The very faint hard state of the persistent neutron star X-ray binary SLX 1737-282 near the Galactic centre

Abstract

We report on a detailed study of the spectral and temporal properties of the neutron star low mass X-ray binary SLX 1737-282, which is located only ~1degr away from Sgr A. The system is expected to have a short orbital period, even within the ultra-compact regime, given its persistent nature at low X-ray luminosities and the long duration thermonuclear burst that it has displayed. We have analysed a Suzaku (18 ks) observation and an XMM-Newton (39 ks) observation taken 7 years apart. We infer (0.5-10 keV) X-ray luminosities in the range 3-6 x10^35erg s-1, in agreement with previous findings. The spectra are well described by a relatively cool (kTbb = 0.5 keV) black body component plus a Comptonized emission component with Γ ~1.5-1.7. These values are consistent with the source being in a faint hard state, as confirmed by the ~ 20 per cent fractional root mean square amplitude of the fast variability (0.1 - 7 Hz) inferred from the XMM-Newton data. The electron temperature of the corona is >7 keV for the Suzaku observation, but it is measured to be as low as ~2 keV in the XMM-Newton data at higher flux. The latter is significantly lower than expected for systems in the hard state. We searched for X-ray pulsations and imposed an upper limit to their semi-amplitude of 2 per cent (0.001 - 7 Hz). Finally, we investigated the origin of the low frequency variability emission present in the XMM-Newton data and ruled out an absorption dip origin. This constraint the orbital inclination of the system to 65 degr unless the orbital period is longer than 11 hr (i.e. the length of the XMM-Newton observation).

7 pages, 4 figures, 1 table. Accepted for publication in MNRAS

References in corpus (14)

• An XMM-Newton survey of broad iron lines in Seyfert galaxies
• Evaluating Spectral Models and the X-ray States of Neutron-Star X-ray Transients
• Six new candidate ultracompact X-ray binaries
• Black hole-like hysteresis and accretion states in neutron star low mass X-ray binaries
• A Prominent Accretion Disk in the Low-Hard State of the Black Hole Candidate SWIFT J1753.5-0127
• Intermediate long X-ray bursts from the ultra-compact binary source SLX 1737-282
• An in-depth study of a neutron star accreting at low Eddington rate: On the possibility of a truncated disk and an outflow
• The return to quiescence of Aql X-1 following the 2010 outburst
• A Hard X-Ray Power-Law Spectral Cutoff in Centaurus X-4
• XMMU J174716.1-281048: a "quasi-persistent" very faint X-ray transient?
• A dichotomy between the hard state spectral properties of black hole and neutron star X-ray~binaries
• Spectral and Timing Properties of the Black Hole X-ray Binary H 1743-322 in the Low/hard State Studied with Suzaku
• Registration of the First Thermonuclear X-ray Burst from AX J1754.2-2754
• Suzaku spectroscopy of the neutron star transient 4U 1608-52 during its outburst decay

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• Multi-wavelength spectroscopy of the black hole candidate MAXI J1813-095 during its discovery outburst
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• Evolution of the disc atmosphere in the X-ray binary MXB 1659-298, during its 2015-2017 outburst
• Resolving SLX 1744-299 and SLX 1744-300 in the hard X-ray band: implications for their ultracompact nature