GRB 100111A

A. Volnova (SAI MSU), M. Ibrahimov, R. Karimov (MAO), A. Pozanenko (IKI) 
report on behalf of  larger GRB  follow-up collaboration:

We observed the afterglow of the Swift GRB 100111A (Vetere et al. GCN 10317
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 ) 
with AZT-22 (1.5 m) telescope of Maidanak observatory (MAO) in R band on 
Jan. 12 (UT) (00:44 - 01:32) under good weather conditions with mean seeing 
of about 0.8 arcsec. The optical afterglow (Vetere et al. GCN 10317
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 ) is 
clearly detected in enhanced XRT error
circle (Beardmore et al. GCN 10321
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 ). A photometry of combined image is based 
on several SDSS DR7 field stars:

T0+     Filter  Exp.    Mag.            UL
mid., days      seconds                 (3 sigma)


0.8687         R       8*300   22.92 +/- 0.18  23.56

Comparing with R-magnitude reported by Xu et al. (GCN 10318
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 ) (R=19.46+/-0.05 
in 0.05 days) one can obtain power-law decay index of about 1.12.

A. N. Morgan, S. B. Cenko, J. S. Bloom, (UC Berkeley), report:

We observed the field of GRB 100111A (Vetere et al., GCN 10317
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 ) with
the 1.3m PAIRITEL located at Mt. Hopkins, Arizona. Observations began
at 2010-01-11 12:20:11 UT, ~8.12 hours after the Swift trigger.
Observations were taken under good weather conditions but at high
airmass before dawn.  In mosaics (effective exposure time of ~2223
seconds) taken simultaneously in the J, H, and Ks filters, we do not
detect the optical afterglow (Vetere et al., GCN 10317
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 ; Xu et al., GCN
10318
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 ; Hoversten et al., GCN 10323
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 ).

The preliminary photometry yields:

post_burst
t_mid(h)    exp(s)  filt    U. Limit (3 sig)
8.60        2223    J       > 19.0
8.60        2223    H       > 18.5
8.60        2223    Ks      > 18.0

All magnitudes given in the Vega system, calibrated to 2MASS.  No
correction for Galactic extinction has been made to the above reported
values.

E. A. Hoversten (PSU) and L. Vetere (PSU) report on behalf of the
Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 100111A
67 s after the BAT trigger (Vetere, et al., GCN Circ. 10317
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 ). A source
is detected at 17.62 magnitudes in the initial white finding chart at
the position RA, Dec (J2000) = 247.04833, 15.55064 which is equivalent
to:

    RA(J2000)  =  16:28:11.60 = 247.04833
    DEC(J2000) = +15:33:02.3  = 15.55064

with a 90%-confidence error radius of about 0.51 arc sec. This
position is 0.8 arcsec from the UVOT-enhanced XRT position (Beardmore,
et al. GCN Circ. 10321
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 ) and the two positions agree within the error
bars.  The source faded by more than a magnitude in the white filter
over the first orbit of observations.  Additionally the source is
detected in the b, u, and uvw1 filters, with a marginal 2.4-sigma
detection in v and a 2.1-sigma detection in uvm2. Given the detection
in the uvw1 filter the redshift of this burst is less than 1.9.

The observed magnitudes and 3-sigma upper limits using the UVOT
photometric system (Poole et al. 2008, MNRAS, 383, 627) for the
initial exposures are:

Filter   T_start(s)   T_stop(s)   Exp(s)          Mag
=============================================================
white        67          217        147      17.62 +/- 0.05
white       858         1007        147      18.73 +/- 0.10
v           609         1057         58         > 18.41
b           535          727         39      18.76 +/- 0.27
u           279          529        245      17.37 +/- 0.07
uvw1        658          851         38      18.57 +/- 0.36
uvm2        633          827         38         > 18.99
uvw2        584         1033         58         > 19.04

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst
(Schlegel et al. 1998).

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU),
L. Vetere (PSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 100111A (trigger #382399)
(Vetere, et al., GCN Circ. 10317
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 ).  The BAT ground-calculated position is
RA, Dec = 247.029, 15.539 deg which is 
   RA(J2000)  =  16h 28m 06.9s 
   Dec(J2000) = +15d 32' 19.1" 
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows a weak peak at ~T-30 sec and the main
FRED-like peak from ~T-10 sec and ending at ~T+25 sec.  T90 (15-350 keV)
is 12.9 +- 2.1 sec (estimated error including systematics).
 
The time-averaged spectrum from T-7.5 to T+8.7 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.69 +- 0.13.  The fluence in the 15-150 keV band is 6.7 +- 0.5 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.03 sec in the 15-150 keV band
is 1.9 +- 0.2 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/382399/BA/

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

Using 5361 s of XRT Photon Counting mode data and 10 UVOT
images for GRB 100111A, 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 = 247.04845, +15.55083 which is equivalent
to:

RA (J2000): 16h 28m 11.63s
Dec (J2000): +15d 33' 03.0"

with an uncertainty of 1.4 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.

L. Vetere (PSU) reports on behalf of the Swift-XRT team:


We have analysed 774 s of XRT data for GRB 100111A (Vetere et al.
GCN Circ. 10317
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 ), from 77 s to 852 s after the BAT trigger. The
data are entirely in Photon Counting (PC) mode. The light curve
can be modelled with a power-law decay with a decay index of
alpha=0.58 +/- 0.16.

A spectrum formed from the PC mode data can be fitted with an
absorbed power-law with a photon spectral index of 2.10 (+0.29,
-0.26). The best-fitting absorption column is 1.7 (+0.8, -0.7) x
10^21 cm^-2, in excess of the Galactic value of 4.1 x 10^20 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 (5.7 x 10^-11) erg cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index
of 0.58, the count rate at T+24 hours will be 0.023 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.7 x
10^-13 (1.3 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/00382399.

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

S. McBreen (UCD/MPE) reports on behalf of the Fermi GBM Team:

"At 04:12:49.70 UT on 11 January 2010, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 100111A (trigger 284875971 / 100111176)
which was also detected by the Swift-BAT (Vetere et al. 2010, GCN 10317
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 ).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 32 degrees.

The GBM light curve consists of one main pulse
with a duration of about 12 s (8-1000 keV).
The time-averaged spectrum from T0-2.7 s to T0+5.5 s is
adequately fit by a simple power law function
with index -1.66 (+0.05/-0.06) (CSTAT 452 for 363 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(1.5 +/- 0.1 )E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.003 s in the 8-1000 keV band
is 3.5 +/- 0.3 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

D. Xu (WIS, DARK/NBI), N. Tanvir (U. Leicester), J.P.U. Fynbo (DARK/NBI),
P. Jakobsson (Univ. of Iceland), T. Liimets (NOT) report on behalf of a
larger collaboration:

We observed the field of GRB100111A (Vetere et al., GCN 10317
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 ) with the
Nordic Optical Telescope equipped with ALFOSC. A 30 s R-band frame was
obtained, starting at 05:25:45 UT on Jan 11, 73 min after the
burst trigger. The afterglow is clearly detected in the frame with
R=19.46+/-0.05 mag calibrated with the nearby #1055-0262005 star in the
USNO B1 catalog.

L. Vetere (PSU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU), C. Gronwall (PSU),
D. Grupe (PSU), S. T. Holland (CRESST/USRA/GSFC),
E. A. Hoversten (PSU), C. B. Markwardt (CRESST/GSFC/UMD),
C. Pagani (PSU), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on
behalf of the Swift Team:

At 04:12:49 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 100111A (trigger=382399).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 247.038, +15.557 which is 
   RA(J2000) = 16h 28m 09s
   Dec(J2000) = +15d 33' 25"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a small precursor
peak followed by a main FRED peak for a total duration of about 30 sec. 
The peak count rate was ~3800 counts/sec (15-350 keV), at ~1 sec after
the trigger. 

The XRT began observing the field at 04:13:52.1 UT, 63.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 247.04766, 15.55090 which is equivalent
to:
   RA(J2000)  = 16h 28m 11.44s
   Dec(J2000) = +15d 33' 03.2"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 40 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 in excess of the Galactic value (4.09e+20
cm^-2, Kalberla et al. 2005), with an excess column of 2 (+2.19/-1.28)
x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 67 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	16:28:11.60 = 247.04833
  DEC(J2000) = +15:33:02.3  = 15.55064
with a 90%-confidence error radius of about 0.62 arc sec. This position is 3.4
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.58 with a 1-sigma error of about 0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.05. 

Burst Advocate for this burst is L. Vetere (vetere 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.)