Issue |
A&A
Volume 378, Number 3, November II 2001
|
|
---|---|---|
Page(s) | 847 - 860 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20011157 | |
Published online | 15 November 2001 |
Neutron star blackbody contraction during flaring in X 1624-490
1
School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK e-mail: mbc@star.sr.bham.ac.uk
2
Institute of Astronomy, Jagiellonian University, ul. Orla 171, 30-244 Cracow, Poland
3
Laboratory for High Energy Astrophysics, Code 662, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA Also, Universities Space Research Association e-mail: alan@osiris.gsfc.nasa.gov
Corresponding author: M. Balucinska-Church, mbc@star.sr.bham.ac.uk
Received:
12
January
2001
Accepted:
16
August
2001
We present results of an extensive investigation of the physical
changes taking place in the emission regions of the LMXB X 1624-490 during
strong flaring in observations made using RXTE in 1997 and 1999.
Based on the detailed light curve,
we propose that the flaring consists of a superposition of X-ray bursts.
It is shown that major changes take place in the blackbody emission
component, the temperature increasing to ∼2.2 keV
in flaring. Remarkably, the blackbody area decreases by a factor of
∼5 in flaring.
During flare evolution, the blackbody luminosity remains approximately
constant, constituting a previously unknown Eddington limiting effect
which we propose is due to radiation pressure of the blackbody
as kTBB increases affecting the inner disk or accretion flow
resulting in a decreased emitting area on the star. We argue that the
large decrease in area cannot be explained in terms of modification
of the blackbody spectrum by electron scattering in the
atmosphere of the neutron star. The height of
the emitting region on the non-flaring neutron star is shown to agree with the
height of the inner radiatively-supported accretion disk
as found for sources in the ASCA survey of
LMXB of Church & Balucinska-Church (2001). The decrease in height
during flaring is discussed in
terms of possible models, including radial accretion flow onto the
stellar surface and the theory of accretion flow spreading on the
neutron star surface of Inogamov & Sunyaev (1999). We demonstrate
that the intensity of the broad iron line at 6.4 keV is strongly correlated
with the luminosity of the blackbody emission from the neutron star,
and discuss the probable origin of this line in the ADC. Finally,
possible reasons for non-detection of a reflection component in this source,
and LMXB in general, are discussed.
Key words: X-rays: stars / stars: individual: X 1624-490 / stars: neutron / binaries: close / accretion, accretion disks
© ESO, 2001
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