GRB 230418A
GCN Circular 33652
Subject
GRB 230418A: Fermi GBM Observation
Date
2023-04-19T03:51:00Z (2 years ago)
From
Oliver J Roberts at USRA/NASA <oliver.roberts@nasa.gov>
O.J. Roberts (USRA/NASA-MSFC) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:
"At 21:11:33.49 UT on 18 April 2023, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 230418A (trigger 703545098 / 230418883).
The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 47.4, Dec = -12.5 (J2000 degrees, equivalent to
J2000 03h 10m, -12d 30'), with a statistical uncertainty of 5.9 degrees
(radius, 1-sigma containment, statistical only; there is additionally a systematic error
which we have characterized as a core-plus-tail model, with 90% of GRBs having a
3.7 deg error and a small tail suffering a larger than 10 deg systematic error.
[Connaughton et al. 2015, ApJS, 216, 32] ).
The angle from the Fermi LAT boresight at the GBM trigger time is 71 degrees.
The GBM light curve consists of single burst
with a duration (T90) of about 0.25 s (50-300 keV).
The time-averaged spectrum from T0-0.064 s to T0+0.256 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.22 +/- 0.08 and
the cutoff energy, parameterized as Epeak, is 838 +/- 71 keV.
The event fluence (10-1000 keV) in this time interval is
(2.51 +/- 0.08)E-06 erg/cm^2. The 64 msec peak photon flux measured
starting from T0+0.13 s in the 10-1000 keV band
is 31 +/- 1 ph/s/cm^2.
A Band function fits the spectrum equally well with Epeak = 836 +/- 75 keV,
alpha = -0.22 +/- 0.08, and beta = -3.9+/- 1.9.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular 33653
Subject
GRB 230418A: Swift/BAT-GUANO detection outside the coded FOV
Date
2023-04-19T07:02:04Z (2 years ago)
From
Aaron Tohuvavohu at University of Toronto <aaron.tohu@gmail.com>
Samuele Ronchini (PSU), Gayathri Raman (PSU), Jamie A. Kennea (PSU), James DeLaunay (UAlabama), Aaron Tohuvavohu (U Toronto), Tyler Parsotan (UMBC/GSFC) report:
Swift/BAT did not localize GRB 230418A onboard (T0: 2023-04-18T21:11:33.49 UTC, Fermi/GBM GCN 33652)
The Fermi notice distributed in near real-time, triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, ApJ, 900, 1).
Upon trigger by this notice, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground.
The BAT likelihood search, NITRATES (DeLaunay + Tohuvavohu 2022, ApJ, 941, 169), detects the burst with a sqrt(TS) of 31.1 in a 0.256 s analysis time bin.
The burst duration as seen by BAT is ~0.25 seconds.
NITRATES results indicate a burst coming from outside the FOV, with DeltaLLHOut of -20.
The NITRATES best fit OFOV position is consistent with the Fermi/GBM localization (GCN 33652).
See Section 9.1 and Figures 10 and 17 in the NITRATES paper for brief descriptions and interpretation of sqrt(TS), DeltaLLHPeak, and DeltaLLHOut.
GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches.
A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/
GCN Circular 33656
Subject
GRB 230418A: AGILE detection
Date
2023-04-19T20:12:42Z (2 years ago)
From
Francesco Verrecchia at SSDC,INAF-OAR <francesco.verrecchia@ssdc.asi.it>
G. Panebianco (Univ. Bologna - INAF/OAS Bologna), F. Verrecchia,
C. Pittori (SSDC, and INAF/OAR) , N. Parmiggiani (INAF/OAS-Bologna),
M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), C. Casentini,
A. Argan, M. Cardillo, Y. Evangelista, L. Foffano, E. Menegoni,
G. Piano, A. Ursi (INAF/IAPS), A. Addis, L. Baroncelli, A.
Bulgarelli, A. Di Piano, V. Fioretti (INAF/OAS-Bologna), F.
Lucarelli (SSDC, and INAF/OAR), M. Romani (INAF/OA-Brera), M.
Marisaldi (INAF/OAS-Bologna, and Bergen University), M. Pilia,
A. Trois (INAF/OA-Cagliari), F. Longo (Univ. Trieste and INFN
Trieste), I. Donnarumma (ASI), A. Giuliani (INAF/IASF-Mi), and
P. Tempesta (TeleSpazio), report on behalf of the AGILE Team:
The AGILE satellite detected the GRB 230418A at T0 = 2023-04-18
21:11:33 s (UTC), reported by Fermi GBM (GCNs #33652, #33653).
The burst is clearly visible in the AGILE scientific ratemeters
of the MiniCALorimeter (MCAL; 0.4-100 MeV), and AntiCoincidence
(AC; 50-200 keV) detectors.
The event lasted about 2 s and it released a total number of
1538 counts in the MCAL detector (above a background rate of 1100
Hz), and 7778 counts in the AC detector (above a background rate
of 3659 Hz). The AGILE ratemeters light curves can be found at
http://www.agilescienceapp.it/notices/GRB230418A_AGILE_RM_ND.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 33657
Subject
GRB 230418A: AstroSat CZTI detection
Date
2023-04-20T05:59:08Z (2 years ago)
From
Gaurav Waratkar at IIT,Bombay <gauravwaratkar@iitb.ac.in>
P K. Navaneeth (IUCAA), G. Waratkar (IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/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., 2021, JApA, 42, 73) showed the detection of a short GRB 230418A which was also detected by Fermi (O.J. Roberts, et al., GCN Circ. 33652), Swift/BAT-GUANO (S. Ronchini, et al., GCN Circ. 33653), and AGILE (G. Panebianco, et al., GCN Circ. 33656).
The source was clearly detected in the 20-200 keV energy range. The light curve peaks at 2023-04-18 21:11:33.56 UTC. The measured peak count rate associated with the burst is 2120 (+893, -443) counts/s above the background in the combined data of all quadrants, with a total of 155 (+52, -45) counts. The local mean background count rate was 488 (+18, -38) counts/s. Using cumulative rates, we measure a T90 of 0.20 (+0.16, -0.06) s.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb
GCN Circular 33659
Subject
IPN triangulation of GRB 230418A (short)
Date
2023-04-20T14:30:46Z (2 years ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,
D. Svinkin, D. Frederiks, A. Ridnaia, A. Lysenko, and
T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi GBM team,
E. Bozzo and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, and A. Tohuvavohu
on behalf of the Swift-BAT team,
and
W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr,
and A.S. Gardner on on behalf of the GRS-Odyssey GRB team,
report:
The short-duration GRB 230418A
(Fermi-GBM detection: Roberts et al., GCN Circ. 33652;
Swift/BAT-GUANO detection: Ronchini et al., GCN Circ. 33653;
AGILE detection: Panebianco et al., GCN Circ. 33656;
AstroSat-CZTI detection: Navaneeth et al., GCN Circ. 33657)
was detected by Fermi (GBM trigger 703545098), Swift (BAT),
Konus-Wind, INTEGRAL (SPI-ACS), AGILE (MCAL, AC), AstroSat (CZTI),
and Mars-Odyssey (HEND) at about 76293 s UT (21:11:33).
The burst was outside the coded field of view of the BAT.
We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
---------------------------------------------
RA(2000), deg Dec(2000), deg
---------------------------------------------
Center:
43.442 (02h 53m 46s) -20.343 (-20d 20' 36")
Corners:
43.565 (02h 54m 16s) -20.460 (-20d 27' 37")
43.510 (02h 54m 02s) -20.481 (-20d 28' 53")
43.320 (02h 53m 17s) -20.226 (-20d 13' 34")
43.375 (02h 53m 30s) -20.205 (-20d 12' 19")
---------------------------------------------
The error box area is 61 sq. arcmin, and its maximum
dimension is 20 arcmin (the minimum one is 3.2 arcmin).
The Sun distance was 35 deg.
This box may be improved.
The IPN localization is consistent with, but reduces the area of,
the Fermi-GBM final localization (GCN 33652).
A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB230418_T76289/IPN
The Konus-Wind time history and spectrum will be given in a forthcoming
GCN Circular.
GCN Circular 33674
Subject
Konus-Wind detection of GRB 230418A
Date
2023-04-22T16:32:46Z (2 years ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
D. Svinkin, D. Frederiks, M. Ulanov, A. Tsvetkova,
A. Lysenko, A. Ridnaia, and T. Cline
on behalf of the Konus-Wind team, report:
The short-duration GRB 230418A
(Fermi-GBM detection: Roberts et al., GCN Circ. 33652;
Swift/BAT-GUANO detection: Ronchini et al., GCN Circ. 33653;
AGILE detection: Panebianco et al., GCN Circ. 33656;
AstroSat-CZTI detection: Navaneeth et al., GCN Circ. 33657;
IPN triangulation: Kozyrev et al., GCN Circ. 33659)
triggered Konus-Wind at T0=76289.941 s UT (21:11:29.941).
The burst light curve shows a multi-peaked structure
which starts at ~T0 s and has a total duration of ~0.3 s.
The emission is seen up to ~2 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB230418_T76289/
As observed by Konus-Wind, the burst
had a fluence of 4.13(-0.64,+0.76)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0+0.048 s,
of 3.84(-1.00,+1.10)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst
(measured from T0 to T0+0.192 s)
is best fit in the 20 keV - 2 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.52(-0.20,+0.23)
and Ep = 1071(-228,+335) keV (chi2 = 16/24 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -1.87
(chi2 = 16/23 dof).
All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.