GRB 151229A

Y.Saito, T.Fujiwara, T. Yoshii, Y. Tano, Y. Tachibana,
Y.Ono, S.Harita, Y.Muraki, Y. Yatsu, and N. Kawai (Tokyo Tech)
report on behalf of the MITSuME collaboration:

We searched for the optical counterpart of GRB 151229A (D. Kocevski et al., GCN Circular #18745
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 ) 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 2015-12-29 08:56:00 UT (~2.1 h after the burst).
We did not find any new point source within XRT circle in all three bands.

We obtained following limits for the magnitudes.

T0+[sec]    MID-UT      T-EXP[sec]           g'            Rc                Ic
-------------------------------------------------------------------------------------------------
7533       09:20:52            2700           > 19.5        > 19.4        > 18.6
-------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
We used GSC2.3 catalog for flux calibration.

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 MITSuME and OISTER collaboration:

We observed the field of GRB 151229A (Kocevski et al., GCNC 18745)
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 2015-12-29 09:07:26 UT (~2.3h after the burst).
We did not find any new point source within the enhanced XRT circle
(Osborne et al., GCNC 18750) in all the three bands.

Three sigma upper limits of the OT are listed below.
We used GSC2.3 catalog for flux calibration.

#T0+[day]  MID-UT    T-EXP[sec]   g'    Rc     Ic
-----------------------------------------------------
0.11774    09:39:59    2940.0   >18.7  >18.7  >18.2
-----------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]

J. Norris (BSU), S. D. Barthelmy (GSFC), A. Y. Lien (GSFC/UMBC) for the Swift-BAT Team:

We report the spectral lag analysis for GRB 151229A (Kocevski, et al.,
GCN Circ. 18745
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 , & Lien 18751) based on the BAT data.  Using 8-ms binned light curve,
the spectral lag for the 25-50 keV to 100-300 keV bands is -47.6 +/-31 ms and
+12 +/-24 for the 15-25 to 50-100 bands.  Although the errors are large,
the values are marginally consistent with zero, therefore we believe
this burst belongs to a short burst category, although we can not rule out
the long burst possibility.  There is no evidence for extended emission.

K.L. Page (U. Leicester), A. Maselli  (INAF-IASFPA), A. Melandri
(INAF-OAB), P. D'Avanzo (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), D.N.
Burrows (PSU), T.G.R. Roegiers (PSU), C. Pagani (U. Leicester), A.P.
Beardmore (U. Leicester) and D. Kocevski report on behalf of the
Swift-XRT team:

We have analysed 7.4 ks of XRT data for GRB 151229A (Kocevski et al.
GCN Circ. 18745
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 ), from 73 s to 32.8 ks after the  BAT trigger. The data
comprise 67 s in Windowed Timing (WT) mode (the first 8 s were 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. 18750
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.832 (+/-0.021).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.04 (+0.15, -0.14). The
best-fitting absorption column is  7.2 (+1.1, -1.0) x 10^21 cm^-2, in
excess of the Galactic value of 2.7 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.3 x 10^-11 (7.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.2 (+1.1, -1.0) x 10^21 cm^-2
Galactic foreground: 2.7 x 10^20 cm^-2
Excess significance: 11.4 sigma
Photon index:	     2.04 (+0.15, -0.14)

If the light curve continues to decay with a power-law decay index of
0.832, the count rate at T+24 hours will be 0.023 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.8 x
10^-13 (1.8 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00668689.

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

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

"At 06:50:27.95 UT on 29 December 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 151229A (trigger 473064631 / 151229285 ),
which was also detected by the Swift/BAT (Kocevski et al. 2015, GCN 18745
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 )
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 53.4 degrees.

The GBM light curve consists of a single peak
with a duration (T90) of about 3.5 s (50-300 keV).
The time-averaged spectrum from T0-0.256: s to T0+1.280 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.19 (+0.10/-0.09) and
the cutoff energy, parameterized as Epeak, is 97.1 (+10.3/-8.3) keV

The event fluence (10-1000 keV) in this time interval is
(9.4 +/- 0.5)E-07 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0-0.128 s in the 10-1000 keV band
is 11.0 +/- 0.3 ph/s/cm^2.

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

M. De Pasquale (UCL-MSSL) and D. Kocevski (NASA/GSFC/ORAU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 151229A
90 s after the BAT trigger (Kocevski et al., GCN Circ. 18745
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 ).
No optical afterglow consistent with the XRT position (Osborne et al.
GCN Circ. 18750
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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            90          240          147         >20.0
u_FC               302          552          246         >19.3
white               90         5493          378         >20.5
v                  632         5904          413         >18.8
b                  558         5288          236         >19.5
u                  302         6513          653         >19.8
w1                 681         6314          413         >19.7
m2                4474         6108          393         >19.9
w2                4064         5699          393         >20.0

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).

-- 

Dr. Massimiliano De Pasquale
Research associate - Swift UVOT scientist
Mullard Space Science Laboratory, University College London

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), D. Kocevski (NASA/GSFC/ORAU),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
 
Using the data set from T-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 151229A (trigger #668689)
(Kocevski, et al., GCN Circ. 18745
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 ).  The BAT ground-calculated position is
RA, Dec = 329.363, -20.732 deg, which is 
   RA(J2000)  =  21h 57m 27.1s 
   Dec(J2000) = -20d 43' 56.2" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 51%.
 
The mask-weighted light curve shows  single peak starting at ~T-0.1 sec,
peaking at ~T+0.1 sec, and ending at ~T+1.7 sec.  T90 (15-350 keV) is
1.78 +- 0.44 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.11 to T+2.34 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.84 +- 0.10.  The fluence in the 15-150 keV band is 5.9 +- 0.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.11 sec in the 15-150 keV band
is 7.2 +- 0.4 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/668689/BA/

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

Using 609 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 151229A, 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 = 329.36981, -20.73203 which is equivalent
to:

RA (J2000): 21h 57m 28.76s
Dec (J2000): -20d 43' 55.3"

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. Kocevski (NASA/GSFC/ORAU), A. Y. Lien (GSFC/UMBC),
K. L. Page (U Leicester) and T. N. Ukwatta (LANL) report on behalf of
the Swift Team:

At 06:50:27 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 151229A (trigger=668689).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 329.380, -20.729 which is 
   RA(J2000) = 21h 57m 31s
   Dec(J2000) = -20d 43' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 1.5 sec.  The peak count rate
was ~7000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 06:51:54.9 UT, 86.9 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 329.3703,
-20.7325 which is equivalent to:
   RA(J2000)  = 21h 57m 28.87s
   Dec(J2000) = -20d 43' 56.9"
with an uncertainty of 2.0 arcseconds (radius, 90% containment). This
location is 35 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 (2.71 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 7.6
(+2.59/-2.28) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 90 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 D. Kocevski (dankocevski AT gmail.com). 
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.)