Evidence for a jet contribution to the optical/infrared light of neutron star X-ray binaries

Dave Russell, R. P. Fender, P. G. Jonker

    Research output: Contribution to journalArticle

    Abstract

    Optical/near-infrared (optical/NIR, OIR) light from low-mass neutron star X-ray binaries (NSXBs) in outburst is traditionally thought to be thermal emission from the accretion disc. Here we present a comprehensive collection of quasi-simultaneous OIR and X-ray data from 19 low magnetic field NSXBs, including new observations of three sources: 4U 0614+09, LMC X-2 and GX 349+2. The average radio-OIR spectrum for NSXBs is α ≈ + 0.2 (where Lν ∝ να) at least at high luminosities when the radio jet is detected. This is comparable to, but slightly more inverted than the α ≈ 0.0 found for black hole X-ray binaries. The OIR spectra and relations between OIR and X-ray fluxes are compared to those expected if the OIR emission is dominated by thermal emission from an X-ray or viscously heated disc, or synchrotron emission from the inner regions of the jets. We find that thermal emission due to X-ray reprocessing can explain all the data except at high luminosities for some NSXBs, namely, the atolls and millisecond X-ray pulsars. Optically thin synchrotron emission from the jets (with an observed OIR spectral index of αthin < 0) dominate the NIR light above and the optical above in these systems. For NSXB Z-sources, the OIR observations can be explained by X-ray reprocessing alone, although synchrotron emission may make a low-level contribution to the NIR, and could dominate the OIR in one or two cases.

    Original languageEnglish (US)
    Pages (from-to)1108-1116
    Number of pages9
    JournalMonthly Notices of the Royal Astronomical Society
    Volume379
    Issue number3
    DOIs
    StatePublished - Aug 1 2007

    Fingerprint

    neutron stars
    x rays
    thermal emission
    synchrotrons
    atolls
    luminosity
    radio
    radio spectra
    accretion disks
    outburst
    pulsars
    near infrared
    accretion
    magnetic field

    Keywords

    • Accretion, accretion discs
    • ISM: jets and outflows
    • Stars: neutron
    • X-rays: binaries

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

    Cite this

    Evidence for a jet contribution to the optical/infrared light of neutron star X-ray binaries. / Russell, Dave; Fender, R. P.; Jonker, P. G.

    In: Monthly Notices of the Royal Astronomical Society, Vol. 379, No. 3, 01.08.2007, p. 1108-1116.

    Research output: Contribution to journalArticle

    Russell, Dave ; Fender, R. P. ; Jonker, P. G. / Evidence for a jet contribution to the optical/infrared light of neutron star X-ray binaries. In: Monthly Notices of the Royal Astronomical Society. 2007 ; Vol. 379, No. 3. pp. 1108-1116.
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