arXiv subjects

E. S. Phinney

Publications and source records attributed to E. S. Phinney.

24 records · Page 2Linked to original sources

arXiv1998

The gamma-ray burst of 980425 and its association with the extraordinary radio emission from a most unusual supernova

Supernova SN 1998bw exploded in the same direction and at the same time as the gamma-ray burst GRB 980425. Here we report radio observations of this type Ic supernova, beginning 4 days after the gamma-ray burst. At its peak the radio source is the most luminous ever seen from a supernova, nu L_nu = 4 x 10^38 erg/s at 5 GHz. More remarkably, the traditional synchrotron interpretation of the radio emission requires that the radio source be expanding at an apparent velocity of at least twice the speed of light, indicating that this supernova was accompanied by a shock wave moving at relativistic speed. The energy U_e associated with the radio-emitting relativistic electrons must lie between 10^49 erg <U_e< 10^52 erg, and thus represents a significant fraction of the total kinetic energy ~10^51 erg associated with supernova explosions. The presence of a relativistic shock in SN 1998bw suggests a physical connection with the gamma-ray burst GRB 980425. We argue that this represents a second class of gamma-ray burst, with much lower emitted energy ~10^48 erg in gamma-rays than the two powerful ~10^53 erg high-redshift gamma-ray bursts previously identified.

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arXiv1998

Why pulsars rotate and move: kicks at birth

RADIO pulsars are thought to born with spin periods of 0.02-0.5 s and space velocities of 100-1000 km/s, and they are inferred to have initial dipole magnetic fields of 10^{11}-10^{13}. The average space velocity of a normal star in the Milky Way is only 30 km/s, which means that pulsars must receive a substantial 'kick' at birth. Here we propose that the birth characteristics of pulsars have a simple physical connection with each other. Magnetic fields maintained by differential rotation between the core and envelope of the progenitor would keep the whole star in a state of approximately uniform rotation until 10 years before the explosion. Such a slowly rotating core has 1000 times less angular momentum than required to explain the rotation of pulsars. Although the specific physical process that 'kicks' the neutron star at birth has not been identified, unless its force is exerted exactly head-on, it will also cause the neutron star to rotate. We identify this process as the origin of the spin of pulsars. Such kicks will cause a correlation between the velocity and spin vectors of pulsars. We predict that many neutron stars are born with periods longer than 2 s, and never become radio pulsars.

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arXiv1997

Binaries in Globular Clusters

Binary stars play a critical role in determining both the dynamical evolution and the observational appearance of globular star clusters. We present a summary of three talks presented at IAU JD15, reviewing the current observational and theoretical status of binaries and related ``exotic'' stars in the Galactic globular cluster system.

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arXiv1997

The fading of young stellar populations and the luminosity functions of dwarf, irregular and starburst galaxies

Dwarf, irregular and infrared-luminous starburst galaxies are all known to have "steep" luminosity functions with faint-end behavior roughly phi(L)-propto- L^(-1.8). This form is exactly what is expected if the luminosities of these objects fade with time as L-propto-t^(-1.3), because the objects spend more time at low luminosities than high, even if they form with a wide range of initial masses. Models of young stellar populations show this fading behavior when the star formation has occured in a single, short, recent burst. Steep luminosity functions therefore do not require steep mass functions if the galaxies are powered by fading bursts. The local-galaxy H-alpha luminosity function---which is less steep than L^(-1.8)---is also well-fit by this mechanism, because ionizing photon flux fades much more quickly than broad-band optical luminosity. An age-luminosity relation and a wavelength-dependence of the luminosity function are both predicted. In the context of this mechanism, the slope of the luminosity function provides a constraint on the stellar initial mass function in the bursts.

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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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arXiv1994

Dynamics and Interactions of Binaries and Neutron Stars in Globular Clusters

We model the dynamics of test binaries in isotropic, multi-mass models of galactic globular clusters. The evolution of binary orbits through the cluster potentials is modeled, including second order diffusion terms, and probabilities for close encounters with field stars are calculated. We carry out Monte Carlo simulations of the effects of the binary--single star encounters on the binary population and distribution in the cluster, and estimate the collision rate for different stellar populations in globular clusters with different structural parameters. Assuming a Salpeter IMF, for low concentration clusters the core encounter rate is dominated by turnoff mass main--sequence stars and medium mass white dwarfs. For high concentration, high density clusters the encounter probabilities are increasingly dominated by neutron stars and heavy white dwarfs. Hence we predict a smaller ratio of blue stragglers and cataclysmic variables to pulsars in high concentration clusters. The total number of millisecond pulsars, and the ratio of single to binary pulsars, is broadly consistent with the observed population, suggesting the binary--single star encounters contribute significantly to the pulsar formation rate in globular clusters, for the whole range of globular cluster types. The number of millisecond pulsars and the ratio of pulsars in different globular clusters is best explained by a total binary fraction comparable to that of the galaxy, and a modest number of primordial neutron stars in the globular clusters.

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