GRB 131002A

C. Guidorzi (U. Ferrara) on behalf of a large collaboration reports:

The 2-m Faulkes Telescope North automatically began observing GRB
131002A on October 02 2013 at 06:57:26 UT (~3.1 min after the burst 
trigger).

Within the XRT error circle  we find a fading uncatalogued object at
coordinates

RA(2000.0)=   16:52:52.86
Dec(2000.0)=  +82:03:16.4  (error 0.5")

with R=15.2 +- 0.2 mag, calibrated against nearby USNOB-1 stars.

B. N. Barlow (High Point University), V. D'Elia (ASDC), P. A. Evans (U  
Leicester), C. Gronwall (PSU), A. Y. Lien (NASA/GSFC/ORAU), D.  
Malesani (DARK/NBI), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U  
Leicester), T. Sakamoto (AGU), M. H. Siegel (PSU) and M. C. Stroh  
(PSU) report on behalf of the Swift Team:
At 06:54:21 UT, the Swift Burst Alert Telescope (BAT) triggered and  
located GRB 131002A (trigger=572721). Swift slewed immediately to the  
burst. The BAT on-board calculated location is
RA, Dec 253.275, +82.057 which is
RA(J2000) = 16h 53m 06s
Dec(J2000) = +82d 03' 26"
with an uncertainty of 3 arcmin (radius, 90% containment, including  
systematic uncertainty). The BAT light curve showed two pulses with  
total duration of ~50 seconds. The first pulse happened at T0 lasting  
around 2 seconds, with peak count rate of ~3000 counts/sec (15-350  
keV). The second pulse happened at ~T+45 with a duration of around 15  
seconds and peak count rate ~2000 counts/sec (15-350 keV).
The XRT began observing the field at 06:55:27.9 UT, 66.7 seconds after  
the BAT trigger. Using promptly downlinked data we find a bright,  
fading, uncatalogued X-ray source with an enhanced position:
RA, Dec 253.2159, 82.0536 which is equivalent to:
RA(J2000) = 16h 52m 51.83s
Dec(J2000) = +82d 03' 13.0"
with an uncertainty of 2.0 arcseconds (radius, 90% containment). This  
location is 31 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 (5.56 x  
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.6  
(+1.37/-1.25) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 9.38e-10 erg cm^-2 s^-1  
(0.2-10 keV).
UVOT took a finding chart exposure of 150 seconds with the White  
filter starting 869 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 0.08.
Burst Advocate for this burst is B. N. Barlow (bbarlow AT  
highpoint.edu). 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.)

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

Using 1599 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 131002A, 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 = 253.22092, +82.05433 which is equivalent
to:

RA (J2000): 16h 52m 53.02s
Dec (J2000): +82d 03' 15.6"

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.

L. Elenin (KIAM), A. Volnova (IKI), I. Molotov (KIAM), A. Pozanenko 
(IKI) report on behalf of  larger GRB follow-up collaboration:

We observed optical transient(Guidorzi et al., GCN 15282
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 )  of  the Swift 
GRB 131002A (Barlow et al., GCN 15283
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 )  with 0.4-m SANTEL-400AN 
telescope of ISON-NM observatory starting on Oct., 2 (UT) 06:55:23 (i.e. 
58 s after burst trigger) in robotic mode. Series of 30 s  exposures 
were obtained in clear filter.  After PSF subtraction of a nearby bright 
star we clearly detect the optical transient in each single  frames of 
initial series. Coordinates of the optical transient are (J2000) 16 52 
53.29 +82 03 15.6 with uncertainty of 0.25" in both coordinates. 
Preliminary photometry  is based  on USNO-B1.0 (R2)  stars. The maximum 
brightness of the OT (15.2  +/-  0.05) was detected in the second frame 
at 0.00141 days after trigger.

Light curve of the initial stage of the OT can be found at
http://grb.rssi.ru/GRB131002A/GRB131002A_ISON-NM_lc.png

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

We have analysed 6.5 ks of XRT data for GRB 131002A,  from 56 s to 29.9
ks after the  BAT trigger. The data comprise 44 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 late-time light curve (from T0+5.1 ks) can be modelled with  a
power-law decay with a decay index of alpha=1.05 (+0.26, -0.24).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.03 (+0.19, -0.18). The
best-fitting absorption column is  1.0 (+0.5, -0.4) x 10^21 cm^-2, in
excess of the Galactic value of 5.6 x 10^20 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.6 x 10^-11 (4.6 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.0 (+0.5, -0.4) x 10^21 cm^-2
Galactic foreground: 5.6 x 10^20 cm^-2
Excess significance: 1.9 sigma
Photon index:	     2.03 (+0.19, -0.18)

If the light curve continues to decay with a power-law decay index of
1.05, the count rate at T+24 hours will be 7.7 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.8 x
10^-13 (3.6 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/00572721.

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

A. A. Breeveld (UCL-MSSL) and B. N. Barlow (High Point University) 
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 131002A 77 
s after the BAT trigger (Barlow et al., GCN Circ. 15283
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 ). A fading 
source consistent with the optical position (Guidorzi GCN Circ. 15282
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 ) 
is detected in the initial UVOT exposures.

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               77          227          147         17.94 � 0.06
white              870         1020          147         19.40 � 0.11
v                  620         1071           59         18.89 � 0.36
b                  546          739           39         19.41 � 0.31
u                  290         7169          736        >21.1
w1                 669         6964          510        >20.7
m2                 645        13293          939        >21.1
w2                 770        11860         1199        >21.5

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.08 in the direction of the 
burst (Schlegel et al. 1998).

A. von Kienlin (MPE) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 06:55:06.99 UT on 2 October 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 131002A (trigger 402389709 / 131002288) which
was also detected by the Swift/BAT (Barlow et al. 2008, GCN 15283
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 ). GBM 
triggered ~46 sec later than Swift/BAT on the second pulse of the GRB.
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight is 128.2 degrees.

The GBM light curve shows a single pulse with a duration (T90) of 
about 12 s (50-300 keV). The time-averaged spectrum from T0-4.096 s to
T0+4.096 s is
well fit by a simple power law function with index -1.6 +/- 0.1 keV. 

The event fluence (10-1000 keV) in this time interval is
(1.4 +/- 0.3)E-06 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0 -2.1 s in the 10-1000 keV band
is 2.1 +/- 0.4 ph/s/cm^2.

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

T. Sakamoto (AGU), B. N. Barlow (High Point University),
S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL),
N. Gehrels (GSFC), J. Norris (BSU), H. A. Krimm (GSFC/USRA),
A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), 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-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 131002A (trigger #572721)
(Barlow, et al., GCN Circ. 15283
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 ).  The BAT ground-calculated position is
RA, Dec = 253.103, 82.036 deg which is
  RA(J2000)  =  16h 52m 24.8s
  Dec(J2000) = +82d 02' 08.3"
with an uncertainty of 3.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 71%.

The mask-weighted light curve shows two peaks separated by ~45 seconds.
The first short peak starts at ~T0 and lasts for ~1 sec,  the second long peak
starts at ~T+40 and ends at ~T+60. T90 (15-350 keV) is 55.59 +- 3.98 sec
(estimated error including systematics).

The spectral lag for the first short pulse is 0.114 s +- 0.04 s (for the 50-100 keV and
15-25 keV bands), and the spectrum is slightly softer than the second long pulse.
Therefore, the spectral and timing properties match better to those of regular long bursts
than those normally seen in short bursts with extended emission.

The time-averaged spectrum from T-0.20 to T+59.67 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.63 +- 0.19.  The fluence in the 15-150 keV band is 6.4 +- 0.8 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+43.17 sec in the 15-150 keV band
is 1.3 +- 0.1 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/572721/BA/