Gamma-ray Burst 230418A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 18 Apr 23 21:12:03 UT
NOTICE_TYPE:     Fermi-GBM Flight Position
RECORD_NUM:      47
TRIGGER_NUM:     703545098
GRB_RA:          305.883d {+20h 23m 32s} (J2000),
                 306.288d {+20h 25m 09s} (current),
                 305.011d {+20h 20m 03s} (1950)
GRB_DEC:         -45.517d {-45d 31' 00"} (J2000),
                 -45.440d {-45d 26' 24"} (current),
                 -45.678d {-45d 40' 40"} (1950)
GRB_ERROR:       4.27 [deg radius, statistical plus systematic]
GRB_INTEN:       4462 [cnts/sec]
DATA_SIGNIF:     38.80 [sigma]
INTEG_TIME:      0.256 [sec]
GRB_DATE:        20052 TJD;   108 DOY;   23/04/18
GRB_TIME:        76293.49 SOD {21:11:33.49} UT
GRB_PHI:          30.00 [deg]
GRB_THETA:       160.00 [deg]
DATA_TIME_SCALE: 0.2560 [sec]
HARD_RATIO:      0.28
LOC_ALGORITHM:   3 (version number of)
MOST_LIKELY:      96%  GRB
2nd_MOST_LIKELY:   1%  Generic Transient
DETECTORS:       1,1,1, 0,0,1, 0,0,0, 0,0,0, 0,0,
SUN_POSTN:        26.56d {+01h 46m 14s}  +10.97d {+10d 58' 05"}
SUN_DIST:         91.10 [deg]   Sun_angle= 5.4 [hr] (West of Sun)
MOON_POSTN:       11.63d {+00h 46m 32s}   +2.95d {+02d 56' 57"}
MOON_DIST:        75.19 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      354.59,-34.70 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:      297.04,-25.39 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230418883/quicklook/glg_lc_medres34_bn230418883.gif
COMMENTS:        Fermi-GBM Flight-calculated Coordinates.  
COMMENTS:        This trigger occurred at longitude,latitude = 272.40,-6.93 [deg].  
COMMENTS:        The LC_URL file will not be created until ~15 min after the trigger.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 18 Apr 23 21:12:21 UT
NOTICE_TYPE:     Fermi-GBM Ground Position
RECORD_NUM:      58
TRIGGER_NUM:     703545098
GRB_RA:           53.830d {+03h 35m 19s} (J2000),
                  54.103d {+03h 36m 25s} (current),
                  53.245d {+03h 32m 59s} (1950)
GRB_DEC:         -13.840d {-13d 50' 23"} (J2000),
                 -13.764d {-13d 45' 48"} (current),
                 -14.005d {-14d 00' 19"} (1950)
GRB_ERROR:       5.04 [deg radius, statistical only]
DATA_SIGNIF:     41.00 [sigma]
DATA_INTERVAL:   0.256 [sec]
GRB_DATE:        20052 TJD;   108 DOY;   23/04/18
GRB_TIME:        76293.49 SOD {21:11:33.49} UT
GRB_PHI:          39.00 [deg]
GRB_THETA:        68.00 [deg]
E_RANGE:         44.032 - 279.965 [keV]
LOC_ALGORITHM:   4173 (Gnd S/W Version number)
SUN_POSTN:        26.56d {+01h 46m 14s}  +10.97d {+10d 58' 05"}
SUN_DIST:         36.85 [deg]   Sun_angle= -1.8 [hr] (East of Sun)
MOON_POSTN:       11.64d {+00h 46m 33s}   +2.95d {+02d 57' 02"}
MOON_DIST:        45.31 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      202.14,-49.60 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       47.44,-32.09 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230418883/quicklook/glg_lc_medres34_bn230418883.gif
POS_MAP_URL:     http://gcn.gsfc.nasa.gov/notices_f/gbm_gnd_loc_map_703545098.fits
COMMENTS:        Fermi-GBM Ground-calculated Coordinates.  
COMMENTS:        Bright hard burst in the GBM.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file will not be created/available until ~15 min after the trigger.  
COMMENTS:        The POS_MAP_URL file will not be created/available until ~1.5 min after the notice.

GCN NOTICE

TITLE:           GCN/FERMI NOTICE
NOTICE_DATE:     Tue 18 Apr 23 21:29:39 UT
NOTICE_TYPE:     Fermi-GBM Final Position
RECORD_NUM:      0
TRIGGER_NUM:     703545098
GRB_RA:           47.440d {+03h 09m 46s} (J2000),
                  47.717d {+03h 10m 52s} (current),
                  46.845d {+03h 07m 23s} (1950)
GRB_DEC:         -12.460d {-12d 27' 35"} (J2000),
                 -12.372d {-12d 22' 20"} (current),
                 -12.649d {-12d 38' 56"} (1950)
GRB_ERROR:       5.89 [deg radius, statistical only]
GRB_DATE:        20052 TJD;   108 DOY;   23/04/18
GRB_TIME:        76293.49 SOD {21:11:33.49} UT
GRB_PHI:          33.00 [deg]
GRB_THETA:        71.00 [deg]
E_RANGE:         50.000 - 300.000 [keV]
LOC_ALGORITHM:   415 (Gnd S/W Version number)
SUN_POSTN:        26.57d {+01h 46m 16s}  +10.97d {+10d 58' 20"}
SUN_DIST:         31.40 [deg]   Sun_angle= -1.4 [hr] (East of Sun)
MOON_POSTN:       11.79d {+00h 47m 09s}   +3.03d {+03d 01' 47"}
MOON_DIST:        38.88 [deg]
MOON_ILLUM:      2 [%]
GAL_COORDS:      195.45,-54.48 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS:       41.00,-28.95 [deg] ecliptic lon,lat of the burst (or transient)
LC_URL:          http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230418883/quicklook/glg_lc_medres34_bn230418883.gif
LOC_URL:         http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2023/bn230418883/quicklook/glg_locplot_all_bn230418883.png
COMMENTS:        Fermi-GBM Final Position.  
COMMENTS:        This Notice was ground-generated -- not flight-generated.  
COMMENTS:        The LC_URL file should be available by the time this FINAL notice is produced.  
COMMENTS:        This notice has human-in-the-loop processing.

GCN Circular #33652
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
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
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
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
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
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.

Back to JG's homepage

Jochen Greiner, last update: 22-Apr-2023 [Disclaimer]