GRB 210818A
GCN Circular 30661
Subject
Swift GRB 210818A: Global MASTER-Net observations report
Date
2021-08-19T01:06:55Z (4 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 210818A ( A. P. Beardmore et al., GCN 30652) errorbox 22995 sec after notice time and 23077 sec after trigger time at 2021-08-18 07:27:44 UT, with upper limit up to 18.9 mag. The observations began at zenith distance = 62 deg. The sun altitude is -47.3 deg.
The galactic latitude b = -25 deg., longitude l = 301 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=1693376
We obtain a following upper limits.
Tmid-T0 | Site |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________
23167 | MASTER-OAFA | C | 180 | 13.8 |
23347 | MASTER-OAFA | C | 540 | 14.9 | Coadd
23379 | MASTER-OAFA | C | 180 | 14.9 |
23559 | MASTER-OAFA | C | 540 | 15.3 | Coadd
23592 | MASTER-OAFA | C | 180 | 14.6 |
23812 | MASTER-OAFA | C | 180 | 14.3 |
24026 | MASTER-OAFA | C | 180 | 14.8 |
24242 | MASTER-OAFA | C | 180 | 15.8 |
24456 | MASTER-OAFA | C | 180 | 15.0 |
24636 | MASTER-OAFA | C | 540 | 17.0 | Coadd
24668 | MASTER-OAFA | C | 180 | 14.9 |
24883 | MASTER-OAFA | C | 180 | 16.4 |
25099 | MASTER-OAFA | C | 180 | 17.3 |
25279 | MASTER-OAFA | C | 540 | 18.0 | Coadd
25329 | MASTER-OAFA | C | 180 | 17.4 |
25546 | MASTER-OAFA | C | 180 | 17.4 |
25762 | MASTER-OAFA | C | 180 | 16.9 |
25942 | MASTER-OAFA | C | 540 | 18.0 | Coadd
25975 | MASTER-OAFA | C | 180 | 18.0 |
26190 | MASTER-OAFA | C | 180 | 17.3 |
26405 | MASTER-OAFA | C | 180 | 17.3 |
26585 | MASTER-OAFA | C | 540 | 17.6 | Coadd
26621 | MASTER-OAFA | C | 180 | 17.7 |
26833 | MASTER-OAFA | C | 180 | 17.5 |
27049 | MASTER-OAFA | C | 180 | 17.7 |
27229 | MASTER-OAFA | C | 540 | 18.3 | Coadd
27264 | MASTER-OAFA | C | 180 | 17.5 |
27479 | MASTER-OAFA | C | 180 | 17.7 |
27691 | MASTER-OAFA | C | 180 | 17.5 |
27871 | MASTER-OAFA | C | 540 | 18.5 | Coadd
27906 | MASTER-OAFA | C | 180 | 17.6 |
28123 | MASTER-OAFA | C | 180 | 18.2 |
28337 | MASTER-OAFA | C | 180 | 17.7 |
28517 | MASTER-OAFA | C | 540 | 18.1 | Coadd
28551 | MASTER-OAFA | C | 180 | 17.3 |
28765 | MASTER-OAFA | C | 180 | 18.0 |
28983 | MASTER-OAFA | C | 180 | 18.0 |
29199 | MASTER-OAFA | C | 180 | 17.9 |
29415 | MASTER-OAFA | C | 180 | 17.7 |
29595 | MASTER-OAFA | C | 540 | 18.0 | Coadd
29630 | MASTER-OAFA | C | 180 | 17.5 |
29810 | MASTER-OAFA | C | 540 | 18.6 | Coadd
29842 | MASTER-OAFA | C | 180 | 18.2 |
30058 | MASTER-OAFA | C | 180 | 18.4 |
30272 | MASTER-OAFA | C | 180 | 18.2 |
30488 | MASTER-OAFA | C | 180 | 17.8 |
30701 | MASTER-OAFA | C | 180 | 18.0 |
30881 | MASTER-OAFA | C | 540 | 18.9 | Coadd
30917 | MASTER-OAFA | C | 180 | 18.1 |
31130 | MASTER-OAFA | C | 180 | 18.3 |
31329 | MASTER-OAFA | C | 180 | 18.3 |
31729 | MASTER-OAFA | C | 180 | 18.4 |
31909 | MASTER-OAFA | C | 540 | 18.5 | Coadd
31928 | MASTER-OAFA | C | 180 | 18.4 |
32127 | MASTER-OAFA | C | 180 | 18.0 |
32327 | MASTER-OAFA | C | 180 | 17.4 |
32507 | MASTER-OAFA | C | 540 | 18.0 | Coadd
32527 | MASTER-OAFA | C | 180 | 17.3 |
32726 | MASTER-OAFA | C | 180 | 17.1 |
32926 | MASTER-OAFA | C | 180 | 17.3 |
33106 | MASTER-OAFA | C | 540 | 17.9 | Coadd
33125 | MASTER-OAFA | C | 180 | 17.5 |
33325 | MASTER-OAFA | C | 180 | 17.1 |
33524 | MASTER-OAFA | C | 180 | 16.7 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 30660
Subject
GRB 210818A: Swift-XRT refined Analysis
Date
2021-08-18T22:39:25Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester), J.P. Osborne (U. Leicester), E. Ambrosi
(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR),
J. D. Gropp (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), K.L.
Page (U. Leicester) and A.P. Beardmore report on behalf of the
Swift-XRT team:
We have analysed 7.1 ks of XRT data for GRB 210818A (Beardmore et al.
GCN Circ. 30652), from 65 s to 69.5 ks after the BAT trigger. The data
comprise 188 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. 30653).
The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=1.04 (+/-0.20). At T+111 s the decay
steepens to an alpha of 6.8 (+0.7, -0.6). The light curve breaks again
at T+157 s to a decay with alpha=0.67 (+0.38, -0.29), before a final
break at T+479 s s after which the decay index is 1.50 (+/-0.06).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 0.86 (+/-0.06). The
best-fitting absorption column is 2.5 (+0.5, -0.4) x 10^21 cm^-2, in
excess of the Galactic value of 1.7 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.64 (+0.14, -0.11)
and a best-fitting absorption column of 1.94 (+0.56, -0.20) x 10^21
cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 4.4 x 10^-11 (5.3 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.94 (+0.56, -0.20) x 10^21 cm^-2
Galactic foreground: 1.7 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.64 (+0.14, -0.11)
If the light curve continues to decay with a power-law decay index of
1.50, the count rate at T+24 hours will be 3.1 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.3 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/01069169.
This circular is an official product of the Swift-XRT team.
GCN Circular 30659
Subject
GRB 210818A: Swift-BAT refined analysis
Date
2021-08-18T21:36:00Z (4 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
H. A. Krimm (NSF), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU),
M. Stamatikos (OSU), 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 210818A (trigger #1069169)
(Beardmore et al., GCN Circ. 30652). The BAT ground-calculated position is
RA, Dec = 148.949, -87.029 deg which is
RA(J2000) = 09h 55m 47.7s
Dec(J2000) = -87d 01' 45.3"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 97%.
The mask-weighted light curve shows many overlapping pulses on top of
a general FRED-like structure. The burst emission starts at ~T0, peaks
at ~T+2 s, and ends at ~T+130 s. T90 (15-350 keV) is 73.56 +- 1.55 sec
(estimated error including systematics).
The time-averaged spectrum from T-0.69 to T+128.97 sec is best fit
by a simple power-law model. The power law index of the time-averaged
spectrum is 1.22 +- 0.03. The fluence in the 15-150 keV band is
2.6 +- 0.03 x 10^-5 erg/cm2. The 1-sec peak photon flux measured from
T+1.20 sec in the 15-150 keV band is 11.2 +- 0.4 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.
GCN Circular 30657
Subject
Konus-Wind detection of GRB 210818A
Date
2021-08-18T18:23:06Z (4 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
D. Frederiks, S. Golenetskii, A.Lysenko, A. Ridnaia,
D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The long GRB 210818A (Swift detection: Beardmore et al., GCN 30652;
AGILE detection: Ursi et al., GCN 30654)
triggered Konus-Wind (KW) at T0=3729.710 s UT (01:02:09.710).
The burst light curve started at ~T0 with a bright, short (<0.5s),
hard-spectrum initial pulse, which was followed, after a ~0.5 s interval,
by a similarly bright and hard, multi-peaked emission, which gradually decays until ~T0+90 s.
We also note a QPO-like behavior of the light curve in the interval
from ~T0+1.6 s to ~T0+3.2 s, with the quasi period of ~0.21 s.
The emission is seen up to ~7 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB210818_T03729/
As observed by Konus-Wind, the burst had
a fluence of (2.67 �� 0.12)x10^-4 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 0.128 s,
of (5.12 �� 0.54)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst (measured from T0 to T0+80.640 s)
is best fit in the 20 keV - 20 MeV range
by a power law with exponential cutoff (CPL) model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.99(-0.03,+0.03) and Ep = 1107(-71,+78) keV (chi2 = 117/98 dof).
Fitting this spectrum by a Band function yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.2 (chi2 = 117/97 dof).
The spectrum near the peak count rate (measured from T0 to T0+0.256 s,
that corresponds to the short initial pulse)
is best fit in the 20 keV - 20 MeV range by the CPL model
with alpha = -0.28(-0.13,+0.14) and Ep = 1247(-133,+47) keV (chi2 = 38/58 dof).
Fitting this spectrum by a Band function yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.4 (chi2 = 38/57 dof).
All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.
GCN Circular 30655
Subject
GRB 210818A: AstroSat CZTI detection
Date
2021-08-18T12:01:28Z (4 years ago)
From
Gaurav Waratkar at IIT,Bombay <gauravwaratkar@iitb.ac.in>
V. Prasad (IUCAA), P. Sawant (IUCAA), G. Waratkar (IITB), A. Vibhute
(IUCAA), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A. R. Rao
(IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat
CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al,
2020, arxiv:2011.07067) showed detection of a bright long GRB 210818A,
which was also detected by Swift-BAT (Beardmore et al., GCN #30652),
Swift-XRT (Osborne et al., GCN #30653) and AGILE (Ursi et al., GCN
#30654).
The source was clearly detected in the 20-200 keV energy range, with the
strongest peak at 2021-08-18 01:02:10.5 UT in the single-peak light
curve. The measured peak count rate associated with the burst is 1018
(+64, -64) cts/s above the background in the combined data of four
quadrants, with a total of 13993 (+552, -512) cts. The local mean
background count rate was 526 (+3, -3) cts/s. Using cumulative rates, we
measure a T90 of 33 (+4, -3) s.
It was also clearly detected in the CsI anticoincidence (Veto) detector
in the 100-500 keV energy range, with the strongest peak at 2021-08-18
01:02:09.9 UT in the single-peak light curve. The measured peak count
rate is 3748 (+116, -126) cts/s above the background in the combined
Veto data of four quadrants, with a total of 52829 (+844, -1097) cts.
The local mean background count rate was 1616 (+5, -5) cts/s. We measure
a T90 of 37 (+3, -2) s from the cumulative Veto light curve.
CZTI GRB detections are reported regularly on the payload site at
http://astrosat.iucaa.in/czti/?q=grb [1]. 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.
Links:
------
[1] http://astrosat.iucaa.in/czti/?q=grb
GCN Circular 30654
Subject
GRB 210818A: AGILE detection
Date
2021-08-18T08:27:40Z (4 years ago)
From
Alessandro Ursi at INAF/IAPS <alessandro.ursi@gmail.com>
A. Ursi (INAF/IAPS), F. Verrecchia (SSDC, and INAF/OAR), C. Casentini
(INAF/IAPS), P. Tempesta (TeleSpazio), M. Tavani (INAF/IAPS, and Univ. Roma
Tor Vergata), A. Argan, M. Cardillo, Y. Evangelista, G. Piano (INAF/IAPS),
F. Lucarelli, C. Pittori, (SSDC, and INAF/OAR), A. Bulgarelli, V.
Fioretti, F. Fuschino, N. Parmiggiani (INAF/OAS-Bologna), M. Marisaldi
(INAF/OAS-Bologna, and Bergen University), M. Pilia, A. Trois
(INAF/OA-Cagliari), I. Donnarumma (ASI), F. Longo (Univ. Trieste and INFN
Trieste), A. Giuliani (INAF/IASF-Mi), report on behalf of the AGILE Team:
The AGILE satellite detected the long GRB 210818A at T0 = 2021-08-18
01:02:08.19 s (UTC), reported by Swift (GCNs #30652, #30653).
The burst is clearly visible in the AGILE scientific ratemeters of the
SuperAGILE (SA; 20-60 keV), MiniCALorimeter (MCAL; 0.4-100 MeV), and
AntiCoincidence (AC; 50-200 keV) detectors. The event lasted about 35 s and
it released a total number of 3020 counts in the SA detector (above a
background rate of 70 Hz), 48170 counts in the MCAL detector (above a
background rate of 1250 Hz), and 130730 counts in the AC detector (above a
background rate of 3650 Hz). The AGILE ratemeter light curves can be found
at http://www.agilescienceapp.it/notices/GRB210818A_AGILE_RM.png .
The event also triggered a partial high time resolution MCAL data
acquisition, from T1 = 2021-08-18 01:02:07.81 s +/- 0.01 (UTC) to T2
=2021-08-18 01:02:21.18 +/- 0.01 s (UTC), and released 21640 counts in the
detector, above a background rate of 625 Hz. The MCAL light curve can be
found at:
http://www.agilescienceapp.it/notices/074408_GRB_556333328.188243.png .
Additional analysis of AGILE data is in progress. Automatic MCAL GRB alert
Notices can be found at: https://gcn.gsfc.nasa.gov/agile_mcal.html.
GCN Circular 30653
Subject
GRB 210818A: Enhanced Swift-XRT position
Date
2021-08-18T05:20:55Z (4 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 1521 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 210818A, 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 = 148.86765, -87.02526 which is equivalent
to:
RA (J2000): 09h 55m 28.23s
Dec (J2000): -87d 01' 30.9"
with an uncertainty of 2.2 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 30652
Subject
GRB 210818A: Swift detection of a burst with an optical counterpart
Date
2021-08-18T01:26:40Z (4 years ago)
From
Kim Page at U.of Leicester <klp5@leicester.ac.uk>
A. P. Beardmore (U Leicester), J. A. Kennea (PSU),
A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester) and
D. M. Palmer (LANL) report on behalf of the Neil Gehrels Swift
Observatory Team:
At 01:02:08 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210818A (trigger=1069169). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 149.131, -87.031 which is
RA(J2000) = 09h 56m 32s
Dec(J2000) = -87d 01' 52"
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 60 sec. The peak count rate
was ~28000 counts/sec (15-350 keV), at ~1 sec after the trigger.
The XRT began observing the field at 01:03:06.9 UT, 59.0 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 148.8666,
-87.0253 which is equivalent to:
RA(J2000) = 09h 55m 27.99s
Dec(J2000) = -87d 01' 31.0"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 53 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.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.74 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 4.7
(+2.38/-2.11) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 1.40e-08 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 66 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 09:55:28.15 = 148.86729
DEC(J2000) = -87:01:28.8 = -87.02467
with a 90%-confidence error radius of about 0.62 arc sec. This position is 1.9
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.93 with a 1-sigma error of about 0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.213.
Although this was originally reported in the GCN Notices as a known source
we believe that this is a GRB.
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/)