GRB 121102A

V. D'Elia (ASDC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
J. R. Cummings (NASA/UMBC), N. Gehrels (NASA/GSFC),
J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL),
B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf
of the Swift Team:

At 02:27:02 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 121102A (trigger=537266).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 270.903, -16.966 which is 
   RA(J2000)  = 18h 03m 37s
   Dec(J2000) = -16d 57' 56"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single FRED-like peak
with a duration of about 25 sec.  The peak count rate
was ~3500 counts/sec (15-350 keV), at ~6 sec after the trigger. 

The XRT began observing the field at 02:27:50.4 UT, 47.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
270.9009, -16.9578 which is equivalent to:
   RA(J2000)  = 18h 03m 36.22s
   Dec(J2000) = -16d 57' 28.2"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 30 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 (5.33 x
10^21 cm^-2, Kalberla et al. 2005), with an excess column of 3.1
(+3.61/-1.55) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 3.45e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White
filter  starting 57 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. Because of the density of catalogued stars,  further
analysis is required to report an upper limit for any afterglow in the
 region. No correction has been made for the large, but uncertain
extinction  expected. 

This event has all appearances of a GRB: hard BAT spectrum,
bright XRT initial detection and fading.  Still, we note that 
the galactic coordinates are l=12 deg, b=2.5 deg, consistent 
with a galactic origin.  We believe it is a GRB, but can not 
rule out a new galactic transient. 

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.)

S.Mereghetti (IASF-Milano), D.Gotz (CEA, Saclay), E.Bozzo, C.Ferrigno, 
R.Boissay (ISDC, Versoix), and J.Borkowski (CAMK, Torun) on behalf of the 
IBAS Localization Team report:

a gamma ray burst lasting about 20 s has been detected by IBAS in the 
IBIS/ISGRI data at 02:27:00 UT of November 2

The refined coordinates are

  RA  = 270.9034  deg 
BDEC = -16.9509  deg

with an uncertainty of 2 arcmin (90% c.l.).

A preliminary analysis gives a burst peak flux of about 1 counts/cm2/s 
(20-200 keV, 1-s integration time) and a fluence in the same energy range 
of about 1e-6 erg/cm2.

A plot of the light curve will posted at
http://ibas.iasf-milano.inaf.it/IBAS_Results.html

W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), 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 the recent telemetry downlink,
we report further analysis of BAT GRB 121102A (trigger #537266)
(D'Elia, et al., GCN Circ. 13938
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 ).  The BAT ground-calculated position is
RA, Dec = 270.896, -16.951 deg, which is 
   RA(J2000)  =  18h 03m 35.1s 
   Dec(J2000) = -16d 57' 03.4" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows a FED peak starting at ~T-0.2 sec,
peaking at ~T+6 sec, and ending at ~T+95 sec.  T90 (15-350 keV) is
24.7 +- 3.4 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.30 to T+35.25 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.88 +- 0.07.  The fluence in the 15-150 keV band is 1.9 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+5.68 sec in the 15-150 keV band
is 2.3 +- 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/537266/BA/

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

We have analysed 9.0 ks of XRT data for GRB 121102A (D'Elia  et al. GCN
Circ. 13938
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 ), from 53 s to 18.8 ks after the  BAT trigger. The data
comprise 203 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The best available XRT position  (using the
promptly downlinked event data, the XRT-UVOT alignment and matching
UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 270.9009,
-16.9576 which is equivalent to:

RA (J2000): 18 03 36.22
Dec(J2000): -16 57 27.5

with an uncertainty of 2.0 arcsec (radius, 90% confidence).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=3.33 (+0.22, -0.24). At T+111 s  the decay
flattens to an alpha of 1.59 (+0.18, -0.11) before breaking again at
T+696 s to a final decay with index alpha=1.04 (+0.08, -0.07).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.95 (+/-0.13). The
best-fitting absorption column is  8.9 (+/-1.0) x 10^21 cm^-2, in
excess of the Galactic value of 5.3 x 10^21 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.74 (+0.23, -0.22)
and a best-fitting absorption column of 7.7 (+1.9, -1.6) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 5.9 x 10^-11 (9.6 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.7 (+1.9, -1.6) x 10^21 cm^-2
Galactic foreground: 5.3 x 10^21 cm^-2
Excess significance: 2.4 sigma
Photon index:	     1.74 (+0.23, -0.22)

If the light curve continues to decay with a power-law decay index of
1.04, the count rate at T+24 hours will be 2.8 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x
10^-13 (2.7 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00537266.

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

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

Using 6668 s of XRT Photon Counting mode data and 8 UVOT
images for GRB 121102A, 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 = 270.90101, -16.95788 which is equivalent
to:

RA (J2000): 18h 03m 36.24s
Dec (J2000): -16d 57' 28.4"

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.

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 121102A
58 s after the BAT trigger (D'Elia et al., GCN Circ. 13938
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 ).
No optical afterglow consistent with the XRT position
(Osborne et al. GCN Circ. 13945
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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            58          207          147         >20.1
u_FC               270          519          246         >19.6
white               58        24618         2113         >21.4
v                 4994        17253         1278         >20.0
b                 5814        23858         2022         >21.4
u                  270        22945         1524         >20.9
w1                5404        18848         1066         >20.8
m2                5200        18158         1279         >21.1
w2                4789        13077         1073         >21.2

The magnitudes in the table are not corrected for the high Galactic extinction
due to the reddening of E(B-V) = 1.48 in the direction of the burst
(Schlegel et al. 1998).