GRB 200922A
GCN Circular 28471
Subject
GRB 200922A: Swift detection of a burst with possible optical counterpart
Date
2020-09-22T12:26:24Z (5 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
M. J. Moss (GWU), E. Ambrosi (INAF-IASFPA), V. D'Elia (SSDC),
J.D. Gropp (PSU), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), B. Sbarufatti (PSU) and M. H. Siegel (PSU) report
on behalf of the Neil Gehrels Swift Observatory Team:
At 12:06:46 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200922A (trigger=997024). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 296.915, -55.204 which is
RA(J2000) = 19h 47m 40s
Dec(J2000) = -55d 12' 12"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a single peak
structure with a duration of about 10 sec. The peak count rate
was ~10000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 12:08:02.2 UT, 75.6 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 296.95425, -55.20245 which
is equivalent to:
RA(J2000) = 19h 47m 49.02s
Dec(J2000) = -55d 12' 08.8"
with an uncertainty of 4.2 arcseconds (radius, 90% containment). This
location is 80 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 https://www.swift.ac.uk/sper. We
cannot determine whether the source is fading at the present time.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 4.71
x 10^20 cm^-2 (Willingale et al. 2013).
The initial flux in the 2.5 s image was 8.21e-10 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White
filter starting 85 seconds after the BAT trigger. The 2.7'x2.7'
sub-image covers 100% of the XRT error circle. There is a 14.4 mag
source at (296.95361,-55.20447) 8.3 arc seconds from the center of
the XRT error region. There is a much weaker source at the same
position in the DSS. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.05.
Burst Advocate for this burst is M. J. Moss (mikejmoss3 AT gmail.com).
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/)
GCN Circular 28473
Subject
GRB 200922A: Enhanced Swift-XRT position
Date
2020-09-22T17:56:59Z (5 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 50 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 200922A, 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 = 296.95259, -55.20359 which is equivalent
to:
RA (J2000): 19h 47m 48.62s
Dec (J2000): -55d 12' 12.9"
with an uncertainty of 2.5 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 28476
Subject
GRB 200922A: Swift-XRT refined Analysis
Date
2020-09-22T20:52:18Z (5 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
A. D'Ai (INAF-IASFPA), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU),
D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), P.A. Evans (U. Leicester), A. Melandri (INAF-OAB), T.
Sbarrato (INAF-OAB) and M.J. Moss report on behalf of the Swift-XRT
team:
We have analysed 6.8 ks of XRT data for GRB 200922A (Moss et al. GCN
Circ. 28471), from 81 s to 23.1 ks after the BAT trigger. The data
comprise 123 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Osborne et al. (GCN Circ. 28473).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.148 (+0.026, -0.025).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.33 (+0.18, -0.17). The
best-fitting absorption column is 1.6 (+0.5, -0.4) x 10^21 cm^-2, in
excess of the Galactic value of 4.7 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.18 (+0.24, -0.23)
and a best-fitting absorption column of 2.4 (+0.9, -0.8) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.3 x 10^-11 (5.0 x 10^-11) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 2.4 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 4.7 x 10^20 cm^-2
Excess significance: 4.3 sigma
Photon index: 2.18 (+0.24, -0.23)
If the light curve continues to decay with a power-law decay index of
1.148, the count rate at T+24 hours will be 4.8 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.6 x
10^-13 (2.4 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/00997024.
This circular is an official product of the Swift-XRT team.
GCN Circular 28477
Subject
Swift GRB 200922A: Global MASTER-Net observations report
Date
2020-09-22T22:36:19Z (5 years ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin,
V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva,
D.Kuvshinov, D. Cheryasov
(Lomonosov Moscow State University, SAI, Physics Department),
R. Podesta, C.Lopez, F. Podesta, C.Francile
(Observatorio Astronomico Felix Aguilar OAFA),
R. Rebolo, M. Serra
(The Instituto de Astrofisica de Canarias),
D. Buckley
(South African Astronomical Observatory),
O.A. Gres, N.M. Budnev, O.Ershova
(Irkutsk State University, API),
A. Tlatov, D. Dormidontov
(Kislovodsk Solar Station of the Pulkovo Observatory),
V. Yurkov, A. Gabovich, Yu. Sergienko
(Blagoveschensk Educational State University)
MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 200922A ( M. J. Moss et al., GCN 28471) errorbox 37015 sec after notice time and 37039 sec after trigger time at 2020-09-22 22:24:05 UT, with upper limit up to 20.5 mag. The observations began at zenith distance = 48 deg. The sun altitude is -57.9 deg.
The galactic latitude b = -30 deg., longitude l = 343 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=1446564
We obtain a following upper limits.
Tmid-T0 | Site |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________
37129 | MASTER-SAAO | C | 180 | 20.5 |
37129 | MASTER-SAAO | C | 180 | 20.4 |
37329 | MASTER-SAAO | C | 180 | 20.5 |
37329 | MASTER-SAAO | C | 180 | 20.4 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 28478
Subject
GRB 200922A: LCO observations
Date
2020-09-22T23:40:25Z (5 years ago)
From
Luca Izzo at DARK/NBI <luca.izzo@gmail.com>
L. Izzo (DARK/NBI), D. B. Malesani (DTU Space) and D. A. Kann (HETH/IAA-CSIC) report:
We observed the field of GRB 200922A (Moss et al., GCN #28471) with the Sinistro instrument mounted on the 1-m telescope of the LCO network located at Siding Spring Observatory, Australia. Observations started on September 22 at 13:53:10 UT (1.77 hours after the GRB trigger). We obtained a series of 5x120s images in r and i filters each.
Within the UVOT-enhanced XRT position at RA (J2000) = 19:47:48.87 (296.95364), Dec. (J2000) = -55:12:15.9 (-55.20442) with an error of 1".5 (improved compared to the one reported in Osborne et al., GCN #28473) we clearly detect the source that had also been seen in the early UVOT observation (Moss et al., GCN #28471) at a white magnitude of 14.4. In our stacked image we measure i = 17.31 +- 0.04 (AB mag), calibrated against nearby SkyMapper catalog stars. This value is brighter than the archival value i = 17.74 +- 0.01 mag from the SkyMapper Data Release 2 (Onken et al., 2019, PASA 36, 33). Our result suggests variability compared to the historic value, and likely fading compared to the earlier UVOT observation. Similar fading is also measured versus archival DECam field images (i = 17.79 +- 0.02 mag, NOIRLab Prop. ID 2017A-0388; PI: A. Zenteno).
The coordinates of the source in our images are (J2000.0):
RA = 19:47:48.9285
Dec = -55:12:16.421
At this stage, it is unclear if this GRB was caused by the likely stellar source, or if it is a background GRB that happens to have occurred very close to a foreground object. Further observations are encouraged.
This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 730890.
GCN Circular 28482
Subject
GRB 200922A: Swift/UVOT Detection
Date
2020-09-23T13:04:40Z (5 years ago)
From
Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>
M. H. Siegel (PSU) and M. J. Moss (GWU)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 200922A
86 s after the BAT trigger (Moss et al., GCN Circ. 28471).
We identify a fading source near the XRT position
(Osborne et al. GCN Circ. 28473) and also at the location of a weak source
in the DSS. The source position is:
RA(J2000) = 19:47:48.76 = 296.95317
DEC(J2000) = -55:12:16.5 = -55.20457
Which is 3.0 arc-second from the enhanced XRT position.
Preliminary detections using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white 86 236 147 14.37+/-0.02
white 4770 4970 196 17.51+/-0.04
white 28889 28909 19 18.62+/-0.20
v 3745 3945 196 17.35+/-0.10
v 9268 23149 1460 17.79+/-0.05
b 4566 4765 196 17.95+/-0.07
b 27982 28889 881 18.49+/-0.05
u 4360 4560 196 17.18+/-0.06
u 15921 16791 848 18.20+/-0.06
uvw1 4156 4355 196 17.23+/-0.10
uvw1 11089 15915 887 18.26+/-0.09
uvw1 50455 56029 225 18.97+/-0.27
uvm2 3950 4150 196 17.12+/-0.12
uvm2 10182 11081 885 18.19+/-0.10
uvm2 50396 55850 223 19.26+/-0.36
uvw2 3541 5089 307 17.14+/-0.09
uvw2 21653 22553 885 18.77+/-0.12
uvw2 50338 55672 223 >19.44
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 28483
Subject
Improved enhanced Swift-XRT position of GRB 200922A
Date
2020-09-23T13:11:07Z (5 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester), A. D���ai (INAF-IASFPA) and M. J. Moss (GWU)
report on behalf of the Swift-XRT team:
The enhanced-XRT position reported in GCN Circ. 28473 was a particularly poor
position and has been improved and shifted by the receipt of further data, as
noted by Izzo et al (GCN. Circ. 28478).
The best XRT position, available at
https://www.swift.ac.uk/xrt_positions/00997024/ is RA, Dec = 296.95364,
-55.20442 degrees which is equivalent to:
RA (J2000) = 19h 47m 48.87s
Dec (J2000) = -55d 12' 15.9���
with an uncertainty of 1.5��� (radius, 90% confidence). This position is
consistent with the source seen by UVOT and LCO (GCN Circs. 28471, 28478).
It is normal for the XRT position to evolve slightly as new data are received, with
the website always being the source of the most recent position. In the case of
this GRB, the first visibility window for Swift was very short, and the
satellite attitude appears to have been less stable than usual; this resulted in
the position in GCN 28473 being unusually inaccurate.
This circular is an official product of the Swift-XRT team.
GCN Circular 28484
Subject
GRB 200922A: Swift-BAT refined analysis
Date
2020-09-23T14:47:47Z (5 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), M. J. Moss (GWU),
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+871 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 200922A (trigger #997024)
(Moss et al., GCN Circ. 28471). The BAT ground-calculated position is
RA, Dec = 296.954, -55.199 deg which is
RA(J2000) = 19h 47m 49.0s
Dec(J2000) = -55d 11' 55.1"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 74%.
The mask-weighted light curve shows a single FRED-like pulse that
starts at ~T-2 s, peaks at ~T+0, and ends at ~T+16 s.
T90 (15-350 keV) is 10.30 +- 1.96 sec (estimated error including
systematics).
The time-averaged spectrum from T-1.91 to T+16.22 sec is best fit
by a power law with an exponential cutoff. This fit gives a photon
index 1.43 +- 0.26, and Epeak of 39.3 +- 5.7 keV (chi squared 52.48
for 56 d.o.f.). For this model the total fluence in the 15-150 keV
band is 2.8 +- 0.1 x 10^-6 erg/cm2 and the 1-sec peak flux measured
from T-0.46 sec in the 15-150 keV band is 11.4 +- 0.5 ph/cm2/sec.
A fit to a simple power law gives a photon index of 2.12 +- 0.06
(chi squared 76.50 for 57 d.o.f.). 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/997024/BA/
GCN Circular 28490
Subject
GRB 200922A: Insight-HXMT/HE detection
Date
2020-09-24T11:02:22Z (5 years ago)
From
YaoGuang Zheng at IHEP <zhengyg@ihep.ac.cn>
Y. Q. Zhang, Y. G. Zheng, C. Cai, Q. Luo, S. Xiao, Q. B. Yi,
C. K. Li, G. Li, X. B. Li, J. Y. Liao, S. L. Xiong,
C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang,
Y. F. Zhang, X. F. Lu, C. L. Zou (IHEP), Y. J. Jin,
Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song,
M. Wu, Y. P. Xu, S. N. Zhang (IHEP),
report on behalf of the Insight-HXMT team:
At 2020-09-22T12:06:46.00 (T0), Insight-HXMT/HE detected
GRB 200922A (trigger ID: HEB200922504) in a routine search of the data,
which also triggered Swift/BAT (Moss et al., GCN #28471).
The Insight-HXMT/HE light curve mainly consists of single
pulses with a duration (T90) of 1.87 s measured from T0+0.04 s.
The 1-ms peak rate, measured from T0+0.18 s, is 629 cnts/sec.
The total counts from this burst is 742 counts.
URL_LC: http://twiki.ihep.ac.cn/pub/HXMT/GRBList/HEB200922504_lc.jpg
All measurements above are made with the CsI detectors operating in the
regular mode with the energy range of about 80-800 keV (deposited 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
funded jointly by the China National Space Administration (CNSA) and
the Chinese Academy of Sciences (CAS).
More information about it could be found at:
http://www.hxmt.org.
GCN Circular 28492
Subject
GRB 200922A: chance superposition between optical afterglow and archival star
Date
2020-09-24T21:15:28Z (5 years ago)
From
Daniele B Malesani at DTU Space <malesani@space.dtu.dk>
D. B. Malesani (DTU Space), L. Izzo (DARK/NBI), D. A. Kann (HETH,
IAA/CSIC), A. de Ugarte Postigo (HETH, IAA/CSIC), A. J. Levan (Radboud
Univ.), D. Xu (NAOC), P. D'Avanzo (INAF/OABr), and A. Rossi (INAF/OAS)
report on behalf of the Stargate collaboration:
For the recent GRB 200922A, several authors have noted the presence of a
bright optical afterglow, initially detected by UVOT onboard the Neil
Gehrels Swift observatory (Moss et al., GCN 28471; Izzo et al., GCN
28478; Siegel & Moss, GCN 28482), superimposed on a point-like object,
seen e.g. in the DSS, DECam, and SkyMapper surveys.
We retrieved the white-band UVOT images (Siegel & Moss, GCN 28482). We
focused on the initial image (344 s exposure starting at 12:08:32 UT on
Sep 22) and on the image taken roughly one day after (274 s exposure
starting at 10:05:38 UT on Sep 23). We also retrieved for comparison the
archival DECam i-band images of the same region (from 2017 August).
We remark that the position of the UVOT object is entirely consistent
with the latest XRT position of the afterglow (Evans et al., GCN 28483;
see also https://www.swift.ac.uk/xrt_positions/), strengthening the
association between the optical transient and GRB 200922A.
We then cross-matched the astrometry between the UVOT and the archival
DECam images. The scatter in the astrometric solution, computed on stars
of brightness similar to the UVOT afterglow, is 0.06 and 0.10 arcsec for
the initial and late exposure, respectively.
In the initial UVOT image, we measure an offset of 0.62" compared to the
object seen in the archival data. While small, this offset is
significant. The same comparison carried out in the late time image,
however, returns no measurable offset to within the errors.
Independently, we also checked that the proper motion of the star
(catalogued in the Gaia DR2; Brown et al. 2018, A&A, 616, A1) is too
small to play any effect in producing the offset.
We thus conclude that this is a rare case of near-perfect chance
superposition between a background afterglow and a bright foreground
star. In the initial UVOT image, the light was dominated by the
afterglow (thus yielding the offset in the position), which subsequently
faded to a level fainter than the foreground star. The light curve of
the X-ray afterglow (D'Ai et al., GCN 28476) is also consistent with
this interpretation, as it shows the typical behaviour of a cosmological
GRB.
A spectrum of the optical transient was taken using the ESO VLT1 UT1
(Antu) equipped with the FORS2 instrument. Observations were carried out
using the grisms 300V and 300I (900 s exposure each), covering the
wavelength range 3500-9200 AA, and started on 2020 Sep 22.997 UT (11.8
hr after the trigger). In the acquisition image, using (old) archival
zeropoints, we measure V = 18.0 (Vega). This value is roughly consistent
with the archival values of the star (for example the Gaia catalog gives
G = 17.85), and indicates only little contribution from the afterglow at
the epoch of our spectrum (at least in the V band).
The spectrum we observe is consistent with the one of a G-type star.
Absorption features are observed at z = 0 from Ca H and K, Mg I, Na I D,
Hdelta, Hgamma, Hbeta, and Halpha. The ordinary type of the star
supports the lack of a connection with the GRB. A search was conducted
for potential emission lines from the background GRB host galaxy, but
the intense and spatially-variable glare from the star does not allow us
to place quantitative limits. We are thus unfortunately unable to
provide constraints on the GRB redshift.
We welcome the reopening of the ESO observatory at Paranal, even if at
reduced capacity. We thank the ESO staff for carrying out our
observations, in particular Steffen Mieske, Claudia Cid, and Romain
Thomas, as well as and the entire support team on- and off-site.
GCN Circular 28505
Subject
GRB 200922A: Chilescope optical observations
Date
2020-09-26T16:18:20Z (5 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
A. Pozanenko (IKI), S. Belkin (IKI), A. Volnova (IKI), P. Minaev (IKI),
N. Pankov (HSE) report on behalf GRB IKI FuN collaboration:
We observed the field of GRB 200922A (Moss et al., GCN 28471) with
RC-1000 Chilescope observatory in r'-filter starting on 2020-09-22 (UT)
23:25:05. In a single obtained image of 1200 s exposure we cannot
resolve the OT reported earlier (Moss et al., GCN 28471; Izzo et al.,
GCN 28478; Siegel et al., GCN 28482; Malesani et al., GCN 28492).
Instead we subtract the flux of nearby star from SkyMapper DR1.1 from
the (nearby star + OT) photometry.
Preliminary photometry of the OT after the above-mentioned procedure is
following.
Date UT start t-T0 Filter Exp. OT(AB) Err. UL(AB)
(mid, days) (s)
2020-09-22 23:25:05 0.478 r' 1200 18.92 0.05 20.7
The photometry is based on nearby SkyMapper DR1.1 stars.