GRB 130131B

M. H. Siegel (PSU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
J. R. Cummings (NASA/UMBC), S. T. Holland (STScI), J. A. Kennea (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL),
B. Sbarufatti (INAF-OAB/PSU) and B.-B. Zhang (PSU) report on behalf of
the Swift Team:

At 19:10:08 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130131B (trigger=547420).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 173.952, +15.036 which is 
   RA(J2000)  =  11h 35m 48s
   Dec(J2000) = +15d 02' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows two peaks
with a total duration of about 5 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~4 sec after the trigger. 

The XRT began observing the field at 19:11:58.3 UT, 109.5 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 173.95398, 15.03873 which
is equivalent to:
   RA(J2000)  = 11h 35m 48.96s
   Dec(J2000) = +15d 02' 19.4"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 11 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 (2.81 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.8
(+2.32/-2.04) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 113 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 100% of
the XRT 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
XRT 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 M. H. Siegel (siegel AT swift.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.)

A. Klotz (IRAP-CNRS-OMP), D. Macpherson (UWA/ICRAR), D. Coward (UWA),
B. Gendre (IRAP-CNRS-OMP), M. Boer, K. Siellez, H. Dereli ,
O. Bardho (UNS-CNRS-OCA), A. Williams (PO-UWA), R. Martin (PO-UWA)
report:

We imaged the field of GRB 130131B detected by SWIFT
(trigger 547420) with the Zadko robotic telescope (D=100cm)
located at the observatory - Gingin, Australia.

The observations started 70.2s after the GRB trigger
(43.4s after the notice). The elevation of the field decreased from
43 degrees above horizon but gibbous moon was at 23 degrees
away from the GRB position.

The first image is trailed with a duration of 60.0s
(see the description in Klotz et al., 2006, A&A 451, L39).
We do not detect any OT at the XRT position (Siegel et al.
GCNC 14159) with a limiting magnitude of:
t0+70.2s to t0+130.2s : R > 15.6

The second image is 30.0s exposure in tracking mode:
t0+149s to t0+179s : R > 16.5

An image follow-up continued until 1.5h after the
GRB showing no optical transcient at the limiting
magnitude 16.5. The gibbous moon prevents to obtain
deeper limiting magnitudes.

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

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

We imaged the field of GRB 130131B detected by SWIFT
(trigger 547420) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

The observations started 1.2h after the GRB trigger
because the GRB occured when the field of view was
under the local horizon. At the start of the observations,
the elevation of the field increased from 10 degrees
above horizon and gibbous moon was at 25 degrees away
from the GRB position.

We co-added a series of exposures. No optical transcient
was detected at the XRT position (Siegel et al. GCNC 14159)
with a limiting magnitude of:
t0+1.3h - 2.2h : R > 17.1

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

T. Sakamoto (AGU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), A. Lien (GSFC/ORAU), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), G. Sato (ISAS), M. H. Siegel (PSU),
M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-119 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 130131B (trigger #547420)
(Siegel, et al., GCN Circ. 14159
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 ).  The BAT ground-calculated position is
RA, Dec = 173.957, 15.033 deg which is 
   RA(J2000)  =  11h 35m 49.6s 
   Dec(J2000) = +15d 01' 59.3" 
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 51%.
 
The mask-weighted light curve shows a single pulse starting at ~T-1 sec,
peaking at ~T+0.5 sec, and ending at ~T+10 sec.  T90 (15-350 keV) is
4.30 +- 0.26 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.28 to T+4.37 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.15 +- 0.20.  The fluence in the 15-150 keV band is 3.4 +- 0.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.28 sec in the 15-150 keV band
is 1.0 +- 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/547420/BA/

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

Using 2472 s of XRT Photon Counting mode data and 5 UVOT
images for GRB 130131B, 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 = 173.95566, +15.03818 which is equivalent
to:

RA (J2000): 11h 35m 49.36s
Dec (J2000): +15d 02' 17.5"

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.

D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ),
S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto)
and N. Kawai(Tokyo Tech)
report on behalf of the MITSuME collaboration:

We observed the field of GRB 130131B (Siegel et al., GCNC 14159)
with the optical three color (g', Rc and Ic) CCD camera attached
to the MITSuME 50cm telescope of Okayama Astrophysical Observatory.

The observation started on 2013-01-31 19:11:04 UT (~57 sec after the burst).
We did not find any new point source within the enhanced XRT circle
(Goad et al., GCNC 14165) in all the three bands.

Three sigma upper limits of the OT are listed below. We used
SDSS catalog for flux calibration.

T0+[day]   MID-UT   T-EXP[sec]    g'     Rc     Ic
------------------------------------------------------
0.03838    20:05:23    4800.0   >19.8  >19.9  >19.2
------------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]

M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 130131B
114 s after the BAT trigger (Siegel et al., GCN Circ. 14159
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 ).
No optical afterglow consistent with the XRT position
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           114          264          147         >20.9
u_FC               327          577          246         >20.2
white              114         6416          449         >22.0
v                 3871         5506          393         >19.8
b                  583         6325          413         >20.5
u                  327         6120          639         >21.0
w1                4281         5915          393         >20.4
m2                4076         5710          393         >20.6
w2                5101         5301          197         >21.1

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).

J. Gorosabel (IAA/CSIC-UPV/EHU), L. Monteagudo Narvion (IAC), D. Malesani
(DARK/NBI), S. Schulze (PUC, MCSS), report on behalf of a larger
collaboration:

"We observed the GRB 130131B (Siegel et al., GCNC 14159) at the Swift/XRT
location reported in Goad et al. (GCNC 14165) with the 82cm IAC80
telescope at the Observatorio del Teide (Tenerife, Spain). I-band images
with a total exposure time of 13x250s were taken on Feb 1.0135-1.0832 UT
(5.2-6.8 hours post burst). No object brighter than I~21.2 mag (Vega,
calibrated against USNO B1.0 and not corrected for Galactic Extinction)
was detected inside the XRT error circle (Goad et al., GCNC 14165)."

F.Knust, K.Varela, J.Greiner (all MPE Garching) report on behalf of the
GROND team:

We observed the field of GRB 130131B (Swift trigger 547420; Siegel et al.,
GCN 14159
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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 MPG/ESO telescope at La Silla
Observatory (Chile).

Observations started at 04:00 UT on February 1st, 9 hrs after the GRB
trigger, only 27 deg away from the moon. They were performed at an average
seeing of 2.9��� and at an average airmass of 1.6.

We do not detect a source within the Swift-XRT error circle reported by
Goad et al. (GCN 14165
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 ) down to 3-sigma AB limiting magnitudes

g' > 23.4,

r' > 23.7,

i' > 23.4,

z' > 23.3,

J > 21.2,

H > 20.5 and

K > 19.7

The given limits are derived based on calibrating the images against GROND
zeropoints in g'r'i'z' and 2MASS field stars in JHK and are not corrected
for the Galactic foreground extinction corresponding to a reddening of
E_(B-V)= 0.03mag in the direction of the burst (Schlegel et al. 1998).

S. Schulze (PUC, MCSS), Z. Cano (U. Iceland), J. Hjorth, D. Malesani,
J. P. U. Fynbo, D. Xu (DARK/NBI) and N. R. Tanvir (U. Leicester) report 
on behalf of a larger collaboration:

We observed GRB 130131B (Siegel et al., GCN Circ. 14159
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 ) with ESO/VLT
X-shooter. Our observation began at 5:49 UT on 1 February, i.e. 10.7 hours
post burst. We imaged the field with the acquisition camera in the r' and z' bands
for 3x100 and 4x100 seconds, respectively.

We found no optical counterpart within the revised Swift/XRT X-ray error circle
reported in Goad et al. (GCN Circ. 14165
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 ) down to a limiting magnitudes of 
approximately 23.2 and 22.7 mag in r' and z' band, respectively. These 
measurements are given in the AB system and not corrected for foreground 
extinction.

We thank the ESO staff at Paranal, and in particular Maja Vuckovic and 
Stephane Brillant for quickly performing the observations.

M.C. Stroh (PSU), D.N. Burrows (PSU), P.A. Evans (U. Leicester), O.M.
Littlejohns (U. Leicester), J.P. Osborne (U. Leicester), V. Mangano
(INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU),
J.A. Kennea (PSU) and M.H. Siegel report on behalf of the Swift-XRT
team:

We have analysed 3.1 ks of XRT data for GRB 130131B (Siegel  et al. GCN
Circ. 14159
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 ),  from 117 s to 6.4 ks after the  BAT trigger. The data
are entirely in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Goad et al. (GCN. Circ 14165).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.15 (+0.09, -0.08).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.2 (+/-0.3). The
best-fitting absorption column is  4.2 (+1.3, -1.1) x 10^21 cm^-2, in
excess of the Galactic value of 2.8 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 3.9 x 10^-11 (7.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.2 (+1.3, -1.1) x 10^21 cm^-2
Galactic foreground: 2.8 x 10^20 cm^-2
Excess significance: 5.6 sigma
Photon index:	     2.2 (+/-0.3)

If the light curve continues to decay with a power-law decay index of
1.15, the count rate at T+24 hours will be 1.7 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.7 x
10^-14 (1.4 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/00547420.

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

Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB)
J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UCSC),
Eleonora Troja (GSFC), Enrico Ramirez���Ruiz (UCSC), José A. de Diego
(UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM), Carlos
Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey
Moseley (GSFC) report:

We observed the field of GRB 130131B (Siegel et al., GCN 14159
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 ) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astronómico
Nacional on Sierra San Pedro Mártir. Between 2013 February 1.42 and
2013 February 1.54 UTC (14.86 to 17.70 hrs after the BAT trigger), we
obtained 1.96 hrs exposure in the r and i bands and 0.73 hrs exposure in
the Z, Y, J, and H bands.

We detect no source within the XRT error circle (Goad et al., GCN 14165
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 ).
In comparison with SDSS DR8 and 2MASS, we derive the following upper limits
(3-sigma) in the AB magnitude system:

 r' > 23.8
 i' > 23.1
Z > 22.1
Y > 21.7
J  > 21.8
H > 21.4

These magnitudes are not corrected for Galactic extinction in the direction
of the GRB.

We thank the staff of the Observatorio Astronómico Nacional in San
Pedro Mártir.

A. Volnova (SAI MSU/IKI), I. Korobtsev (ISTP), E. Klunko (ISTP),   A. 
Pozanenko (IKI) report on behalf of  larger GRB  follow-up collaboration:

We observed the field of the Swift GRB 130131B (Siegel et al., GCN 
14159
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 ) with AZT-33IK telescope of Sayan observatory (Mondy) on Jan. 31 
between (UT) 19:51:32-20:51:58. We took several images in R-filter of 60 
s exposure. Within enhanced XRT position (Goad et al., GCN 14165
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 ) we do 
not detect any source in a combined image. Photometry is based on nearby 
SDSS DR8 stars.

UT start,    t-t0           filter      Exp.   OT      UL (3 sigma)
             (mid, days)                (s)

19:51:32     0.04973        R          60x60   n/d     22.5

M. Hayashi, T. Yoshii, R. Usui, Y.Aoki, S. Kurita,
Y. Saito, Y. Yatsu, and N. Kawai (Tokyo Tech)
report on behalf of the MITSuME collaboration:

We observed GRB 130131B (Siegel et al., GCNC 14159) with the optical
three color (g, Rc, and Ic) CCD cameras attached to the MITSuME 50 cm
telescope of Akeno Observatory, Yamanashi, Japan.

The observation started on 2013-01-31 19:10:57 UT (~49 sec after
the burst). And we could not find any new point source within the XRT
error circle in all the three bands.
The results of photometry (3 sigma upper limits) are listed below.

The photon flux were calibrated against GSC2.3 catalog.

T0+[sec]   MID-UT   T-EXP[sec]    g'           Rc          Ic
-------------------------------------------------------------------------------------------
     70       19:12:07       60        >16.4   >16.4   >16.2
    178      19:13:55      240       >17.4   >17.6   >17.4
   1183     19:30:40      1320      >18.6   >19.0   >18.9
   2769     19:57:06     4200       >19.1   >19.6   >19.5
-------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst [sec]
T-EXP: Total Exposure time [sec]

D. Calder�n Espinoza, B. Indahl, L. Paredes Alvarez, C. Kaleida (CTIO), and F. J. Virgili (LJMU) report:

"As part of the REU/PIA student program at the Cerro Tololo Inter-American Observatory (CTIO) we observed
GRB 130131B (Siegel et al., GCN 14159
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 ) with the SMARTS 0.9-m telescope beginning 11.6 hrs after the Swift
trigger.  No optical counterpart is detected within the XRT error circle to the following conservative limits:

Midtime of exposure     Exposure time     Filter     Magnitude
--------------------------------------------------------------------------
      12.7 hr               7x450s            R        > 20.7
      12.8 hr               7x450s            V        > 20.3
--------------------------------------------------------------------------

Magnitudes are calibrated using nearby USNOB-1 (R-band) and NOMAD (V-band) stars."

Johan P. U. Fynbo, Dong Xu, Daniele Malesani, Thomas Kruehler 
(DARK/NBI), Dan A. Perley (Caltech), Valerio D'Elia (ASDC, INAF), report 
on behalf of the X-shooter GTO GRB collaboration:

We observed the field of GRB 130131B (Siegel et al., GCN 14159
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 ) using 
the Keck-I telescope equipped with the LRIS instrument. Observations 
were carried out on 2013 February 10 (9.62 days after the burst), 
simultaneously in the g and I bands, for a total exposure time of 750 
and 720 s, respectively.

A source with g = 25.7 (AB) and I = 24.9 (Vega) is detected inside the 
enhanced XRT error circle (which has a radius of 1.8"; Goad et al., GCN 
14165
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 ), at coordinates:

R.A.(J2000) = 11:35:49.31
Dec.(J2000) = +15:02:18.0

We consider this object to be the likely host galaxy of GRB 130131B.

A spectrum of this source was taken on 2013 March 9 with the ESO VLT 
equipped with the X-shooter spectrograph, covering the wavelength range 
3000-20000 AA. The exposure time was 8x900 s. In the NIR arm, we detect 
three emission lines, interpreted as [O III] (4960, 5007) and [O II] 
(3727), all at a common redshift z = 2.539. In the UVB arm, the host 
continuum is detected down to ~4400 AA, which corresponds to the onset 
of the Lyman alpha forest at the proposed redshift.

We acknowledge excellent support from the observing staff at Mauna Kea 
and Paranal, in particular Emanuela Pompei, Claudio Melo, and Thomas 
Rivinius.