Single X-ray Bursts and the Model of a Spreading Layer of Accreting Matter over the Neutron Star Surface

Abstract

The excess of the rate of type I X-ray bursts over that expected when the matter fallen between bursts completely burns out in a thermonuclear explosion is explained in terms of the model of a spreading layer of matter coming from the accretion disk over the neutron star surface. Such excess is observed in bursters with a high persistent luminosity, $4\times 10^{36}\ \mbox{erg s}^{-1}\leq L_{X}\leq 2\times 10^{37}\ \mbox{erg s}^{-1}$. In this model the accreting matter settles to the stellar surface mainly in two high-latitude ring zones. Despite the subsequent spreading of matter over the entire star, its surface density in these zones turns out to be higher than the average one by 2-3 orders of magnitude, which determines the predominant ignition probability. The multiple events whereby the flame after the thermonuclear explosion in one ring zone (initial burst) propagates through less dense matter to another zone and initiates a second explosion in it (recurrent burst) make a certain contribution to the observed excess of the burst rate. However, the localized explosions of matter in these zones, after which the burning in the zone rapidly dies out without affecting other zones, make a noticeably larger contribution to the excess of the burst rate over the expected one.

5 pages, 1 figure

References in corpus (8)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• Spread of Matter over a Neutron-Star Surface During Disk Accretion: Deceleration of Rapid Rotation
• Sedimentation and Type I X-ray Bursts at Low Accretion Rates
• Discovery of X-ray burst triplets in EXO 0748-676
• The Latitude of Type I X-Ray Burst Ignition on Rapidly Rotating Neutron Stars
• Registration of the First Thermonuclear X-ray Burst from AX J1754.2-2754
• Hard X-ray Bursts Detected by the IBIS Telescope Onboard the INTEGRAL Observatory in 2003-2004
• Multiple X-ray bursts and the model of a spreading layer of accreting matter over the neutron star surface

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• Thermonuclear X-ray Bursts with late secondary peaks observed from 4U 1608-52
• The efficiency of nuclear burning during thermonuclear (Type I) bursts as a function of accretion rate
• New Gamma-Ray Bursts Found in the Archival Data from the IBIS/ISGRI Telescope of the INTEGRAL Observatory