Plasma radiation during γ-ray bursts

Abstract

Most γ-ray bursts are thought to originate from or near the surface of neutron stars¹. Their spectra, however, have been measured only in the 30 keV–10 MeV energy range², with possible detection of some 1–12 keV X rays reported for several events³ (notably the Apollo event of 27 April 1972)⁴ at a level ≃0.01–0.02 of the γ-ray flux. Here I propose that γ-ray bursters may also strongly emit 0.05–1 keV XUV radiation simultaneously with the γ-rays, in the form of two narrow spectral lines, corresponding to the ω_e and 2ω_e plasma radiation, where ω_e = (4πn_ee²/m_e)^1/2 is the electron plasma frequency of the γ- emitting (and pair annihilation) region of the burster. As estimates based on observed annihilation line intensities and other theoretical arguments typi cally give n_e≳10²⁴–10²⁶ cm⁻³ (ref. 5), hω_e≳37–373 eV, in the XUV range. If detected and their frequencies accurately measured with high time resolution, such radiation could be a valuable diagnostic tool for the emission region, as in the case of solar radio bursts⁶. Failure to detect them would also put strong con-traints on the γ-emission models.