EDP Sciences
Free access
Issue
A&A
Volume 418, Number 2, May I 2004
Page(s) 617 - 624
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20040037


A&A 418, 617-624 (2004)
DOI: 10.1051/0004-6361:20040037

The properties of outbursts and long-term activity of the soft X-ray transient 4U 1608-52 (QX Nor)

V. Simon

Astronomical Institute, Academy of Sciences of the Czech Republic, 251 65 Ondrejov, Czech Republic
(Received 18 April 2003 / Accepted 26 November 2003 )

Abstract
An analysis of the long-term activity of 4U 1608-52, based on the ASM/RXTE data, is presented. Although the individual outbursts in 4U 1608-52 differ in both their duration and peak intensity, their rising and final decay branches display remarkable similarities. The variations of the soft X-ray color between 1.5-4 keV are found to follow the luminosity during the decay of outburst much better than the variations between 4-12 keV. The recurrence time $T_{\rm C}$ of outbursts was analyzed by the method of the $\rm O{-}C$ residuals. The mean value of  $T_{\rm C}$ is 330 days between the years 1996-2003 but a strong long-term trend of a decreasing $T_{\rm C}$ can be resolved. A series of four or five consecutive outbursts displays a clear correlation between the decreasing $T_{\rm C}$ and increasing peak intensity, but no correlation with the outburst duration. The observed behaviour is discussed in terms of the thermal instability model. We argue that the disk viscosity achieves similar values for the individual outbursts in 4U 1608-52. Only during the brightest outbursts does the luminosity appear to be high enough for the disk to be ionized out to its outer rim by the X-rays from the neutron star, according to the model by King & Ritter (1998). We also argue that the disk is never considerably depleted in outburst. A comparison with the similar system, Aql X-1, helps us to find the common links between the disk behaviour in the individual neutron-star soft X-ray transients.


Key words: stars: neutron  -- stars: binaries: close  -- stars: binaries: general  -- stars: circumstellar matter  -- stars: individual: 4U 1608-52, QX Nor

Offprint request: V. Simon, simon@asu.cas.cz

SIMBAD Objects



© ESO 2004

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.