The cooling phase of Type I X-ray bursts observed with RXTE in 4U 1820-30 does not follow the canonical F ∝ T4 relation. García, F., Zhang, G., & Méndez, M. Monthly Notices of the Royal Astronomical Society, 429:3266–3271, March, 2013.
Paper doi abstract bibtex We analysed the complete set of bursts from the neutron star low-mass X-ray binary 4U 1820-30 detected with the Rossi X-ray Timing Explorer (RXTE). We found that all are photospheric radius expansion bursts, and have similar duration, peak flux and fluence. From the analysis of time-resolved spectra during the cooling phase of the bursts, we found that the relation between the bolometric flux and the temperature is very different from the canonical F ∝ T4 relation which is expected if the apparent emitting area on the surface of the neutron star remains constant. The flux-temperature relation can be fitted using a broken power law, with indices ν1 = 2.0 ± 0.3 and ν2 = 5.72 ± 0.06. The departure from the F ∝ T4 relation during the cooling phase of the X-ray bursts in 4U 1820-30 could be due to changes in the emitting area of the neutron star while the atmosphere cools down, variations in the colour-correction factor due to chemical evolution, or the presence of a source of heat, e.g. residual hydrogen nuclear burning, playing an important role when the burst emission ceases.
@article{garciaCoolingPhaseType2013,
title = {The cooling phase of {Type} {I} {X}-ray bursts observed with {RXTE} in {4U} 1820-30 does not follow the canonical {F} ∝ {T4} relation},
volume = {429},
issn = {0035-8711},
url = {http://adsabs.harvard.edu/abs/2013MNRAS.429.3266G},
doi = {10.1093/mnras/sts583},
abstract = {We analysed the complete set of bursts from the neutron star low-mass
X-ray binary 4U 1820-30 detected with the Rossi X-ray Timing Explorer
(RXTE). We found that all are photospheric radius expansion bursts, and
have similar duration, peak flux and fluence. From the analysis of
time-resolved spectra during the cooling phase of the bursts, we found
that the relation between the bolometric flux and the temperature is
very different from the canonical F ∝ T4 relation which
is expected if the apparent emitting area on the surface of the neutron
star remains constant. The flux-temperature relation can be fitted using
a broken power law, with indices ν1 = 2.0 ± 0.3 and
ν2 = 5.72 ± 0.06. The departure from the F ∝
T4 relation during the cooling phase of the X-ray bursts in
4U 1820-30 could be due to changes in the emitting area of the neutron
star while the atmosphere cools down, variations in the
colour-correction factor due to chemical evolution, or the presence of a
source of heat, e.g. residual hydrogen nuclear burning, playing an
important role when the burst emission ceases.},
urldate = {2021-06-10},
journal = {Monthly Notices of the Royal Astronomical Society},
author = {García, Federico and Zhang, Guobao and Méndez, Mariano},
month = mar,
year = {2013},
keywords = {X-rays: binaries, X-rays: bursts, stars: individual: 4U 1820-30, stars: neutron},
pages = {3266--3271},
}
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