Skip to main content

Research Repository

Advanced Search

High-resolution imaging of the He II λ4686 emission line nebula associated with the ultraluminous X-ray source in Holmberg II

Kaaret, P.; Ward, M.J.; Zezas, A.

Authors

P. Kaaret

A. Zezas



Abstract

We present Hubble Space Telescope images of the He iii region surrounding the bright X-ray source in the dwarf irregular galaxy Holmberg II. Using Chandra, we find a position for the X-ray source of (J2000) with an uncertainty of 0.6 arcsec. We identify a bright, point-like optical counterpart centred in the nebula with the X-ray source. The optical magnitude and colour of the counterpart are consistent with a star with spectral type between O4V and B3 Ib at a distance of 3.05 Mpc or reprocessed emission from an X-ray illuminated accretion disc. The nebular He ii luminosity is 2.7 × 1036 erg s-1. The morphology of the He ii, Hβ and [O i] emission is consistent with being due to X-ray photoionization and is inconsistent with narrow beaming of the X-ray emission. A spectral model consisting of a multicolour disc blackbody with inverse-Compton emission from a hot corona gives a good fit to X-ray spectra obtained with XMM–Newton. Using the fitted X-ray spectrum, we calculate the relation between the He ii and X-ray luminosity and find that the He ii flux implies a lower bound on the X-ray luminosity in the range 4 to 6 × 1039 erg s-1 if the extrapolation of the X-ray spectrum between 54 and 300 eV is accurate. A compact object mass of at least 25 to 40 M would be required to avoid violating the Eddington limit.

Citation

Kaaret, P., Ward, M., & Zezas, A. (2004). High-resolution imaging of the He II λ4686 emission line nebula associated with the ultraluminous X-ray source in Holmberg II. Monthly Notices of the Royal Astronomical Society, 351(3), L83-L88. https://doi.org/10.1111/j.1365-2966.2004.08020.x

Journal Article Type Article
Publication Date 2004-07
Deposit Date Apr 29, 2008
Publicly Available Date Mar 29, 2024
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 351
Issue 3
Pages L83-L88
DOI https://doi.org/10.1111/j.1365-2966.2004.08020.x
Keywords Black hole physics, Individual, Holmberg II, Starburst, Stellar content, X-rays.

Files





You might also like



Downloadable Citations