[ITAL]RXTE[/ITAL] Observations of the B[CLC]e[/CLC] Star X-Ray Transient X0726−260 (4U 0728−25): Orbital and Pulse Periods

Corbet, R. H. D.; Peele, Andrew G.

doi:10.1086/310972

Cited by 23 publications

(19 citation statements)

References 18 publications

(20 reference statements)

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“…There is a second subclass of Be/X-ray binaries characterised by low-luminosity, persistent X-ray emission with little variation, e.g., X Persei (Haberl et al 1998), but they are believed to have large orbital periods (Reig & Roche 1999) -which is certainly the case for X Persei (Delgado-Marti et al 2001). The 9.5-d period of 4U 2206+54 makes a connection unlikely, though the low X-ray luminosity Be/X-ray binary 3A 0726−26 (P s = 103.2 s) could have a short period P orb = 34.5 d (Corbet & Peele 1997). Moreover, the decrease in L x by more than one order of magnitude reported by SA92 is also atypical for these systems.…”

Section: Discussionmentioning

confidence: 92%

On the nature of the hard X-ray source 4U 2206+54

Negueruela

Reig

2001

A&A

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Abstract. The recent discovery of a ∼9.5d period in the X-ray lightcurve of the massive X-ray binary 4U 2206+54 has opened the possibility that it is a Be/X-ray binary with an unusually close orbit, which, together with its low intrinsic luminosity, suggests that the system is actually a Be + WD binary, in which a white dwarf accretes material from the dense circumstellar disc surrounding a classical Be star. In this paper we present new X-ray observations and for the first time high-resolution optical spectroscopy of the source. We show that both the X-ray behaviour and the characteristics of the optical counterpart, BD +53 • 2790, are more consistent with a neutron star accreting from the wind of an early-type star. The X-ray lightcurve shows irregular flaring and no indications of pulsations, while the very high hydrogen column density supports accretion from a dense wind. BD +53 • 2790 is shown not to be a classical Be star, as believed until now, but rather a very peculiar late O-type active star, exhibiting emission components in the He ii lines, complex spectral variability and strong wind resonance lines in the ultraviolet. Though many of the characteristics of the spectrum resemble those of the He-rich stars, the absence of He i variability makes a connection unlikely. The spectrum is compatible with a composite of two stars of similar spectral type, though circumstantial evidence points to a single very peculiar active early-type star. This adds weight to the growing evidence that the traditional subdivisions of supergiant and Be/X-ray binaries fail to cover the whole phenomenology of massive X-ray binaries.

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Section: Discussionmentioning

confidence: 92%

On the nature of the hard X-ray source 4U 2206+54

Negueruela

Reig

2001

A&A

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“…In the second case, if the orbit plane is inclined to the plane of an equational circumstellar disc, two possible outbursts could occur when the neutron star passes through the disc. This scenario has been proposed to explain two modulation periods detected in two X-ray binaries: a Be/neutron star binary GRO J2058+42 (Corbet et al 1997) and a supergiant system 4U 1907+09 (Mashall & Ricketts 1980). Though 4U 2206+54 has the difference in the nature of the mass donor, the orbit behavior may be similar to the case in GRO J2058+42 and 4U 1907+09.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Evidence for a magnetic neutron star in high-mass X-ray binary 4U 2206+54 withINTEGRAL/IBIS observations

Wang

2009

Monthly Notices of the Royal Astronomical Society

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The hard X-ray source 4U 2206+54 is a peculiar high-mass X-ray binary with a main-sequence donor star. Recent X-ray observations suggested that the compact object in 4U 2206+54 may be a neutron star. The X-ray emission comes from the accretion of stellar winds from the massive donor star, and variability of its luminosity may be due to changes in its orbital phase. To reveal further the nature of the compact object, we studied 4U 2206+54 with INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL)/IBIS observations over two years, and found that for most of this time 4U 2206+54 was in a quiescent state, sometimes undergoing an active phase. In the quiescent state the spectrum can be fitted by a power-law model of ∼ 2.1 with a hard X-ray luminosity of ∼5 × 10 34 erg s −1 (20-100 keV). While the source is in the active state, the 20-100 keV hard X-ray luminosity reaches ∼ 2 × 10 35 erg s −1 and the spectrum is fitted by a thermal bremsstrahlung model of kT ∼ 43 keV plus two cyclotron absorption lines at ∼30 and 60 keV. We then derived a magnetic field of 3.3 × 10 12 G for the compact object in 4U 2206+54. During the active state, we found a pulsation period of ∼5400 s in the light curve of 4U 2206+54. The compact object in 4U 2206+54 should therefore be a magnetic neutron star with slow pulsation. The detection of cyclotron absorption lines in the active state and their non-detection in the quiescent state suggested that the two different accretion states have possible different hard X-ray emission regions: the surface of the neutron star in the active state and the magnetic-accretion pressure equivalent point in the quiescent state. Re-analysis of the RXTE/ASM light curve found modulation periods at ∼9.56 and 19.11 d, and the orbital period of 4U 2206+54 should be 19.11 d.

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“…Corbet & Peele (1997) have suggested a possible 34.5‐d period for the Be/X‐ray binary 3A 0726‐260. If this period was to be confirmed, the comparison between V0332+53 and 3A 0726‐260 would be most interesting, since the two systems would have neutron stars orbiting Oe stars of almost identical spectral types with extremely similar orbital periods.…”

Section: Discussionmentioning

confidence: 99%

The Be/X-ray transient V0332+53: evidence for a tilt between the orbit and the equatorial plane?

Negueruela

Roche

Fabregat

et al. 1999

Monthly Notices of the Royal Astronomical Society

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We present optical and infrared observations of BQ Cam, the optical counterpart to the Be/X‐ray transient system V0332+53. BQ Cam is shown to be an O8–9Ve star, which places V0332+53 at a distance of ∼7 kpc. Hα spectroscopy and infrared photometry are used to discuss the evolution of the circumstellar envelope. Owing to the low inclination of the system, parameters are strongly constrained. We find strong evidence for a tilt of the orbital plane with respect to the circumstellar disc (presumably on the equatorial plane). Even though the periastron distance is only ≈10R*, during the present quiescent state the circumstellar disc does not extend to the distance of periastron passage. Under these conditions, X‐ray emission is effectively prevented by centrifugal inhibition of accretion. The circumstellar disc is shown to be optically thick at optical and infrared wavelengths, which, together with its small size, is taken as an indication of tidal truncation.

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[ITAL]RXTE[/ITAL] Observations of the B[CLC]e[/CLC] Star X-Ray Transient X0726−260 (4U 0728−25): Orbital and Pulse Periods

Cited by 23 publications

References 18 publications

On the nature of the hard X-ray source 4U 2206+54

On the nature of the hard X-ray source 4U 2206+54

Evidence for a magnetic neutron star in high-mass X-ray binary 4U 2206+54 withINTEGRAL/IBIS observations

The Be/X-ray transient V0332+53: evidence for a tilt between the orbit and the equatorial plane?

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