A&A 399, 663-680 (2003)
DOI: 10.1051/0004-6361:20021781

Photospheric radius expansion X-ray bursts as standard candles

E. Kuulkers^{1, 2}, P. R. den Hartog^{1, 2}, J. J. M. in 't Zand¹, F. W. M. Verbunt², W. E. Harris³ and M. Cocchi<sup>4

1</sup>  SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
    e-mail: Erik.Kuulkers@rssd.esa.int
²  Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
³  Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada
⁴  Istituto di Astrofisica Spaziale e Fisica Cosmica (IASF) Area Ricerca Roma Tor Vergata, Via del Fosso del Cavaliere, 00133 Roma, Italy

(Received 21 May 2002 / Accepted 29 November 2002 )

Abstract
We examined the maximum bolometric peak luminosities during type I X-ray bursts from the persistent or transient luminous X-ray sources in globular clusters. We show that for about two thirds of the sources the maximum peak luminosities during photospheric radius expansion X-ray bursts extend to a critical value of erg s ^-1, assuming the total X-ray burst emission is entirely due to black-body radiation and the recorded maximum luminosity is the actual peak luminosity. This empirical critical luminosity is consistent with the Eddington luminosity limit for hydrogen poor material. Since the critical luminosity is more or less always reached during photospheric radius expansion X-ray bursts (except for one source), such bursts may be regarded as empirical standard candles. However, because significant deviations do occur, our standard candle is only accurate to within 15%. We re-evaluated the distances to the twelve globular clusters in which the X-ray bursters reside.

Key words: binaries: close -- stars: neutron -- globular clusters: general -- X-rays: binaries -- X-rays: bursts

Offprint request: E. Kuulkers, ekuulker@rssd.esa.int

SIMBAD Objects

© ESO 2003

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.