GRB 081011

D. Grupe (PSU), A. P. Beardmore (U Leicester),
P. A. Evans (U Leicester), S. T. Holland (CRESST/USRA/GSFC),
E. A. Hoversten (PSU), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), J. L. Racusin (PSU), M. Stamatikos (NASA/ORAU),
M. C. Stroh (PSU), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU)
report on behalf of the Swift Team:

At 00:28:50 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081011 (trigger=331332).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 220.361, +33.607 which is 
   RA(J2000) = 14h 41m 27s
   Dec(J2000) = +33d 36' 27"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single complex peak
structure with a duration of about 15 sec.  The peak count rate
was ~1100 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 00:30:24.4 UT, 93.9 seconds after
the BAT trigger. No source was detected in the promptly available XRT
data. This is highly unusual for a long GRB  
with a prompt Swift slew.  We are waiting for the full dataset 
to detect and localise the XRT counterpart. 


UVOT took a finding chart exposure of 150 seconds with the White (160-650 nm)
filter starting 98 seconds after the BAT trigger. No afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of
the BAT error circle. The typical 3-sigma upper limit has been about 18.5 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
BAT 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
0.01. 




Burst Advocate for this burst is D. Grupe (grupe AT astro.psu.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.)

T. Sakamoto (GSFC/UMBC), 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), C. B. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD),
D. M. Palmer (LANL), A. M. Parsons (GSFC), G. Sato (ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 081011 (trigger #331332)
(Grupe, et al., GCN Circ. 8355
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 220.363, 33.548 deg which is 
   RA(J2000)  =  14h 41m 27.2s 
   Dec(J2000) = +33d 32' 54.4" 
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows two peaks around T+2 and T+9 sec.  
There is a hint of a weak extended emission until T+60 sec.  
T90 (15-350 keV) is 9 +- 2 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.9 to T+9.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.47 +- 0.28.  The fluence in the 15-150 keV band is 1.6 +- 0.3 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+1.06 sec in the 15-150 keV band
is 0.4 +- 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/331332/BA/

J. A. Kennea and D. Grupe (PSU) report on behalf of the Swift/XRT Team

We have analyzed downlinked data from the XRT observations of GRB 081011 
(Grupe et al, GCN #8355
Loading...
 
 ). The XRT began observing the field at 00:30:24.4 
UT, 94 seconds after the BAT trigger. Data from the first orbit of 
observations reveal an uncatalogued fading point source at RA, Dec = 
220.34435, +33.544771 which is the equivalent to:

RA(J2000) = 14h 41m 22.6s
Dec(J2000) = +33d 32m 41.1s

with an estimated uncertainty of 8 arcseconds radius (90% confidence). 
This position is 57 arcseconds from the BAT refined position (Sakamoto et 
al, GCN #8357
Loading...
 
 ).

P. Schady (MSSL-UCL) and D.Grupe (PSU) report on behalf of the Swift/UVOT 
team:

The Swift/UVOT observed the field of GRB 081011 (Grupe et al., GCN Circ. 
8355
Loading...
 
 ) with settled exposures starting 99s after the trigger. A new fading 
source is detected in the white and u-band finding chart (fc) exposures 
and marginally in a co-added b-band exposure at
RA(J2000) = 14:41:22.627 (220.34428)
Dec(J2000) = +33:32:37.12 (+33.54364)
consistent with the XRT position (Kennea et al., GCN Circ. 8358
Loading...
 
 ). These 
detections imply an upper limit on the redshift of z < ~3.8. The source is 
decaying with an approximate optical decay rate of alpha~1.1 (where the 
afterglow flux is proportional to t^-alpha).

The detections and 3 sigma upper limits in the UVOT photometric system 
(Poole et al. 2008, MNRAS, 383, 627) are:

Filter������������T_start T_stop�� Exp��    Mag or 3-sigma UL
������������������������(s)�� �� ��(s)���� �� (s)
========================================================
white (FC)����99�� �� ����249����������145.8��  19.25 +/- 0.08
white��������������537���� �� 1878��������283.5�� ��20.33 +/- 0.13
u (FC)������������257���� �� 507�������� 245.8���� 18.62 +/- 0.10
u����������������������660���� �� 2003������ 155.6���� 19.91 +/- 0.30
v�������������������� 586���� �� 7371������ 548.8�� ��> 20.29
b����������������������512���� �� 6756����  351.4������21.13 +/- 0.39
uvw1����������������636�������� 7781����  548.8���� > 20.96
uvm2������������ ��611���� �� 7576�� �� 548.9��  > 20.74
uvw2���������� �� 562�������� 7167����  548.8������> 21.06

The values quoted above are not corrected for the expected Galactic 
extinction corresponding to a reddening of E(B-V) = 0.01 mag in the 
direction of the burst (Schlegel et al. 1998).

P. Schady (MSSL-UCL) report on behalf of the Swift/UVOT team:

Due to formatting problems, the data table in GCN Circ 8359
Loading...
 
  (Schady et 
al.) is unreadable. Below is the properly formatted version of the UVOT 
data table for GRB 0810111

Filter     T_start T_stop  Exp    Mag or 3-sigma UL
            (s)     (s)     (s)
===================================================-
white (FC)  99      249    145.8  19.25 +/- 0.08
white       537     1878   283.5  20.33 +/- 0.13
u (FC)      257     507    245.8  18.62 +/- 0.10
u           660     2003   155.6  19.91 +/- 0.30
v           586     7371   548.8  > 20.29
b           512     6756   351.4  21.13 +/- 0.39
uvw1        636     7781   548.8  > 20.96
uvm2        611     7576   548.9  > 20.74
uvw2        562     7167   548.8  > 21.06

The values quoted above are not corrected for the expected Galactic 
extinction corresponding to a reddening of E(B-V) = 0.01 mag in the 
direction of the burst (Schlegel et al. 1998).

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

Using 12236 s of XRT Photon Counting mode data and 7 UVOT
images for GRB 081011, 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 = 220.34404, +33.54332 which is equivalent
to:

RA (J2000): 14h 41m 22.57s
Dec (J2000): +33d 32' 35.9"

with an uncertainty of 1.5 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
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an
extension of this method.

This circular was automatically generated, and is an official product of the
Swift-XRT team.

Dirk Grupe (PSU)  reports on behalf of the Swift-XRT team:


The XRT began observing the field of GRB 081011 (trigger=331332; Grupe 
et al.,
GCN Circ 8355
Loading...
 
 ) on 2008 October 11 00:30:24.4 UT, 93.9 s after
the BAT trigger.

The enhanced XRT position given in GCN Circ 8380
Loading...
 
  (Goad et al.)
is 59.3" away from the ground-processed BAT position given in GCN Circ. 
8357
Loading...
 
 
(Sakamoto et al.),  consistent with that position. This position was
outside the central 200x200 pixel XRT window which is telemetered as 
SPER data,
hence the non-detection reported in GCN 8357
Loading...
 
 .


The 0.3-10 keV X-ray light curve starts at a level of 7e-11 ergs/s/cm2 (1.8
counts/s) in the XRT with a steep decay slope at these early times of
alpha1 = 1.10+/-0.23 The light curve breaks at about 4+/-2 ks after the 
burst
and flattens to alpha2 = 0.24+/-0.17. Due to the proximity to the sun
constraint, it was decided to cancel the observations after the
first day. No further observations are planned and possible due the sun
constraint.


The spectrum of the Photon Counting mode data
can be fitted by an absorbed single powerlaw with a photon
index Gamma = 2.04 +/- 0.13 and column density fixed to the Galactic 
value of
1.04e20 cm-2 in the direction of the burst. The count rate to observed flux
conversion factor is 2.2e-11 (ergs/s/cm2)/(counts/s) in the 0.3-10 keV 
band.


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