Gamma-ray Burst 131231A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 31 Dec 13 04:45:22 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      44
TRIGGER_NUM:     410157919
GRB_RA:           21.433d {+01h 25m 44s} (J2000),
                  21.612d {+01h 26m 27s} (current),
                  20.797d {+01h 23m 11s} (1950)
GRB_DEC:          -2.250d {-02d 15' 00"} (J2000),
                  -2.178d {-02d 10' 38"} (current),
                  -2.510d {-02d 30' 34"} (1950)
GRB_ERROR:       18.15 [deg radius, statistical plus systematic]
GRB_INTEN:       64 [cnts/sec]
DATA_SIGNIF:     5.60 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        16657 TJD;   365 DOY;   13/12/31
GRB_TIME:        17116.08 SOD {04:45:16.08} UT
GRB_PHI:         280.00 [deg]
GRB_THETA:        30.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      1.45
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   1%  Generic SGR
DETECTORS:       1,0,0, 0,1,0, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       280.51d {+18h 42m 03s}  -23.09d {-23d 05' 05"}
SUN_DIST:         99.33 [deg]   Sun_angle= -6.7 [hr] (East of Sun)
MOON_POSTN:      261.22d {+17h 24m 53s}  -19.53d {-19d 32' 03"}
MOON_DIST:       117.63 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      142.65,-63.80 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       18.95,-10.44 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 231.42,25.50 [deg].

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 31 Dec 13 04:45:27 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      57
TRIGGER_NUM:     410157919
GRB_RA:           18.000d {+01h 12m 00s} (J2000),
                  18.177d {+01h 12m 42s} (current),
                  17.368d {+01h 09m 28s} (1950)
GRB_DEC:          -5.800d {-05d 47' 59"} (J2000),
                  -5.726d {-05d 43' 32"} (current),
                  -6.065d {-06d 03' 54"} (1950)
GRB_ERROR:       7.60 [deg radius, statistical plus systematic]
GRB_INTEN:       196 [cnts/sec]
DATA_SIGNIF:     16.80 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        16657 TJD;   365 DOY;   13/12/31
GRB_TIME:        17116.08 SOD {04:45:16.08} UT
GRB_PHI:         290.00 [deg]
GRB_THETA:        30.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      1.14
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      98%  GRB
2nd_MOST_LIKELY:   1%  Generic SGR
DETECTORS:       1,0,0, 0,1,0, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       280.51d {+18h 42m 03s}  -23.09d {-23d 05' 05"}
SUN_DIST:         94.76 [deg]   Sun_angle= -6.5 [hr] (East of Sun)
MOON_POSTN:      261.22d {+17h 24m 53s}  -19.53d {-19d 32' 03"}
MOON_DIST:       113.06 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      136.77,-68.12 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       14.34,-12.42 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 231.42,25.50 [deg].

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 31 Dec 13 04:45:30 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      56
TRIGGER_NUM:     410157919
GRB_RA:           10.890d {+00h 43m 34s} (J2000),
                  11.068d {+00h 44m 16s} (current),
                  10.254d {+00h 41m 01s} (1950)
GRB_DEC:          -5.050d {-05d 02' 59"} (J2000),
                  -4.973d {-04d 58' 24"} (current),
                  -5.324d {-05d 19' 24"} (1950)
GRB_ERROR:       6.08 [deg radius, statistical only]
DATA_SIGNIF:     13.10 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        16657 TJD;   365 DOY;   13/12/31
GRB_TIME:        17116.08 SOD {04:45:16.08} UT
GRB_PHI:         297.00 [deg]
GRB_THETA:        36.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4143 (Gnd S/W Version number)
SUN_POSTN:       280.51d {+18h 42m 03s}  -23.09d {-23d 05' 05"}
SUN_DIST:         88.56 [deg]   Sun_angle= -6.0 [hr] (East of Sun)
MOON_POSTN:      261.22d {+17h 24m 53s}  -19.53d {-19d 32' 03"}
MOON_DIST:       106.84 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      117.72,-67.84 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:        8.01, -8.95 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 31 Dec 13 04:45:36 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      68
TRIGGER_NUM:     410157919
GRB_RA:           14.430d {+00h 57m 43s} (J2000),
                  14.607d {+00h 58m 26s} (current),
                  13.796d {+00h 55m 11s} (1950)
GRB_DEC:          -5.530d {-05d 31' 47"} (J2000),
                  -5.455d {-05d 27' 15"} (current),
                  -5.800d {-05d 48' 00"} (1950)
GRB_ERROR:       3.23 [deg radius, statistical only]
DATA_SIGNIF:     23.90 [sigma]
DATA_INTERVAL:   4.096 [sec]
GRB_DATE:        16657 TJD;   365 DOY;   13/12/31
GRB_TIME:        17116.08 SOD {04:45:16.08} UT
GRB_PHI:         294.00 [deg]
GRB_THETA:        33.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4143 (Gnd S/W Version number)
SUN_POSTN:       280.51d {+18h 42m 03s}  -23.09d {-23d 05' 05"}
SUN_DIST:         91.61 [deg]   Sun_angle= -6.3 [hr] (East of Sun)
MOON_POSTN:      261.22d {+17h 24m 53s}  -19.53d {-19d 32' 03"}
MOON_DIST:       109.91 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      127.17,-68.35 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       11.11,-10.78 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 31 Dec 13 04:45:37 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      69
TRIGGER_NUM:     410157919
GRB_RA:           14.600d {+00h 58m 24s} (J2000),
                  14.778d {+00h 59m 07s} (current),
                  13.963d {+00h 55m 51s} (1950)
GRB_DEC:          -2.617d {-02d 37' 00"} (J2000),
                  -2.541d {-02d 32' 28"} (current),
                  -2.887d {-02d 53' 10"} (1950)
GRB_ERROR:       5.68 [deg radius, statistical plus systematic]
GRB_INTEN:       367 [cnts/sec]
DATA_SIGNIF:     30.20 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        16657 TJD;   365 DOY;   13/12/31
GRB_TIME:        17116.08 SOD {04:45:16.08} UT
GRB_PHI:         290.00 [deg]
GRB_THETA:        35.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      1.01
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      98%  GRB
2nd_MOST_LIKELY:   1%  Generic SGR
DETECTORS:       1,0,0, 0,1,0, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       280.51d {+18h 42m 03s}  -23.09d {-23d 05' 05"}
SUN_DIST:         92.92 [deg]   Sun_angle= -6.3 [hr] (East of Sun)
MOON_POSTN:      261.22d {+17h 24m 54s}  -19.53d {-19d 32' 03"}
MOON_DIST:       111.19 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      127.12,-65.43 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       12.42, -8.17 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 231.42,25.50 [deg].

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 31 Dec 13 04:45:42 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      71
TRIGGER_NUM:     410157919
GRB_RA:           12.840d {+00h 51m 22s} (J2000),
                  13.018d {+00h 52m 04s} (current),
                  12.205d {+00h 48m 49s} (1950)
GRB_DEC:          -4.870d {-04d 52' 11"} (J2000),
                  -4.794d {-04d 47' 38"} (current),
                  -5.142d {-05d 08' 29"} (1950)
GRB_ERROR:       1.62 [deg radius, statistical only]
DATA_SIGNIF:     50.30 [sigma]
DATA_INTERVAL:   0.512 [sec]
GRB_DATE:        16657 TJD;   365 DOY;   13/12/31
GRB_TIME:        17116.08 SOD {04:45:16.08} UT
GRB_PHI:         295.00 [deg]
GRB_THETA:        35.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4143 (Gnd S/W Version number)
SUN_POSTN:       280.51d {+18h 42m 03s}  -23.09d {-23d 05' 05"}
SUN_DIST:         90.42 [deg]   Sun_angle= -6.2 [hr] (East of Sun)
MOON_POSTN:      261.22d {+17h 24m 54s}  -19.53d {-19d 32' 03"}
MOON_DIST:       108.71 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      122.88,-67.74 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:        9.89, -9.55 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 31 Dec 13 04:45:43 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      74
TRIGGER_NUM:     410157919
GRB_RA:           18.600d {+01h 14m 24s} (J2000),
                  18.777d {+01h 15m 06s} (current),
                  17.969d {+01h 11m 53s} (1950)
GRB_DEC:          -5.967d {-05d 58' 00"} (J2000),
                  -5.893d {-05d 53' 33"} (current),
                  -6.231d {-06d 13' 51"} (1950)
GRB_ERROR:       3.82 [deg radius, statistical plus systematic]
GRB_INTEN:       1833 [cnts/sec]
DATA_SIGNIF:     151.30 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        16657 TJD;   365 DOY;   13/12/31
GRB_TIME:        17116.08 SOD {04:45:16.08} UT
GRB_PHI:         290.00 [deg]
GRB_THETA:        30.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.76
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      97%  GRB
2nd_MOST_LIKELY:   2%  Generic Transient
DETECTORS:       1,0,0, 0,1,0, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       280.51d {+18h 42m 03s}  -23.09d {-23d 05' 05"}
SUN_DIST:         95.24 [deg]   Sun_angle= -6.6 [hr] (East of Sun)
MOON_POSTN:      261.22d {+17h 24m 54s}  -19.53d {-19d 32' 03"}
MOON_DIST:       113.53 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      138.43,-68.14 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       14.84,-12.80 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 231.42,25.50 [deg].

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 31 Dec 13 04:45:47 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      73
TRIGGER_NUM:     410157919
GRB_RA:           10.650d {+00h 42m 36s} (J2000),
                  10.829d {+00h 43m 19s} (current),
                  10.012d {+00h 40m 03s} (1950)
GRB_DEC:          -3.130d {-03d 07' 47"} (J2000),
                  -3.053d {-03d 03' 11"} (current),
                  -3.404d {-03d 24' 13"} (1950)
GRB_ERROR:       1.00 [deg radius, statistical only]
DATA_SIGNIF:     201.80 [sigma]
DATA_INTERVAL:   2.048 [sec]
GRB_DATE:        16657 TJD;   365 DOY;   13/12/31
GRB_TIME:        17116.08 SOD {04:45:16.08} UT
GRB_PHI:         295.00 [deg]
GRB_THETA:        38.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4143 (Gnd S/W Version number)
SUN_POSTN:       280.51d {+18h 42m 03s}  -23.09d {-23d 05' 05"}
SUN_DIST:         89.09 [deg]   Sun_angle= -6.0 [hr] (East of Sun)
MOON_POSTN:      261.22d {+17h 24m 54s}  -19.53d {-19d 32' 03"}
MOON_DIST:       107.33 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      117.52,-65.91 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:        8.55, -7.09 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        In the LAT Field-of-view.  
COMMENTS:        Bright hard burst in the GBM.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 31 Dec 13 04:45:49 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      94
TRIGGER_NUM:     410157919
GRB_RA:           18.750d {+01h 15m 00s} (J2000),
                  18.927d {+01h 15m 42s} (current),
                  18.119d {+01h 12m 29s} (1950)
GRB_DEC:          -6.017d {-06d 01' 00"} (J2000),
                  -5.943d {-05d 56' 34"} (current),
                  -6.281d {-06d 16' 50"} (1950)
GRB_ERROR:       3.48 [deg radius, statistical plus systematic]
GRB_INTEN:       4130 [cnts/sec]
DATA_SIGNIF:     342.50 [sigma]
INTEG_TIME:      4.096 [sec]
GRB_DATE:        16657 TJD;   365 DOY;   13/12/31
GRB_TIME:        17116.08 SOD {04:45:16.08} UT
GRB_PHI:         290.00 [deg]
GRB_THETA:        30.00 [deg]
DATA_TIME_SCALE: 4.0960 [sec]
HARD_RATIO:      0.73
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      97%  GRB
2nd_MOST_LIKELY:   2%  Generic Transient
DETECTORS:       1,0,0, 0,1,0, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:       280.51d {+18h 42m 03s}  -23.09d {-23d 05' 05"}
SUN_DIST:         95.35 [deg]   Sun_angle= -6.6 [hr] (East of Sun)
MOON_POSTN:      261.23d {+17h 24m 54s}  -19.53d {-19d 32' 03"}
MOON_DIST:       113.65 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      138.85,-68.16 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       14.96,-12.90 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 231.42,25.50 [deg].

GCN NOTICE

TITLE:          GCN/INTEGRAL NOTICE
NOTICE_DATE:    Tue 31 Dec 13 04:46:28 UT 
NOTICE_TYPE:    INTEGRAL SPI ACS Trigger
TRIGGER_NUM:    6416,   Sub_Num: 0
GRB_INTEN:      9.03 [sigma]
GRB_TIME:       17114.32 SOD {04:45:14.32} UT
GRB_DATE:       16657 TJD;   365 DOY;   13/12/31
COMMENTS:       INTEGRAL SPI_ACS GRB Trigger.
COMMENTS:       Time_Scale=2.0000 and Time_Error=1.0000.
COMMENTS:
COMMENTS:       NOTE: This SPIACS event is temporally(2.0<100sec) coincident with the FERMI_GBM event (trignum=410157919).
COMMENTS:
COMMENTS:       The SPIACS lightcurve can be found at:
COMMENTS:       ftp://isdcarc.unige.ch/arc/FTP/ibas/spiacs/2013-12/2013-12-31T04-45-14.1400-02325-48016-0.lc

GCN Circular #15640
E. Sonbas (Adiyaman Univ.), J. L. Racusin (NASA/GSFC), D. Kocevski (NASA/GSFC) and J. McEnery (NASA/GSFC), report on behalf of the Fermi-LAT team:
At 04:45:16.08 on Dec 31, 2013, Fermi LAT detected high energy emission from GRB 131231A, which was also detected by Fermi-GBM (trigger 410157919/131231198).
The best LAT on-ground location is found to be RA, Dec 10.585, -1.845 (J2000) with an error radius of 0.149 deg (90% containment, statistical error only), this was 40 deg from the LAT boresight at the time of the trigger. The GRB was detected at high enough peak flux in the GBM detectors to trigger an autonomous repoint of the spacecraft, which kept the source in the LAT field of view for 900 seconds.
The data from the Fermi LAT are temporally correlated with the GBM emission with high significance. More than 37 photons above 100 MeV and more than 11 photons above 1 GeV are observed within 900 seconds. The highest energy photon is a 9.7 GeV event which is observed at 700 seconds after the GBM trigger.
A Swift ToO request has been submitted.
The Fermi LAT point of contact for this burst is Eda Sonbas ( edasonbas@yahoo.com).
The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
GCN Circular #15641
D. Xu (DARK/NBI), H.-B. Niu, X. Zhang, A. Esamdin, L. Ma (XAO) report:
We observed the LAT field of GRB 131231A (Sonbas et al., GCN 15640) using the 1m telescope located on Mt. Nanshan, Xinjiang, China, equipped with a 1.2x1.2 deg^2 CCD camera. We obtained a series of 120s and 300s frames at the mean time 12:40 UT on 2013-12-31 (i.e., 7.91 hr after the Fermi trigger).
Within the LAT error circle (RA, Dec 10.585, -1.845 with an error radius of 0.149 deg, error statistical only) reported in Sonbas et al. (GCN 15640), no new prominent uncatalogued source is found and the depth of the Nanshan image is similar to that of DSS II. Given that the above LAT error is statistical only, we thus inspect that surrounding region the LAT error circle and discovered a bright source, not present in both DSS II and SDSS, at coordinates
```
R.A.=00:42:21.66
Dec.=-01:39:10.79
```
Err Radius: ~1.5 arcsec
with a magnitude of R~17.6, calibrated with nearby USNO B1 stars.
Follow-up observations are encouraged to check whether the source is the afterglow of the burst.
GCN Circular #15642
D. Malesani, D. Xu (DARK/NBI), I. R. Losada (Stockholm), F. Duval (Stockholm), report on behalf of a larger collaboration:
We observed the afterglow candidate of GRB 131231A (Sonbas et al., GCN 15640; Xu et al., GCN 15641) using the 2.56m Nordic Optical Telescope (NOT) equipped with MOSCA. Observations started at 22:05:40 UT on 2013 Dec 31 (i.e., 17.3 hr after the Fermi trigger).
The afterglow candidate noted by Xu et al. (GCN 15641) has decayed to R=18.6, using the same calibration. We thus suggest that this source is very likely the afterglow of GRB 131231A. The coordinates of the afterglow can be refined to
```
R.A. = 00:42:21.665
Dec. = -01:39:10.61
```
with an error of 0.3".
We also wish a happy new year to everyone.
GCN Circular #15643
L. P. Singer (Caltech), S. B. Cenko (NASA/GSFC), and M. M. Kasliwal (Carnegie Observatories) report on behalf of the intermediate Palomar Transient Factory (iPTF) collaboration:
Upon receiving the final GBM localization for GRB 131231A, we selected ten fields to observe with the Palomar 48-inch Oschin telescope (P48) covering 62 deg^2, most of the 1-sigma GBM error circle. Due to the short remaining visibility window at Palomar, we obtained only one epoch of images of five of the ten fields covering 30 deg^2. This includes ~90% of the LAT error localization (Sonbas et al., GCN 15640).
Sifting through 50 candidate variable sources near the LAT error circle using standard iPTF vetting procedures, at 1.45 hours after the burst we identify multiple uncatalogued sources, including iPTF13ekl at R=15.7 mag, at the coordinates
```
 RA(J2000)  =  00h 42m 21.67s
 DEC(J2000) = -01d 39' 11.0"
```
This position coincides with the Nanshan optical afterglow candidate at 7.91 hours after the burst (Xu et al., GCN 15641). There are no coincident sources in SDSS and no associated minor planets in the IAU Minor Planet Center database at this location.
Despite the low ecliptic latitude of -5.7 deg, the two coincident optical detections separated by 6.46 hours strongly disfavor a solar system origin. These two observations fit a power-law decay with an index of alpha=-1.03, suggesting that the source is indeed associated with the GRB trigger.
See <http://www.its.caltech.edu/~lsinger/iptf/Fermi410157919.pdf> for a depiction of the LAT error circle in relation to the P48 optical candidates, with iPTF13ekl highlighted, and a selection of the P48 fields observed.
GCN Circular #15644
P. Jenke (UAH) and S. Xiong (UAH) reports on behalf of the Fermi GBM Team:
"At 04:45:16.083 UT on December 31 2013, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 131231A (trigger 410157919/131231198). This GRB was detected in a ground analysis by the Fermi LAT (Sonbas et al. GCN 15640). It was also detected in optical follow-up observations of the GBM position by DARK/NBI (Xu et al. GCN 15641) and iPTF (Singer et al. GCN 15643), and confirmed by NOT observations of the Fermi LAT position (Malesani et al. GCN 15642). The on-ground calculated location from GBM is consistent with the positions reported from these follow-up observations.
The trigger resulted in an Autonomous Repoint Request (ARR) that was accepted and the LAT slewed to the GBM in-flight location. The initial angle from the LAT boresight is 38 deg from Fermi/GBM position.
The GBM light curve consists of a single large peak preceded by a smaller peak which resulted in the trigger. The duration (T90) of the burst was about 31 s (50-300 keV). The time-averaged spectrum from T0+.003 s to T0+56 s is best fit with a Band function with Epeak = 146 +/- 3 keV, alpha = -1.10 +/- 0.01 and beta = -2.14 +/- 0.01.
The event fluence (10-1000 keV) in this time interval is (2.51 +/- 0.01)E-06 erg/cm^2. The 1.0-sec peak photon flux measured starting from T0+22 s in the 10-1000 keV band is 67.3 +/- 0.8 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
GCN Circular #15645
D. Xu (DARK/NBI), D. Malesani (DARK/NBI), N. R. Tanvir (Univ. Leicester), V. D'Elia (ASI/ASDC), A. de Ugarte Postigo (IAA/CSIC and DARK/NBI), T. Kruehler (ESO), J. P. U. Fynbo (DARK/NBI) report on behalf of a larger collaboration:
We observed the optical counterpart of the Fermi/LAT GRB 131231A (Sonbas et al., GCN 15640; Jenke & Xiong, GCN 15644; Xu et al., GCN 15641) with the ESO VLT equipped with the X-shooter spectrograph. The mean time of our observation is 2014 Jan 1.04 UT, that is 20.2 hr after the GRB. The spectrum covers the wavelength range 3200 to 18,000 AA.
The trace of the afterglow is well visible in all arms. We detect several absorption features which we interpret as due to Fe II, Mg II, Ca H and K, all at a common redshift z = 0.642 (wavelength solution based on archival calibration lamps). Emission lines corresponding to the [O III] doublet are also detected at the same redshift.
We acknowledge excellent support from the observing staff in Paranal, in particular Steffen Mieske.

GCN Circular #15646
J. P. Halpern (Columbia U.) reports:
I observed the afterglow of GRB 131231A (Sonbas et al., GCN 15640; Xu et al., GCN 15641) using the 1.3m McGraw-Hill telescope of the MDM Observatory on 2014 January 1, from 01:40 to 03:18 UT. Nineteen 5-minute exposures were obtained in the R-band. Conditions were photometric, and the Landolt standard-star field around PG0231+051 was used for calibration. The afterglow magnitudes measured for the first and last exposures of the sequence are:

                --------------------------------
                 Jan 1 UT  t-t0(hr)   R    +/-
                --------------------------------
                  01:40     20.92   18.48  0.02
                  03:18     22.55   18.61  0.02
                --------------------------------

The following stars in field were calibrated, and can be used for comparison:

           -----------------------------------------
            Star  R.A.(2000)   Decl.(2000)      R
           -----------------------------------------
             A    00 42 30.4    -01 36 13     16.07
             B    00 42 11.7    -01 37 29     17.95
             C    00 42 15.9    -01 39 08     17.92
             D    00 42 20.0    -01 41 53     17.22
             E    00 42 28.8    -01 40 16     17.96
           -----------------------------------------

GCN Circular #15647
L. P. Xin, J. Y. Wei, X. F. Wang, Y. L. Qiu, J. S. Deng, J. Wang, X. H. Han and C. Wu on behalf of EAFON report:
We began to observe GRB 131231A (Sonbas et al., GCN 15640; Xu et al., GCN 15641,15645; Malesani et al., GCN 15642; Singer et al. GCN 15643; Halpern GCN 15646) with Xinglong 0.8-m TNT telescope at 10:29:40 (UT) , Jan. 1th, at 2014, about 29.73 hours after the burst. 12*300 sec B,V,R-band images were obtained.
The optical afterglow (Xu et al., GCN 15641) was clearly detected with a magnitude of 18.97+/-0.1 mag in R band, calibrated by USNO B1.0 R2mag at the mean time of 29.73 hours after the burst.
Compared with the report by Halpern GCN 15646, the brightness of this afterglow decayed for 0.36 mag during the epoch between 22.55 hours and 29.73 hours after the burst.
This message may be cited.
GCN Circular #15648
V. Mangano (PSU), K. Page (U. Leicester), D. Malesani (DARK/NBI) report on behalf of the Swift-XRT team:
We have analysed 4.0 ks of XRT data for the Fermi/LAT-detected burst: GRB 131231A, from 52.1 ks to 62.5 ks after the Fermi/LAT trigger. The data are entirely in Photon Counting (PC) mode. An X-ray source is detected at a position consistent with the optical afterglow (Xu et al., GCN 15641) at a mean count rate of 0.4 ct/s. The refined XRT position is RA, Dec = 10.5904, -1.6519 which is equivalent to:
```
RA (J2000): 00 42 21.70
Dec(J2000): -01 39 06.7
```
with an uncertainty of 3.5 arcsec (radius, 90% confidence). This position is 695 arcsec from the Fermi/LAT position and 4 arcsec from the optical afterglow.
The light curve can be modelled with a power-law decay with an index of alpha=1.6 (+/-0.7).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.86 (+0.13, -0.13). The best-fitting absorption column at the redshift of 0.642 (Xu et al., GCN 15645) is 1.4 (+0.7, -0.6) x 10^21 cm^-2, in excess of the Galactic value of 2.6 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 3.0 x 10^-11 (4.0 x 10^-11) erg cm^-2 count^-1.
Further ToO observations have already been scheduled for today.
This circular is an official product of the Swift-XRT team.
GCN Circular #15650
D. A. Perley (Caltech) reports on behalf of a larger collaboration:
We imaged the location of GRB 131231A with the Palomar 60-inch (P60) robotic telescope on UT 2014-01-01 between 03:28:31 and 04:22:05, and again on 2014-01-02 between 01:56:28 and 02:37:12. Observations were taken in the g, r, i, and z filters during each epoch.
The afterglow (Xu et al., GCN 15641) is well-detected in individual exposures in all bands. Both nights were photometric and we calibrated the field using an observation of the nearby standard field SA92.
Some photometry of the GRB afterglow in the gri bands (all on the SDSS/AB system) is:
```
r = 18.84 +/- 0.02  (t = 0.965 d)
i = 18.72 +/- 0.02  (t = 0.970 d)
g = 19.14 +/- 0.02  (t = 0.982 d)

r = 19.77 +/- 0.03  (t = 1.886 d)
i = 19.64 +/- 0.04  (t = 1.893 d)
g = 20.06 +/- 0.03  (t = 1.907 d)
```
The power-law temporal decay index in all bands is approximately alpha=1.3.
We also give gri magnitudes of the five nearby calibration stars presented by Halpern (GCN 15646) for reference:
```
star  RA          dec       R         g      r      i
  A    00:42:30.4 -01:36:13  16.07     16.86  16.28  16.11
  B    00:42:11.7 -01:37:29  17.95     19.50  18.24  17.66
  C    00:42:15.9 -01:39:08  17.92     19.16  18.20  17.85
  D    00:42:20.0 -01:41:53  17.22     17.62  17.48  17.58
  E    00:42:28.8 -01:40:16  17.96     18.76  18.18  18.02
```
GCN Circular #15652
A. Cucchiara (ORAU/NASA-GSFC) reports on behalf of a larger collaboration:
"On January 1.09 UT (~21.5 hours after the trigger) we observed the afterglow of GRB 131231A (Sombas et al. GCN 15640, Xu et al. GCN 15641, Malesani et al. 15642, Singer et al. GCN 15643) with the Gemini South telescope equipped with the GMOS camera.
A series of spectroscopic observations in Nod & Shuffle more, was carried out using the R400 grating covering the 6000-10000 A wavelength range at an average airmass of 2.1.
The resulting spectra show absorption features from CaH+K, as well as emission lines from forbidden [OII]3727 and [OIII]4959,5007 transitions at the common redshift of z=0.6439, consistent with the one reported by Xu et al. (GCN 15645).
We thank the Gemini staff for performing these observations, in particular E. Marin and E. Wenderoth."
GCN Circular #15670
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 131231A (Fermi-LAT detection: Sonbas, et al., GCN 15640; Fermi-GBM observation: Jenke & Xiong, GCN 15644) triggered Konus-Wind at T0=3D17132.361 s UT (04:45:32.361).
The light curve shows a broad mult-peaked pulse from ~T0-13 s to ~T0+35 s. The emission is seen up to ~15 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB131231_T17132/ Note: periodic 'dips' in the count rate are due to the GRB source occultation by the s/c structure.
As observed by Konus-Wind, the burst had a fluence of (1.55 =B1 0.05)x10-4 erg/cm2, and a 64-ms peak flux, measured from T0+7.488 s, of (2.14 =B1 0.13)x10-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum (measured from T0 to T0+34.303 s) is best fit in the 35 keV - 18 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha =3D -1.28 =B1 0.04, the high energy photon index beta =3D -2.47 =B1 0.05, the peak energy Ep =3D 163 =B1 6 keV, chi2 =3D 93.8/95 dof.
The spectrum near the maximum count rate (measured from T0+5.888 s to T0+8.448 s) is best fit in the 35 keV - 10 MeV range by the cutoff power law with the following model parameters: the photon index alpha =3D -0.76 =B1 0.09, and the peak energy Ep =3D 226 =B1 14 keV, chi2 =3D 94.3/82 dof.
Assuming the redshift z=3D0.644 (Xu, et al., GCN 15645; Cucchiara, GCN 15652), and a standard cosmology model with H_0 =3D 70 km/s/Mpc, Omega_M =3D 0.27, and Omega_Lambda =3D 0.73, we estimate the following rest-frame parameters: the isotropic energy release E_iso is (1.7 =B1 0.1)x10^53 erg, the peak luminosity L_iso is (3.9 =B1 0.2)x10^52 erg/s, and the rest-frame peak energy Ep,i =3D (270 =B1 10) keV
All the quoted results are preliminary.
GCN Circular #15672
P. Jenke (UAH) reports on behalf of the Fermi GBM team:
"The quoted fluence (10-1000 keV) in GCN 15644 (P. Jenke et al) was in fact the time integrated average energy flux for this burst. The actual fluence (10-1000 kev) for this event is (1.400 +/- 0.001)E-4 ergs/cm^2."
GCN Circular #15673
S. T. Holland (STScI) and V. Mangano (PSU) report on behalf of the Swift/UVOT team:
The Swift/UVOT began observations of the field of GRB 131231A 136.5 ks after the Fermi/LAT trigger (Sonbas et al., 2013, GCNC 15640). The preliminary UVOT position is
```
     RA (J2000)  00:42:21.66  =  10.59025 (deg)
    Dec (J2000) -01:39:10.6   =  -1.65294 (deg)
```
with an estimated uncertainty of 0.43 arcsec (radius, 90% confidence, statistical + systematic). We detect the optical afterglow at the position reported by Xu et al. (2013, GCNC 15641). Preliminary UVOT photometry is presented below.
```
------------------------------------------------------
Filter      TSTART     TSTOP    Exposure     Mag   Err
------------------------------------------------------
u          246,875   248,554        1652   19.57  0.10
white      136,762   138,942        1650   19.37  0.05
white      228,985   231,172        1639   20.07  0.07
------------------------------------------------------
```
The quoted magnitudes and upper limits have not been corrected for the Galactic extinction along the line of sight to this burst of E_{B-V} = 0.02 mag (Schlafly et al. 2011, ApJS, 737, 103). The photometry is in the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373).
The white observations yield a power-law decay index of alpha ~ 1.25 between 1.6 and 2.7 days. This is consistent with that found by Perley et al. (2014, GCNC 15650) between 1.0 and 1.9 days. The power-law decay index in the X-ray band at this time is alpha ~ 1.6 (Mangano et al. 2014, 15648), suggesting that there may be a cooling break between the optical and X-ray regimes.
GCN Circular #15676
S.B. Pandey, Brajesh Kumar and Archana Soam (ARIES Nainital India, on behalf of larger Indian GRB collaboration)
The Fermi-LAT detected GRB 131231A (Sonbas et al., GCN 15640; Xu et al., GCN 15641) was monitored with the 1.04m and 1.3m telescopes at ARIES Nainital starting at 2014-01-01 13:15:13 (UT). Several images in R_c and I_c pass-bands were obtained.
The optical afterglow was clearly detected in individual frames. The preliminary photometry of the first R_c frame (exposure time 300 sec) yields afterglow magnitude to be 19.2+-0.1 mag.
The nearby USNO stars have been used for calibrate.
This massage may be cited.
GCN Circular #15680
D. A. Perley (Caltech) reports on behalf of a larger collaboration:
We observed the position of GRB 131231A (Sonbas et al., GCN 15640; Jenke and Xiong, GCN 15644) with the Combined Array for Research in Millimeter Astronomy between 2013-01-01 23:54:54 UT and 2013-01-02 02:02:17 UT (1.798-1.887 days post-GRB) at a mean frequency of ~93 GHz, under good conditions.
We identify a weak source consistent with the optical localization (Xu et al., GCN 15651; Singer et al., GCN 15643) in the reduced map. The afterglow flux at this time is measured to be 0.85 +/- 0.25 mJy.
We thank observers B. A. Zauderer and M. Balokovic and the CARMA staff for executing the observation.
GCN Circular #15681
K.Y. Huang (NTNU), Y. Urata (NCU) on behalf of EAFON report:
We observed the optical afterglow of GRB131231A (Xu et al., GCN 15641) using the Lulin One-meter Telescope (LOT) with g, r, i, and z filters. The monitoring observation was made on the night of 1, 2 and 4, Jan, 2014. Based on nearby stars reported by Halpern (GCN15646) and Perley (GCN15650), we made photometry of the GRB afterglow. The temporal decay index alpha remains ~1 including the latest epoch. Some of photometry is summarized below.
```
epoch(d) g-mag g-err
1.259    19.6  0.1
2.247    20.3  0.1
4.377    20.9  0.1
```
GCN Circular #15711
A. Volnova (IKI), R. Inasaridze (AAO), G. Inasaridze (AAO), V. Zhuzhunadze (AAO), Yu. Krugly (IA KhNU), I. Molotov (KIAM), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration:
We observed the optical counterpart of the Fermi/LAT GRB 131231A (Sonbas et al., GCN 15640; Xu et al. GCN 15641) with AS-32 (0.7m) telescope of Abastumani Observatory on Jan. 3, 4, and 5. We obtained several unfiltered images of 120 s exposure during each observational set. On stacked images we clearly detect the afterglow. The photometry based on the reference stars, R-mag, from Halpern (GCN 15646) is following:
```
Date        T_start   t-t0,     exp,    OT
              (UT)      mid, d    s

2014-01-03  17:08:16  3.54893  33x120  20.26 =C2=B1 0.06
2014-01-04  16:53:04  4.53207  29x120  20.32 =C2=B1 0.08
2014-01-05  15:59:46  5.50061  34x120  20.74 =C2=B1 0.13
```
1401.7283 from 29 Jan 14
Bin Liu et al.: GRB 131231A: Implications of the hard GeV emission
GRB 131231A was detected by the Large Area Telescope onboard Fermi Space Gamma-ray Telescope. The high energy gamma-ray ($> 100$ MeV) afterglow emission spectrum is as hard as $F_\nu \propto \nu^{-0.50\pm0.13}$ in the first $\sim 1300$ s after the trigger, and the most energetic photon has an energy $\sim 62$ GeV. Such a hard spectrum is at odds with the model of synchrotron radiation of the external forward shock. Instead, both its spectrum and temporal behavior are found to be consistent with the synchrotron self-Compton radiation of the forward shock-accelerated electrons. We show that the prospect for detecting GRB 131231A-like GRBs with Cherenkov Telescope Array (CTA) is quite promising, and with an exposure time of $\sim 0.5$ hour, the $25$ GeV, $40$ GeV, and $100$ GeV gamma-ray emission of such GRBs could be detected within $1$ hour, $4$ hours, and $12$ hours after the burst, respectively.
GCN Report 458.1
GCN_Report 458.1 has been posted: http://gcn.gsfc.nasa.gov/reports/report_458_1.pdf by V. Mangano at PSU titled: "Swift Observations of LAT burst GRB 131231A"

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