GRB 101201A

GRB 101201A detected in ground analysis of BAT data

J. R. Cummings (GSFC/UMBC/CRESST), H. A. Krimm (GSFC/USRA/CRESST),
D. M. Palmer (LANL), S. D. Barthelmy (GSFC)
on behalf of the Swift-BAT team

At 10:01:48, Swift-BAT detected GRB 101201A (BAT triggers 439595-6, Fermi GBM
312890511). There was no source found onboard. A strong source was found in
ground analysis at RA, Dec 1.955, -16.196, which is:

RA (J2000)    00h 07m 49s
Dec (J2000)  -16d 11m 46s

with an estimated uncertainty radius of 2 arcmin (90% containment). This point
is 1.8 degrees from the GBM position, within the GBM error circle. It was
about 3% coded.

The burst was about 50 seconds long, with 3 overlapping peaks.  The available
BAT event-by-event data covers most of the second peak.

A Swift TOO for XRT follow-up is in progress.

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

We observed the field of GRB 101201A (Swift trigger 439595-6, Fermi  
GBM 312890511; Cummings et al., GCN #11429
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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 during twilight, at 00:36 UT on 2010-12-02, 14.6  
hours after the GRB trigger, and are continuing. They were performed  
at an average seeing of better than 0.8" and at an average airmass of 1.

We found a bright, uncatalogued point source within the 2 arcmin Swift- 
BAT error circle at

RA (J2000.0) = 00:07:52.19 s

DEC (J2000.0) = -16:11: 05.42

with an uncertainty of 0.5" in each coordinate.

The source is detected in all optical and NIR GROND filters and had a  
preliminary AB magnitude or r' = 19.67+/-0.01 10 mins after the start  
of our observations. The source faded by ~0.3 magnitudes within the  
first 1.5 hours of GROND observations, leading us to conclude that  
this is the afterglow of GRB101201A.

The detection of the source in the reddest GROND filter puts an upper  
limit on the redshift of this GRB of z < ~3. Given magnitudes are  
calibrated against USNO zeropoints and are not corrected for the  
expected Galactic foreground extinction corresponding to a reddening  
of E_(B-V)=0.02 mag in the direction of the burst (Schlegel et al.  
1998).

M. H. Siegel (PSU) and V. Magnano (INAF-IASFPA) report on behalf of
the Swift/UVOT team:

The Swift/UVOT began observations of the field of GRB101201A
approximately 14 hours after the BAT detection (GCN Circ. 11429
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 ).
We confirm the uncataloged source reported Guelbenzu et al.
(GCN Circ. 11430
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 ).  We also find evidence of fading between
the two orbits.  Magnitudes for the first and second orbit exposures
are listed below.

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

white            52065        52087           21         19.90+-0.49
white            57847        58387          531         20.01+-0.11
u                51218        52058          827         19.50+-0.17
u                57000        57840          826         20.01+-0.26

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.02 (Schlegel et al.,
1998, ApJS, 500, 525). The photometry is on the UVOT photometric
system described in Poole et al. (2008, MNRAS, 383, 627).

V. Mangano (INAF/IASF Pa), B. Sbarufatti (INAF/OAB - IASF Pa) report on
behalf of the Swift-XRT team:

We have analysed 4.9 ks of XRT data for GRB 101201A (Cummings  et al.
GCN Circ. 11429
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 ), from 51.2 ks to 69.7 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. Using 3879 s of PC mode
data and 3 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 = 1.96750, -16.18540 which is equivalent to:

RA (J2000): 00h 07m 52.21s
Dec(J2000): -16d 11' 07.4"

with an uncertainty of 1.9 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=3.80 (+0.03, -1.25).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.4 (+0.7, -0.6). The
best-fitting absorption column is  8 (+14, -6) x 10^20 cm^-2,
consistent with the Galactic value of 2.2 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 3.2 x 10^-11 (4.6 x
10^-11) erg cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
Total column:        8 (+14, -6) x 10^20 cm^-2
Galactic foreground: 2.2 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:        2.4 (+0.7, -0.6)

If the light curve continues to decay with a power-law decay index of
3.80, the count rate at T+24 hours will be 4.9 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.6 x
10^-13 (2.2 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020152.

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

S. Foley (MPE)
reports on behalf of the Fermi GBM Team:

"At 10:01:49.74 UT on 01 Dec 2010, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 101201A (trigger 312890511 / 101201418)
which was also detected by the SWIFT-BAT
(Cummings et al. 2010, GCN 11429
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 ).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 74 degrees.

The GBM light curve consists of 3 main pulses
with a duration (T90) of about 79 (+/-11) s (50-300 keV).
The time-averaged spectrum from T0+2.048 s to T0+81.922 s is
well fit by a power law function with an exponential
high energy cutoff.  The power law index is -1.50 (+/-0.03) and
the cutoff energy, parameterized as Epeak, is 275.70 (+37.20/-27.80) keV
(CSTAT 1263.1 for 480 d.o.f.).

The event fluence (10-1000 keV) over the T90 duration is
(2.41 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+31.74 s in the 10-1000 keV band
is 6.7 +/- 0.2 ph/s/cm^2.


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