GRB 090912

T. N. Ukwatta (GSFC/GWU), S. D. Barthelmy (GSFC), M. M. Chester (PSU),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
V. Mangano (INAF-IASFPA), K. L. Page (U Leicester),
P. Romano (INAF-IASFPA), T. Sakamoto (NASA/UMBC),
B. Sbarufatti (INAF-IASFPA), R. L. C. Starling (U Leicester) and
E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift Team:

At 15:50:29 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090912 (trigger=362633).  Swift executed a delayed slewed
to the burst. 
The BAT on-board calculated location is 
RA, Dec 188.092, +61.513, which is 
   RA(J2000)  =  12h 32m 22s
   Dec(J2000) = +61d 30' 45"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows two peaks at T+0 and
at T+90 with a total duration of about 130 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 16:03:42.4 UT, 792.6 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 188.0422, 61.4843 which
is equivalent to:
   RA(J2000)  = 12h 32m 10.13s
   Dec(J2000) = +61d 29' 03.5"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 134 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 (1.28e+20
cm^-2, Kalberla et al. 2005), with an excess column of 6.2
(+4.43/-3.60) x 10^21 cm^-2 (90% confidence). 


UVOT took a finding chart exposure of 150 seconds with the White filter
starting 795 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 none of
the XRT error circle. 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 0.01. 




Burst Advocate for this burst is T. N. Ukwatta (tilan.ukwatta AT gmail.com). 
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 1374 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 090912, 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 = 188.04297, +61.48454 which is equivalent
to:

RA (J2000): 12h 32m 10.31s
Dec (J2000): +61d 29' 04.4"

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.

Arto Oksanen (Hankasalmi Obs., Hankasalmi, Finland) reports to the AAVSO 
International High Energy Network the following optical observations of 
the field of GRB090912 (GCN Circ. #9905
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 , Ukwatta et al.):

A. Oksanen reports an upper limit on the optical afterglow of CR=21.6, 
measured relative to USNO-A2.0 1500-05568008 (R=15.7).  The X-ray 
afterglow position (Beardmore et al., GCN #9906
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 ) was observed using the 
0.4-m Hankasalmi Observatory RC telescope with an SBIG STL-1001E CCD 
camera and clear filter.  A total of 57 one-minute exposures were 
obtained, with the mid-point of the exposures at 2009 Sept 12 19:33 UT, 
approximately 3.7 hours post-burst.  Two faint stars near the burst 
location are present in DSS2 images, but there is no transient source at 
the burst location to a limit of CR=21.6.

A detailed report of these observations may be found at the following URL:
ftp://ftp.aavso.org/grb/ArtoOksanen_GRB090912_2455087.38910_.txt

A fits image is also available at
ftp://ftp.aavso.org/grb/ArtoOksanen_GRB090912_2455087.38910_.fits

The AAVSO thanks the Curry Foundation for its support of the
AAVSO International High Energy Network.

P.A. Curran (MSSL-UCL) and T. N. Ukwatta (GSFC/GWU) report on behalf of 
the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 090912 796s after 
the BAT trigger (Ukwatta et al., GCN 9905
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 ). No optical afterglow consistent 
with the enhanched Swift XRT position (Beardmore et al., GCN 9906
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 )  is detected 
in the 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) and subsequent exposures are:


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

white          796          946           147         >20.50 (FC)
white          796          7707          608         >21.09
v              1129         8118          294         >19.04
b              1228         7502          254         >19.91
u              1204         7297          313         >19.58
w1             1179         7092          313         >19.82
m2             6688         8273          344         >19.78
w2             7713         7913          197         >19.78

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

T. N. Ukwatta (GSFC/GWU), 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),
D. M. Palmer (LANL), A. M. Parsons (GSFC),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC)
(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 090912 (trigger #362633) (Ukwatta, et al.,
GCN Circ. 9905
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 ). The BAT ground-calculated position is
RA, Dec = 188.046, 61.475 deg which is
   RA(J2000)  =  12h 32m 11.1s
   Dec(J2000) = +61d 28' 29.4"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90%
containment). The partial coding was 30%.

The mask-weighted light curve shows two peaks. The first
start around T-4 sec, shows three sub peaks at ~T+0 sec,
~T+4 sec, and ~T+7 sec, and ends around T+25 sec. The
second peak starts at ~T+70 sec, peaks at ~T+88, and ends
around T+145 sec. T90 (15-350 keV) is 144.0 +- 22.6 sec
(estimated error including systematics).

The time-averaged spectrum from T-15.9 to T+160.1 sec is
best fit by a power law with an exponential cutoff.
This fit gives a photon index 0.91 +- 0.44, and Epeak
of 69.3 +- 19.5 keV (chi squared 42.50 for 56 d.o.f.).
For this model the total fluence in the 15-150 keV band
is 4.5 +- 0.3 x 10^-6 erg/cm2 and the 1-sec peak flux
measured from T+87.56 sec in the 15-150 keV band is
1.0 +- 0.1 ph/cm2/sec.  A fit to a simple power law
gives a photon index of 1.66 +- 0.09
(chi squared 52.84 for 57 d.o.f.). 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/362633/BA/

Sbarufatti B., Mangano V. (INAF-IASFPA) and T. Ukwatta (GSFC/GWU)
report on behalf of the Swift Team:

We have analyzed the first 22.5 ks of of Swift-XRT data of
GRB 090912 (trigger 362633; Ukwatta, et al., GCN Circ. 9905
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 ).
The data are entirely in Photon Counting (PC) mode, from T+806 s to
T+66 ks. The enhanced XRT position for this burst was given by
Beardmore et al. (GCN. Circ 9906).

The 0.3-10 keV X-ray light curve is best fitted by a power-law
with decay index -0.75+/-0.03. Faint flaring activity is
detected along the decay. If decaying at the present rate, the
predicted rate for T+ 48h is 1.0e-2 counts/s.

The average spectrum is best fit by a power-law with index
2.1+/-0.1. The absorbing column is NH = (5.2+/-0.7)E20 cm^-2,
in excess with respect to the Galactic value of 1.3E20 cm^-2
(Kalberla et al. 2005). The average observed (unabsorbed) fluxes are
3.0(5.7)E-12 ergs cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00362633 .

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

V. Rumyantsev, V.Biryukov (CrAO), A. Pozanenko (IKI)  report on behalf of 
larger GRB follow-up collaboration:

We observed the field of  the Swift GRB 090912 (Ukwatta  et al., GCN 9905
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 ) 
with Zeiss-600 telescope of  SAI MSU Crimean branch in  R-filter on Sep.12 
between  (UT) 17:41:36 - 19:08:10.  Within XRT error circle (Beardmore et 
al., GCN  9906
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 ) we do not detect any source. However  in a stacked image we 
detect faint source at the coordinates RA(J2000)=  12 32 09.82 Dec(J2000)= 
+61 29 04.54 with uncertainty of 0.5 arcsec. It is 3.5" apart from XRT 
center of the circle of 1.8" radius. We suggest the detected source as 
afterglow candidate and urge  deep observation to confirm variable nature of 
the source.

The photometry of the source against nearby USNO-B1.0 star 1515-0196640 
RA(J2000)= 12:32:18.77 Dec(J2000)= +61:30:00.3 assuming R=19.06 is 
following:

T0+     Filter, Exposure, mag.,     err.
(d)                (s)

0.1086  R     4620     21.8 +/- 0.3