Swift J1357.2-0933: the faintest black hole?
Abstract
Swift J1357.2-0933 is a confirmed very faint black hole X-ray transient and has a short estimated orbital period of 2.8 h. We observed Swift J1357.2-0933 for ∼50 ks with XMM-Newton in 2013 July during its quiescent state. The source is clearly detected at a 0.5-10 keV unabsorbed flux of ∼3 × 10-15 erg cm-2 s-1. If the source is located at a distance of 1.5 kpc (as suggested in the literature), this would imply a luminosity of ∼8 × 1029 erg s-1, making it the faintest detected quiescent black hole low-mass X-ray binary. This would also imply that there is no indication of a reversal in the quiescence X-ray luminosity versus orbital period diagram down to 2.8 h, as has been predicted theoretically and recently supported by the detection of the 2.4 h orbital period black hole MAXI J1659-152 at a 0.5-10 keV X-ray luminosity of ∼1.2 × 1031 erg s-1. However, there is considerable uncertainty in the distance of Swift J1357.2-0933 and it may be as distant as 6.3 kpc. In this case, its quiescent luminosity would be LX ∼ 1.3 × 1031 erg s-1, i.e. similar to MAXI J1659-152 and hence, it would support the existence of such a bifurcation period. We also detected the source in optical at r' ∼ 22.3 mag with the Liverpool telescope, simultaneously to our X-ray observation. The X-ray/optical luminosity ratio of Swift J1357.2-0933 agrees with the expected value for a black hole at this range of quiescent X-ray luminosities.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2014
- DOI:
- 10.1093/mnras/stu1487
- arXiv:
- arXiv:1404.2134
- Bibcode:
- 2014MNRAS.444..902A
- Keywords:
-
- accretion;
- accretion discs;
- black hole physics;
- stars: individual: Swift J1357.2-0933;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 5 pages, 3 figures, Accepted for publication in MNRAS