Gamma-ray Burst 181225A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

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Results of Observations

GCN Circular #23560
A. Ursi (INAF/IAPS), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), A. Argan, M. Cardillo, C. Casentini, Y. Evangelista, G. Piano (INAF/IAPS), F. Lucarelli, C. Pittori, F. Verrecchia (SSDC, and INAF/OAR), A. Bulgarelli, V. Fioretti, F. Fuschino, N. Parmiggiani (INAF/OAS-Bologna), M. Marisaldi (INAF/OAS-Bologna, and Bergen University), M. Pilia, A. Trois (INAF/OA-Cagliari), I. Donnarumma (ASI), F. Longo (Univ. Trieste and INFN Trieste), A. Giuliani (INAF/IASF-Mi), report on behalf of the AGILE Team:
The AGILE Mini-CALorimeter (MCAL) detected a short burst at T0 = 2018-12-25 11:44:11.76 +/- 0.01 s (UTC). The event lasted about 1.2 s and released a total number of ~1580 counts in the detector (in the 0.4-100 MeV energy range), above an average background rate of 750 counts / s.
Further analysis is still in progress.
The AGILE-MCAL detector has a full solid angle acceptance, and is operational in the range 0.4 - 100 MeV.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 25 Dec 18 11:44:35 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      47
TRIGGER_NUM:     567431055
GRB_RA:          163.033d {+10h 52m 08s} (J2000),
                 163.355d {+10h 53m 25s} (current),
                 162.178d {+10h 48m 43s} (1950)
GRB_DEC:         +68.667d {+68d 40' 00"} (J2000),
                 +68.566d {+68d 33' 56"} (current),
                 +68.932d {+68d 55' 57"} (1950)
GRB_ERROR:       7.32 [deg radius, statistical plus systematic]
GRB_INTEN:       329 [cnts/sec]
DATA_SIGNIF:     12.60 [sigma]
INTEG_TIME:      1.024 [sec]
GRB_DATE:        18477 TJD;   359 DOY;   18/12/25
GRB_TIME:        42250.53 SOD {11:44:10.53} UT
GRB_PHI:         260.00 [deg]
GRB_THETA:       165.00 [deg]
DATA_TIME_SCALE: 1.0240 [sec]
HARD_RATIO:      0.00
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:     100%  Below horizon
2nd_MOST_LIKELY:   0%  n/a
DETECTORS:       0,0,0, 1,0,0, 0,1,0, 0,0,0, 0,0,
SUN_POSTN:       273.95d {+18h 15m 48s}  -23.39d {-23d 23' 10"}
SUN_DIST:        119.17 [deg]   Sun_angle= 7.4 [hr] (West of Sun)
MOON_POSTN:      134.13d {+08h 56m 32s}  +18.52d {+18d 30' 57"}
MOON_DIST:        53.27 [deg]
MOON_ILLUM:      90 [%]
GAL_COORDS:      137.73, 44.88 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      126.64, 54.33 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2018/bn181225489/quicklook/glg_lc_medres34_bn181225489.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 109.23,-10.43 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 25 Dec 18 21:07:53 UT
NOTICE_TYPE:     Fermi-LAT Offline Position
TRIGGER_NUM:     567431057 
GRB_RA:          348.070d {+23h 12m 17s} (J2000),
                 348.317d {+23h 13m 16s} (current),
                 347.419d {+23h 09m 41s} (1950)
GRB_DEC:          -9.480d {-09d 28' 47"} (J2000),
                  -9.377d {-09d 22' 35"} (current),
                  -9.752d {-09d 45' 06"} (1950)
GRB_ERROR:       7.80 [arcmin radius, 90% containment, statistical only]
GRB_DATE:        18477 TJD;   359 DOY;   18/12/25
GRB_TIME:        42252.00 SOD {11:44:12.00} UT
TRIGGER_ID:      0x0
MISC:            0x40000000
SUN_POSTN:       274.39d {+18h 17m 32s}  -23.37d {-23d 22' 29"}
SUN_DIST:         71.62 [deg]   Sun_angle= -4.9 [hr] (East of Sun)
MOON_POSTN:      140.09d {+09h 20m 22s}  +17.31d {+17d 18' 51"}
MOON_DIST:       151.45 [deg] 
MOON_ILLUM:      87 [%]
GAL_COORDS:       65.26,-60.70 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      345.33, -4.01 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS:        Fermi LAT Offline position.
COMMENTS:        This Notice was ground-generated -- not flight-generated.
COMMENTS:        It is the result of human-in-the-loop processing.
COMMENTS:        This is a human generated position of a LAT ground detection.
COMMENTS:        This source corresponds to GBM trigger.

GCN Circular #23561
M. Arimoto (Kanazawa Univ.), M. Palatiello (University of Udine and INFN Trieste), F. Longo (University and INFN, Trieste), D. Kocevski (NASA/MSFC), E. Bissaldi (Politecnico and INFN, Bari), G. Vianello (Stanford), and E. Moretti (IFAE) report on behalf of the Fermi-LAT team:
On December 25, 2018, Fermi-LAT detected high-energy emission from GRB 181225A, which was also detected by Fermi-GBM (trigger 567431055 / 181225489) and AGILE-MCAL (A. Ursi et al., GCN 23560). The best LAT on-ground location is found to be
RA, Dec = 348.07, -9.48 (degrees, J2000)
with an error radius of 0.13 deg (90% containment, statistical error only). This was 44 deg from the LAT boresight at the time of the GBM trigger:
T0 = 11:44:10.5 UT.
The data from the Fermi-LAT show a significant increase in the event rate after the GBM trigger that is temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0-1000 s after the GBM trigger is (2.4 +/- 0.5) E-5 ph/cm2/s, the one above 1 GeV is (1.5 +/- 0.5)E-5 ph/cm2/s.
The estimated photon index above 100 MeV is -2.24 +/- 0.18.
The highest-energy photon is a 13 GeV event which is observed ~4 seconds after the GBM trigger.
A Swift ToO has been requested for this burst.
The Fermi-LAT point of contact for this burst is Michele Palatiello (michele.palatiello@ts.infn.it).
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 #23562
S.Poolakkil(UAH), C. Meegan (UAH) and E. Bissaldi (Politecnico & INFN Bari) report on behalf of the Fermi GBM Team:
"At 11:44:10.53 UT on 25 December 2018, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 181225A (trigger 567431055/ 181225489), which was also detected by the Fermi LAT (M. Arimoto et al. 2018, GCN 23561). The GBM on-ground location is consistent with the LAT position.
The angle from the Fermi LAT boresight at the GBM trigger time is 44 degrees.
The GBM light curve shows multiple peaks with a duration (T90) of about 41.5 s (50-300 keV). The time-averaged spectrum from T0-2.0 s to T0+36.8 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.04 +/- 0.10 and the cutoff energy, parameterized as Epeak, is 1887 +/- 966 keV.
The event fluence (10-1000 keV) in this time interval is (5.569 +/- 0.370)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.54 s in the 10-1000 keV band is 3.74 +/- 0.19 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."
GCN Circular #23563
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Fermi/LAT GRB 181225A. Automated analysis of the XRT data will be presented online at http://www.swift.ac.uk/ToO_GRBs/00020849
Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Fermi/LAT event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
GCN Circular #23564
D.Kobtsev, V. Yurkov, A. Gabovich, Yu. Sergienko, (Blagoveschensk State Pedagogical University, Russia)
V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, D. Vlasenko, (Lomonosov Moscow State University, SAI)
R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres (The Instituto de Astrofisica de Canarias)
D. Buckley (South African Astronomical Observatory)
A. Tlatov, V.Senik, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory)
O. Gres, N.M. Budnev, S. Yazev, O. Chuvalaev (API, Irkutsk State University)
R. Podesta, C.Lopez, F. Podesta (Observatorio Astronomico Felix Aguilar of San Juan National University, Argentina)
H. Levato (Instituto de Ciencias Astronomicas, de la Tierra y del Espacio of San Juan National University, Argentina)
Global MASTER-Net (http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) was pointed to LAT GRB 181225A (Arimoto et al. GCN 23561, first detected by AGILE in GCN 23560 Ursi et al. ) by MASTER-SAAO (at 2018-12-25 21:08:21UT, alert_altitude=9deg.) and by MASTER-IAC.
MASTER-IAC robotic telescope, located in Spain (IAC Teide Observatory), was pointed to the LAT GRB181225.49 ( 23h 12m 16.80s , -09d 28m 48.00s, R=0.13) 34022 sec after trigger time at 2018-12-25 21:11:14 UT, with upper limit up to 19.9 mag.
We didn't find OT brighter 19.9 (unfiltered).
The observations started at zenit distance = 60 deg. The sun altitude was -38.0 deg. The galactic latitude b = -60 deg., longitude l = 98 deg.
Updated in real-time cover map and discovered OT will be available here: https://master.sai.msu.ru/site/master2/observ.php?id=893244
The observation and reduction will be continued.
The message may be cited.
GCN Circular #23565
V. D’Elia (SSDC), A. D’Ai (INAF-IASFPA), and M. H. Siegel (PSU) report on behalf of the Swift team
Swift-XRT and Swift-UVOT have performed follow-up observations of the AGILE-, GBM- and LAT-detected burst GRB 181225A (Ursi et al., GCN Circ. 23560; Arimoto et al. GCN Circ., 23561; Poolakkil et al., GCN Circ. 23562). The XRT total exposure time is 5 ks. The data were collected ~15 hr after the trigger, and are entirely in Photon Counting (PC) mode. Swift-UVOT data were collected simultaneously with the XRT data in UVOT’s u, v and white filters.
Two sources are detected in the XRT field of view, at the border of the LAT error circle (0.13 deg, 90% containment, statistical error only, Arimoto et al. GCN Circ. 23561).
The first one is located at:
```
RA(J2000)   =  23h 12m 12.2s
Dec(J2000) = -09d 19’ 29.5”
```
and is 0.156 deg away from the best LAT localization. Its count rate is (2.5 +/- 0.3)E-2 cts/s. However, its position is coincident with SDSSJ23122-0919, a radio source with a ROSAT X-ray counterpart, and thus it is likely unrelated with the X-ray afterglow of GRB181225A.
This source is detected in all three UVOT filters with magnitudes and colors roughly consistent with archival values.
```
Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white          55175        61751         1213      17.89+/-0.03
u                54338        66054         1868      19.45+/-0.15
v                56013        62624         1373      18.56+/-0.12
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.04 in the direction of the burst (Schlegel et al. 1998).
The second X-ray source is located at:
```
RA(J2000)   = 23h 12m 51.5s 
Dec(J2000) = -09d 30’ 08.9”
```
and is 0.144 deg away from the LAT localization. Its count rate is (3.7 +/-1.1)E-3 cts/s. This source is not related with any known astrophysical object, and it is thus a candidate X-ray afterglow for GRB181225A. This source was too far off the pointing to be imaged by UVOT. No new source is detected in the UVOT images. Given its faintness, low significance (S/N ~3), and no current information on variability in X-ray, we cannot confirm at the present stage if it is the X-ray afterglow.
This is an official product of the Swift team.
GCN Circular #23567
Q. B. Yi, C. K. Li, X. B. Li, G. Li, J. Y. Liao, S. L. Xiong, C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, X. F. Lu, J. L. Zhao, A. M. Zhang, Y. F. Zhang, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), T. P. Li (IHEP/THU), L. M. Song, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team:
At 2018-12-25T11:44:10.000 (T0), the Insight-HXMT/HE detected GRB 181225A (trigger ID: HEB181225489) in a routine search of the data, which was also triggered by by AGILE/MCAL (A. Ursi et al.,GCN23560)、 Fermi/LAT (M. Arimoto et al., GCN23561) and Fermi/GBM (S.Poolakkil., GCN23562).
The Insight-HXMT/HE light curve mainly consists of multiple pulses with a duration (T90) of 1.23 s measured from T0+0.46 s. The 50-ms peak rate, measured from T0+1.208 s, is 2963.2 cnts/s. The total counts from this burst 2350.8 counts. URL_LC: http://www.hxmt.org/images/GRB/HEB181225489_lc.jpg
All measurements above are made with the CsI detectors operating in the GRB mode with the energy range of about 200-3000 keV (record energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.
Insight-HXMT is the first Chinese space X-ray telescope, which was fundedjointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information could be found at: http://www.hxmt.org.
GCN Circular #23572
WeiKang Zheng, Keto Zhang, Alexei V. Filippenko, and Sergiy Vasylyev (UC Berkeley) report on behalf of the KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of the AGILE-, GBM- and LAT-detected burst GRB 181225A (Ursi et al., GCN Circ. 23560; Arimoto et al. GCN Circ., 23561; Poolakkil et al., GCN Circ. 23562). More than 250 galaxies near the Fermi/LAT localization (Arimoto et al. GCN Circ., 23561) were selected from the Glade catalog (http://aquarius.elte.hu/glade/) according to their priority score. On 2018 Dec. 26 UT, KAIT observed 82 of them having top-priority scores, with each clear-filter exposure time being 60 s. The first image was taken at 01:47:23 UT, about 14.05 hr after AGILE/MCAL trigger time, and the last image at 04:24:11 UT.
For the two Swfit/XRT sources reported by D'Elia (GCN 23565), the first one was not covered by KAIT images. The second source, which was considered to be a candidate X-ray afterglow for GRB181225A, was covered by one of the KAIT image taken at 03:46:38 UT (namely 16.04 hours after AGILE/MCAL trigger. However, we do not detect any optical afterglow candidate around the second XRT source, with limiting mag ~19.0 calibrated to the Pan-STARRS1 catalog.
GCN Circular #23573
V. Pal'shin, A. Yoshida, T. Sakamoto, S. Sugita (AGU), Y. Kawakubo (LSU), A. Tezuka, S. Matsukawa, H. Onozawa, T. Ito, H. Morita, Y. Sone (AGU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN), I. Takahashi (IPMU), Y. Asaoka, S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), W. Ishizaki (ICRR), M. L. Cherry (LSU), S. Ricciarini (U of Florence), A. V. Penacchioni, P. S. Marrocchesi (U of Siena), and the CALET collaboration:
The hard GRB 181225A (AGILE/MCAL detection: Ursi et al., GCN Circ. 23560; Fermi-LAT detection: Arimoto et al., GCN Circ. 23561; Fermi GBM detection: Poolakkil et al., GCN Circ. 23562) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 11:44:11.011 UTC on 25 December 2018. The burst signal was seen by all CGBM detectors.
The burst light curve shows the initial hard pulse which starts at T-0.6 sec and ends at T+1.1 sec, followed by a weaker and softer tail seen up to T+10.8 sec. The T90 and the T50 durations measured by the SGM data are 10.6 +- 0.8 sec and 7.5 +- 0.8 sec (40-1000 keV), respectively.
The ground processed light curve is available at
http://cgbm.calet.jp/cgbm_trigger/ground/1229773383/
Although the measured durations put this GRB in the long class, its hard initial pulse which has a duration of ~1.7 sec and the weaker and softer tail may imply that this GRB is in fact a short GRB with extended emission or it is similar to the famous "long-short" GRB 060614 (Gehrels et al. 2006, Nature, 444, 1044: https://www.nature.com/articles/nature05376).
The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at the Waseda University.
GCN Circular #23595
V. D Elia (SSDC) reports on behalf of the Swift-XRT team:
Swift-XRT has performed a second follow-up observation of the AGILE-, GBM- and LAT-detected burst GRB 181225A (Ursi et al., GCN Circ. 23560; Arimoto et al. GCN Circ., 23561; Poolakkil et al., GCN Circ. 23562). The XRT total exposure time is 7 ks. The data were collected 5.6 days after the trigger, and are entirely in Photon Counting (PC) mode.
The two sources detected in the first XRT observation (D’Elia et al., GCN Circ 23565) are still present in the XRT field of view of the new observation, with consistent rates and positions. We thus conclude that they are unrelated to the X-ray afterglow of GRB181225A.
This is an official product of the Swift-XRT team.

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