Properties of the Extremely Energetic GRB 221009A from Konus-WIND and SRG/ART-XC Observations

Abstract

We report on Konus-WIND (KW) and Mikhail Pavlinsky Astronomical Roentgen Telescope – X-ray Concentrator (ART-XC) observations and analysis of a nearby GRB 221009A, the brightest γ-ray burst (GRB) detected by KW for >28 yr of observations. The prompt, pulsed phase of the burst emission lasts for ∼600 s and is followed by a steady power-law decay lasting for more than 25 ks. From the analysis of the KW and ART-XC light curves and the KW spectral data, we derive time-averaged spectral peak energy of the burst E p ≈ 2.6 MeV, E p at the brightest emission peak ≈ 3.0 MeV, the total 20 keV–10 MeV energy fluence of ≈0.22 erg cm−2, and the peak energy flux in the same band of ≈0.031 erg cm−2 s−1. The enormous observed fluence and peak flux imply, at redshift z = 0.151, huge values of isotropic energy release E iso ≈ 1.2 × 1055 erg (or ≳6.5 solar rest mass) and isotropic peak luminosity L iso ≈ 3.4 × 1054 erg s−1 (64 ms scale), making GRB 221009A the most energetic and one of the most luminous bursts observed since the beginning of the GRB cosmological era in 1997. The isotropic energetics of the burst fit nicely both “Amati” and “Yonetoku” hardness–intensity correlations for >300 KW long GRBs, implying that GRB 221009A is most likely a very hard, super-energetic version of a “normal” long GRB.

The Power of the Rings: The GRB 221009A Soft X-Ray Emission from Its Dust-scattering Halo

“…Our best estimate of the X-ray fluence of GRB 221009A in the 0.5-5 keV band (2.6 × 10 −3 erg cm −2 ) is about 1 order of magnitude larger than the value obtained by extrapolating to lower energies the model of the prompt emission observed above 20 keV by Konus-Wind (Frederiks et al 2023) and GECAM-C (An et al 2023) during the GRB 221009A main event. 22 Considering also the other dust models producing reasonable fits to the ring spectra (Table 2) and different proxies for the quantity of dust producing them (Appendix C), our analysis constrains the 0.5-5 keV fluence of GRB 221009A between 10 −3 and 7 × 10 −3 erg cm −2 (corresponding to 2.4 × 10 −3 to 1.3 × 10 −2 erg cm −2 in the 1-10 keV range).…”

“…Considering only the dust models giving reasonable fits to the 19 complete rings detected by XMM-Newton, the powerlaw photon index spans from 1 to 1.4. The steepest spectrum (Γ GRB = 1.37 ± 0.04) is derived from the best-fitting model (BARE-GR-B), whereas a harder slope (Γ GRB ∼ 0.8, with significant variability during the GRB evolution) is observed at the lowest energies by hard X-ray detectors during the peak of the main event (An et al 2023;Frederiks et al 2023;Ripa et al 2023). Together with the larger GRB fluence derived from our analysis of the X-ray rings, this suggests the presence of a soft excess in the prompt emission of GRB 221009A.…”

GRANDMA and HXMT Observations of GRB 221009A: The Standard Luminosity Afterglow of a Hyperluminous Gamma-Ray Burst—In Gedenken an David Alexander Kann

“…Even these preliminary estimates show that GRB 221009A exceeded GRB 130427A in fluence by a factor of at least 10. Recently, Frederiks et al (2023) presented the full Konus-Wind analysis, which yields a fluence more than twice as high as that derived by Kann & Agui Fernandez (2022), leading to an isotropic energy release E iso > 10 55 erg, twice as high as the previous record holder.…”

“…The first peak, ≈20 s long, would already place GRB 221009A among the brightest GRBs ever detected, exceeding all but a handful of GBM/Konus detections. This peak is followed by two ultrabright peaks and finally a fourth, less bright but longer peak that fades into a high-energy afterglow at ≈600 s. The extreme fluence led to a saturation of all sensitive gamma-ray detectors, such as Fermi GBM (Lesage et al 2022), Fermi LAT (Omodei et al 2022a(Omodei et al , 2022bBissaldi et al 2022;Pillera et al 2022), Konus-Wind (Frederiks et al 2022(Frederiks et al , 2023, Insight-HXMT/HE (Tan et al 2022;Ge et al 2022), AGILE/MCAL+AC (Ursi et al 2022), and INT-EGRAL SPI/ACS (Gotz et al 2022).…”

“…Several smaller orbital detectors were not saturated, stemming from size, environment, or off-axis detection, such as detectors on Insight (the low-energy, LE, telescope and the particle monitors; Ge et al 2022), SATech-01/GECAM-C HEBS (Liu et al 2022), GRBAlpha (Ripa et al 2022(Ripa et al , 2023, STPSat-6/SIRI-2 (Mitchell et al 2022), and SRG/ART-XC (Lapshov et al 2022;Frederiks et al 2023).…”