The Curious Case of Swift J1753.5-0127: A Black Hole Low-mass X-ray Binary Analogue to Z Cam Type Dwarf Novae

TL;DR

This paper presents evidence that Swift J1753.5-0127, a black hole low-mass X-ray binary, exhibits outburst behavior similar to Z Cam dwarf novae, driven by variable mass transfer influenced by irradiation effects.

Contribution

It introduces the idea that J1753's long outburst is due to variable mass transfer, modeling it as an analogue to Z Cam systems, which is a novel interpretation for BH-LMXBs.

Findings

J1753's outburst duration exceeds predictions of the disc-instability model.

Modeling indicates variable mass transfer driven by irradiation influences system behavior.

J1753 behaves similarly to Z Cam dwarf novae, linking stellar binary classes.

Abstract

Swift J1753.5-0127 (J1753) is a candidate black hole low-mass X-ray binary (BH-LMXB) that was discovered in outburst in May 2005. It remained in outburst for $\sim12$ years, exhibiting a wide range of variability on various timescales, before entering quiescence after two short-lived, low-luminosity "mini-outbursts" in April 2017. The unusually long outburst duration in such a short-period ($P_{\rm orb}\approx3.24$ hrs) source, and complex variability observed during this outburst period, challenges the predictions of the widely accepted disc-instability model, which has been shown to broadly reproduce the behaviour of LMXB systems well. The long-term behaviour observed in J1753 is reminiscent of the Z Cam class of dwarf novae, whereby variable mass transfer from the companion star drives unusual outbursts, characterized by stalled decays and abrupt changes in luminosity. Using sophisticated modelling of the multi-wavelength light curves and spectra of J1753, during the $\sim12$ years the source was active, we investigate the hypothesis that periods of enhanced mass transfer from the companion star may have driven this unusually long outburst. Our modelling suggests that J1753 is in fact a BH-LMXB analogue to Z Cam systems, where the variable mass transfer from the companion star is driven by the changing irradiation properties of the system, affecting both the disc and companion star.