Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008jgra..11307307t&link_type=abstract
Journal of Geophysical Research, Volume 113, Issue A7, CiteID A07307
Astronomy and Astrophysics
Astrophysics
8
Ionosphere: Ionospheric Disturbances, Solar Physics, Astrophysics, And Astronomy: X-Rays, Gamma Rays, And Neutrinos, Ionosphere: Ionization Processes (7823), Radio Science: Ionospheric Propagation (0689, 2487, 3285, 4275, 4455)
Scientific paper
On 27 August 1998, the Soft Gamma Ray Repeater (SGR) 1900+14, which is an exotic neutron star located near the Galactic Center, produced a giant flare. Gamma rays from the giant flare unusually ionized the lower ionosphere, and the ionospheric disturbance was detected as a large-amplitude change of the VLF signal whose propagation distance is relatively short (870 km). The peak flux of the flare was so huge that it saturated all the gamma ray detectors on the spacecraft; consequently, the flux and the spectrum during the most intense period was poorly determined. Tanaka et al. (2007) have recently derived the accurate peak flux of the flare from the Geotail data. By means of model calculations based on this accurate estimation and their comparisons with the short-distance VLF data, we have found that the spectrum during the most intense period was one temperature (kT = 240 keV) optically thin thermal Bremsstrahlung (OTTB). This result provides us with a clue to reveal the emission and triggering mechanisms of the giant flare.
Hayakawa Masahiko
Horie Takumi
Tanaka Yasuyuki T.
Terasawa Toshio
Yoshida Makiko
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