GRB 111018A

F. E. Marshall (NASA/GSFC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
M. M. Chester (PSU), V. D'Elia (ASDC), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), V. Mangano (INAF-IASFPA),
D. M. Palmer (LANL), M. H. Siegel (PSU),
R. L. C. Starling (U Leicester), C. A. Swenson (PSU),
G. Tagliaferri (INAF-OAB), E. Troja (NASA/GSFC/ORAU) and
B.-B. Zhang (PSU) report on behalf of the Swift Team:

At 17:26:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 111018A (trigger=505801).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 271.500, -3.871 which is 
   RA(J2000)  =  18h 06m 00s
   Dec(J2000) = -03d 52' 16"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows two weak peaks
at T+0 and T+30 sec with a total duration of about 40 sec.  The peak count rate
was ~500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 17:28:27.6 UT, 123.0 seconds after
the BAT trigger. The position determined from promptly downlinked data
differs significantly from the on-board position, suggesting that the
XRT may have centroided on a cosmic ray; the initial XRT position
notice should be treated with caution. Using promptly downlinked data
we find an uncatalogued X-ray source located at RA, Dec 271.48887,
-3.90719 which is equivalent to:
   RA(J2000)  = 18h 05m 57.33s
   Dec(J2000) = -03d 54' 25.9"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 135 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.  We cannot determine whether the source is
fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 2.54
x 10^21 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 132 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
2.16. 

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.)

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

Using 1590 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 111018A, 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 = 271.48854, -3.90728 which is equivalent
to:

RA (J2000): 18h 05m 57.25s
Dec (J2000): -03d 54' 26.2"

with an uncertainty of 2.0 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.

M. Nardini (Uni. Milano-Bicocca), J. Elliott and J. Greiner (both MPE  
Garching) report on behalf of the GROND team:

We observed the field of GRB111018A (Swift trigger 505801; Marhsal et  
al., GCN #12450
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et  
al. 2008, PASP 120, 405) mounted at the 2.2 m MPI/ESO telescope at La  
Silla Observatory (Chile).

Observations started at 23:47 UT on 18 October 2011, 6.35 hours after  
the trigger. They were performed at an average seeing of 2.8 and at 
an average airmass of 1.9.

Based on images with total exposures of 1500 s in g'r'i'z' and 1200 s  
in JHK, we do not detect a source within the Swift-XRT error circle  
reported by Goad et al. (GCN #12453
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 ) down to (all AB):

g' > 23.2,
r' > 23.5,
i' > 22.5,
z' > 22.2,
J  > 20.0,
H  > 18.9, 
K  > 18.6

Given magnitudes are calibrated against GROND zeropoints as well as  
2MASS field stars and are not corrected for the expected Galactic  
foreground extinction corresponding to the heavy reddening of 
E(B-V)=2.16 in the direction of the burst (Schlegel et al. 1998).

V. Mangano (INAF IASFPA) and F. E. Marshall (NASA/GSFC) reports on
behalf of the Swift-XRT team:

We have analysed 11 ks of XRT data for GRB 111018A (Marshall  et al.
GCN Circ. 12450
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 ), from 115 s to 36.2 ks after the  BAT trigger. The
data comprise 37 s in Windowed Timing (WT) mode (the first 6 s were
taken while Swift was slewing) with the remainder in Photon Counting
(PC) mode. The enhanced XRT position for this burst was given by Goad
et al. (GCN. Circ 12453).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.01 (+0.15, -0.13).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.8 (+0.8, -0.7). The
best-fitting absorption column is  1.2 (+0.8, -0.6) x 10^22 cm^-2, in
excess of the Galactic value of 2.5 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 6.7 x 10^-11 (1.2 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.2 (+0.8, -0.6) x 10^22 cm^-2
Galactic foreground: 2.5 x 10^21 cm^-2
Excess significance: 3.4 sigma
Photon index:	     1.8 (+0.8, -0.7)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00505801.

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

J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC), 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-239 to T+963 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 111018A (trigger #505801)
(Marshall, et al., GCN Circ. 12450
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 ).  The BAT ground-calculated position is
RA, Dec = 271.482, -3.880 deg, which is 
   RA(J2000)  =  18h 05m 55.6s 
   Dec(J2000) = -03d 52' 48.5" 
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 80%.
 
The mask-weighted light curve shows a couple overlapping peaks starting 
at ~T-4 sec, peaking at ~T-1 and ~T+22 sec, and ending at ~T+35 sec,
possibly out to T+75 sec.  T90 (15-350 keV) is 36 +- 5 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-4.08 to T+37.30 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.18 +- 0.27.  The fluence in the 15-150 keV band is 4.0 +- 0.7 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+21.71 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/505801/BA/

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 111018A 
132 s after the BAT trigger (Marshall et al., GCN Circ. 12450
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 ). No 
optical afterglow consistent with the refined XRT position (Goad et 
al., GCN Circ. 12453
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 ) is detected in the initial UVOT exposures. 
Preliminary 3-sigma upper limits using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC) 
exposure and subsequent exposures are:

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

white_FC           132          282          147         >21.1
white              132         7508          653         >21.8
v                  462        12028          673         >20.2
b                  388         6000          333         >20.9
u                  291         5794          329         >20.6
uvw1               512         5590          314         >20.4
uvm2               487         5384          333         >20.2
uvw2               438        11672         1040         >21.4

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 2.16 in the direction of the burst
(Schlegel et al. 1998).