arXiv subjects

E. P. J. van den Heuvel

Publications and source records attributed to E. P. J. van den Heuvel.

45 records · Page 3Linked to original sources

arXiv2000

GRB990712: First Indication of Polarization Variability in a Gamma-ray Burst Afterglow

We report the detection of significant polarization in the optical afterglow of GRB990712 on three instances 0.44, 0.70 and 1.45 days after the gamma-ray burst, with (P, theta) being (2.9% +- 0.4%, 121.1 degr +- 3.5 degr), (1.2% +- 0.4%, 116.2 degr +- 10.1 degr) and (2.2% +- 0.7%, 139.2 degr +- 10.4 degr) respectively. The polarization is intrinsic to the afterglow. The degree of polarization is not constant, and smallest at the second measurement. The polarization angle does not vary significantly during these observations. We find that none of the existing models predict such polarization variations at constant polarization angle, and suggest ways in which these models might be modified to accommodate the observed behavior of this afterglow.

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arXiv2000

New Direct Observational Evidence for Kicks in SNe

We present an updated list of direct strong evidence in favour of kicks being imparted to newborn neutron stars. In particular we discuss the new cases of evidence resulting from recent observations of the X-ray binary Circinus X-1 and the newly discovered binary radio pulsar PSR J1141-6545. We conclude that the assumption that neutron stars receive a kick velocity at their formation is unavoidable (van den Heuvel & van Paradijs 1997).

astro-ph↗

arXiv2000

Formation of Millisecond Pulsars with Heavy White Dwarf Companions - Extreme Mass Transfer on Sub-Thermal Timescales

We have performed detailed numerical calculations of the non-conservative evolution of close X-ray binary systems with intermediate-mass (2.0-6.0 M_sun) donor stars and a 1.3 M_sun accreting neutron star. We calculated the thermal response of the donor star to mass loss, in order to determine its stability and follow the evolution of the mass transfer. Under the assumption of the "isotropic re-emission model" we demonstrate that in many cases it is possible for the binary to prevent a spiral-in and survive a highly super-Eddington mass-transfer phase (1 << M_dot/M_Edd < 10^5) on a sub-thermal timescale, if the convective envelope of the donor star is not too deep. These systems thus provide a new formation channel for binary millisecond pulsars with heavy CO white dwarfs and relatively short orbital periods (3-50 days). However, we conclude that to produce a binary pulsar with a O-Ne-Mg white dwarf or P_orb ~1 day (e.g. PSR B0655+64) the above scenario does not work, and a spiral-in phase is still considered the most plausible scenario for the formation of such a system.

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arXiv1999

Constraints on mass ejection in black hole formation, derived from black hole X-ray binaries

Both the recently observed high runaway velocities of Cyg X-1 (~50 km/s) and X-ray Nova Sco 1994 (> ~100 km/s) and the relatively low radial velocities of the black hole X-ray binaries with low mass donor stars, can be explained by symmetric mass ejection in the supernovae (SNe) which formed the black holes in these systems. Assuming symmetric mass ejection in black hole formation, we estimate the amount of mass that must have been ejected in the stellar core collapse in order to explain the velocities of the above X-ray binaries. We find that at least 2.6 M_sun and 4.1 M_sun must have been ejected in the formation of Cyg X-1 and Nova Sco, respectively. A similar mass loss fraction (f = 0.35) for the black hole binaries with low mass donors, gives low velocities, in agreement with the observations. We conclude that the black holes in X-ray binaries are all consistent with being formed in a successful SN in which mass is ejected. A possible kick at the formation of the black hole is not needed to explain their space velocities.

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arXiv1999

Circinus X-1: survivor of a highly asymmetric supernova

We have analyzed the kinematical parameters of Cir X-1 to constrain the nature of its companion star, the eccentricity of the binary and the pre-supernova parameter space. We argue that the companion is most likely to be a low-mass (< 2.0 M_sun) unevolved star and that the eccentricity of the orbit is 0.94 +/- 0.04. We have evaluated the dynamical effects of the supernova explosion and we find it must have been asymmetric. On average, we find that a kick of 740 km/s is needed to account for the recently measured radial velocity of +430 km/s (Johnston, Fender & Wu) for this extreme system. The corresponding minimum kick velocity is 500 km/s. This is the largest kick needed to explain the motion of any observed binary system. If Cir X-1 is associated with the supernova remnant G321.9-0.3 then we find a limiting minimum age of this remnant of 60000 yr. Furthermore, we predict that the companion star has lost 10% of its mass as a result of stripping and ablation from the impact of the supernova shell shortly after the explosion.

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arXiv1999

Is SAX J1808.4-3658 a Strange Star ?

One of the most important questions in the study of compact objects is the nature of pulsars, including whether they are composed of $β$-stable nuclear matter or strange quark matter. Observations of the newly discovered millisecond X-ray pulsar \sax with the Rossi X-Ray Timing Explorer place firm constraint on the radius of the compact star. Comparing the mass - radius relation of \sax with the theoretical mass - radius relation for neutron stars and for strange stars, we find that a strange star model is more consistent with SAX J1808.4-3658, and suggest that it is a likely strange star candidate.

hep-ph↗

arXiv1999

Could 2S 0114+650 be a magnetar?

We investigate the spin evolution of the binary X-ray pulsar 2S 0114+650, which possesses the slowest known spin period of $\sim 2.7$ hours. We argue that, to interpret such long spin period, the magnetic field strength of this pulsar must be initially $\gsim 10^{14}$ G, that is, it was born as a magnetar. Since the pulsar currently has a normal magnetic field $\sim 10^{12}$ G, our results present support for magnetic field decay predicted by the magnetar model.

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arXiv1997

Stability Criteria for Mass Transfer in Binary Stellar Evolution

The evolution of a binary star system by various analytic approximations of mass transfer is discussed, with particular attention payed to the stability of these processes against runaway on the thermal and dynamical timescales of the mass donating star. Mass transfer in red giant - neutron star binary systems is used as a specific example of such mass transfer, and is investigated. Hjellming and Webbink's (1987) results on the dynamic timescale response of a convective star with a core to mass loss are applied, with new results. It is found that mass transfer is usually stable, so long as the the wind's specific angular momentum does not exceed the angular momentum per reduced mass of the system. This holds for both dynamical and thermal timescales. Those systems which are not stable will usually transfer mass on the thermal timescale. Included are graphs illustrating the variation of the Roche radius exponent with mass ratio in the binary, for various parameters in the non-conservative mass transfer, as well as evolutionary paths of interacting red giant neutron star binaries.

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arXiv1995

WRAY 977 (GX301-2): A HYPERGIANT WITH PULSAR COMPANION

Wray 977, the B supergiant companion of the X-ray pulsar GX301-2, should be classified as B1~Ia+, based on a comparison of its optical spectrum to that of zeta1 Sco, a well-known B hypergiant and ONE OF THE BRIGHTEST STARS IN THE GALAXY. The classification of Wray 977 as a hypergiant results in a new distance determination of the binary system, i.e. 5.3 kpc (previously 1.8 +/- 0.4 kpc). The ``average'' X-ray luminosity of the pulsar is then ~10^37 erg/s, in good agreement with the predicted X-ray luminosity resulting from accretion of a dense, low-velocity (v_infty = 400 km/s) stellar wind. A mass-loss rate of <= 10^-5 M_sun/yr is estimated from the Halpha profile. A new upper limit for the inclination of the system is derived which provides a lower limit to the (present) mass of Wray 977 (48 M_sun). Regarding current binary evolution scenarios, the empirical lower mass limit for BLACK-HOLE formation in a binary increases to M_zams >= 50 M_sun.

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