GRB 200925B
GCN Circular 28499
Subject
GRB 200925B: Swift detection of a burst
Date
2020-09-25T22:00:50Z (5 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
S. B. Cenko (GSFC), C. Gronwall (PSU), J.D. Gropp (PSU),
N. J. Klingler (PSU), H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL) and A. Tohuvavohu (U Toronto) report on behalf of
the Neil Gehrels Swift Observatory Team:
At 21:50:37 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200925B (trigger=997453). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 246.851, +78.394 which is
RA(J2000) = 16h 27m 24s
Dec(J2000) = +78d 23' 39"
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 40 sec. The peak count rate
was ~2000 counts/sec (15-350 keV), at ~5 sec after the trigger.
The XRT began observing the field at 21:51:55.3 UT, 78.4 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 246.78990, 78.39033 which is equivalent
to:
RA(J2000) = 16h 27m 09.58s
Dec(J2000) = +78d 23' 25.2"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 46 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 4.59
x 10^20 cm^-2 (Willingale et al. 2013).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 81 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. The typical 3-sigma upper limit has been about 19.6 mag.
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.04.
Burst Advocate for this burst is S. B. Cenko (brad.cenko AT nasa.gov).
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 28500
Subject
GRB 200925B: Prompt enhanced Swift-XRT position
Date
2020-09-25T23:04:05Z (5 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Using promptly downlinked XRT event data for GRB 200925B, we find an
enhanced XRT position of the afterglow: RA, Dec: 246.7868, 78.3904
which is equivalent to:
RA (J2000) = 16 27 08.83
Dec (J2000) = +78 23 25.5
with an uncertainty of 2.0 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/997453.
Position enhancement is is described by Goad et al. (2007, A&A, 476,
1401) and Evans et al. (2009, MNRAS, 397, 1177).
This circular is an official product of the Swift-XRT team.
GCN Circular 28501
Subject
GRB 200925B: OSN Afterglow Candidate Discovery
Date
2020-09-25T23:14:27Z (5 years ago)
From
Alexander Kann at IAA-CSIC <kann@iaa.es>
A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. A. Kann, C. C. Thoene,
M. Blazek, J. F. Agui Fernandez (all HETH/IAA-CSIC), and F. Aceituno
(IAA-CSIC) report:
We observed the location of the Swift GRB 200925B (Cenko et al., GCN
#28499) with the 1.5m telescope of the Observatorio Sierra Nevada, in
Granada, Spain. We obtained a 300 s image each in the BVRc bands and
multiple 100 s images in Ic, beginning 2020-09-25 22:27:07 UT.
We detect a source in all filters at
RA (J2000) = 16:27:08.50
Dec. (J2000) = +78:23:24.9
with an error of 0".5, within the UVOT-enhanced XRT position (Evans, GCN
#28500). We note this source is also clearly detected in the initial
Swift UVOT white finding chart, at a significantly brighter magnitude
relative to the nearby field star.
This strongly suggests the source is fading and is therefore the
afterglow of GRB 200925B.
At 0.034294 days after the GRB, we measure r' = 19.46 +/- 0.1 (AB
magnitude) vs. nearby SDSS field stars.
[GCN OPS NOTE(26Sep20): Per the author's request: in the Title the "25A" was changed to "25B",
the affiliation of A. de Ugarte Postigo is "*-CSIC" not "*-CSIS",
"Thoene" not "Thone", and in the first sentence, the "200906A" should be "200925B".]
GCN Circular 28502
Subject
Swift GRB 200925B: Global MASTER-Net OT detection
Date
2020-09-26T00:05:19Z (5 years ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
V. Lipunov, N.Tyurina, E. Gorbovskoy, V.Kornilov, 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),
O.A. Gres, N.M. Budnev, O.Ershova
(Irkutsk State University, API),
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),
A. Tlatov, D. Dormidontov
(Kislovodsk Solar Station of the Pulkovo Observatory),
V. Yurkov, A. Gabovich, Yu. Sergienko
(Blagoveschensk Educational State University)
MASTER-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy,
vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station)
was pointed to the Swift GRB200925A (trigger No 997453,16h 27m 24.24s , +78d 23m 38.4s, R=0.05) errorbox
14 sec after notice time and 58 sec after trigger time at 2020-09-25 21:51:35 UT,
with upper limit up to 18.4 mag. The observations began at zenith distance = 53 deg. The sun altitude is -47.0 deg.
On our 4-th (40s exposure) set , obtained 229 sec after tigger time at 2020-09-25 21:54:16 UT, we found an optical transient within Swift error-box (ra=246.851 dec=+78.394 r=0.05).
T-Tmid Date Time Expt. Ra Dec Mag
---------|---------------------|-------|-----------------|-----------------|-----
229 2020-09-25 21:54:16 40 (246.7866 d, +78.3896 d) 17.9
The OT position in within enhanced XRT position (GCN 28500) and is coincident with OSN afterglow candidate position (A. de Ugarte Postigo et al, GCN 28501)
The 5-sigma upper limit has been about 18.4 mag
The message may be cited.
GCN Circular 28503
Subject
GRB 200925B: Enhanced Swift-XRT position
Date
2020-09-26T04:08:17Z (5 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1704 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 200925B, 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 = 246.78522, +78.39052 which is equivalent
to:
RA (J2000): 16h 27m 8.45s
Dec (J2000): +78d 23' 25.9"
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 28506
Subject
GRB 200925B: Swift-BAT refined analysis
Date
2020-09-26T18:03:43Z (5 years ago)
From
Hans Krimm at NSF/NASA-GSFC <hkrimm@nsf.gov>
M. Stamatikos (OSU), S. D. Barthelmy (GSFC), S. B. Cenko (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):
Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 200925B (trigger #997453)
(Cenko, et al., GCN Circ. 28499). The BAT ground-calculated position is
RA, Dec = 246.892, 78.393 deg which is
RA(J2000) = 16h 27m 34.1s
Dec(J2000) = +78d 23' 33.5"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 50%.
The mask-weighted light curve shows two peaks, the first beginning ~T-2 sec,
peaking at T+5 sec, and decaying by T+12 sec. The second, weaker, peak runs
from T+16 to T+22 sec. T90 (15-350 keV) is 18.25 +- 0.97 sec (estimated error
including systematics).
The time-averaged spectrum from T+0.20 to T+19.59 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
2.01 +- 0.14. The fluence in the 15-150 keV band is 1.0 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+4.38 sec in the 15-150 keV band
is 3.0 +- 0.3 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/997453/BA/
GCN Circular 28507
Subject
GRB 200925B: Swift/UVOT Detection
Date
2020-09-26T20:14:25Z (5 years ago)
From
Samantha Oates at MSSL <samantha.oates@alumni.ucl.ac.uk>
S. R. Oates (U.Birmingham) and S. B. Cenko (GSFC)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 200925B
82 s after the BAT trigger (Cenko et al., GCN Circ. 28499).
A source consistent with the XRT position (Beardmore et al. GCN Circ. 28503)
and the optical position reported by the OSN
(de Ugarte Postigo et al., GCN Circ. 28501) and MASTER
(Lipunov et al., GCN Circ. 28502) is detected in the initial UVOT exposures.
Preliminary detections and 3-sigma upper limits 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 (FC) 82 232 147 19.80 +/- 0.20
white 574 1714 264 20.77 +/- 0.37
v 623 1763 136 >18.9
b 549 1689 117 >19.6
u (FC) 294 544 246 >19.7
u 294 1663 343 >19.9
w1 672 1813 136 >19.0
m2 1249 1441 39 >17.7
w2 599 1739 117 >18.9
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).
GCN Circular 28508
Subject
GRB 200925B: Swift-XRT refined Analysis
Date
2020-09-26T22:00:05Z (5 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), A.P.
Beardmore (U. Leicester), P.A. Evans (U. Leicester), J.P. Osborne (U.
Leicester), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB), P. D'Avanzo
(INAF-OAB) and S.B. Cenko report on behalf of the Swift-XRT team:
We have analysed 5.1 ks of XRT data for GRB 200925B (Cenko et al. GCN
Circ. 28499), from 87 s to 47.2 ks after the BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Beardmore et al. (GCN Circ. 28500). The
late-time light curve (from T0+29.2 ks) is consistent with a constant
source of mean count rate 1.3e-01 ct/sec. A power-law fit gives an
index of 1.0 (+/-1.2).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.12 (+0.19, -0.18). The
best-fitting absorption column is 7.5 (+4.4, -2.9) x 10^20 cm^-2,
consistent with the Galactic value of 4.6 x 10^20 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum is 3.1 x 10^-11 (3.8 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 7.5 (+4.4, -2.9) x 10^20 cm^-2
Galactic foreground: 4.6 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 2.12 (+0.19, -0.18)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00997453.
This circular is an official product of the Swift-XRT team.
GCN Circular 28511
Subject
GRB 200925B NUTTelA-TAO / BSTI Early Measurements (Preliminary)
Date
2020-09-27T05:14:22Z (5 years ago)
From
Bruce Grossan at LBNL/UCB SSL <Bruce_Grossan@lbl.gov>
B. Grossan (UCB, NU) , Z. Maksut (NU), A. Kim (NU), M. Krugov (FAI), G. F. Smoot (HKUST, UCB, NU), E. Linder (UCB, NU), report on behalf of the Energetic Cosmos Laboratory:
The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB200925B on receipt of an automated GCN / BAT position alert. We report measurements made with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32,14) instrument ***during commissioning phase*** and we note cautions with these measurements below.
Calibration with bright Pan-STARRS catalog I stars on our images, for our standard SDSS filters and 45 s co-added images yields, *without color corrections*, the following photometric values for the OT consistent with the position given in Evans et al. (GCN 28503):
# tc-t0(s) g'(mag) r'(mag) i'(mag)
-- --------- ----------- ----------- ------------
1 67.5 UL18.27 UL18.07 UL17.32
2 136.5 UL18.15 18.62 17.94**
3 181.5 UL18.21 17.99 17.47
4 226.5 UL18.25 18.09 17.63
5 271.5 UL18.27 18.17 17.48
6 316.5 UL18.31 18.26 17.70
7 361.5 UL18.14 18.60 17.83
8 406.5 UL18.17 18.55 17.87*
UL = 5 sigma upper limit
** = very large certainty, close to limit ; poor by-eye confirmation and aperture centering
* = large uncertainty ; poor by-eye confirmation and aperture centering
Other uncertainties are estimated at ~ 0.1 mag
tc-t0 = trigger time minus image center time.
The measurements suggest that the early emission peaked ~180 s after trigger.
We caution the reader that the BSTI instrument is in commissioning phase, with known imperfections, and we have not extensively tested our results, e.g. against other simultaneous measurements, or near our detection limits. Please also note that the times are approximate. We anticipate additional analysis in 15-30 days posted at http://ecl.nu.edu.kz/gamma-ray-burst/grb200925b. Some earlier images may have usable data.
----------------------------------
UCB = University of California, Berkeley, USA
NU = Nazarbayev University, Nur-Sultan, Kazakhstan
HKUST = Hong Kong University of Science and Technology
FAI = Fesenkov Astrophysical Institute, Kazakhstan
The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan.
GCN Circular 28512
Subject
GRB 200925B: Swift-XRT refined analysis update
Date
2020-09-27T11:32:20Z (5 years ago)
From
Andy Beardmore at U Leicester <ab271@leicester.ac.uk>
A.P. Beardmore (U. Leicester) and S. B. Cenko (GSFC) report on
behalf of the Swift-XRT team:
An additional 4.9 ks of Swift-XRT Photon Counting mode data have
been collected on GRB 200925B (Cenko et al. GCN Circ. 28499,
Sbarufatti et al. GCN Circ. 28508), bringing the total XRT
exposure to 10 ks, from 87 s to 86.3 ks after the BAT trigger.
The late time X-ray light curve from T0+29.2 ks to 86.3 ks
is now decaying with a power-law decay slope of 1.1 +/- 0.4.
If the light curve continues to decay at the same rate than
the predicted count rate at T0+3 days will be 3.4e-03 count/sec,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of
1.05 x 10^-13 (1.28 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/00997453.
This circular is an official product of the Swift-XRT team.