- GCN Circular #22305
A. P. Beardmore (U Leicester), A. Y. Lien (GSFC/UMBC) and
D. M. Palmer (LANL) report on behalf of the Swift Team:
At 01:08:30 UT on 3 Jan 2018, BAT detected a rate increase.
However further analysis was truncated by a pre-planned slew.
Using the limited data available (including 10 seconds of
event-by-event data from the rising edge of the burst overlapping
the start of the slew) ground analysis finds a strong peak
in the reconstructed image, which is GRB 180103A (Trigger #803066).
The image peak is at
RA,Dec = 159.585, -53.555 which is
RA(J2000) = 10h 38m 20.3s
Dec(J2000) -53d 33' 16.9"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a multi-peaked
structure with a duration of about 170 sec. The peak count rate
was ~37,000 counts/sec (15-350 keV), at ~103 sec after the trigger.
Due to the lack of onboard image detection, Swift did not slew to the
GRB and so there were no immediate XRT or UVOT follow-up observations.
Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk).
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.)
- GCN Circular #22306
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Swift/BAT GRB 180103A.
Automated analysis of the XRT data will be presented online at
http://www.swift.ac.uk/ToO_GRBs/00020786
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 Swift/BAT 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 #22308
A. Melandri (INAF-OAB), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), J.A.
Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester),
P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC) and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the
Swift/BAT-detected burst GRB 180103A (Beardmore et al. GCN Circ.
22305), collecting 2.0 ks of Photon Counting (PC) mode data between
T0+344.2 ks and T0+350.7 ks.
One uncatalogued X-ray source has been detected consistent with being
within 296 arcsec of the Swift/BAT position, it is below the RASS limit
and shows no definitive signs of fading. Therefore, at the present time
we cannot confirm this as the afterglow. Details of this source are
given below:
Source 1:
RA (J2000.0): 159.6016 = 10:38:24.37
Dec (J2000.0): -53.5560 = -53:33:21.6
Error: 3.8 arcsec (radius, 90% conf. [Enhanced position])
Count-rate: 0.0207 +/- 0.0054 ct s^-1
Distance: 35 arcsec from Swift/BAT position.
Flux: (4.9 +/- 1.3)e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV)
The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
http://www.swift.ac.uk/ToO_GRBs/00020786.
This circular is an official product of the Swift-XRT team.
- GCN Circular #22309
N.P.M. Kuin (UCL-MSSL) and A..P. Beardmore (U. Leicester) report
on behalf of the Swift/UVOT team:
The Swift/UVOT performed observations of the field of GRB 180103A
(Beardmore et al. GCN Circ. 22305). No optical afterglow consistent
with the XRT position (Melandri et al. GCN. Circ. 22308) is
detected in the UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are:
Filter T_start(ks) T_stop(ks) Exp(s) Mag
v 344.2 350.7 1044 >19.9
u 344.2 350.7 848 >20.4
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.48 in the direction of the burst
(Schlegel et al. 1998).
- GCN Circular #22310
V. Sharma and D. Bhattacharya (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the Astrosat CZTI collaboration:
Analysis of Astrosat CZTI data showed the detection of a long GRB 180103A, which was also detected by Swift (Beardmore A. P. et al., GCN 22305).
The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple peaks of emission with strongest peak at 01:10:08.500 UT, ~98 s after the Swift-BAT trigger. The measured peak count rate is 2009.4 cts/s above the background in combined data of four quadrants, with a total of 56951 cts. The local mean background count rate was 459 cts/s. Using cumulative rates, we measure a T90 of 147.1 s.
It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.
CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.
- GCN Circular #22314
D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, P. Oleynik,
M. Ulanov, A. Tsvetkova, A. Lysenko, A.Kozlova, and T. Cline
on behalf of the Konus-Wind team, report:
The bright long-duration GRB 180103A
(Swift-BAT detection: Beardmore et al., GCN Circ. 22305;
AstroSat-CZTI detection: Sharma et al., GCN Circ. 22310)
triggered Konus-Wind at T0=4122.424 s UT (01:08:42.424).
The burst light curve shows a multipeaked structure
which starts at ~T0-19.5 s and has a total duration of ~237 s.
The emission is seen up to ~10 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180103_T04122/
As observed by Konus-Wind, the burst
had a fluence of 3.41(-0.36,+0.33)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+91.200 s,
of 1.86(-0.27,+0.26)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst
(measured from T0 to T0+219.136 s)
is best fit in the 20 keV - 20 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.31(-0.06,+0.06),
the high energy photon index beta = -2.30(-0.30,+0.15),
the peak energy Ep = 282(-33,+40) keV
(chi2 = 81/96 dof).
The spectrum near the maximum count rate
(measured from T0+81.664 to T0+93.952 s)
is best fit in the 20 keV - 20 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.00(-0.04,+0.04),
the high energy photon index beta = -2.81(-0.99,+0.31),
the peak energy Ep = 589(-48,+52) keV
(chi2 = 107/97 dof).
All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.
- GCN Circular #22315
C. Guidorzi (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell (U. Bath), A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU) on behalf of a large collaboration report:
We observed the field of Swift GRB180103A (Beardmore et al. GCN 22305) on January 06, from 22:12 to 22:35 UT (3.9 days post burst) with one of the 1-m LCO telescopes in Sutherland in the SDSS-I filter. Within the XRT error circle of the source mentioned by Melandri et al. (GCN 22308) we see two sources, for which we measure the following magnitudes:
RA(J2000.0) DEC(J2000.0) Exposure Filter Magnitude (AB)
(s)
-------------------------------------------------------------------------
10:38:24.24 -53:33:17.3 9x120 SDSS-I 19.68 +- 0.07
10:38:24.64 -53:33:21.3 9x120 SDSS-I 19.19 +- 0.05
-------------------------------------------------------------------------
as calibrated against USNO UCAC4 field stars. Although we presently cannot make any statement about possible variability, the crowded field suggests that both sources are likely to be unrelated to the GRB. No other sources down to i<20.8 mag are seen within the same XRT error circle.
- GCN Circular #22326
A. Melandri (INAF-OAB), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), J.A.
Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester),
P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC) and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team:
Swift-XRT has conducted further observations of the field of the
Swift/BAT-detected burst GRB 180103A (Beardmore et al. GCN Circ.
22305). The observations now extend from T0+344.2 ks to T0+849.2 ks.
The source previously reported by Melandri et al. (GCN Circ. 22308),
"Source 1", is fading with 3-sigma significance, and is therefore
likely the GRB afterglow. Using 995 s of PC mode data and 1 UVOT image,
we find an enhanced XRT position (using the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
159.60155, -53.55600 which is equivalent to:
RA (J2000): 10h 38m 24.37s
Dec(J2000): -53d 33' 21.6"
with an uncertainty of 3.8 arcsec (radius, 90% confidence). This
position is 35 arcsec from the Swift/BAT position.
The light curve can be modelled with a power-law decay with a decay
index of alpha=2.53 (+0.05, -1.07).
The results of the XRT-team automatic analysis of the likely afterglow
are at http://www.swift.ac.uk/ToO_GRBs/00020786/Source1.php.
The results of the full analysis of the XRT observations are available
at http://www.swift.ac.uk/ToO_GRBs/00020786.
This circular is an official product of the Swift-XRT team.
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