Query : 2017A&A...604A..77K

2017A&A...604A..77K - Astronomy and Astrophysics, volume 604A, 77-77 (2017/8-1)

Flux decay during thermonuclear X-ray bursts analysed with the dynamic power-law index method.


Abstract (from CDS):

The cooling of type-I X-ray bursts can be used to probe the nuclear burning conditions in neutron star envelopes. The flux decay of the bursts has been traditionally modelled with an exponential, even if theoretical considerations predict power-law-like decays. We have analysed a total of 540 type-I X-ray bursts from five low-mass X-ray binaries observed with the Rossi X-ray Timing Explorer. We grouped the bursts according to the source spectral state during which they were observed (hard or soft), flagging those bursts that showed signs of photospheric radius expansion (PRE). The decay phase of all the bursts were then fitted with a dynamic power-law index method. This method provides a new way of probing the chemical composition of the accreted material. Our results show that in the hydrogen-rich sources the power-law decay index is variable during the burst tails and that simple cooling models qualitatively describe the cooling of presumably helium-rich sources 4U 1728-34 and 3A 1820-303. The cooling in the hydrogen-rich sources 4U 1608-52, 4U 1636-536, and GS 1826-24, instead, is clearly different and depends on the spectral states and whether PRE occurred or not. Especially the hard state bursts behave differently than the models predict, exhibiting a peculiar rise in the cooling index at low burst fluxes, which suggests that the cooling in the tail is much faster than expected. Our results indicate that the drivers of the bursting behaviour are not only the accretion rate and chemical composition of the accreted material, but also the cooling that is somehow linked to the spectral states. The latter suggests that the properties of the burning layers deep in the neutron star envelope might be impacted differently depending on the spectral state.

Abstract Copyright: © ESO, 2017

Journal keyword(s): stars: neutron - X-rays: binaries - X-rays: bursts - accretion, accretion disks - accretion, accretion disks

Simbad objects: 5

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Number of rows : 5
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 V* QX Nor LXB 16 12 43.0 -52 25 23           ~ 886 1
2 V* V801 Ara LXB 16 40 55.5976953528 -53 45 04.948107156 17.50 18.20 17.5   17.07 ~ 844 1
3 NAME Slow Burster LXB 17 31 57.73 -33 50 02.5     15.50     ~ 803 1
4 X Sgr X-4 LXB 18 23 40.57 -30 21 40.6   19.06 18.81     ~ 965 1
5 V* V4634 Sgr LXB 18 29 28.2 -23 47 49 18.90 19.40 19     ~ 327 0

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