GRB 120102A

F. E. Marshall (NASA/GSFC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), E. A. Hoversten (PSU),
A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (NASA/GSFC),
T. Sakamoto (NASA/UMBC), C. J. Saxton (UCL-MSSL), C. A. Swenson (PSU)
and T. N. Ukwatta (MSU) report on behalf of the Swift Team:

At 02:15:55 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120102A (trigger=510922).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 276.201, +24.732 which is 
   RA(J2000)  =  18h 24m 48s
   Dec(J2000) = +24d 43' 54"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows an initial small peak
and then a much larger peak 32 sec later with a toal duration of about 50 sec. 
The peak count rate was ~15,000 counts/sec (15-350 keV), at ~33 sec
after the trigger. 

The XRT began observing the field at 02:17:47.9 UT, 112.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 276.22495,
24.71375 which is equivalent to:
   RA(J2000)  = 18h 24m 53.99s
   Dec(J2000) = +24d 42' 49.5"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 102 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 (1.03 x
10^21 cm^-2, Kalberla et al. 2005), with an excess column of 4.1
(+2.17/-1.89) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 4.02e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 121 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	18:24:53.90 = 276.22457
  DEC(J2000) = +24:42:47.3  =  24.71314
with a 90%-confidence error radius of about 0.62 arc sec. This position is 3.3
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.04 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.13. 

Burst Advocate for this burst is F. E. Marshall (marshall AT milkyway.gsfc.nasa.gov). 
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.)

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

Using 967 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 120102A, 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 = 276.22471, +24.71352 which is equivalent
to:

RA (J2000): 18h 24m 53.93s
Dec (J2000): +24d 42' 48.7"

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.

A. A. Breeveld (MSSL-UCL) and F. E. Marshall (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120102A
121 s after the BAT trigger (Marshall et al., GCN Circ. 12794
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 ).
A fading source consistent with the XRT position (Beardmore et al., GCN 
Circ. 12795
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 ) is detected in the initial UVOT exposures.

The preliminary UVOT position is:
     RA  (J2000) =  18:24:53.89 = 276.22456 (deg.)
     Dec (J2000) = +24:42:47.1  =  24.71309 (deg.)
with an estimated uncertainty of 0.51 arc sec. (radius, 90% confidence).

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

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

white (FC)         121          271          147         18.10 � 0.06
white              788         1014          167         19.9  � 0.2
v                  663         1239           78         18.16 � 0.31
b                  589        11310         1147        >20.8
u                  334          583          246         18.52 � 0.14
w1                 713         6983          452        >20.2
m2                 688         6778          452        >20.1
w2                 639        12879         1112        >20.9

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).

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

We have analysed 12 ks of XRT data for GRB 120102A (Marshall  et al.
GCN Circ. 12794
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 ), from 119 s to 34.6 ks after the  BAT trigger. The
data comprise 240 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Beardmore et al. (GCN. Circ 12795).

The late-time light curve (from T0+4.5 ks) can be modelled with an
initial power-law decay with an index of alpha=1.99 (+0.27, -0.11),
followed by a break at T+13.0 ks to an alpha of 0.97 (+0.27, -0.22).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.04 (+/-0.08). The
best-fitting absorption column is  2.59 (+0.26, -0.25) x 10^21 cm^-2,
in excess of the Galactic value of 1.0 x 10^21 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.0 x 10^-11 (6.2 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.59 (+0.26, -0.25) x 10^21 cm^-2
Galactic foreground: 1.0 x 10^21 cm^-2
Excess significance: 10.3 sigma
Photon index:	     2.04 (+/-0.08)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00510922.

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

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), 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-240 to T+962 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120102A (trigger #510922)
(Marshall, et al., GCN Circ. 12794
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 ).  The BAT ground-calculated position is
RA, Dec = 276.224, 24.713 deg, which is 
   RA(J2000)  =  18h 24m 53.8s 
   Dec(J2000) = +24d 42' 46.7" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 78%.
 
The mask-weighted light curve shows a weak peak starting at ~T_0 and returning
to baseline at ~T+20 sec.  The main emission starts at ~T+25 sec with 2, or
possibly 3, overlapping peaks, with the peak emission at ~T+33 sec,
which then approximately exponentially decays out to 510 sec or possibly
out to ~750 sec.  At the 3- or 4-sigma level, there is a possible precursor
peak at ~T-70 sec with a duration of 10-20 sec.  T90 (15-350 keV) is
38.7 +- 3.5 sec (estimated error including systematics).
 
The time-averaged spectrum from T+0.77 to T+53.94 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.59 +- 0.05.  The fluence in the 15-150 keV band is 4.3 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+32.75 sec in the 15-150 keV band
is 10.3 +- 0.4 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/510922/BA/

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 long GRB 120102A (Swift-BAT trigger=510922: Marshall et al., GCN 
12794
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 ; Markwardt et al., GCN 12799
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 ) triggered Konus-Wind at T0=8181.530 
s UT (02:16:21.530).

The burst light curve shows a single pulse with a duration of ~15 s. 
There is a weak precursor marginally seen at ~T0-30 s.

As observed by Konus-Wind the burst had a fluence of 
1.75(-0.26,+0.30)x10^-5 erg/cm2,
and a 256-ms peak flux measured from T0+3.536 s
of 5.56(-1.02, +1.12)x10^-6 erg/cm2/s
(both in the 20 keV - 4 MeV energy range).

The time-integrated spectrum of the burst
(from T0 to T0+16.640 s) is well fitted (in the 20 keV - 4 MeV
range) by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), with
alpha = -1.47(-0.07, +0.09),  and
Ep = 805(-180, +288) keV (chi2 = 68.4/73 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and only an upper limit on the high energy
photon index: beta < -2.04.

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

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB120102_T08181/

S. Xiong (UAH)
reports on behalf of the Fermi GBM Team:

"At 02:16:23.24 UT on 02 Jan 2012, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 120102A (trigger 347163385 / 120102095),
which was also detected by the Swift BAT/XRT/UVOT
(F. E. Marshall et al. 2012, GCN 12794
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 )
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 84 degrees.

The GBM light curve consists of two main pulses
with a duration (T90) of about 17 s (50-300 keV).
The time-averaged spectrum from T0-1 s to T0+13 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.19 +/- 0.03 and
the cutoff energy, parameterized as Epeak, is 380 +/- 33 keV.
A Band function fits the spectrum equally well with
Epeak = 291 +/- 33 keV, alpha = -1.13 +/- 0.04, and beta = -2.14 +/- 0.13.

The event fluence (10-1000 keV) in this time interval is
(1.26 +/- 0.03)E-5 erg/cm^2. The 64 ms peak photon flux measured
starting from T0+4.8 s in the 10-1000 keV band
is 22.8 +/- 1.6 ph/s/cm^2.

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

V. V. Golovnya (Main Astro Obs, Kyiv)
report: 
We have undertaken the review of the sky area in vicinity of 
GRB 120102A (A.P. Beardmore et al., GCN Circ.12795
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 ) on 
astronegatives, collected in Ukrainian NAS Main astronomical
observatory plate archive (1976-1996). All the plates with 
the possible object appearance are digitized using Microtek 
ScanMaker 9800XL TMA and Epson Expression 10000XL flatbed 
scanners and have been placed into Golosiiv Plate Archive 
database DBGPA with open access to them.
 	The list of plates is given in the table:
YYYYMMDD/TimeUT	--Plates---	Exp.	LimM	Star USNOA2 
19890629/211821	EAO040B001801	13.5	16.50	1125-09467284
19890708/212336	GUA040C001487	16.0	16.45	1125-09467782
19890803/192540	GUA040C001492A	16.0	16.00	1125-09466499
19890803/194958	GUA040C001493	16.0	16.00	1125-09466499
19890905/172315	EAO040B001991	13.5	16.50	1125-09467284
Plates-the plate's identifier in	
GUA040C archive of DWA (D/F=400/2000, M=103"/mm) of the	
	Ukrainian NAS Main Astro obs in Kyiv	
	(Marsden's number - 83) and	
EAO040B archive of DWAZ (D/F=400/2000, M=103"/mm) of the 
	Engelhardt South. St. Zelenchuk Russia	
	(Marsden's number - 114) [1].	
Exp.   - Duration of the maximum exposure (minutes).	
LimM - Limited V mag, derived in the 8 minutes area around 
	the location given in GCN Circ.12795
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 :		
	RA(J2000): 18h 24m 53.93s, Dec(J2000): +24d 42' 48.7"
Star USNOA2 - Comparison star.	
  The preview images of 5 areas together with  
the 8x8 min.of arc area from SkyMap can be found in  
http://gua.db.ukr-vo.org/img/grb/120102A/index.html
The images with full resolution are available via e-mail on 
demand.
References: 
1.L.Pakuliak DATABASE of GOLOSIIV PLATE ARCHIVE (DBGPA V2.0),
http://gua.db.ukr-vo.org