Pulsating ULXs: Large pulsed fraction excludes strong beaming

Alexander A. Mushtukov, Simon Portegies Zwart, Sergey S. Tsygankov, Dmitrij I. Nagirner, Juri Poutanen

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


The recent discovery of pulsating ultraluminous X-ray sources (ULXs) shows that the apparent luminosity of accreting neutron stars can exceed the Eddington luminosity by a factor of 100s. The relation between the actual and apparent luminosity is a key ingredient in theoretical models of ULXs, but it is still under debate. A typical feature of the discovered pulsating ULXs is a large pulsed fraction (PF). Using Monte Carlo simulations, we consider a simple geometry of accretion flow and test the possibility of simultaneous presence of a large luminosity amplification due the geometrical beaming and a high PF. We argue that these factors largely exclude each other and only a negligible fraction of strongly beamed ULX pulsars can show PF above 10 per cent. Discrepancy between this conclusion and current observations indicates that pulsating ULXs are not strongly beamed and their apparent luminosity is close to the actual one.

Translated title of the contributionПульсирующие ультра яркие рентгеновские пульсары: большая доля пульсаций исключает пучкование
Original languageEnglish
Pages (from-to)2424-2429
Number of pages6
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - 1 Feb 2021

Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • accretion, accretion discs
  • stars: neutron
  • stars: oscillations
  • X-rays: binaries


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