GRB 131209A

Dirk Grupe (Swift MOC, PSU)  reports on behalf of the 
Swift team:

We report on further Swift XRT observations of the field of the 
FERMI/LAT-discovered GRB 131209A (Vianello et al., GCN circ. 
15587
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 ). As reported in GCN circular 15592
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  (Grupe & Breeveld) 
there was one uncatalogued X-ray source found within the IPN error
box reported by Hurley et al. (GCN circ. 15588
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 ). We followed this
source  with Swift on 2013-December 17. This observation 
suggested a decaying source with a decay slope of about 1. 
Although this is a rather flat decay slope during the normal decay 
phase of a GRB X-ray afterglow, it is not uncommon (e.g. Grupe et 
al. 2013, ApJS, 209, 20). Nevertheless, it is also consistent with
a variability by a factor of 2.5 which is quite common for an AGN
(e.g. Grupe et al. 2010, ApJS, 187, 64). Therefore the data were
not conclusive. We therefore performed two additional observations
which were performed on 2014-January 02 and 03. During the
2014-January 02 observation the source had brightened again to a
count rate in the XRT of (6.4+2.2-1.7)e-3 counts s^-1 and then 
dropped again down to (1.8+1.1-0.8)e-3 counts s^-1 during the
January 03 observation. These observations suggest that the
uncatalogued source in the IPN error box is not the X-ray
afterglow of GRB 131209A. The rapid X-ray variability may suggest
that this is either a Narrow Line Seyfert 1 Galaxy or a blazar if
this is a background AGN. 


This report is an official product of the Swift team.

Dirk Grupe (PSU) and Alice Breeveld (MSSL) report on behalf of the 
Swift team:

We report on Swift observations of the field of the FERMI/LAT-
discovered GRB 131209A (Vianello et al., GCN circ. 15587
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 ) starting
26.5 hours after the FERMI/LAT trigger. Swift  performed three 
observations with and exposure tome of 3 ks each to cover most of 
the IPN error box reported by Hurley et al. (GCN circ. 15588
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 ). 
We found two X-ray sources with in the IPN error box, one 
of which coincides with a radio source, NVSS J090753-333724. The
second source at the position 
 
RA-2000:   09 07 19.2 
Dec-2000: -33 51 20.0

does not have an entry in the NED or Simbad. Its count rate in the
XRT is at a level of (4.7+/-1.9)e-3 counts/s which is equivalent to
a flux in the 0.3-10 keV band of (1.9+/-0.7)e-13 erg/s/cm2.
Swift started observing the tile that covered this source 33 hours
after the Fermi/LAT trigger (Vianello et al., GCN Circ. 15587
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 ). 

Only one of the XRT potential candidate 
sources (source 2) is in the field of view of the UVOT and there 
is no new source found at this position. Preliminary 3-sigma upper 
limits using the UVOT photometric system (Breeveld et al. 2011, 
AIP Conf. Proc. 1358, 373) for the initial summed exposures are:

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

white        33.16          33.37          754         >21.8
v            33.37          33.60          801         >20.1
u            32.94          34.78         1367         >21.1

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.36 in the direction 
of the burst (Schlegel et al. 1998).

A. von Kienlin (MPE) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 13:07:56.97 UT on 09 December 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 131209A (trigger 408287279 / 131209547),
which was also detected by the Fermi/LAT(Vianello et al. 2013, GCN 15587
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 ),
Konus-Wind (Golenetskii et al. 2013, GCN 15589
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 ) and INTEGRAL SPI-ACS. 
The GBM on-ground location is consistent with the error box derived by
the intersection of the IPN annulus with the Fermi-LAT 1 sigma 
error circle (Hurley et al. 2013, GCN 15588
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 ).

The GBM light curve shows a structured pulse
with a duration (T90) of about 14 s (50-300 keV).
The time-averaged spectrum from T0-2.560 s to T0+19.968 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.46 (+0.04/-0.04)  and
the cutoff energy, parameterized as Epeak, is 287 (+12/-11)keV

The event fluence (10-1000 keV) in this time interval is
(1.44 +/- 0.03)E-05 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+11.328 s in the 10-1000 keV band
is 8.0 +/- 0.3  ph/s/cm^2.

A Band function fits the spectrum equally well with Epeak= 267 (+17/-14)
keV, 
alpha = -0.41 (+0.06/-0.05)  and beta = -2.79 (+0.24/-0.61).

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

P. A. Evans (U. Leicester) reports on behalf of the Swift team:

Swift has initiated a series of observations, tiled on the sky, of the
Fermi/LAT GRB 131209A. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00022

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. The probability of finding
serendipitous sources, unrelated to the Fermi/LAT event is high: any X-ray source
considered to be a probable afterglow candidate will be reported via a GCN Circular
after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; and 2009, MNRAS, 397, 1177).

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

S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:

The long-duration GRB 131209A
(Fermi LAT detection: Vianello & Omodei, GCN 15587
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 ;
IPN triangulation: Hurley at al., GCN 15588
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 )
triggered Konus-Wind at T0=47280.491 s UT (13:08:00.491).

The burst light curve shows a broad pulse from ~T0-3 s to ~T0+17 s.
The emission is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB131209_T47280/

As observed by Konus-Wind, the burst
had a fluence of (1.4 � 0.1)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0+7.744 s,
of (3.2 � 0.3)x10-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum (measured from T0 to T0+16.640 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.49 � 0.19,
the high energy photon index beta = -2.68 � 0.46,
the peak energy Ep = 235 � 29 keV,
chi2 = 91.2/97 dof.

The spectrum near the maximum count rate
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.17 � 0.17,
the high energy photon index beta = -2.49 � 0.22,
the peak energy Ep = 246 � 18 keV,
chi2 = 87.2/97 dof.

All the quoted values are preliminary.

K. Hurley and J. Goldsten, on behalf of the MESSENGER NS GRB team,

S. Golenetskii, R. Aptekar, V. Pal'shin, D. Frederiks,
D. Svinkin, and T. Cline on behalf of the Konus-Wind team,

A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C.
Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,

S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, and D. Palmer, on 
behalf of the Swift-BAT team, and

V. Connaughton, M. S. Briggs, C. Meegan, V. Pelassa, and A. Goldstein, 
on behalf of the Fermi GBM team, report:

The long-duration GRB 131209A (Vianello et al., GCN Circ. 15587
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 ) has 
been observed by Fermi (GBM: trigger 408287279), Konus-Wind, INTEGRAL 
(SPI-ACS), Swift (BAT), and MESSENGER (GRNS), so far, at about 47277 s 
UT (13:07:57). The burst was outside the coded field of view of the BAT.

We have triangulated this GRB to a Konus-MESSENGER annulus centered at 
RA(2000)=64.917 deg (04h 19m 40s)  Dec(2000)=+21.195 deg (+21d 11' 41"), 
whose radius is 87.724 +/- 0.105 deg (3 sigma).

This annulus intersects the Fermi-LAT 1 sigma error circle (Vianello et 
al., GCN Circ. 15587
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 ) to form an error box whose area is about 16 times 
smaller than that of the LAT error circle (2.5 sq. deg.), and whose 
corners are:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
   Corners:
    137.365 (09h 09m 28s) -32.668 (-32d 40' 06")
    137.509 (09h 10m 02s) -32.892 (-32d 53' 32")
    136.780 (09h 07m 07s) -34.069 (-34d 04' 09")
    136.475 (09h 05m 54s) -34.100 (-34d 05' 59")
  ---------------------------------------------
The error box area is 559 sq. arcmin, and its maximum dimension is
1.48 deg (the minimum one is 12.6 arcmin).

This box may be improved.

The distance between the annulus center line and the center of Fermi-LAT 
location is 0.5 deg.

A triangulation map is posted at 
http://www.ioffe.ru/LEA/GRBs/GRB131209_T47280/IPN/

The time history and spectrum will be given in forthcoming GCN Circulars.

G.Vianello (Stanford), N.Omodei (Stanford), report on behalf of the
Fermi-LAT team:

At 13:07:56.97on December 9, 2013, Fermi LAT detected a faint high energy
signal from GRB131209A, which was also detected by Fermi-GBM (trigger
408287279/131209547).

The data from the Fermi LAT show a significant increase in the event rate
within 10 degree of the GBM location after the GBM trigger that is
spatially and temporally correlated with the GBM emission. Although the
detection is slightly above the 5 sigma level, there are only 4 photons
likely associated with this GRB in the first 200 s after the trigger. The
localization has therefore a large statistical error. The best LAT
on-ground location is found to be RA, DEC 136.5, -33.2 (J2000) with an
error radius of 0.9 deg (68% containment, statistical error only), this was
20 deg from the LAT boresight at the time of the trigger.

The Fermi LAT point of contact for this burst is Giacomo Vianello (
giacomov@stanford.edu).

The Fermi LAT is a pair conversion telescope designed to cover the energy
band from 20 MeV to greater than 300 GeV. It is the product of an
international collaboration between NASA and DOE in the U.S. and many
scientific institutions across France, Italy, Japan and Sweden.