GRB 121226A

H. A. Krimm (CRESST/GSFC/USRA), J. R. Cummings (NASA/UMBC),
V. D'Elia (ASDC), S. T. Holland (STScI), K. L. Page (U Leicester),
T. Sakamoto (AGU), M. H. Siegel (PSU) and
R. L. C. Starling (U Leicester) report on behalf of the Swift Team:

At 19:09:43 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 121226A (trigger=544027).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 168.658, -30.414 which is 
   RA(J2000) = 11h 14m 38s
   Dec(J2000) = -30d 24' 51"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak
with a duration of about 2 sec.  The peak count rate was ~2700 counts/sec
(15-350 keV), at ~0 sec after the trigger.  Although the duration of this
burst is moderately short, it has a fairly soft spectrum.  Therefore we must
wait for further data to determine whether to classify GRB 121226A as
a short or long burst. 

The XRT began observing the field at 19:11:24.4 UT, 100.6 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 168.6424, -30.4066
which is equivalent to:
   RA(J2000)  = 11h 14m 34.17s
   Dec(J2000) = -30d 24' 23.8"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 55 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.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (6.11 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 6.4
(+3.77/-3.06) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 104 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
0.05. 

Burst Advocate for this burst is H. A. Krimm (krimm 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.)

S. Guziy (Mykolaiv Nat. Univ.), O. Lara-Gil, R. Cunniffe, J. Gorosabel, M.
Jelinek (IAA-CSIC), P. Kubanek (IP AS CR), Y. Fan, X. Zhao, J. Bai, C.
Wang, Y. Xin (Yunnan Nacional Astronomical Observatory), Ch. Cui (Beijing
National Astronomical Observatory) and A. J. Castro-Tirado (IAA-CSIC), on
behalf of a larger collaboration, report:

�Following the detection of GRB 121226A by Swift (Krimm et al. GCNC
14105), the 0.6m BOOTES-4/MET robotic telescope at the Lijiang
Astronomical Observatory (China) responded automatically to the trigger
alert at 19:10:21 UT, 9 s after the GCN reception (i.e. 36 s after the
onset of the event). After initial 0.5 s exposures, the first 19
unfiltered images (5 s exposure time each) starting 6 m 24 s postburst,
show no optical afterglow at the refined XRT position down to 19th mag
limiting magnitude (for the combined image). Observations are ongoing.�

[GCN OPS NOTE(26dec12): Per author's request, "Lara" was changed to "Lara-Gil".]

A. Klotz (IRAP-CNRS-OMP), D. Macpherson (UWA/ICRAR), D. Coward (UWA),
B. Gendre (ASDC/INAF-OAR), M. Boer (UNS-CNRS-OCA),
A. Williams (PO-UWA), R. Martin (PO-UWA) report:

We imaged the field of GRB 121226A detected by SWIFT
(trigger 544027) with the Zadko robotic telescope (D=100cm)
located at the observatory - Gingin, Australia.

The observations started 62.8s after the GRB trigger
(38.6s after the notice). The elevation of the field
increased from 64 degrees above horizon and weather
conditions were good.

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 in the XRT error box with a
limiting magnitude of:
t0+62.8s to t0+122.8s : Rlim 17.5

The second image is 30.0s exposure in tracking mode:
t0+138s to t0+168s : Rlim 18.7

We co-added a series of exposures:
t0+138s to t0+335s : Rlim 19.4

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.

This message may be cited.

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 121226A (Krimm et al., GCNC 14105)
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 2012-12-26 19:11:59 UT (~2.3 min after the burst).
We did not find any new point source within the XRT circle
(Krimm et al., GCNC 14105) 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
------------------------------------------------------
0.04333    20:12:06    6360.0   >20.2  >20.2  >19.5
------------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]

V.K. Bhatt, S.B. Pandey and Brajesh Kumar ((ARIES Nainital, India, on
behalf 
of larger Indian GRB collaboration)

We observed GRB 121226A (Swift trigger 518731, Krimm et al. 2012, GCNC
14105) field with the 1.04m telescope at ARIES, Nainital starting at
2012-12-26 
21:09:09 (UT). Several frames in R_c and I_c pass-bands, with an exposure
time 
of 300 sec each, were obtained.

Within the XRT error-circle, we do not detect any optical source down to 
following limiting magnitudes.

Dec 26.9118 UT, 300sx4, I_c ~ 18.8 mag
Dec 26.9292 UT, 300sx6, R_c ~ 19.5 mag

The nearby USNO stars have been used for calibrate.

This massage may be cited.

D. Xu (DARK/NBI), O. Smirnova, T. Purismo (NOT), J. P. U. Fynbo
(DARK/NBI), P. Jakobsson (U. Iceland) report on behalf of a larger
collaboration:

We observed the field of GRB 121226A (Krimm et al., GCN 14105
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 ) using
the 2.5m Nordic Optical Telescope (NOT) equipped with ALFOSC. We
obtained 3x600s R-band and 3x360s z-band images with their median time
of 06:14:49 UT on 2012-12-27 (i.e., 11.085 hr after the BAT trigger)
and 06:53:54 UT (i.e., 11.736 hr post-trigger), respectively.

No optical source was detected within the XRT error circle in both
R-and z-bands, down to a 3sigma limit of R~23.0 mag ,calibrated with
the USNO B1 catalogue.

W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
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-61 to T+111 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 121226A (trigger #544027)
(Krimm, et al., GCN Circ. 14105
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 ).  The BAT ground-calculated position is
RA, Dec = 168.620, -30.413 deg which is
    RA(J2000)  =  11h 14m 28.7s
    Dec(J2000) = -30d 24' 47.0"
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 35%.  The mask-weighted light curve shows a single peak
with duration approximately 1.5 seconds, with no sign of extended emission.
T90 (15-350 keV) is 1.00 +- 0.20 sec (estimated error including systematics).

The time-averaged spectrum from T-0.36 to T+0.80 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.51 +- 0.29.  The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.21 sec in the 15-150 keV band
is 1.6 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

When plotting GRB 121226A on the T90-hardness diagram (see web link below),
we see that it falls within the short-hard region of phase space, with T90 = 1.0 
sec and Hardness ratio (energy fluence ratio 50-100 keV/25-50 keV) = 1.4.
Therefore we now suggest that GRB 121226A should be classified as a short-hard 
burst.  We do not have a lag analysis available at this time.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/544027/BA/

O.M. Littlejohns (U. Leicester), B. Sbarufatti (INAF-OAB/PSU), G.
Stratta (ASDC), P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU), J.A. Kennea
(PSU), M.C. Stroh (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester) and H.A. Krimm report on behalf of the Swift-XRT team:

We have analysed 10 ks of XRT data for GRB 121226A (Krimm  et al. GCN
Circ. 14105
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 ),  from 109 s to 35.4 ks after the	BAT trigger. The data
are entirely in Photon Counting (PC) mode. The best available XRT
position  (using the promptly downlinked event data, the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue) is
RA, Dec = 168.6423, -30.4064 which is equivalent to:

RA (J2000): 11 14 34.14
Dec(J2000): -30 24 23.1

with an uncertainty of 2.1 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.98 (+/-0.06).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.4 (+/-0.4). The
best-fitting absorption column is  8.2 (+2.5, -2.1) x 10^21 cm^-2, in
excess of the Galactic value of 6.1 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 4.4 x 10^-11 (1.2 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.2 (+2.5, -2.1) x 10^21 cm^-2
Galactic foreground: 6.1 x 10^20 cm^-2
Excess significance: 6.0 sigma
Photon index:	     2.4 (+/-0.4)

If the light curve continues to decay with a power-law decay index of
0.98, the count rate at T+24 hours will be 1.5 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.7 x
10^-14 (1.9 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/00544027.

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

A. A. Breeveld (MSSL-UCL) and H. A. Krimm (CRESST/GSFC/USRA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 121226A 
104 s after the BAT trigger (Krimm et al., GCN Circ. 14105
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 ). No optical 
afterglow consistent with the XRT position (Littlejohns et al. GCN Circ. 
14112
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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           104          254          147         >20.6
u_FC               317          566          246         >19.6
white              104        18160         1317         >21.6
v                  646        10716         1121         >20.4
b                  572        17397         1317         >21.3
u                  317        16485         1544         >20.9
w1                 696        12390         1163         >20.7
m2                 671        11621         1298         >21.0
w2                 622         6620          351         >20.2

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.055 in the direction of 
the burst (Schlegel et al. 1998).

A.J. Castro-Tirado, M. Jelinek, R. Sánchez-Ramírez, J.C. Tello (IAA-CSIC),
J.M. González-Pérez (GTC/IAC), S. Guziy (Mykolaiv Nat. Univ.), D.
Pérez-Ramírez (Univ. de Jaén), P. Ferrero (IAC), J.M. Castro Cerón (ESAC),
A. Fernández-Soto (IFCA-UNICAN) and J. Gorosabel (IAA-CSIC), report:

We have obtained deep r'i'z' images with the 10.4m GTC telescope at
Observatorio del Roque de los Muchachos for GRB 121226A (Krimm et al. GCNC
14105; Baumgartner et al. GCNC 14111) starting on Dec 27.230--27.261 UT
(i.e., 10.3--11.1 hr post burst). A faint object is detected at
RA(J2000)=11:14:34.14, DEC(J2000)=-30:24:22.9 (0.7" error in each
coordinate), consistent with the position of the X-ray afterglow
(Littlejohns et al. GCNC 14112). The object shows a magnitude around
r'~25. At this stage we cannot conclude whether this is the GRB 121226A
optical afterglow or the underlying host galaxy.

W. Fong, B. A. Zauderer and E. Berger (Harvard) report:

"We observed the position of the short-duration GRB 121226A (Krimm et al.,
GCN 14105
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 ; Baumgartner et al. GCN 14111
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 ) with the Karl G. Jansky Very Large
Array (VLA) beginning on 2012 December 28.54 UT (1.75 days post-burst) at a
mean frequency of 5.8 GHz. In 35-min on source, we detect a faint, 3-sigma
radio source at:

RA (J2000) = 11:14:34.12
DEC (J2000) = -30:24:22.89
with an uncertainty of ~0.2" in each coordinate.

This position is coincident with the XRT and optical positions (Littlejohns
et al., GCN 14112
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 ; Castro-Tirado et al., GCN 14114
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 ). Further observations
are planned."

D. Malesani (DARK/NBI), P. D'Avanzo (INAF/OABr), A. Melandri 
(INAF/OABr), S. Covino (INAF/OABr), A. Fiorenzano (INAF/TNG), L. Di 
Fabrizio (INAF/TNG), and G. Andreuzzi (INAF/TNG) report on behalf of the 
CIBO collaboration:

We observed the optical counterpart (Castro-Tirado et al., GCN 14114
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 ) of 
the short GRB 121226A (Krimm et al., GCN 14105
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 ) with the TNG telescope 
located in the Canary Islands. A total two hour exposure in the SDSS r 
filter was acquired, with mean time 2013 Jan 11.227 UT (15.4 days after 
the GRB). Sky conditions were good and the seeing was 1.1", despite the 
large airmass (around 2).

Consistent with the position reported by Castro-Tirado et al. (GCN 
14114
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 ) and Fong et al. (GCN 14126
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 ), we clearly detect an object with 
r(AB) = 24.68 +- 0.15. Photometric calibration was carried out by 
observing a standard field at similar airmass (for reference, we find r 
= 19.35 for the USNO star at RA = 11:14:33.12, Dec = -30:23:51.2). 
Coupled with the measurement by Castro-Tirado et al. (GCN 14114
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 ), 
obtained ~0.5 days after the GRB, our observation suggests that the 
object is the host galaxy of the GRB, with negligible afterglow 
contribution at both epochs. We note that the radio detection (Fong et 
al., GCN 14126
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 ) makes the association with the GRB secure.

The coordinates of the object as measured in our image are (J2000, 
astrometry calibrated against USNO-B1):

RA = 11:14:34.125
Dec = -30:24:22.88

with an estimated uncertainty of 0.3". We note the presence of two 
further, nearby objects, roughly 2" S and 4" NE of the optical/radio 
counterpart. A finding chart is available at the following URL:

http://www.astro.ku.dk/~malesani/GRB/121226A/GRB121226A_finder_TNG.jpg