GRB 101204A

J. R. Cummings (GSFC/UMBC/CRESST) on behalf of the Swift-BAT team

At 23:53:29 UTC on December 4, 2010 Swift-BAT detected GRB 101204A (BAT
trigger # 439806).  No source was detected onboard. An automated script
on the ground detected a source at RA, Dec 167.548, -20.434, which is

RA (J2000)    11h 10m 11.6s
Dec (J2000)  -20d 26m 04s

The source was 3.5% coded.

As seen by BAT, the burst was a single gradual pulse about 10 seconds
long. In the 10-second interval for which we have detailed event data,
which covers almost all of the burst, the spectrum is best fitted by
a simple power law with a photon index of 1.3 +- 0.2.  The fluence from
15 to 150 keV was 1.2 +- 0.4 x 10^-6 erg/cm^2.  The spectrum may be
slightly distorted by edge of FOV effects, tending to reduce the number
of lower-energy photons detected relative to higher-energy photons.

A Swift TOO has been requested.

B. Sbarufatti (INAF-OAB/IASFPA), S. Oates (MSSL) report
on behalf of the Swift-XRT and Swift-UVOT teams

We have analysed 4.9 ks of XRT data for GRB 101204A (Cummings  et al. GCN
Circ. 11440
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 ), from 126.2 ks to 134.4 ks after the  BAT trigger. The data
are entirely in Photon Counting (PC) mode. Using 4956 s of PC mode data
and 2 UVOT images, we find an enhanced XRT position (using the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec = 167.53712, -20.41924 which is equivalent to:

RA (J2000): 11h 10m 08.91s
Dec(J2000): -20d 25' 09.2"

with an uncertainty of 2.3 arcsec (radius, 90% confidence). The source is
detected at a level of 2.0+/-0.2E-3 counts/s, corresponding to a  0.3-10
keV flux of 1.4E-12 erg cm-2 s-1. At this time we are not able to tell if
the source is fading.

The Swift/UVOT began settled observations of the field of GRB 101204A
126199 s after the BAT trigger (Cummings et al., GCN Circ. 11440
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 ). An
uncatalogued source is found at the UVOT position RA(J2000)=
167.53683 deg, DEC(J2000) = -20.42014, which is:

    RA (J2000) =   11:10:08.84
   Dec (J2000) = -20:25:12.5

with an estimated uncertainty of 0.6 arcsec (radius, 90% confidence). This
position is consistent with the XRT candidate position.

At this time we are not able to tell if this source is fading. Preliminary
magnitudes 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
#####################################################
v       126194       127496     1281   20.28 +/- 0.24
v       131976       133278     1281   20.71 +/- 0.34
u       127505       128780     1255   19.79 +/- 0.13
u       133286       134378     1074   19.91 +/- 0.15
#####################################################

The values quoted above are not corrected for the Galactic extinction due
to the reddening of E(B-V) = 0.03 in the direction of the burst (Schlegel
et al. 1998).

P. Garnavich and J. Pagnini (Notre Dame) report:

We observed field of GRB 101204A beginning on Dec. 6.51 (UT) with
the Vatican Advanced Technology Telescope (VATT) and VATT4K CCD
camera. The imaging was centered on the original BAT position
(Cummings, GCN 11440
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 ) and were obtained 1.52 days after the burst.
Six R-band images were taken in poor conditions. The optical
afterglow candidate identified by Swift-UVOT (Sbarufatti et al., GCN
11442
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 ) is detected in the VATT images.

The deepest images centered on Dec. 6.521 give R=20.0+/-0.1 mag calibrated
from the USNO B1.0 star at 11:10:13.908 -20:26:07.8 with R2=17.74 mag.
The observations span less than 20 minutes so it is not possible to
determine if the source is fading.

A. Nicuesa Guelbenzu (Tautenburg Obs.), R. Filgas, J. Greiner and P.
Schady (all MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 101204A (Swift trigger 439806; Cummings,
GCN #11440
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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 05:55 UT on December 7, 2.2 days after the GRB
trigger,and ended at 08:36 UT. They were performed at an average seeing of
1.2" and at an average airmass of 1.5.

We confirm the afterglow candidate reported by Sbarufatti et al.(GCN
#11442
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 ). After calibrating against the comparison star from Garnavich et
al.(GCN #11444
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 ), we find the afterglow candidate to have faded by at least
0.6 mag in the time between the VATT (Garnavich et al.) and GROND
observations. We also find the SED of this source to be well-fit by a
power-law, providing further evidence of this being the afterglow of
GRB101204A.

Based on the best 7.7 min of total exposures in g'r'i'z' and 8 min in
JHK taken at 08:18 UT, we estimate preliminary magnitudes (all in AB) of

g' = 21.3 +- 0.1 mag,

r' = 21.0 +- 0.1 mag,

i' = 20.8 +- 0.1 mag,

z' = 20.5 +- 0.1 mag,

J = 20.3 +- 0.1 mag and

H = 19.6 +- 0.1 mag

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 a reddening of E_(B-V)=0.033 mag in the
direction of the burst (Schlegel et al. 1998).

We thank the ESO staff at LaSilla observatory, and in particular A. Sanchez,
for their excellent support and assistance with the observations.

B. Sbarufatti (INAF/OAB-IASF Pa) reports on behalf of the Swift-XRT
team:

We have analysed 24 ks of XRT data for GRB 101204A (Cummings  et al.
GCN Circ. 11440
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 ), from 126.2 ks to 383.1 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. Using 9912 s of PC mode
data and 4 UVOT images, we find an enhanced XRT position (using the
XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec = 167.53700, -20.41980 which is equivalent to:

RA (J2000): 11h 10m 8.88s
Dec(J2000): -20d 25' 11.5"

with an uncertainty of 1.6 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.33 (+0.24, -0.23).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.14 (+0.34, -0.18). The
best-fitting absorption column is  consistent with the Galactic value
of 3.3 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 3.4 x 10^-11 (3.9 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.3 (+4.4, -0.0) x 10^20 cm^-2
Galactic foreground: 3.3 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.14 (+0.34, -0.18)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020153.

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

S. R. Oates (MSSL-UCL) & B. Sbarufatti (INAF-OAB/IASFPA) report
on behalf of the Swift-XRT and Swift-UVOT teams

The Swift/UVOT began settled observations of the field of GRB 101204A
126195 s after the BAT trigger (Cummings et al., GCN Circ. 11440
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 ).

In agreement with report from Nicuesa Guelbenzu et al., (GCN Circ.  
11445
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 ), we
find the afterglow candidate in (Sbarufatti et al. GCN Circ. 11442
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 )
to have faded. Preliminary magnitudes using the UVOT photometric
system (Poole et al. 2008, MNRAS, 383, 627) for summed exposures are:

Filter  T_start(s)  T_stop(s)   Exp(s)       Mag
#####################################################
v       126195       133279     2563    20.51 +/- 0.19
v       271960       336155     3553    > 21.62
u       127505       134378     2329    20.03 +/- 0.12
u       272471       336626     3273    21.27 +/- 0.26
#####################################################

The values quoted above are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).