photometric solution to field stars from the SDSS in the optical filters and 2MASS in the NIR, we derive the following AB magnitudes centered at a midtime of 00:01 UTC on September 23 (approx 1.5 hrs after the trigger):

g' = 20.53 +/- 0.05
r' = 19.69 +/- 0.04
i' = 19.44 +/- 0.04
z' = 19.28 +/- 0.04 
J = 18.92 +/- 0.06
H = 18.79 +/- 0.07
K = 18.63 +/- 0.10

After correcting these magnitudes for the expected Galactic foreground extinction corresponding to a reddening of E_B-V = 0.15 mag (Schlegel et al. 1998), the SED is well fit with a simple power law of spectral index \beta = 0.5 +/- 0.2 and no strong evidence for host-intrinsic reddening. The significant drop in flux in the g'-band suggests a photometric redshift of 3.1 +/- 0.2, consistent with the lack of detection in the bluer UVOT filters (Kuin et al., GCN 13808
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 ).

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

"At 22:32:09.47 UT on 22 September 2012, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 120922A (trigger 370045932 / 120922939)
which was also detected by the Swift/BAT (Yershov et al. 2012, GCN 13793
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 ).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight is 85 degrees.

The GBM light curve consists of a multiple peaks with a duration (T90)
of about 180 s (50-300 keV).
The time-averaged spectrum from T0-121 s to T0+6 s is
best fit by a Band function with Epeak = 37.7 +/- 3.5 keV,
alpha = 1.6 +/- 0.7 , and beta = -2.3 +/- 0.1.

The event fluence (10-1000 keV) in this time interval is
(6.5 +/- 0.4)E-06 ergs/cm^2. The 1-sec peak photon flux measured
starting from T0-1.8 s in the 10-1000 keV band
is 3.4 +/- 0.3  ph/s/cm^2.

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

N. P. M. Kuin (MSSL/UCL) and V.N. Yershov (MSSL/UCL)  report on
behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of
GRB 120922A  127 s after the BAT trigger (Yershov et al., GCN
Circ. 13793
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 ).  A source consistent with the XRT position (Evans et al.
GCN Circ. 13800
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 ),  and the initial optical detection by GROND (Knust
et al., GCN Circ. 13795
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 )  is detected in the initial UVOT exposures
(Yershov et al. GCN Circ. 13803
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 ).

The uvot observations show a slow initial rise in brightness peaking
around 900s after the trigger.  The burst is only detected in the v,b and
white filters which is probably due to the high galactic reddening.

Preliminary detections and 3-sigma upper limits using the UVOT
photometric system  (Breeveld et al. 2011, AIP Conf. Proc. 1358,
373) for the early exposures are:

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

white              126          276          147        >20.67
white              865         1014          147         19.34 +/- 0.14
v                  615         1239           78         17.94 +/- 0.22
b                  541          733           78        >19.17
b                 1145         2030          119         19.62 +/- 0.36
u                  285          534          250        >19.98
u                  688         1139           40        >18.82
w1                 664        16852         1434        >20.95
m2                 639        11081         1232        >20.96
w2                 590        12900         1424        >21.20

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.15 in the direction of the burst
(Schlegel et al. 1998).

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC),
T. N. Ukwatta (MSU), V. N. Yershov (UCL-MSSL)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+303 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120922A (trigger #534394)
(Yershov, et al., GCN Circ. 13793
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 ).  The BAT ground-calculated position is
RA, Dec = 234.758, -20.181 deg, which is 
   RA(J2000)  =  15h 39m 02.0s 
   Dec(J2000) = -20d 10' 51.8" 
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 33%.
 
The mask-weighted light curve shows low-level emission starting at T-200 sec,
possibly sooner before the data capture started, with peaks at ~T_0, ~T+60, & ~T+105 sec,
and ending at ~T+205 sec.  T90 (15-350 keV) is 173 +- 33 sec (estimated error
including systematics).
 
The time-averaged spectrum from T-22.58 to T+215.73 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.58 +- 0.36, 
and Epeak of 38.2 +- 0.0 keV (chi squared 54.3 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 6.2 +- 0.7 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+99.21 sec in the 15-150 keV band is
2.0 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 2.09 +- 0.08 (chi squared 61.1 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/534394/BA/

A. Melandri (INAF-OAB), D.N. Burrows (PSU), J.A. Kennea (PSU), M.C.
Stroh (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester),
P.A. Evans (U. Leicester), B. Sbarufatti (INAF-OAB/PSU), G. Stratta
(ASDC) and V.N. Yershov report on behalf of the Swift-XRT team:

We have analysed 9.3 ks of XRT data for GRB 120922A (Yershov  et al.
GCN Circ. 13793
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 ), from 120 s to 19.4 ks after the  BAT trigger. The
data comprise 484 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN. Circ 13794).

The light curve can be modelled with a series of power-law decays. The
light curve initially rises, with an index alpha=-1.5 (+0.0, -1.3). At
T+130 s it breaks to an alpha of 3.09 (+0.09, -0.08). The light curve
breaks again at T+243 s to a decay with alpha=3.83 (+0.09, -0.10), 
before a final break at T+737 s s after which the decay index is 0.85
(+0.04, -0.05).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.33 (+/-0.04). The
best-fitting absorption column is  2.15 (+/-0.09) x 10^21 cm^-2, in
excess of the Galactic value of 7.7 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.11 (+0.13, -0.12)
and a best-fitting absorption column of 1.06 (+0.28, -0.27) x 10^21
cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.5 x 10^-11 (4.6 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.06 (+0.28, -0.27) x 10^21 cm^-2
Galactic foreground: 7.7 x 10^20 cm^-2
Excess significance: 1.8 sigma
Photon index:	     2.11 (+0.13, -0.12)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00534394.

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

V.N. Yershov (UCL-MSSL), aN. P. M. Kuin (MSSL-UCL) and A. A. Breeveld
(MSSL-UCL), report on behalf of the Swift-UVOT team:

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 864 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =  15:38:59.60 = 234.74832
  DEC(J2000) = -20:10:54.3  = -20.18175
with a 90%-confidence error radius of about 0.65 arc sec. This position
is 2.0 arc sec. from the center of the XRT error circle. The estimated
magnitude is 18.91 with a 1-sigma error of about  0.16. No correction
has been made for the expected extinction corresponding to E(B-V) of
0.15.

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

Using 1474 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 120922A, 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 = 234.74858, -20.18203 which is equivalent
to:

RA (J2000): 15h 38m 59.66s
Dec (J2000): -20d 10' 55.3"

with an uncertainty of 1.7 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.

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 120922A detected by SWIFT
(trigger 534394) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 56 min after the GRB trigger
(starting at twilight). The elevation of the field decreased
from 46 degrees above horizon and weather conditions
were good.

Co addition of TAROT images from 56 to 85 minutes
after the GRB, shows the optical candidate reported
by Knust et al. (GCNC 13795) at magnitude R~20
(close to the limiting magnitude of TAROT).
Note the source NOMAD1 0698-0330778 (R.A.=234.7496389
Decl=-20.1828917 J2000) R=19.79 few arcsec southeastern
from the OT.

This message may be cited.

F. Knust (MPE Garching), T. Kruehler (DARK), J. Greiner (MPE) and
S. Klose (TLS Tautenburg) report on behalf of the GROND team:

We observed the field of GRB 120922A (Swift trigger 534394; Yershov et 
al., GCN 13793
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 
2008, PASP 120, 405) mounted at the 2.2m MPG/ESO telescope at La Silla 
Observatory (Chile).

Observations started at 23:30 UT on Sep 22, 60 min after the GRB trigger.
We detect a bright source within the enhanced Swift/XRT error circle 
reported by Evans (GCN 13794
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 ) at coordinates RA, DEC (J2000) = 
15:38:59.64, -20:10:54.2 (+/- 0.3 arcsec) with (AB mag)

r' = 19.5 +/- 0.1,

calibrated against the GROND zeropoint and not corrected for the Galactic 
foreground reddening of E_(B-V)= 0.15 mag in the direction of the burst 
(Schlegel et al. 1998).

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

Using  promptly downlinked XRT event data for GRB 120922A, we find an
enhanced XRT position of the afterglow: RA, Dec: 234.7483, -20.1821
which is equivalent to:
   RA (J2000)  = 15 38 59.60
   Dec (J2000) = -20 10 55.4
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/534394.

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.

V. N. Yershov (UCL-MSSL), S. D. Barthelmy (GSFC),
H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL),
C. J. Mountford (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), M. H. Siegel (PSU) and T. N. Ukwatta (MSU) report
on behalf of the Swift Team:

At 22:30:28 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120922A (trigger=534394).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 234.756, -20.177 which is 
   RA(J2000) = 15h 39m 01s
   Dec(J2000) = -20d 10' 36"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiple-peaked
structure with a duration of at least 130 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~102 sec after the trigger. 

The XRT began observing the field at 22:32:25.0 UT, 116.5 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 234.7505, -20.1839 which is equivalent to:
   RA(J2000)  = +15h 39m 0.12s
   Dec(J2000) = -20d 11' 02.0"
with an uncertainty of 5.6 arcseconds (radius, 90% containment). This
location is 31 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. 

The initial flux in the 0.1 s image was 2.53e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 126 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
0.15. 

Burst Advocate for this burst is V. N. Yershov (vny AT mssl.ucl.ac.uk). 
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.)