GRB240918B

This page lists all entries on GRB240918B in GRBweb

Summary IPN GCN 37558 GCN 37602 GCN 37603

Summary table
Variable Value Source
T0 20:56:55.787 UTC GCN_circulars,Konus-Wind Det
ra 143.2792° IPN
decl -17.4333° IPN
pos_error 5.60e+00° IPN
GBM_located False
mjd 60571.87286790509 GCN_circulars,Konus-Wind Det
IPN table
GRB_name GRB240918B
ra 143.2792°
decl -17.4333°
pos_error 5.60e+00°
GCN 37558 table
GRB_name GRB240918B
GCN_number 37558
Detection_method Fermi GBM Det
t_trigger 20:56:58 UTC
ra 142.5400°
decl -17.3600°
Circular_text TITLE: GCN CIRCULAR NUMBER: 37558 SUBJECT: GRB 240918B: Fermi GBM Detection DATE: 24/09/19 15:47:35 GMT FROM: rachel.hamburg@ijclab.in2p3.fr The Fermi GBM team reports the detection of a likely LONG GRB. At approximately 20:56:58 UT on 18 Sep 2024, the Fermi Gamma-ray Burst Monitor (GBM) detected GRB 240918B, which was observed about 107 s after GBM triggered on GRB 240918A (trigger 748385716/240918872) (Fermi GBM Team 2024; GCN 37549). Due to the GBM trigger buffer of 10 min, the GBM did not trigger on this GRB. The on-ground calculated location, using the Fermi GBM trigger data from 107.52 s to 115.71 s after trigger time, is RA = 142.54, Dec = -17.36 (J2000 degrees, equivalent to J2000 9h 30m, -17d 36'), with a statistical uncertainty of 2.03 degrees. The angle from the Fermi LAT boresight is 64 degrees. The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals, was also used to identify GRB-like emission around the time of GRB 240918B. This search finds a multi-peaked emission episode on timescales up to 4.096 s and showing a localization consistent with the on-ground location. The brightest peak (at 20:57:01 UT) was found to be the most significant (FAR = 5.4e-06 Hz) on the 0.512 s timescale and best fit with a "normal" GRB spectrum as described in [1]." [1] Goldstein et al. 2019 arXiv:1903.12597
GCN 37602 table
GRB_name GRB240918B
GCN_number 37602
Detection_method IPN Triangulation
t_trigger 20:56:56 UTC
ra 143.2800°
decl -17.4350°
Circular_text TITLE: GCN CIRCULAR NUMBER: 37602 SUBJECT: IPN triangulation of GRB 240918B DATE: 24/09/24 19:25:27 GMT FROM: Anna Ridnaia at Ioffe Institute 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, 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 long-duration GRB 240918B (Fermi-GBM detection: The Fermi GBM team, GCN 37558; INTEGRAL SPI-ACS detection: Pawar, GCN 37560; AstroSat CZTI detection: Joshi et al., GCN 37588) was detected by Fermi (GBM), Konus-Wind, INTEGRAL (SPI-ACS), AstroSat (CZTI), and Mars-Odyssey (HEND) at about 75416 s UT (20:56:56). We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: --------------------------------------------- RA(2000), deg Dec(2000), deg --------------------------------------------- Center: 143.280 (09h 33m 07s) -17.435 (-17d 26' 07") Corners: 141.159 (09h 24m 38s) -19.395 (-19d 23' 40") 141.379 (09h 25m 31s) -19.587 (-19d 35' 15") 145.293 (09h 41m 10s) -15.401 (-15d 24' 02") 145.075 (09h 40m 18s) -15.211 (-15d 12' 41") --------------------------------------------- The error box area is 1.6 sq. deg, and its maximum dimension is 5.6 deg (the minimum one is 17 arcmin). The Sun distance was 35 deg. The IPN localization is consistent with, but reduces the area of, the Fermi-GBM localization (GCN 37558). This localization may be improved. A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB240918_T75415/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density. The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular.
GCN 37603 table
GRB_name GRB240918B
GCN_number 37603
Detection_method Konus-Wind Det
t_trigger 20:56:55.787 UTC
Circular_text TITLE: GCN CIRCULAR NUMBER: 37603 SUBJECT: Konus-Wind detection of GRB 240918B DATE: 24/09/24 19:27:38 GMT FROM: Anna Ridnaia at Ioffe Institute A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 240918B (Fermi-GBM detection: The Fermi GBM team, GCN 37558; INTEGRAL SPI-ACS detection: Pawar, GCN 37560; AstroSat CZTI detection: Joshi et al., GCN 37588; IPN triangulation: Kozyrev et al., GCN 37602) triggered Konus-Wind at T0=75415.787 s UT (20:56:55.787). The burst light curve shows a multipeaked structure which starts at ~T0-1.9 s and has a total duration of ~4.4 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/GRB240918_T75415/ As observed by Konus-Wind, the burst had a fluence of 4.19(-0.60,+0.71)x10^-6 erg/cm2, and a 64-ms peak flux, measured from T0+1.264 s, of 2.56(-0.89,+0.93)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.49(-0.44,+0.56) and Ep = 173(-28,+45) keV (chi2 = 112/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.2 (chi2 = 111/98 dof). All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.