Stability of Radiative Shock Waves

Abstract

Radially accreting degenerate dwarfs are thought to produce hard X-rays in radiative shocks formed when the accreting plasma strikes their surfaces. Recent nonlinear time-dependent numerical calculations of funneled accretion onto magnetic degenerate dwarfs found that such shocks are unstable under certain circumstances (Langer, Chanmugam, and Shaviv 1982a, hereafter LCS). LCS found that radiative shocks with power law cooling functions proportional to p² T^ά oscillate in shock thickness x_s and luminosity L_S with a period of 3t_cool whenever ά < i.6. Here p is the mass density, T is the temperature, and t_cool is the postshock plasma cooling time scale. Because bremsstrahlung emission (ά=0.5) may be the dominant loss process for many accreting degenerate dwarfs, LCS suggested that pulsed X-ray emission might be a common property of these source. In this talk, we review our study of this instability. We first present results of our own linear and nonlinear analyses. We then compare our result to those of LCS and discuss the observational implications of our work. Lastly, we summarize our major conclusion.