- GCN Circular #20570
GRB 170131A detected in Swift/BAT ground processing
David Palmer (LANL), on behalf of the Swift team, reports:
At 23:15:13 UT on 2017-01-31, the Swift Burst Alert Telescope (BAT)
detected a marginal peak in a rate-triggered image (Swift Trigger #736107).
Because it was below the image significance threshold, it did not yield a GRB
follow-up. However, ground analysis shows that it is at the same location
as a Fermi/GBM trigger (#507597304). KONUS/WIND also reported a trigger
at the same time.
The BAT on-board calculated location is
RA, Dec 341.447, 64.006, which is
RA(J2000) = 22h 45m 55s
Dec(J2000) = +64d 00' 22"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows a ~30 s long
FRED structure starting at ~T-20 (consistent with the Fermi/GBM
trigger time) superimposed with a ~5 second peak near the BAT
trigger time. The peak count rate was ~3000 counts/sec (15-350 keV),
at ~3 sec after the BAT trigger.
A Swift ToO observation has been scheduled.
- GCN Circular #20571
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Swift/BAT GRB 170131A.
Automated analysis of the XRT data will be presented online at
http://www.swift.ac.uk/ToO_GRBs/00020738
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 #20572
B. Mailyan (UAH) and O.J Roberts (NASA-MSFC/USRA) report on
behalf of the Fermi GBM Team:
"At 23:14:59.36 UT on January 31st 2017, the Fermi Gamma-Ray
Burst Monitor triggered and located GRB 170131A
(trigger 507597304 /170131969) which was also detected by
the Swift/BAT (Palmer, GCN 20570). The GBM on-ground location
is consistent with the Swift-BAT position.
The angle from the Fermi LAT boresight at the GBM trigger
time using the Swift-BAT position is 18 degrees.
The GBM light curve shows a FRED-like burst with overlapping
pulses with a duration (T90) of about 23 s (50-300 keV).
The time-averaged spectrum from T0-1.0 s to T0+18.4 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -1.37+/-0.06
and the cutoff energy, parameterized as Epeak, is 209 +/- 34 keV.
The event fluence (10-1000 keV) in this time interval is
(4.56 +/- 0.27)E-06 erg/cm^2. The 1 s peak photon flux measured
starting from T0+15.4 s in the 10-1000 keV band is
4.9 +/- 0.3 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
- GCN Circular #20573
A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), B.
Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A. Cholden-Brown (PSU),
B. Mingo (U. Leicester), A.P. Beardmore (U. Leicester) 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 170131A (David Palmer et al. GCN Circ.
20570), collecting 4.9 ks of Photon Counting (PC) mode data between
T0+78.4 ks and T0+96.6 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): 341.3994 = 22:45:35.85
Dec (J2000.0): +64.0090 = +64:00:32.6
Error: 5.8 arcsec (radius, 90% conf.)
Count-rate: (2.19 [+0.93, -0.75])e-3 ct s^-1
Distance: 75 arcsec from Swift/BAT position.
Flux: (6.2 [+2.6, -2.1])e-14 erg cm^-2 s^-1 (observed, 0.3-10 keV)
A uncatalogued source was also detected, however this was too far from
the GRB position to be the afterglow.
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/00020738.
This circular is an official product of the Swift-XRT team.
- GCN Circular #20574
A. A. Breeveld (UCL-MSSL), M. Stamatikos (OSU) and F. E. Marshall
(NASA/GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 170131A
78368 s after the BAT trigger (Palmer, GCN Circ. 20570) using the UVW2
filter only.
No optical afterglow consistent with the XRT source 1 position (Melandri
et al., GCN Circ. 20573) is detected in the initial UVOT exposures.
However, there is a USNO-B1.0 source at this position (USNO-B1.0
1540-029147), but it is not detected in the UVW2 filter.
The preliminary 3-sigma upper limit using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial
exposures is:
Filter T_start(s) T_stop(s) Exp(s) Mag
w2 78368 96539 4888 >21.2
The magnitude in the table is not corrected for the large, but uncertain
Galactic extinction due to the reddening of E(B-V) = 1.19 in the
direction of the burst (Schlegel et al. 1998).
- GCN Circular #20600
Yi Zhao (IHEP), Xing Wen (IHEP), Yuanhao Wang (IHEP)
report on behalf of the POLAR collaboration:
At 2017-01-31T23:14:59.00 UT (T0), during a routine on-ground
search of data, POLAR detected the GRB 170131A,
which was also detected by the
Fermi/GBM (trigger 507597304/170131969, Circ 20572),
Swift (Circ 20570) and Konus-Wind.
The POLAR light curve consists of multiple peaks,
with a duration (T90) of 21.88 s measured from T0-1.21 s.
The 1-s peak rate measured from T0+16.00 s is 888.4 cnts/s.
The total counts is about 7085 cnts. The above measurements
are in the energy range of about 20-500 keV.
LC_URL:
http://polar.ihep.ac.cn/grb/2017/01/GRB170131A/lc/POLAR_lc_grb170131A.png
Using the best location from the Swift/BAT, which is (J2000):
RA: 341.447 [deg]
Dec: +64.006 [deg]
Err: 3.00 [arcmin]
the incident angle in POLAR coordinate at T0 is:
theta: 76.5 [deg]
phi: 22.2 [deg]
All analysis results presented above are preliminary.
POLAR is a dedicated Gamma-Ray Burst polarimeter (50-500 keV)
on-board the Chinese space laboratory Tiangong-2 launched on
Sep 15,2016. More information about POLAR can be found at
http://polar.ihep.ac.cn/en/ , http://isdc.unige.ch/polar/
and http://polar.psi.ch/pub/.
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