Giant Flare in SGR 1806-20 and Its Compton Reflection from the Moon

Abstract

We analyze the data obtained when the Konus-Wind gamma-ray spectrometer detected a giant flare in SGR 1806-20 on December 27, 2004. The flare is similar in appearance to the two known flares in SGR 0526-66 and SGR 1900+14 while exceeding them significantly in intensity. The enormous X-ray and gamma-ray flux in the narrow initial pulse of the flare leads to almost instantaneous deep saturation of the gamma-ray detectors, ruling out the possibility of directly measuring the intensity, time profile, and energy spectrum of the initial pulse. In this situation, the detection of an attenuated signal of Compton back-scattering of the initial pulse emission by the Moon with the Helicon gamma-ray spectrometer onboard the Coronas-F satellite was an extremely favorable circumstance. Analysis of this signal has yielded the most reliable temporal, energy, and spectral characteristics of the pulse. The temporal and spectral characteristics of the pulsating flare tail have been determined from Konus-Wind data. Its soft spectra have been found to contain also a hard power-law component extending to 10 MeV. A weak afterglow of SGR 1806-20 decaying over several hours is traceable up to 1 MeV. We also consider the overall picture of activity of SGR 1806-20 in the emission of recurrent bursts before and after the giant flare.

29 pages including 18 figures; to appear in Astronomy Letters, 2007, 33, p 1-18

Cited by in corpus (19)

• The strongest cosmic magnets: Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars
• GRB 221009A, The BOAT
• Properties of the extremely energetic GRB~221009A from Konus-WIND and SRG/ART-XC observations
• A bright gamma-ray flare interpreted as a giant magnetar flare in NGC 253
• Pulsar-wind nebulae and magnetar outflows: observations at radio, X-ray, and gamma-ray wavelengths
• Identification of a Local Sample of Gamma-Ray Bursts Consistent with a Magnetar Giant Flare Origin
• SGR 1806-20 about two years after the giant flare: Suzaku, XMM-Newton and INTEGRAL observations
• A search for giant flares from soft gamma-repeaters in nearby galaxies in the Konus-Wind short burst sample
• Minutes-duration Optical Flares with Supernova Luminosities
• Dynamics of baryon ejection in magnetar giant flares: implications for radio afterglows, r-process nucleosynthesis, and fast radio bursts
• The effect of X-ray dust-scattering on a bright burst from the magnetar 1E 1547.0-5408
• r-Process Nucleosynthesis and Radioactively Powered Transients from Magnetar Giant Flares
• Multi-wavelength afterglow emission from bursts associated with magnetar flares and fast radio bursts
• Extragalactic Magnetar Giant Flare GRB 231115A: Insights from Fermi/GBM Observations
• GRB 180128A: A Second Magnetar Giant Flare Candidate from the Sculptor Galaxy
• Detection of short high-energy transients in the localuniverse with SVOM/ECLAIRs
• Sub-MeV Band Observation of a Hard Burst from AXP 1E 1547.0-5408 with the Suzaku Wide-band All-sky Monitor
• Magnetar giant flare high-energy emission
• From Rare Events to a Population: Discovering Overlooked Extragalactic Magnetar Giant Flare Candidates in Archival Fermi Gamma-ray Burst Monitor Data