Modelling the high-mass accretion rate spectra of GX 339−4: black hole spin from reflection?

Abstract

We extract all the XMM–Newton European Photon Imaging Camera (EPIC) pn burst mode spectra of GX 339−4, together with simultaneous/contemporaneous RXTE data. These include three disc‐dominated and two soft intermediate spectra, and the combination of broad bandpass/moderate spectral resolution gives some of the best data on these bright soft states in black hole binaries. The disc‐dominated spectra span a factor of 3 in luminosity, and all show that the disc emission is broader than the simplest multicolour disc model. This is consistent with the expected relativistic smearing and changing colour temperature correction produced by atomic features in the newest disc models. However, these models do not match the data at the 5 per cent level as the predicted atomic features are not present in the data, perhaps indicating that irradiation is important even when the high‐energy tail is weak. Whatever the reason, this means that the data have smaller errors than the best physical disc models, forcing use of more phenomenological models for the disc emission. We use these for the soft intermediate state data, where previous analysis using a simple disc continuum found an extremely broad residual, identified as the red wing of the iron line from reflection around a highly spinning black hole. However, the iron line energy is close to where the disc and tail have equal fluxes, so using a broader disc continuum changes the residual ‘iron line’ profile dramatically. With a broader disc continuum model, the inferred line is formed outside of 30Rg, so it cannot constrain black hole spin. We caution that a robust determination of black hole spin from the iron line profile is very difficult where the disc makes a significant contribution at the iron line energy, i.e. in most bright black hole states.

The effect of advection at luminosities close to Eddington: The ULX in M 31

“…However, these changes make very little difference to the emitted spectrum for L < L Edd , and we show here that this cannot be the reason for the mismatch between data and models seen in moderate luminosity (0.1−0.5 L Edd ) spectra from both this ULX and from galactic black hole binaries (Kolehmainen et al 2011). Real accretion discs at these moderate luminosities have a spectrum which is subtly broader than is currently expected from the best disc models.…”

“…We cannot constrain a weak high energy tail in our data, but this could potentially illuminate the disc and hence change the structure of the photosphere. However, we note that the most disc dominated GX339-4 spectrum in Kolehmainen et al (2011), where the tail carries less than a few per cent of the total bolometric flux, shows this additional broadening. This is a very low level of illumination to cause a noticeable change in disc structure.…”

Black hole spin of Cygnus X-1 determined from the softest state ever observed

“…This is not true in our data. Instead we use the xilconv model which converts the xillver reflection table models into a convolution for use with any continuum (Kolehmainen et al 2011), parameterized by the ionization parameter ξ = L/(nR 2 ) of the illuminated disc. We then convolved this with the relativistic smearing model relconv ) in order to model reflection from the disc.…”

Broad-band spectral analysis of the accreting millisecond X-ray pulsar SAX J1748.9−2021

“…We test the REFLIONX (Ross & Fabian 2005) and the RFXCONV (e.g. Kolehmainen et al 2011) models. We remove the Fe DISKLINE model and we left only the gaussian models for those low energy lines not included in the models (specifically Ar and Ca lines).…”