GRB 141221A

E. Sonbas (NASA/GSFC/Adiyaman Univ.), J. R. Cummings (NASA/UMBC),
V. D'Elia (ASDC), L. Izzo (URoma/ICRA), A. Y. Lien (GSFC/UMBC),
K. L. Page (U Leicester), B. Sbarufatti (INAF-OAB/PSU) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 08:07:10 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 141221A (trigger=622006).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 198.269, +8.210 which is 
   RA(J2000) = 13h 13m 05s
   Dec(J2000) = +08d 12' 36"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 20 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 08:08:30.3 UT, 79.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 198.28642, 8.20536 which is equivalent
to:
   RA(J2000)  = 13h 13m 08.74s
   Dec(J2000) = +08d 12' 19.3"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 64 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 (2.27 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.5
(+2.80/-2.41) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 83 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	13:13:08.80 = 198.28666
  DEC(J2000) = +08:12:18.8  =	8.20523
with a 90%-confidence error radius of about 0.61 arc sec. This position is 4.2
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.18 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.03. 

Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.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.)

S. Covino (INAF/OAB) on behalf of the REM team:

We observed the field of the GRB141221A (Sonbas et al., GCN 17206
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 ) simultaneously in the optical and near infrared with the 60-cm robotic telescope REM at La Silla Observatory (Chile). The observations started about 1 min after the GRB, when the field was at an airmass of about 2.5 and continued for about one hour till the local twilight.

A bright source at a position consistent with the UVOT candidate afterglow is detected in all filter (grizJHK). 
At about 1.5 min after the GRB the afterglow was H~13.1 and faded down to H~15.8 more than 30 min later, with a decay index alpha~0.8.

C. Guidorzi, S. Dichiara (U. Ferrara), D. Kopac, A. Gomboc (U. Ljubljana)
on behalf of a larger collaboration report:

The 1-m LCOGT McDonald telescope began observing Swift GRB 141221A
(Sonbas et al. GCN 17206
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 ) on Dec 21 at 10:26:35 UT, corresponding
to 2.3 hours after the burst trigger, with SDSS r' and i' filters.
We detect the optical afterglow (Sonbas et al. GCN 17206
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 ; Covino
GCN 17208
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 ) with i'=20.1 +- 0.3 mag at a mid time of 2.61 hours
post burst (total exposure of 600 s).

A. Trotter, J. Haislip, D. Reichart, A. Aji, R. Beauchemin, T. Berger, 
A. Dow, A. Foster, N. Frank, M. Hinckle, K. Ivarsen, A. LaCluyze, M. 
Maples, J. Moore, M. Nysewander, C. Salemi, L. Zbinden, and J. A. Crain 
report:

Skynet observed the Swift BAT/XRT localization of GRB 141221A (Sonbas et 
al., GCN 17206
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 , Swift trigger=622006) with two 14" telescopes of the 
PROMPT array at Cerro Tololo, Chile. Starting at 2014-12-21 08:07:56 UT 
and continuing until 08:35 UT (t=45s-28m post-trigger), Skynet took a 
total of 44 exposures ranging from 5s to 160s in the V and I bands. We 
clearly detect the optical afterglow (Covino, GCN 17208
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 , Guidorzi et 
al., GCN 17209
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 ) with a rising light curve prior to t=2min, where it 
peaks at I=14.8.

A preliminary light curve is at:

http://www.skynet.unc.edu/grb/grb141221a.png

Magnitudes are in the Vega System, calibrated to 3 APASS stars in the 
field.  Magnitudes have not been corrected for line-of-sight Milky Way 
dust extinction, with expected E(B-V)=0.024 (Schlafly & Finkbeiner 2011).

Skynet observations will continue.

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

Using 4183 s of XRT Photon Counting mode data and 6 UVOT
images for GRB 141221A, 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 = 198.28686, +8.20510 which is equivalent
to:

RA (J2000): 13h 13m 8.85s
Dec (J2000): +08d 12' 18.4"

with an uncertainty of 1.6 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.

GRB 141221A: GROND Detection of the Optical/NIR Afterglow

T. Schweyer, P. Wiseman, P. Schady and J. Greiner (all MPE Garching),
report on behalf of the GROND team:

We observed the field of GRB 141221A (Swift trigger 622006; Sonbas et al.,
GCN #17206
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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 telescope at ESO La Silla
Observatory (Chile).

Observations started at 08:09:33 UT on 21/12/2014, 142 seconds after the
GRB trigger, and continued in all bands for ~18 minutes of exposures until
the beginning of twilight, and in NIR for another 4 minute exposure. They
were performed at an average seeing of 1.7" and at an average airmass of
2.1.

We find a single point source, consistent with the enhanced SWIFT-XRT
position of Beardmore et al. (GCN #17211
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 ) and that reported by e.g. Covino
(GCN 17208
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 ), Trotter et al. (GCN #17210
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 ),  at:

RA (J2000.0) = 13h 13m 08.80s

DEC (J2000.0) = + 08d 12' 18.9"

with an uncertainty of 0.2" in both co-ordinates.

There were problems with telescope pointing throughout the observations,
Based on our first short exposures in grizJHK, we estimate preliminary
magnitudes (all in AB system) of

g' = 17.1 +/- 0.1 mag,
r' = 16.6 +/- 0.1 mag,
i' = 16.4 +/- 0.1 mag,
z' = 16.1 +/- 0.1 mag,
J = 15.7 +/- 0.1 mag,
H = 15.4 +/- 0.1 mag, and
K = 15.3 +/- 0.1 mag.

The best-fit SED has a spectral index beta = 1.0 +/- 0.1.

Given magnitudes are not corrected for the expected Galactic foreground
extinction corresponding to a reddening of E_(B-V)=0.024 mag in the
direction of the burst (Schlegel et al. 1998).

T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), E. Sonbas (NASA/GSFC/Adiyaman Univ.), M. Stamatikos (OSU),
J. Tueller (GSFC)
(i.e. the Swift-BAT team):
 
Using the data set from T-61 to T+242 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 141221A (trigger #622006)
(Sonbas, et al., GCN Circ. 17206
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 ).  The BAT ground-calculated position is
RA, Dec = 198.283, 8.197 deg, which is 
   RA(J2000)  =  13h 13m 07.9s 
   Dec(J2000) = +08d 11' 49.8" 
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 78%.
 
The mask-weighted light curve shows some low-level precursor emission
starting at ~T-23 sec with the first peak starting at ~T-3 sec, peaking
at ~T+1 sec, and the second peak peaking at ~T+14 sec, and ending at T+35 sec.
T90 (15-350 keV) is 36.9 +- 4.0 sec (estimated error including systematics).
 
The time-averaged spectrum from T-24.11 to T+20.33 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.74 +- 0.08.  The fluence in the 15-150 keV band is 2.1 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.10 sec in the 15-150 keV band
is 3.1 +- 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/622006/BA/

A. Maselli  (INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti
(INAF-OAB/PSU), D.N. Burrows (PSU), J.A. Kennea (PSU), V. Mangano
(PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), C. Pagani
(U. Leicester) and E. Sonbas report on behalf of the Swift-XRT team:

We have analysed 8.9 ks of XRT data for GRB 141221A (Sonbas  et al. GCN
Circ. 17206
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 ),  from 64 s to 34.9 ks after the  BAT trigger. The data
comprise 48 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 Beardmore
et al. (GCN Circ. 17211
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 ).

The late-time light curve (from T0+3.9 ks) can be modelled with  a
power-law decay with a decay index of alpha=1.26 (+0.17, -0.16).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.26 (+0.21, -0.20). The
best-fitting absorption column is  3.1 (+0.8, -0.7) x 10^21 cm^-2, in
excess of the Galactic value of 2.3 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 3.3 x 10^-11 (5.6 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.1 (+0.8, -0.7) x 10^21 cm^-2
Galactic foreground: 2.3 x 10^20 cm^-2
Excess significance: 6.7 sigma
Photon index:	     2.26 (+0.21, -0.20)

If the light curve continues to decay with a power-law decay index of
1.26, the count rate at T+24 hours will be 3.5 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 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/00622006.

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

H.-F. Yu (MPE) reports on behalf of the Fermi GBM Team:

"At 08:07:11.22 UT on 21 Dec 2014, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 141221A (trigger 440842034 / 141221338),
which was also detected by Swift (Sonbas et al. 2014, GCN 17206
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 ).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight is about 76 degrees.

The GBM light curve consists of two pulses with a duration (T90) of
about 23.8 s (50-300 keV). The time-averaged spectrum from T0-1.024 s
to T0+17.408 s is best fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.07 +/- 0.13 and the
cutoff energy, parameterized as Epeak, is 152.4 +/- 28.5 keV.

The event fluence (8-1000 keV) in this time interval is
(3.4 +/- 0.4)E-06 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0-0.192 s in the 8-1000 keV band
is 5.4 +/- 0.3 ph/s/cm^2.

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

F. E. Marshall (NASA/GSFC) and E. Sonbas (NASA/GSFC/Adiyaman Univ.)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 141221A
84 s after the BAT trigger (Sonbas et al., GCN Circ. 17206
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 ).
A source consistent with the enhanced XRT position
(Beardmore et al. GCN Circ. 17211
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  13:13:08.81 = 198.28672 (deg.)
    Dec (J2000) = +08:12:18.8  =   8.20522 (deg.)
with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: 

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

white               84          234          147         17.33 � 0.04
v                  626          646           19         17.43 � 0.26
b                  552          571           20         17.92 � 0.21
u                  296          546          246         17.62 � 0.07
w1                4061         4261          197        >20.0
m2                3856        10742          414        >20.9
w2                6231         6399          165        >20.5

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).

A. Trotter, J. Haislip, D. Reichart, A. Aji, R. Beauchemin, T. Berger, 
A. Dow, A. Foster, N. Frank, M. Hinckle, K. Ivarsen, A. LaCluyze, M. 
Maples, J. Moore, M. Nysewander, C. Salemi, L. Zbinden, and J. A. Crain 
report:

Skynet continued to observe the Swift UVOT localization of GRB 141221A 
(Sonbas et al., GCN 17206
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 , Swift trigger=622006) with two 16" telescopes 
of the PROMPT array at Cerro Tololo, Chile. Starting at 2014-12-22 07:08 
UT and continuing until 08:34 UT (t=23.0h-24.5h post-trigger), Skynet 
took a total of 64 exposures of 160s each in the V and I bands. We 
stacked subsets of these images to maximize the signal-to-noise ratio. 
We no longer detect the optical afterglow that we described in Trotter 
et al. (GCN 17210
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 ).

Our limiting magnitudes are:

==================================
tmid  expos  fil  limit
==================================
23.8h 32x160s V   >21.2
23.8h 31x160s I   >20.7

A preliminary light curve is at:

http://www.skynet.unc.edu/grb/grb141221a_2.png

Magnitudes are in the Vega System, calibrated to 3 APASS stars in the 
field.  Magnitudes have not been corrected for line-of-sight Milky Way 
dust extinction, with expected E(B-V)=0.024 (Schlafly & Finkbeiner 2011).

No further Skynet observations are scheduled.

Y. Ono, T. Yoshii, Y. Saito, Y. Tachibana, H. Ohuchi,
Y. Yano, S. Kurita, T. Fujiwara, Y. Yatsu, and N. Kawai (Tokyo Tech)
report on behalf of the MITSuME collaboration:

We observed the field of GRB 141221A (E .Sonbas et al., GCN Circular #17206
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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 2014-12-21 17:20:13 UT (~9.1 h after the burst).
We did not find any new point source within the refined XRT error circle
(A.P. Beardmore., GCN Circular #17211
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 ) in all the three bands.

The measured magnitudes are listed below.

T0+[sec]     MID-UT    T-EXP[sec]        g'         Rc        Ic
-----------------------------------------------------------------------------
33183        18:51:55        9600          >21.3   >20.8   >20.2
-----------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
We used GSC2.3 catalog for flux calibration.

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

We imaged the field of GRB 141221A detected by SWIFT
(trigger 622006) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 31.2s after the GRB trigger
(14.2s after the notice). The elevation of the field increased from
23 degrees above horizon and weather conditions
were good but the dawn interrupted the observations
after 41 minutes.

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 the optical counterpart between 31s
and 68s at a limiting magnitude Rlim = 16.6. Then
the end of the trail shows a sudden appearance of the
optical counterpart (cf. Sonbas et al. GCNC 17206).
Measures are:

  start    end  magnitude
  (sec)  (sec)
   31.2   68.5  Rlim = 16.6
   68.5   74.5  R = 16.0 +/- 0.2
   74.5   80.5  R = 15.7 +/- 0.2
   80.5   86.5  R = 15.5 +/- 0.2
   86.5   92.5  R = 15.6 +/- 0.3

Next images (in tracking mode) show the optical transcient:

  start    end  magnitude
  (sec)  (sec)  R    +/-
  104.6  134.6 15.47 0.03
  145.1  175.1 15.36 0.03
  185.7  215.7 15.40 0.03
  226.0  256.0 15.42 0.03
  266.3  296.3 15.39 0.03
  306.7  396.7 15.60 0.09
  401.3  491.3 16.17 0.02
  715.6  805.6 16.63 0.02
  816.2  906.2 16.68 0.08
1029.4 1119.4 16.95 0.08
1130   1525   17.22 0.08
1536   2486   17.82 0.08

The early afterglow observed by TAROT is compatible
with that observed by PROMPT (Trotter et al. GCNC
17210 and GCNC 17221).

Magnitudes were estimated with the nearby star
NOMAD-1 0982-0272573 R=12.23 and are not corrected
for galactic dust extinction.

D. A. Perley, Y. Cao (Caltech), and S. B. Cenko (GSFC) report:

We observed the optical afterglow of GRB 141221A (Sonbas et al., GCN 
17206
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 ) with the DEIMOS spectrograph on the Keck II telescope between 
12:48 and 13:10 UT on 2014-12-21.  Two 900-second exposures were 
acquired at high airmass.

We detect significant continuum flux across the entire spectral range 
between 4490-9660 Angstroms.  Inspection of the 1D spectrum shows two 
apparent absorption features at 6854 and 6873 Angstroms which we 
tentatively associate with the Mg II doublet at z=1.452. 
Lower-significance probable absorption lines are also seen at the 
wavelengths of the Fe II 2599, 2585, 2383, 2374, and 2344 lines at 
similar redshift, lending additional credence to this association. 
However, due to a failure of the blue arc calibration lamps, we note 
that our wavelength solution is preliminary and this result should be 
considered tentative.