GRB 061102

S. T. Holland (GSFC/USRA), S. D. Barthelmy (GSFC),
M. M. Chester (PSU), N. Gehrels (NASA/GSFC), C. Gronwall (PSU),
J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC),
K. M. McLean (LANL/UTD), K. L. Page (U Leicester),
D. M. Palmer (LANL), A. M. Parsons (GSFC), M. Stamatikos (NASA/ORAU)
and R. L. C. Starling (U Leicester) report on behalf of the Swift
Team:

At 01:00:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 061102 (trigger=236430). Swift slewed immediately to the
burst. The BAT on-board calculated location is RA,Dec 148.405,
-17.066 {09h 53m 37s, -17d 03' 58"} (J2000) with an uncertainty of 3
arcmin (radius, 90% containment, including systematic uncertainty). 
The BAT light curve shows a weak pulse ~15 sec long. The peak count
rate was ~500 counts/sec (15-350 keV) at ~5 sec after the trigger. 

The XRT began observing the field at 01:02:11 UT, 100 seconds after the
BAT trigger. XRT found an uncatalogued fading X-ray source
located at RA(J2000) = 09h 53m 37.7s, Dec(J2000) = -17d 01' 28.1", with an
estimated uncertainty of 6.1 arcseconds (90% confidence radius). 
This location is 150 arcseconds from the BAT on-board position, within
the BAT error circle. The initial flux in the 2.5s image was
6.0e-10 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 110 seconds after the BAT trigger. No
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 3-sigma
upper limit is approximately 18.5 mag. No correction has been made
for the expected extinction corresponding to E(B-V) of 0.04.

GRB 061102, Swift-BAT refined analysis
 
J. Tueller (GSFC), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
S.T. Holland (GSFC/USRA), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU)
on behalf of the Swift-BAT team:
 
Using the data set from T-120 to T+182 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 061102 (trigger #236430)
(Holland, et al., GCN Circ. 5776
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 ).  The BAT ground-calculated position
is RA,Dec = 148.393, -17.000 deg {9h 53m 34.2s, -17d 0' 0.8"} (J2000)
+- 2.7 arcmin, (radius, sys+stat, 90% containment).  The partial coding was 100%.
 
The mask-weighted lightcurve shows a FRED starting at T+0 and ending 
about T+50 sec.  T90 (15-350 keV) is 17.6 +- 1 sec (estimated error
including systematics).
 
The time-averaged spectrum from T-1.0 to T+18.9 is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.45 +- 0.33.  The fluence in the 15-150 keV band is 1.9 +- 0.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+3.37 sec in the 15-150 keV band
is 0.2 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

R. L. C. Starling, K. L. Page (U Leicester) and S. T. Holland (GSFC/USRA) 
report on behalf of the Swift XRT team:

We have analysed the first 3 orbits of Swift XRT data obtained for GRB 
061102 (trigger 236430, GCN 5776
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  Holland et al.). The data consist of 208 
s of WT mode data beginning at 112s since BAT trigger and 2560s of 
subsequent PC mode data.


Using the PC mode data we obtain a refined position of:
RA(J2000)  =  09 53 37.64
Dec(J2000) = -17 01 26.5

with an estimated uncertainty of 4.9 arcsec (90% containment) taking into 
account the new TELDEF files.
This location is 1.8 arcsec from the initial XRT position (GCN Circ. 5776
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 ) 
and 98.7 arcsec from the ground-calculated BAT position (GCN Circ. 5777
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 ;
Tueller et al.)


The lightcurve shows a steep decay over the first 400s with a slope of 
alpha = 4.0+/-0.1. At ~400s the lightcurve breaks to a slope of 
alpha~1.


The first orbit WT-mode spectrum can be well fitted with an absorbed power 
law with index Gamma = 3.6+/-0.2. The total column density required is 
1.6E21 cm^-2 which exceeds the Galactic value of 5.0E20 cm^-2 (Dickey & 
Lockman 1990). 
The total flux in the 0.3-10 keV band is 1.2E-10 erg cm^-2 s^-1.
All errors are quoted at the 90% confidence limit.
 
From these data we predict a count rate of 3.3E-4 counts s^-1, 
corresponding to a flux of approximately 8E-15 erg cm^-2 s^-1 at T+24h.


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

GRB 061102: Swift/UVOT Magnitude Upper Limits

S. T. Holland (NASA/GSFC & USRA) reports on behalf of the Swift/UVOT
team:

        The Swift/UVOT began observing the field of GRB 061102 at
01:02:02 on 2006-11-02, 92 s after the BAT trigger (Holland et al.,
GCN Circ. 5776
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 ).  No optical afterglow was detected in any of the
individual UVOT exposures, or in the coadded exposures, down to the
following 3-sigma limiting magnitudes.  The start and stop times are
relative to the BAT trigger.

Filter     Start   Stop   Exposure    3-sigma
             (s)     (s)      (s)     Upper Limit

Finding Charts
  White       112    209       97        19.9
    V         216    275       59        18.3

Coadded Exposures
    V         216  10154     1141        20.5
    B        4078  16849     1278        21.6
    U        3873  15938     1278        21.3
   UVW1      3669  11845     1160        21.3
   UVM2      3464  11059     1279        21.7
   UVW2      4488   6061      336        20.9
  White       112  17629     1247        21.5

The values quoted above are not corrected for the expected Galactic
extinction of E_{B-V} = 0.04 mag (Schlegel et al. 1998).