TY - JOUR

T1 - Pulsating ULXs: Large pulsed fraction excludes strong beaming

AU - Mushtukov, Alexander A.

AU - Portegies Zwart, Simon

AU - Tsygankov, Sergey S.

AU - Nagirner, Dmitrij I.

AU - Poutanen, Juri

N1 - Funding Information: This work was supported by The Dutch Research Council (NWO) Veni Fellowship (AAM) and the grant 14.W03.31.0021 of the Ministry of Science and Higher Education of the Russian Federation. We are grateful to Paolo Esposito, Valery Suleimanov, and an anonymous referee for useful comments and discussions. Publisher Copyright: © 2021 The Author(s). Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

PY - 2021/2/1

Y1 - 2021/2/1

N2 - 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.

AB - 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.

KW - accretion, accretion discs

KW - stars: neutron

KW - stars: oscillations

KW - X-rays: binaries

UR - http://www.scopus.com/inward/record.url?scp=85100299986&partnerID=8YFLogxK

U2 - 10.1093/mnras/staa3809

DO - 10.1093/mnras/staa3809

M3 - Article

AN - SCOPUS:85100299986

VL - 501

SP - 2424

EP - 2429

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 2

ER -