A Remarkable 3 Hour Thermonuclear Burst from 4U 1820–30

摘要: We present a detailed observational and theoretical study of ~3 hr long X-ray burst (the "superburst") observed by the Rossi X-Ray Timing Explorer (RXTE) from low-mass binary 4U 1820-30. This is longest ever this source perhaps one in great detail any source. show that superburst thermonuclear origin. Its peak luminosity ~3.4 × 1038 ergs s-1 consistent with helium Eddington limit for neutron star at ~7 kpc as well other, shorter, bursts same The begins decaying tail more typical (≈20 s duration) burst. These frequent are well-known flashes level accretion-driven flux energy release upward 1.5 1042 indicate could not be superburst. outline physics relevant to carbon production burning on helium-accreting stars calculations thermal evolution stability layer process most likely explanation Ignition temperatures deep "ocean" requires than 30 times mass inferred energetics unless He flash able trigger deflagration much smaller carbon. show, however, large columns accreted fuel, substantial fraction released carbon-burning radiated away neutrinos, heat conducted part flows inward, only timescales longer Thus, during event possibly exceeds X-rays factor 10, making scenario depths fluence without invoking additional trigger. A strong constraint recurrence time: accrete an ignition column 1013 g cm-2 takes ~13/(/3 1017 s-1) yr. Spectral analysis reveals presence broad emission line between 5.8 6.4 keV edge 8-9 keV, due reflection inner accretion disk believe first time such signature has been unambiguously detected spectrum