GRB 100902A

T. Sakamoto (NASA/UMBC), W. H. Baumgartner (GSFC/UMBC),
A. P. Beardmore (U Leicester), J. R. Cummings (NASA/UMBC),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
J. M. Gelbord (PSU), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU),
W.B Landsman (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL),
A. Rowlinson (U Leicester), B. Sbarufatti (INAF-OAB/IASFPA),
M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC),
R. L. C. Starling (U Leicester) and M. C. Stroh (PSU) report on behalf
of the Swift Team:

At 19:31:54 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 100902A (trigger=433160).  BAT slewed to the location
after a brief delay due to observing constraints. 
The BAT on-board calculated location is 
RA, Dec 48.646, +30.973 which is 
   RA(J2000) = 03h 14m 35s
   Dec(J2000) = +30d 58' 21"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a small spike 
around the trigger time.  There are brighter spikes around T+150 sec 
and T+200 sec with a duration of 50 sec.  The peak count rate
was ~1200 counts/sec (15-350 keV), at ~210 sec after the trigger. 

The XRT began observing the field at 19:37:10.1 UT, 316.2 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
48.6294, 30.9791 which is equivalent to:
   RA(J2000)  = 03h 14m 31.05s
   Dec(J2000) = +30d 58' 44.8"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 56 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 (1.13e+21
cm^-2, Kalberla et al. 2005), with an excess column of 4.1
(+2.41/-2.03) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 0.1 s image was 2.20e-07 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of nominal 150 seconds with the
White filter  starting 325 seconds after the BAT trigger. No credible
afterglow candidate has  been found in the initial data products. Data
from the 2.7'x2.7' sub-image are  not available at this time. 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 0.31. 

Burst Advocate for this burst is T. Sakamoto (Taka.Sakamoto AT 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.)

V.Krushinski, I.Zalozhnich, T.Kopytova, A. Popov
Ural State University, Kourovka

E. Gorbovskoy, V. Lipunov, V.Kornilov, A.Belinski, N.Shatskiy, N.Tyurina,
D.Kuvshinov, P.Balanutsa, V.V.Chazov, P.V.Kortunov, A.Kuznetsov,
D.Zimnukhov, M. Kornilov
Sternberg Astronomical Institute, Moscow State University


K.Ivanov, O.Chuvalaev, V.Poleschuk, E.Konstantinov, V.Lenok, O.Gres,
S.Yazev, N.M.Budnev,
Irkutsk State University


A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik
Kislovodsk Solar Station of the Pulkovo Observatory


V.Yurkov, Yu.Sergienko, D.Varda, I.Kudelina
Blagoveschensk Educational State University, Blagoveschensk



MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru)
located at Ural (Kourovka)  was pointed to the
Swift GRB 100902A (Sakamoto et al., GCN Circ 11181
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 ) 27  sec  after 
Notice time (104 s after trigger time) in two polarizations.

Thre is no optical transient at XRT position (Sakamoto et al., GCN Circ 
1118
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 ) brighter 17 mag (exposition 20 s).

The message may be cited.

mailto: lipunov@sai.msu.ru

C. Guidorzi (U. Ferrara), A. Melandri (INAF-OAB),
N. Tanvir (U. Leicester) on behalf of a large collaboration report:

The 2-m Faulkes Telescope South automatically began observing
GRB 100902A (Sakamoto et al. GCN Circ. 11181
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 ) on September 02,
19:34:38 UT, 164 seconds from the GRB trigger time and during
the major gamma-ray spikes (GCN 11181
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 ).
Within the XRT error circle we do not find any source
down to the following limiting magnitudes:

Mid time from      Exposure    Filter   Limiting Magnitude
trigger (s)           (s)
------------------------------------------------------------
169                   10          R > 15.6
203                 3x10          R > 16.0
------------------------------------------------------------

Calibration is against some nearby USNOB-1 stars.
The relatively poor limits are due to the vicinity to the Moon.

E. Gorbovskoy, V. Lipunov, V.Kornilov, A.Belinski, N.Shatskiy, N.Tyurina,
D.Kuvshinov, P.Balanutsa, V.V.Chazov, P.V.Kortunov, A.Kuznetsov,
D.Zimnukhov, M. Kornilov
Sternberg Astronomical Institute, Moscow State University

V.Krushinski, I.Zalozhnich, T.Kopytova, A. Popov
Ural State University, Kourovka

K.Ivanov, O.Chuvalaev, V.Poleschuk, E.Konstantinov, V.Lenok, O.Gres,
S.Yazev, N.M.Budnev,
Irkutsk State University


A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik
Kislovodsk Solar Station of the Pulkovo Observatory


V.Yurkov, Yu.Sergienko, D.Varda, I.Kudelina
Blagoveschensk Educational State University, Blagoveschensk



MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru)
located at Ural (Kourovka)  was pointed to the
Swift GRB 100902A (Sakamoto et al., GCN Circ 11181
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 ) 27  sec  after Notice time 
(104 s after trigger time) in two polarizations.

Thre is no optical transient at XRT position (Sakamoto et al., GCN Circ 1118
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 ) 
with next limits:

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd? Filter
--------------------------------------------------------------------------
19:33:38       19:33:58     20        17.0      104.0          N  Polariz
19:34:12       19:34:42     30        17.3      132.0          N  Polariz
19:34:57       19:35:57     40        17.3      177.0          N  Polariz
19:35:51       19:36:41     50        17.4      231.0          N  Polariz
19:33:38       19:36:41    140        18.0      104.0          Y  Polariz
--------------------------------------------------------------------------

The message may be cited.

mailto: lipunov@sai.msu.ru

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

Using 4941 s of XRT Photon Counting mode data and 6 UVOT
images for GRB 100902A, 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 = 48.62930, +30.97904 which is equivalent
to:

RA (J2000): 03h 14m 31.03s
Dec (J2000): +30d 58' 44.5"

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) and Evans
et al. (2009, MNRAS, 397, 1177).

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

M. Andreev, A. Sergeev (Terskol Branch of Institute of Astronomy) and 
A.Pozanenko (IKI) on behalf of larger GRB follow up collaboration report:

We observed  the field of the Swift GRB 100902A (Sakamoto  et al, GCN 11181
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 ) 
with the Z-600 telescope of Mt.Terskol observatory in R-filter between (UT) 
00:52:20 - 01:26:40. In enhanced XRT error circle (Beardmore et al, GCN 
11188
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 ) we do not detect  any object. The object at distance of 4" from the 
center of the enhanced  XRT error circle (Beardmore et al, GCN 11188
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 ) in 
coordinates (J2000) RA =03 14 31.35 Dec= +30 58 44.8 with uncertainty of 1" 
is detected at magnitude R ~ 20 and upper limit of stacked image of R=21 (3 
sigma). At present time we cannot confirm variability of the object.

The finding chart can be found at
http://grb.rssi.ru/GRB100902A/GRB100902A_R_Z600.jpg

W. Landsman (GSFC/Adnet) and T. Sakamoto (NASA/UMBC) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 100902A 326 s after the BAT trigger (Sakamoto et al., GCN Circ. 11181
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 ).   No optical afterglow consistent with the XRT position (Beardmore et al., GCN Circ.  11188
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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           326          475          147>20.4
white              326         1008          295>20.8
w1                 532        18249          823>20.7
m2                1063        14541         1136>20.8
w2                 632        12947         1528>21.2

The values quoted above are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.31 in the direction of the burst (Schlegel et al. 1998).

R.L.C. Starling (U. Leicester) and T. Sakamoto (NASA/UMBC) report on behalf of 
the Swift-XRT team:

We have analysed 7.9 ks of XRT data for GRB 100902A (Sakamoto et al. GCN Circ. 
11181
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 ), from 306 s to 18.2 ks after the BAT trigger. The data comprise 306 s in 
Windowed Timing (WT) mode (the first 8 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 Beardmore et al. (GCN. Circ 11188).

The light curve can be modelled with an initial power-law decay with an index 
of alpha=2.4 (+/-0.1), followed by a break at T+1730 (+/-210) s to an alpha of 
0.8 (+/-0.1). Overlaid on this broken power law decay are two large flares, 
which peak at 400 and 420 s with count rates of 1390 (+/-140) and 1440 (+/-150) 
count s^-1 respectively.

A spectrum formed from all the PC mode data to date can be fitted with an 
absorbed power-law with a photon spectral index of 2.5 (+/-0.2). The 
best-fitting absorption column is 3.39 (+/-0.6) x 10^21 cm^-2, in excess 
of the Galactic value of 1.1 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 3.8 x 10^-11 (9.7 x 10^-11) erg cm^-2 count^-1.
We do not report a WT time averaged spectral fit here as this would be 
affected by the spectral evolution during the flaring activity, evident
in the hardness ratio.

If the light curve continues to decay with a power-law decay index of 0.8, the 
count rate at T+24 hours will be 0.013 count s^-1, corresponding to an 
observed (unabsorbed) 0.3-10 keV flux of 5.7 x 10^-13 (1.4 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at 
http://www.swift.ac.uk/xrt_products/00433160.

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

S. Campana (INAF-OAB), R. L. C. Starling (U Leicester), P. A. Evans  (U 
Leicester), and T. Sakamoto (NASA/UMBC) report on behalf of the Swift Team:

Swift BAT triggered on the early activity of GRB 100902A (Sakamoto et 
al. 2010, GCN 11181
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 ). Swift XRT started observing 316 s after the 
trigger observing the main event. By using the Swift/XRT spectrum 
repository at http://www.swift.ac.uk/xrt_spectra/ (see Evans et al. 
2009, MNRAS, 397, 1177) we selected two time intervals with an almost 
constant hardness ratio. These are at the end of the main event between 
500-550 s (in Window Timing, WT, mode) and the entire first orbit in 
Photon Counting (PC) mode (between 600-3000 s). We then fit the two 
spectra with XSPEC using the model tbabs*ztbabs (cutoff), keeping the 
same absorption pattern and leaving free the cutoff power-law model for 
the two spectra (the cutoff power-law model provides much better results 
in terms of column density evaluation with respect to a simple power-law 
model when small spectral variations are present).
We assume a Galactic column density of 1.1x1021 cm-2 (Kalberla et al. 
2005, A&A 440 775) and we allow for a 30% uncertainty in the fit.  We 
fit the spectrum using C-statistics. In the intrinsic column density vs. 
redshift plane there is just one deep minimum hinting for a redshift 
z=4.5^+0.3_-0.2 (90% confidence level) and an intrinsic column density 
N_H(z)=(2.3^+0.5_-0.3)x1023 cm-2. The X-ray spectrum is very soft with 
Gamma~3.9 at the end of the prompt phase (with a cut-off energy >17 keV) 
and with Gamma~1.9 and E_cut~5 keV in the PC spectrum. The two spectra 
indicate the same redshift even separately.
The high redshift and the large absorbing column density are in line 
with the non-detection with UVOT and other ground based optical facilities.

The contour plot is available at
http://www.brera.inaf.it/utenti/campana/100902.gif

J.C. Tello, R. S�nchez-Ram�rez, A. Sota, J. Gorosabel, A.J. Castro-Tirado
(IAA-CSIC, Granada), report on behalf of a larger collaboration:

"We have carried out I-band observations of the  Swift GRB 100902A
(Sakamoto et al. GCNC  11181) on Sep 3.1076 - 3.1492 UT (~7.05 hr after
the onset of the burst, mean observing time) with the  1.5m  telescope at
Observatorio  de Sierra  Nevada, Spain. We do not detect any optical
source within the SWIFT/XRT error circle (Beardmore et al. GCNC 11188).
The 3 sigma limiting magnitude of the co-added I-band image (Texp=16x200s)
is I ~ 21.8, calibrated against the USNO B1.0 catalogue."

M. Stamatikos (OSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+963 sec from telemetry downlinks,
we report further analysis of BAT GRB 100902A (trigger #433160)
(Sakamoto, et al., GCN Circ. 11181
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 ).  The BAT ground-calculated position is
RA, Dec = 48.626, 30.970 deg, which is 
   RA(J2000)  =  03h 14m 30.3s 
   Dec(J2000) = +30d 58' 13.2" 
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 72%.
 
The mask-weighted light curve shows several strong peaks.  The first starts
around T-60 sec and returns to background around T+70 sec.  We note that
this burst location came into the BAT FoV around T-80 sec, so there could have been
prior activity for this burst.  Then come two stronger peaks at ~T+130 and 
~T+205 sec; then a smaller peak at ~T+400 sec.  T90 (15-350 keV) is
428.8 +- 43.0 sec (estimated error including systematics).
 
The time-averaged spectrum from T-49.5 to T+409.6 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.98 +- 0.13.  The fluence in the 15-150 keV band is 3.2 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+207.89 sec in the 15-150 keV band
is 1.0 +- 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/433160/BA/

D. Kuroda (OAO, NAOJ),  H. Hanayama, T. Miyaji, J. Watanabe(IAO, NAOJ),
K. Yanagisawa (OAO, NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto)
and N. Kawai(Tokyo Tech) report on behalf of the MITSuME collaboration:

We observed the field of GRB 100902A (Sakamoto et al. GCNC 11181)
with the optical three color (g', Rc and Ic) CCD camera attached
to the Murikabushi 1m telescope of Ishigakijima Astronomical
Observatory.

The observation started on 2010-09-03 18:04:55 UT (~0.94 day after the
burst). We did not find any new point source within the Enhanced
XRT error circle (Beardmore et al. GCNC 11188) in all the three bands.

Three sigma upper limits of the OT are listed below. We used
GSC2.3 catalog for flux calibration.

T0+[day]   MID-UT   T-EXP[sec]    g'     Rc     Ic
------------------------------------------------------
0.94445    18:11:55   720.0      >21.8  >21.4  >20.2
------------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]

A. Updike (Clemson Univ.), A. Nicuesa Guelbenzu, S. Klose (both TLS 
Tautenburg), and J. Greiner (MPE Garching), report on behalf of the GROND 
team:

GROND (Greiner et al. 2008, PASP 120, 405), the 7-channel imager mounted 
at the 2.2m ESO/MPI telescope on La Silla, started follow-up observations 
of GRB 100902A (Sakamoto et al. 2010, GCN 11181
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 ) on September 4 at 7:40 UT 
(about 1.5 days after the trigger). Airmass was around 2. Due to bad 
weather on La Silla no earlier observations were possible.

Within the enhanced 1.5 arcsec XRT error circle (Beardmore et al. 2010, 
GCN 11188
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 ) we find a faint source at coordinates RA, DEC (J2000) = 
03:14:30.96, +30:58:44.8 (+/-0.5 arcsec).

Preliminary measured AB mags are:

r' = 24.1 +/- 0.3
i' = 24.0 +/- 0.4

using GROND zeropoints.

At present it is not clear if this is the afterglow or the underling host. 
No statements about variability or fading can be made at the moment.

Myungshin Im, Changsu Choi, Hyunsung Jun, Eugene Kang (CEOU/Seoul
  National University), Y. Urata (NCU), P. Choi (Pomona College),
  and  T. Sakamoto (NASA/GSFC), on behalf of a larger collaboration

   We observed GRB 100902A (Sakamoto et al. GCN 11181
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 ) in J and K filters
  using UKIRT. The observation started at Sept. 04, 14:24:39 UT or roughly
  1.79 days after the BAT alert.
   The reduced images with non-optimal calibration frames do not show a clear
  sign of the afterglow candidate reported in Updike et al.
  (GCN 11209
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 ), although both the J and K images show a faint smudge at
  the reported location which may corresponds to the afterglow.
   The significance of the detection is only ~3 sigma (J ~ 20.8 mag,
  K ~ 19 mag in Vega), therefore it is difficult to draw a firm conclusion
  on detection or non-detection of the afterglow in our data. Further
  analysis of the UKIRT data is ongoing.

GRB 100902A :  Confirmation of afterglow and re-brightening with CFHT r��\200\231-band imaging

K.Y. Huang (ASIAA), Y. Urata (NCU), M. Im (CEOU/SNU) and T. Sakamoto (NASA/GSFC)

We made r��\200\231-band observation using CFHT for the GRB 100902A field. The observation started at 5.8 days after the
Swift/BAT trigger (Sakamoto et al. GCN 11181
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 ).  The stacked image show a point source at the position of the optical
afterglow candidate reported by Updike et al. (GCN 11209
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 ). The brightness against with several USNO-B stars is 23.2
+/-0.1, which is about 1 magnitude brighter than the report of GROND. This  result implies the source could be the
optical afterglow and show the re-brightening.
Combined with reports of GROND (Updike et al. GCN 11209
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 ) and UKIRT (Im et al GCN 11210
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 ), the GRB 1000902A
afterglow shows the extremely red color (r-K~ 5 mag).

Further photometric and spectroscopic observations are encouraged.

We thank Dr. Thomas Kruehler and Dr. Sylvio Klose for providing the reference image taken by GROND. We also
thank Dr. Nadine Manset and QSO team for arranging the CFHT observations.

Jan Strobl (1,2), Martin Nekola (1), Martin Blazek (1,2), Martin Jelinek
(3), Cyril Polasek (1), Petr Kubanek (3,4), Matus Kocka (1) and
Rene Hudec (1,2)
(1. ASU AVCR Ondrejov, 2. FEL CVUT Praha, 3. IAA Granada, 4. IPL UV
Valencia)

We report on the observation of the field of the Swift GRB 100902A 
(Sakamoto et al., GCN 11181
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 ) with the 0.5m telescope D50 in Ondrejov 
(Czech Republic), starting at 22:03:08 UT, i.e. ~2.5h after the trigger.
A sequence of 20s unfiltered images was obtained. We coadded 225x20s 
exposure, obtaining an image with a limitting magnitude Rc~19.1, with an 
effective exposure time 3.68h after the trigger (23:13 UT). We do not 
detect any new source within the XRT error circle (Beardmore et al., GCN 
11188
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 ).

This message can be cited.

[GCN OPS NOTE(13oct10):  Per author's request, the affilation footnotes
were fixed.]