Towards a dynamical mass of the ultraluminous X-ray source NGC 5408 X-1

D. Cseh, F. Grisé, P. Kaaret, S. Corbel, S. Scaringi, P. Groot, H. Falcke, E. Körding

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

We obtained multi-epoch Very Large Telescope optical spectroscopic data in 2011 and 2012 on the ultraluminous X-ray source NGC 5408 X-1. We confirm that the He II λ4686 line has a broad component with an average full width at half-maximum of u = 780 ± 64 km s-1 with a variation of ~13 per cent during observations spanning over four years, and is consistent with the origin in the accretion disc. The deepest optical spectrum does not reveal any absorption line from a donor star. Our aim was to measure the radial velocity curve and estimate the parameters of the binary system. We find an upper limit on the semi-amplitude of the radial velocity of K = 132 ± 42 km s-1. A search for a periodic signal in the data resulted in no statistically significant period. The mass function and constraints on the binary system imply a black hole mass of less than ~510 M⊙.Whilst, a disc irradiationmodel may imply a black hole mass smaller than ~431-1985 M⊙, depending on inclination. Our data can also be consistent with an unexplored orbital period range from a couple of hours to a few days, thus with a stellar-mass black hole and a subgiant companion.

Original languageEnglish
Pages (from-to)2896-2902
Number of pages7
JournalMonthly Notices of the Royal Astronomical Society
Volume435
Issue number4
DOIs
StatePublished - Nov 2013

Keywords

  • Accretion, accretion discs
  • Black hole physics
  • X-rays: binaries

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