GRB 170531B
GCN Circular 21210
Subject
GRB 170531B: Zeiss-1000/CrAO optical observations
Date
2017-06-07T21:38:36Z (8 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
E. Mazaeva (IKI), A. Pozanenko (IKI), D. Chestnov (ISON), A. Novichonok
(ISON), V. Agletdinov (KIAM), I. Nikolenko (CrAO), A. Volnova (IKI),
report on behalf of larger GRB follow-up collaboration:
We report refined analysis of Zeiss-1000/CrAO observations. Results
reported below supersede GCN cir. 21174.
We observed the field of the GRB 170531B (Evans et al., GCN 21171) with
Zeiss-1000/Koshka (CrAO) telescope between May 31 (UT) 22:32:32 and
June 01 (UT) 00:58:11. We took several unfiltered images with
exposure of 180 s. The afterglow (Lipunov et al. GCN 21173;
Pozanenko et al. GCN 21174) is clearly visible in each image in first
initial images, and detected later in combined images. The finding chart
of the combined image can be found at
http://grb.rssi.ru/GRB170531B/GRB170531B_Koshka_170531_sources.png
The coordinates of the afterglow (source A in the finding chart) are
(J2000) 19:07:32.10 -16:25:06.0 with uncertainty of 0.5 arcsec in both
coordinates. The coordinates are consistent with the position reported
by de Ugarte Postigo et al., GCN 21177, Tyurina et al., GCN 21179,
and Siegel et al., GCN 21188.
Preliminary photometry of the afterglow can be found in the light curve at
http://grb.rssi.ru/GRB170531B/GRB170531B_light_curve_v2.png
The photometry is based on nearby USNO-B1.0 stars, calibrated against to
R2 magnitudes
USNO-B.1_id R2
0736-0718845 16.77
0735-0729622 16.96
0735-0729439 16.59
0735-0729327 17.22
Due to presence of sources in near vicinity to the afterglow the
photometry of wide FOV telescopes might be affected by the sources. In
particular our photometry reported in GCN 21189 is apparently biased by
the two sources C and D (see the finding chart). We report coordinates
and brightness of the nearby sources.
Source coordinates(J2000) AG distance filter mag. err.
C 19:07:32.34 -16:25:09.1 4.6" CR 20.46 0.04
D 19:07:31.83 -16:25:05.6 3.9" CR 20.47 0.04
GCN Circular 21209
Subject
GRB 170531B: WHT spectroscopy
Date
2017-06-07T09:17:35Z (8 years ago)
From
Klaas Wiersema at U Leicester <kw113@leicester.ac.uk>
K. Wiersema, N. Tanvir (Leicester), A. Levan (Warwick) report:
We observed the afterglow of GRB 170531B (Evans et al. GCN 21171; Lipunov et al. GCN 21173;
Pozanenko et al. GCN 21174) with the 4.2m William Herschel Telescope on La Palma, using the
ACAM instrument. We obtained a spectrum, consisting of 4x900 seconds exposure time, starting
at 02:55 UT on 1 June 2017. Our wavelength coverage is ~4500 - 9500 A. We detect a small
number metal lines (at low S/N) at a redshift consistent with that obtained by de Ugarte-Postigo
et al. (GCN 21177).
We warmly thank the staff of ING, in particular Raine Karjalainen, for their assistance.
GCN Circular 21189
Subject
GRB 170531B: ISON/Terskol optical observations
Date
2017-06-02T15:22:42Z (8 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
E. Mazaeva (IKI), A. Mokhnatkin (KIAM), A. Pozanenko (IKI), A.
Volnova (IKI), I. Molotov (KIAM) report on behalf of larger GRB
follow-up collaboration:
We observed the field of GRB 170531B (Evans et al.,GCN 21171) with
K-800 (0.8m) telescope of ISON/Terskol observatory starting on May,
31 (UT) 22:21:31. We obtained several unfiltered images of 40 s
exposure. The optical afterglow (Lipunov et al., GCN 21173 Pozanenko et
al. GCN 21174) is clearly visible in combined images. Preliminary
photometry of the afterglow is following
Date UT start t-T0 Filter Exp. OT Err. UL
(mid, days) (s)
2017-05-31 22:21:31 0.01810 CR 18*40 18.90 0.10 21.0
2017-05-31 22:35:41 0.02949 CR 21*40 19.10 0.10 21.0
Photometry is based on nearby USNO-B1.0 stars
USNO-B.1_id R2
0736-0718845 16.77
0735-0729626 17.35
0735-0729622 16.96
0735-0729439 16.59
0735-0729327 17.22
GCN Circular 21188
Subject
GRB 170531B: Swift/UVOT Detection
Date
2017-06-02T04:27:30Z (8 years ago)
From
Mike Siegel at PSU/Swift MOC <siegel@swift.psu.edu>
M. H. Siegel (PSU) and P. A. Evans (U. Leicester)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 170531B
152 s after the BAT trigger (Evans et al., GCN Circ. 21171).
We detect a possible afterglow consistent with the position given by GTC
(de Ugarte Postigo et al., GCN Circ. 21177) and MASTER (Tyurin et al.,
GCN CIrc. 21179).
The preliminary UVOT position is:
RA (J2000) = 19:07:32.10 = 286.88373 (deg.)
Dec (J2000) = -16:25:05.8 = -16.41829 (deg.)
with an estimated uncertainty of 0.1 arc sec. (radius, 90% confidence).
This position is 3.0 arc sec away from the enhanced XRT position
(Osborne et al. GCN Circ. 21175). Given the fading, detection
by other observatories and lack of matching source in the DSS, we find it
likely to be the GRB afterglow.
Preliminary 3-sigma magnitudes upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white (fc) 152 302 147 20.50+-0.29
white 590 1532 244 >21.03
v 640 1581 116 >18.88
b 566 1508 97 >19.77
u (fc) 310 560 245 >20.07
u 713 1643 85 >19.17
uvw1 689 1630 97 >18.91
uvm2 664 1606 116 >18.88
uvw2 615 1557 116 >19.14
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.19 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 21187
Subject
GRB 170531B: SMARTS optical/IR observations
Date
2017-06-01T18:25:15Z (8 years ago)
From
Bethany Cobb at GWU <bcobb@gwu.edu>
B. E. Cobb (GWU), reports:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 170531B
(GCN 21171, Evans et al.) at two epochs (with mid-exposure times
of 2017-06-01 04:22 UT & 08:19 UT). For each epoch, several
dithered images were obtained with total summed exposure times
amounting to 36 minutes in I and 30 minutes in J.
No source is detected at the position of the X-ray/optical
afterglow (GCN 21175, Osborne et al.; GCN 21174, Pozanenko et al.;
GCN 21177, de Ugarte Postigo et al.; GCN 21178, Schady & Kruehler;
GCN 21179, Tyurina et al.) to the approximate 3-sigma limiting
magnitudes listed below:
mid-exposure
time post-burst
(hours) I-limit J-limit
6.33056 >20.8 >18.5
10.27333 >21.2 >18.7
(Optical photometry is calibrated against USNO-B1.0 stars
and IR photometry is calibrated against 2MASS stars in the
field.)
GCN Circular 21186
Subject
GRB 170531B: Swift-BAT refined analysis
Date
2017-06-01T16:18:59Z (8 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), P. A. Evans (U Leicester),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170531B (trigger #755354)
(Evans et al., GCN Circ. 21171). The BAT ground-calculated position is
RA, Dec = 286.901, -16.414 deg which is
RA(J2000) = 19h 07m 36.3s
Dec(J2000) = -16d 24' 51.6"
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 96%.
The mask-weighted light curve shows a multi-peaked structure that starts
at ~T0 and ends at ~T+180 s. T90 (15-350 keV) is 164.13 +- 8.82 sec
(estimated error including systematics).
The time-averaged spectrum from T+0.55 to T+181.67 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.95 +- 0.14. The fluence in the 15-150 keV band is 2.0 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+42.71 sec in the 15-150 keV band
is 0.8 +- 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/755354/BA/
GCN Circular 21183
Subject
GRB 170531B: LCO observations
Date
2017-06-01T15:49:04Z (8 years ago)
From
Antonino Cucchiara at UVI <antonino.cucchiara@uvi.edu>
A. Cucchiara, D. Morris (U. of Virgin Islands), C. Guidorzi
(U. Ferrara), reports on behalf of a larger collaboration:
"On June 1.00 UT (T_0 +2.0h) we began observing the center
of the field of GRB 170531B (Evans et al. GCN 211171)
using the Las Cumbres Observatory 1m Sutherland facility.
We performed a series of 10x60s observations in R and I band
for a total of 10 minutes on sky in each filter. Seeing
conditions were poor.
We identified no optical counterpart within the center of
Swift-XRT refined position (Evans et al. GCN 21175), or at
the location of the identified counterpart (Lipunov et al.
GCN 21173, Pozanenko et al. GCN 21174, Schady et al. GCN 21178)
at the following 3-sigma limits:
R > 19.9 mag
I > 19.6 mag
These magnitude are calibrated against nearby USNO-B1 sources,
and are not corrected for Galactic extinction."
GCN Circular 21182
Subject
GRB 170531B: Swift-XRT refined Analysis
Date
2017-06-01T13:55:38Z (8 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P. D'Avanzo (INAF-OAB), J.A. Kennea (PSU), B. Sbarufatti
(INAF-OAB/PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), B. Mingo
(U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (ASDC), A.
D'Ai (INAF-IASFPA) and P.A. Evans report on behalf of the Swift-XRT
team:
We have analysed 6.8 ks of XRT data for GRB 170531B (Evans et al. GCN
Circ. 21171), from 129 s to 52.1 ks after the BAT trigger. The data
comprise 303 s in Windowed Timing (WT) mode (the first 10 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 Osborne et
al. (GCN Circ. 21175).
The late-time light curve (from T0+5.5 ks) can be modelled with a
power-law decay with a decay index of alpha=1.18 (+0.25, -0.20).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.45 (+/-0.04). The
best-fitting absorption column is 6.5 (+2.7, -2.5) x 10^21 cm^-2, at a
redshift of 2.366, in addition to the Galactic value of 1.4 x 10^21
cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index
of 2.07 (+0.13, -0.12) and a best-fitting absorption column consistent
with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV
flux conversion factor deduced from this spectrum is 3.4 x 10^-11 (4.7
x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.4 x 10^21 cm^-2
Intrinsic column: 1.4 (+2.2, -0.0) x 10^21 cm^-2 at z=2.366
Photon index: 2.07 (+0.13, -0.12)
If the light curve continues to decay with a power-law decay index of
1.18, the count rate at T+24 hours will be 3.3 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x
10^-13 (1.6 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/00755354.
This circular is an official product of the Swift-XRT team.
GCN Circular 21179
Subject
GRB 170531B: MASTER Net optical counterpart refind position and magnitude
Date
2017-06-01T11:21:45Z (8 years ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
N.Tyurina, V. Lipunov, V.Kornilov, E.Gorbovskoy, I.Gorbunov, D.Kuvshinov,
A.V.Krylov, P.Balanutsa, A.Kuznetsov, V.V.Chazov, D. Vlasenko
Lomonosov Moscow State University, Sternberg Astronomical Institut of MSU
A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov
Kislovodsk Solar Station of the Pulkovo Observatory
N.M.Budnev, O.Gres, O. Ershova
Irkutsk State University
A.Gabovich, V.Yurkov, Yu.Sergienko
Blagoveschensk Educational State University, Blagoveschensk
D.Buckley, S. Potter, A.Kniazev, M.Kotze
South African Astronomical Observatory
R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias
R.Podesta, C.Lopez, F. Podesta Observatorio Astronomico Felix Aguilar (OAFA),
National University of San Juan, Argentina
H. Levato, C. Saffe
Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE),
San Juan, Argentina
MASTER-Kislovodsk robotic telescope (2x4 square degrees, MASTER-Net:
http://observ.pereplet.ru) was pointed to the GRB170531B (Evans et al.,
GCN #21171) 12 sec after notice time and 452 sec after trigger time on
2017-05-31 22:09:44 UT (Lipunov et al., GCN #21173).
Id Date time Exp Proc.type Limit* Tube OT Err
UT sec 5sigma
1240587 2017-05-31 22:09:44 90 Alert (SWIFT) 18.3 EAST 18.3 0.5
1240589 2017-05-31 22:11:23 110 Alert (SWIFT) 18.4 EAST 18.4 0.5
1240591 2017-05-31 22:13:24 130 Alert (SWIFT) 18.5 EAST 18.4 0.5
1240593 2017-05-31 22:15:44 160 Alert (SWIFT) 18.5 EAST 18.5 0.5
1240596 2017-05-31 22:18:35 180 Alert (SWIFT) 18.5 EAST 18.5 0.5
1240652 2017-05-31 22:09:44 490 SumAlert(SWIFT) 19.1 EAST 18.3 0.2
1240597 2017-05-31 22:21:59 180 Alert (SWIFT) 18.3 EAST no -
1240599 2017-05-31 22:25:24 180 Alert (SWIFT) 18.5 EAST no -
.................................................................
1240629 2017-05-31 23:16:43 180 Alert (SWIFT) 18.5 EAST no -
* - unfiltered magnitude with respect to USNO B1.0 stars reference stars
m=0.2B + 0.8R
We refind OT preliminary astrometric position (Lipunov et al., GCN
#21173) which was done visually.
Our refind position are:
RA,DEC = 19 07 32.19 -16 25 06.9
3 sigma error = (+/-)2 arcsec (the source is marginaly visible). Our pixel
is 2 arcsec.
The offset from X-ray Swift position (Osborne at all) is 1.9 arcsec .
The position of the Postigo et al. ( GCN 21177) is inside our error box
(offset ~ 1.9 arcsec).
The possible OT position Pozanenko et al.( GCN #21174) offset ~ 8.2 arc
sec.
The OT detection image is available.
The message may be cited.
====================================================================
The observations made on zenit distance = 64 degrees, galaxy latitude b = -11
degree.
The moon (44 % bright part) below the horizon (The Moon altitude is -6 degree).
The sun altitude is -22.7 degree.
The object can be observed till sunrise at 2017-06-01 01:30:50 .
The message may be cited.
GCN Circular 21178
Subject
GROND observations of GRB 170531B
Date
2017-06-01T09:42:36Z (8 years ago)
From
Patricia Schady at MPE/Swift <pschady@mpe.mpg.de>
P. Schady and T. Kruehler (both MPE) report
We observed the field of GRB 170531B (Swift trigger 755354; Evans et al.,
GCN #21171) 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 03:55 UT on 01-06-2017, 5.9 hours the GRB trigger.
They were performed at an average seeing of 1.3" and at an average airmass
of 1.3.
We detect a point source within the 1.8" enhanced Swift/XRT error circle
(Osborne et al., GCN #21175), and consistent with the afterglow position
reported by Ugarte Postigo et al. (GCN #21177).
Based on a total exposure of 54 min in g'r'i'z' and 45 min in JHK, we
estimate preliminary magnitudes (all in AB) of
g' = 22.65 +/- 0.04
r' = 22.15 +/- 0.04
i' = 21.99 +/- 0.05
z' = 21.84 +/- 0.06
J = 21.8 +/- 0.3
H = 21.5 +/- 0.3
K > 19.9
Given magnitudes are calibrated against PanSTARRS and 2MASS field stars
and are not corrected for the expected Galactic foreground extinction
corresponding to a reddening of E_(B-V)=0.16 mag in the direction of the
burst (Schlafly & Finkbeiner 2011).
We acknowledge the excellent support provided by the Chilean observer at
the telescope, and the support astronomer, Sam Kim, in obtaining these
data.
GCN Circular 21177
Subject
GRB 170531B: Redshift from GTC/OSIRIS
Date
2017-06-01T06:34:45Z (8 years ago)
From
Antonio de Ugarte Postigo at IAA-CSIC <deugarte@iaa.es>
A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), L. Izzo (IAA-CSIC),
D.A. Kann (IAA-CSIC), C.C. Thoene (IAA-CSIC), Z. Cano
(IAA-CSIC), J.P.U. Fynbo (DARK/NBI), D. Garcia Alvarez
(GTC, IAC), D. Perez Valladares (GTC), A. Nu��ez (GTC), M. Huertas (GTC)
report on behalf of a larger collaboration:
We observed the afterglow of GRB 170531B (Evans et al. GCN
21171, Lipunov et al. GCN 21173, Pozanenko et al. GCN 21174)
using OSIRIS at the 10.4 m GTC telescope in La Palma (Spain).
Observation consisted in 3x900s exposures using the R1000B
grism, covering the range between 3700 and 7880 AA. The mean
epoch of the combined spectrum is 03:09:29 UT (5.12 hr after the
GRB onset). Additionally, g, r, i, and z-band observations were
obtained. We note that the coordinates of the afterglow are
19:07:32.09, -16:25:05.8 (J2000 +/-0.5���), which places the GRB
approximately 5��� away from those of the source identified by
Lipunov et al. (GCN 21173) and Pozanenko et al. (GCN 21174).
The afterglow can be also detected in the early Swift/UVOT
images. In the acquisition image we measure a magnitude of
r_AB = 21.9 for the afterglow, as compared to PANSTARRS
catalogue field stars.
The afterglow spectrum shows continuum throughout the
wavelength range and several strong absorption features
corresponding to Lyman-alpha, SiII, OI, CII, SiIV, CIV, AlII and AlII
at a common redshift of 2.366, which we identify as the redshift of
the GRB.
[GCN OPS NOTE(01jun17): Per author's request, authors DPV, AN, & MH
were added to the list.]
GCN Circular 21175
Subject
GRB 170531B: Enhanced Swift-XRT position
Date
2017-06-01T00:59:47Z (8 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1160 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 170531B, 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 = 286.88369, -16.41911 which is equivalent
to:
RA (J2000): 19h 07m 32.09s
Dec (J2000): -16d 25' 08.8"
with an uncertainty of 1.8 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.
GCN Circular 21174
Subject
GRB 170531B: CrAO confirmation of the afterglow
Date
2017-06-01T00:11:21Z (8 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
A. Pozanenko (IKI), D. Chestnov (ISON), A. Novichonok (ISON), A. Mokhnatkin
(ISON) report on behalf of larger GRB follow-up collaboration:
We observed the field of the GRB 170531B (Evans et al.,GCN 21171) with
with Zeiss-1000/Koshka telescope starting on May 31 (UT) 22:32:32, i.e. ~30
minutes after burst onset. We took several images in filter R with
exposures of 180 s. Near the border of XRT error circle (Evans et al.,GCN
21171) we detect the source in coordinates (J2000) 19:07:31.67 -16:25:09.3
with uncertainity of 0.5 arcsec in both coordinates. The source is probably
coincedent with the object reported by (Lipunov et al., GCN 21172). The
source is fading from R=19.1 at (UT) 22:32:32 down to R=19.5 at (UT)
23:30:56. Most probably the source is an afterglow of GRB 170531B.
GCN Circular 21173
Subject
GRB 170531B: MASTER Net OT detection
Date
2017-05-31T23:19:01Z (8 years ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
V. Lipunov, V.Kornilov, N.Tyurina, E.Gorbovskoy, D.Kuvshinov, A.V.Krylov,
I.Gorbunov, P.Balanutsa, A.Kuznetsov, V.V.Chazov, D. Vlasenko
Lomonosov Moscow State University, Sternberg Astronomical Institut of MSU
A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov
Kislovodsk Solar Station of the Pulkovo Observatory
N.M.Budnev, O.Gres, O. Ershova
Irkutsk State University
A.Gabovich, V.Yurkov, Yu.Sergienko
Blagoveschensk Educational State University, Blagoveschensk
D.Buckley, S. Potter, A.Kniazev, M.Kotze
South African Astronomical Observatory
R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias
R.Podesta, C.Lopez, F. Podesta Observatorio Astronomico Felix Aguilar (OAFA),
National University of San Juan, Argentina
H. Levato, C. Saffe
Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE),
San Juan, Argentina
MASTER-Kislovodsk robotic telescope (2x4 square degrees, MASTER-Net:
http://observ.pereplet.ru) was pointed to the GRB170531B (Evans et al.,
GCN #21171) 12 sec after notice time and 452 sec after trigger
time on 2017-05-31 22:09:44 UT.
There is marginally seen optical transient at the position 19h 07m 32.03s
-16d 25' 10.4" with m_OT~19.0+-0.5
The 5-sigma upper limit is about 18.5mag
The message may be cited.
====================================================================
The observations made on zenit distance = 64 degrees, galaxy latitude b = -11 degree.
The moon (44 % bright part) below the horizon (The Moon altitude is -6 degree).
The sun altitude is -22.7 degree.
The object can be observed till sunrise at 2017-06-01 01:30:50 .
The message may be cited.
GCN Circular 21171
Subject
GRB 170531B: Swift detection of a burst
Date
2017-05-31T22:23:52Z (8 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
P.A. Evans (U Leicester), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), A. Cholden-Brown (PSU), A. Y. Lien (GSFC/UMBC),
K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of
the Swift Team:
At 22:02:09 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170531B (trigger=755354). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 286.895, -16.426 which is
RA(J2000) = 19h 07m 35s
Dec(J2000) = -16d 25' 34"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a complex
structure with a duration of at least 50 sec. The peak count rate
was ~2000 counts/sec (15-350 keV), at ~6 sec after the trigger.
The XRT began observing the field at 22:04:30.1 UT, 140.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 286.8835,
-16.4196 which is equivalent to:
RA(J2000) = 19h 07m 32.03s
Dec(J2000) = -16d 25' 10.4"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 45 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 consistent with the Galactic value of 1.41
x 10^21 cm^-2 (Willingale et al. 2013).
The initial flux in the 2.5 s image was 2.73e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 152 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. The 8'x8' region for the list of sources generated on-board covers
100% of the XRT error circle. Because of the density of catalogued stars,
further analysis is required to report an upper limit for any afterglow in the
region. No correction has been made for the expected extinction corresponding
to E(B-V) of 0.19.
Burst Advocate for this burst is P.A. Evans (pae9 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.)