GRB 131105A

J. R. Cummings (NASA/UMBC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), A. Y. Lien (NASA/GSFC/ORAU),
P. T. O'Brien (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), T. Sakamoto (AGU) and C. A. Swenson (PSU) report
on behalf of the Swift Team:

At 02:04:44 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 131105A (trigger=576738).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 71.011, -62.981 which is 
   RA(J2000)  =  04h 44m 03s
   Dec(J2000) = -62d 58' 52"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multple peaks
with a total duration of about 120 sec.  The peak count rate
was ~1100 counts/sec (15-350 keV), at ~44 sec after the trigger. 

The XRT began observing the field at 02:09:35.6 UT, 290.9 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 70.96452, -62.99394 which
is equivalent to:
   RA(J2000)  = 04h 43m 51.48s
   Dec(J2000) = -62d 59' 38.2"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 89 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 (2.91 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.2
(+2.11/-1.84) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 294 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 5% of
the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
BAT 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
0.03. 

Burst Advocate for this burst is J. R. Cummings (jayc AT milkyway.gsfc.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.)

D. Xu (DARK/NBI), D. Malesani (DARK/NBI), N. R. Tanvir (U. Leicester),
T. Kruehler (ESO), report on behalf of a larger collaboration:

We observed the field of GRB 131105A (Cummings et al., GCN 15446
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 ) with
the acquisition camera of the X-shooter spectrograph at the VLT. The
observation was taken around 03:24 UT on November 5, that is 1.3 hr
after the GRB. Inside the current XRT error circle (2.0" radius; see
http://www.swift.ac.uk/xrt_positions/), we detect a single source at
coordinates (J2000):

RA = 04:43:52.27
Dec = -62:59:43.7

with an uncertainty of <0.5". Its magnitude is R = 22.4 +- 0.1,
compared to three nearby bright USNO stars.

At the moment we cannot conclude whether this source is variable or
associated to the GRB, but we propose it as a candidate counterpart.

We acknowledge excellent support from the ESO staff in Paranal, in
particular Dimitri Gadotti and Roger Wesson.

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

Using 704 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 131105A, 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 = 70.96782, -62.99505 which is equivalent
to:

RA (J2000): 04h 43m 52.28s
Dec (J2000): -62d 59' 42.2"

with an uncertainty of 1.8 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.

Klotz A., Turpin D. (IRAP-CNRS-OMP), Gendre B.,
Boer M., Siellez K., Dereli H., Bardho O. (UNS-CNRS-OCA),
Atteia J.L. (IRAP-CNRS-OMP) report:

We imaged the field of GRB 131105A detected by SWIFT
(trigger 576738) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 231s after the GRB trigger
(14s after the notice). The elevation of the field increased from
37 degrees above horizon and weather conditions
were good.

A first series of 30.0s exposure images was acquired in tracking mode.
We do not detect the afterglow candidate of Xu et al. (GCNC 15447)
with limiting magnitudes of:
t0+231s to t0+261s : Rlim = 18.3
t0+311s to t0+341s : Rlim = 18.3
t0+351s to t0+381s : Rlim = 18.3
t0+391s to t0+421s : Rlim = 18.3
t0+432s to t0+462s : Rlim = 18.3

Next series were co added by drizzling to increase the detectivity.
t0+ 472s to t0+1131s : Rlim = 19.0
t0+1141s to t0+1658s : Rlim = 19.0

Magnitudes were estimated with the nearby NOMAD1 stars
and are not corrected for galactic dust extinction.

This message may be cited.

D. Xu, D. Malesani (DARK/NBI), N. Tanvir (U. Leicester), T. Kruehler (ESO),
J. Fynbo (DARK/NBI) report on behalf of the X-shooter GRB
collaboration:

We have obtained spectroscopic observations of the afterglow of GRB 131105A
(Cummings et al., GCN 15446
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 ; Xu et al., GCN 15447
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 ), beginning at 03:46 UT,
approximately 102 minutes post-trigger.  We used the ESO VLT equipped
with the X-shooter spectrograph, covering the wavelength range 3000-20000 AA.

The exposure time was 8x600 s. In the NIR arm, we detect two emission lines,
interpreted as [O III] (5007) and H-alpha at a common redshift z = 1.686.
In the spectrum we also detect absorption lines at the same redshift, albeit at 
low signal-to-noise ratio. Furthermore, we measure significant fading of the source 
between two sets of acquisition images, confirming that we are seeing 
afterglow and host light.  Hence, we consider z = 1.686 the likely redshift of 
GRB 131105A. The afterglow appears to be red presumably due to dust extinction.

We acknowledge excellent support from the observing staff at Paranal, in
particular Dimitri Gadotti, Roger Wesson, and Claudia Reyes.

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 131105A
(Swift-BAT trigger 576738: Cummings et al., GCN 15446
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 )
triggered Konus-Wind at T0=7527.233 s UT (02:05:27.233).

The burst light curve shows multiple peaks in the time
interval from ~T0-35 s till ~T0+90 s.
The emission is seen up to ~3 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB131105_T07527/

As observed by Konus-Wind, the burst
had a fluence of (2.3 � 0.2)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0+1.600 s,
of (2.0 � 0.2)x10-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum (measured from T0 to T0+90.368 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 = -0.88 � 0.38,
the high energy photon index beta = -2.33 � 0.33,
the peak energy Ep = 156 � 38 keV,
chi2 = 97/96 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 = -1.04 � 0.27,
the high energy photon index beta = -2.64 � 0.76,
the peak energy Ep = 174 � 41 keV,
chi2 = 87.9/97 dof.

Assuming the redshift z=1.686 (Xu, et al., GCN 15450
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 )
and a standard cosmology model with H_0 = 70 km/s/Mpc,
Omega_M = 0.27, and Omega_Lambda = 0.73,
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is (1.7 � 0.1)x10^53 erg,
the peak luminosity L_iso is (4.0 � 0.4)x10^52 erg/s,
and the rest-frame peak energy Ep,i = (420 � 100) keV

All the quoted values are preliminary.

M. De Pasquale (UCL-MSSL) and J. R. Cummings (NASA/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 131105A
295 s after the BAT trigger (Cummings et al., GCN Circ. 15446
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 ).
No optical afterglow consistent with the optical position
(Xu et al. GCN Circ. 15447
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 ) is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

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

white_FC           295          444          147         >21.5
white              295         1544          353         >22.0
v                  774         1594           97         >19.3
b                 1152         1520           58         >19.9
u                  848         1495           78         >19.8
w1                 823         1471           78         >19.4
m2                 798         1619           39         >18.4
w2                 750         1570           78         >19.5

The magnitudes in the table 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).

G. Fitzpatrick (UCD) and P. Jenke (UAH) report on behalf of the Fermi GBM
Team:

At 02:04:53.49 UT on 05 November 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 131105A (trigger 405309896/131105087), which
was also detected by Swift (Cummings et al., GCN 15446
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 ) and Konus-Wind
(Golenetskii et al, GCN 15452
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 ).  The GBM on-ground location is consistent
with the Swift/XRT position (Osborne et al., GCN 15448
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 ). The angle from
the Fermi LAT boresight is 37 degrees.

The GBM light curve consists of a multiple-peak structure with a duration
(T90) of about 112 s (50-300 keV). The time-averaged spectrum from
T0-3 s to T0+121 s is adequately fit by a Band function with Epeak =
203.9 +/- 31.1 keV, alpha = -1.2 +/- 0.1, and beta = -1.8 +/- 0.1.

The event fluence (10-1000 keV) in this time interval is
(2.9 +/- 0.1)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+108 s in the 10-1000 keV band is 8.4 +/- 0.3 ph/s/cm^2.

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

J.A. Kennea (PSU), V. Mangano (PSU), K.L. Page (U. Leicester), C.
Pagani (U. Leicester), A.P. Beardmore (U. Leicester), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), A. Maselli  (INAF-IASFPA), M.C. Stroh
(PSU) and J.R. Cummings report on behalf of the Swift-XRT team:

We have analysed 8.3 ks of XRT data for GRB 131105A (Cummings  et al.
GCN Circ. 15446
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 ),  from 276 s to 36.2 ks after the  BAT trigger. The
data comprise 7 s in Windowed Timing (WT) mode (taken while Swift was
slewing), with the remainder in Photon Counting (PC) mode. The enhanced
XRT position for this burst was given by Osborne et al. (GCN. Circ
15448).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=8.0 (+0.0, -1.5). At T+353 s  the decay
flattens to an alpha of 0.62 (+/-0.04) before breaking again at T+21.4
ks to a final decay with index alpha=2.3 (+0.9, -0.8).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.22 (+0.16, -0.15). The
best-fitting absorption column is  2.2 (+0.5, -0.4) x 10^21 cm^-2, in
excess of the Galactic value of 2.9 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 3.5 x 10^-11 (5.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.2 (+0.5, -0.4) x 10^21 cm^-2
Galactic foreground: 2.9 x 10^20 cm^-2
Excess significance: 7.5 sigma
Photon index:	     2.22 (+0.16, -0.15)

If the light curve continues to decay with a power-law decay index of
2.3, the count rate at T+24 hours will be 3.4 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-13 (2.0 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/00576738.

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

W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (NASA/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU), J. Tueller (GSFC),
T. N. Ukwatta (MSU) (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 131105A (trigger #576738)
(Cummings, et al., GCN Circ. 15446
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 ).  The BAT ground-calculated position is
RA, Dec = 70.973, -63.005 deg which is
  RA(J2000)  =  04h 43m 53.5s
  Dec(J2000) = -63d 00' 17.7"
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 7%.

The mask-weighted light curve shows a multi-peak structure starts
at ~T+0 sec and ends at ~T+126 sec. The light curve consists of
~ 5 obvious peaks. T90 (15-350 keV) is 112.3 +- 4.1 sec (estimated
error including systematics).

The time-averaged spectrum from T+6.8 to T+125.6 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.45 +- 0.11.  The fluence in the 15-150 keV band is 7.1 +- 0.5 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+116.64 sec in the 15-150 keV band
is 3.5 +- 0.6 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/576738/BA/