Transient X-ray Binaries Research Articles

Discovery of a new transient X-ray pulsar in the Small Magellanic Cloud

Systematic Rossi X-Ray Timing Explorer (RXTE) observations of the Small Magellanic Cloud (SMC) have revealed a previously unknown transient X-ray pulsar with a pulse period of 95s. The 95s pulsar, provisionally designated XTE SMC95, was detected in three Proportional Counter Array (PCA) observations during an outburst spanning 4 weeks in March/April 1999. The pulse profile is double peaked reaching a pulse fraction of ≈ 0.8. The X-ray spectrum is well represented by an absorbed power-law with a photon index of 1.4 and mean unabsorbed flux of $\ga$8.95$\times 10^{-11}$ ergs cm -2 s -1 (3–25 keV). The source is proposed as a Be/neutron star system on the basis of its pulsations, transient nature and characteristically hard X-ray spectrum. The 2–10 keV X-ray luminosity implied by our observations is $\ga$2$\times$10 37 ergs s -1 which is consistent with that of normal outbursts seen in Galactic systems. This discovery adds to the emerging picture of the SMC as containing an extremely dense population of transient high mass X-ray binaries.

Very Low Luminosities from the Accretion‐driven Millisecond X‐Ray Pulsar SAX J1808.4−3658 during Quiescence

We have observed the millisecond X-ray pulsar SAX J1808.4-3658 on three occasions during its 2000 outburst with the BeppoSAX satellite. The source was highly variable and erratic during this outburst, and by coincidence we obtained data only during times when the source had very low luminosities. During our observations, we detected four faint sources. The source closest to the position of SAX J1808.4-3658 is still ~1.6' away. This source can only be identified with SAX J1808.4-3658 if we assume that the BeppoSAX positional reconstruction is not completely understood. We also reanalyzed a BeppoSAX observation taken in March 1999 when the source was in quiescence and during which the source was thought to have been detected (Stella et al. 2000). Based on the similarities (position and luminosity) of this source with the above mentioned source ~1.6' away from SAX J1808.4-3658, it is possible that they are the same source. If this source is not the millisecond pulsar, then during all BeppoSAX observations of SAX J1808.4-3658 (the 2000 outburst ones and the 1999 quiescent one), the millisecond pulsar was not detected. A reanalysis of the ASCA quiescent data of SAX J1808.4-3658 (Dotani, Asai, & Wijnands 2000) confirms that during this observation the source was securely detected in quiescence. We discuss our results for SAX J1808.4-3658 in the context of the quiescent properties of low-mass X-ray binary transients.

Li abundances in late-type companions to neutron stars and black hole candidates

view Abstract Citations (80) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Li Abundances in Late-Type Companions to Neutron Stars and Black Hole Candidates Martin, Eduardo L. ; Rebolo, Rafael ; Casares, Jorge ; Charles, Philip A. Abstract Following our recent report of a strong Li lambda 6708 resonance line in the secondary of the black hole candidate V404 Cyg, we present here its detection in the quiescent spectrum of the neutron star binary Cen X-4. We obtain, via a spectral synthesis Local Thermodynamic Equilibrium (LTE) analysis, a surface lithium abundance in the K-type secondary of log N(Li) = 3.3 +/- 0.4. Taking into account non-LTE effects reduces the abundance by 0.2 dex. Using the same analysis, lithium abundances are also derived for the secondaries of the black hole binaries A0620-00, where a lithium detection has very recently been reported, and V404 Cyg. High lithium abundances appear to be a common feature of late-type secondaries in neutron star and black hole binaries, a result totally unexpected mainly because of post-main-sequence dilution and the mass transfer history of these stars. Convective mixing may cause additional depletion if lithium is taken to layers where it is burnt. In order to counteract the depletion it seems necessary to invoke a process of lithium production. Several mechanisms are plausible: for instance, lithium synthesis in a supernova explosion of the compact primary's progenitor, or an on-going process such as alpha-alpha reactions during the repeated strong outbursts that characterize transient X-ray binaries. The spallative mechanism can be tested by future high-resolution gamma-ray and optical spectroscopic observations. Implications on the Li enrichment of the Galactic interstellar medium are briefly discussed. Publication: The Astrophysical Journal Pub Date: November 1994 DOI: 10.1086/174857 Bibcode: 1994ApJ...435..791M Keywords: Black Holes (Astronomy); Lithium; Neutron Stars; Stellar Luminosity; Stellar Spectra; Astronomical Spectroscopy; X Ray Binaries; Astrophysics; BLACK HOLE PHYSICS; STARS: ABUNDANCES; STARS: INDIVIDUAL CONSTELLATION NAME: CENTAURUS X-4; STARS: NEUTRON full text sources ADS | data products SIMBAD (3)

X-ray variability in transient X-ray sources

The X-ray variability of transient X-ray binaries is analyzed in terms of the orbital motion of the neutron star, centrifugal inhibition of accretion and of the variable moss loss rate due to activity of the optical counterpart. The systems A0535+26 and V0332+53 are studied in this respect.

A0535+26 and the structure of the outflowing gas from Be stars

We propose a hybrid model, a gas disk plus a slowly accelerating stellar wind, for the gas outflow from the Be star in transient hard X-ray binaries. We give the velocity structure in the outflow, calculate the variation of the X-luminosity and explain many observed features of A0535+26.