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Search Results: 1 - 10 of 84446 matches for " W. Kluzniak "
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Neutrino oscillations and gamma-ray bursts
W. Kluzniak
Physics , 1998, DOI: 10.1086/311712
Abstract: If the ordinary neutrinos oscillate into a sterile flavor in a manner consistent with the Super-Kamiokande data on the zenith-angle dependence of atmospheric mu-neutrino flux, an energy sufficient to power a typical cosmic gamma-ray burst (GRB) (about 10^{52} erg) can be carried by sterile neutrinos away from the source and deposited in a region relatively free of baryons. Hence, ultra-relativistic bulk motion (required by the theory of and observations of GRBs and their afterglows) can easily be achieved in the vicinity of plausible sources of GRBs. Oscillations between sterile and ordinary neutrinos would thus provide a solution to the ``baryon-loading problem'' in the theory of GRBs.
General-relativistic constraints on the equation of state of dense matter implied by kilohertz quasi-periodic oscillations in neutron-star X-ray binaries
W. Kluzniak
Physics , 1997, DOI: 10.1086/311748
Abstract: If the observed millisecond variability in the X-ray flux of several neutron-star low-mass X-ray binaries (LMXBs) is interpreted within a general-relativistic framework (Kluzniak, Michelson \& Wagoner 1990) extant at the time of discovery, severe constraints can be placed on the equation of state (e.o.s.) of matter at supranuclear densities. The reported maximum frequency (1.14 +- 0.01 kHz) of quasiperiodic oscillations observed in sources as diverse as Sco X-1 and 4U 1728-34 would imply that the neutron star masses in these LMXBs are M > 1.9 M_solar, and hence many equations of state would be excluded. Among the very few still viable equations of state are the e.o.s. of Phandaripande and Smith (1975), and e.o.s. AV14 + UVII of Wiringa, Fiks \& Fabrocini (1988).
Is the Universe transparent to TeV photons?
W. Kluzniak
Physics , 1999,
Abstract: If Lorentz invariance is broken at an energy scale Eq, as has recently been suggested in the context of attempts to quantize gravity, the kinematics of photon-photon collisions would be profoundly affected at lower energies. Specifically, electron-positron pair creation on soft photons may be forbidden at photon energies as low as 30 TeV times square root of (Eq/10**17 GeV) and the Universe would then be transparent to high energy photons. The proposition that Lorentz invariance is broken may be falsified by the techniques of TeV astronomy.
Neutron stars and strong-field effects of general relativity
W. Kluzniak
Physics , 2000,
Abstract: The basic observed properties of neutron stars are reviewed. I suggest that neutron stars in low-mass X-ray binaries are the best of all known sites for testing strong-field effects of general relativity.
Relativistic models of kHz QPOs
W. Kluzniak
Physics , 2000,
Abstract: After reviewing the general-relativistic ``gap'' model of accretion, I discuss its relation to the high frequency quasi-periodic oscillations observed in low-mass X-ray binaries. The ``300'' Hz frequency seen in some X-ray bursts may be a relativistic signature of keplerian rotation of the neutron star.
Non-linear resonances in accretion disks and qpos
W lodek Kluzniak
Revista mexicana de astronomía y astrofísica , 2004,
Abstract: Secundamos las oscilaciones no-lineales en el disco de acreci on como una explicaci on de las oscilaciones cuasi- peri odicas" de alta frecuencia observadas en las curvas de luz de las binarias de rayos X de baja masa que contienen estrellas de neutrones, agujeros negros o enanas blancas.
Millisecond oscillators in accreting neutron stars and black holes
W. Kluzniak,M. Abramowicz
Physics , 2003,
Abstract: Millisecond variability detected in low-mass X-ray binaries (LMXBs) probably reflects motions of accreting fluid in the strong-field gravity of neutron stars or neutron stars. Parametric resonance between two oscillators with unequal eigenfrequencies provides a natural explanation for the 2:3 frequency ratio observed in some black-hole systems, and probably also in the brightest neutron stars. The two oscillators likely correspond to the meridional and radial epicyclic motions.
Three-dimensional structure of an alpha accretion disk
W. Kluzniak,D. Kita
Physics , 2000,
Abstract: An analytic solution is presented to the three-dimensional problem of steady axisymmetric fluid flow through an accretion disk. The solution has been obtained through a systematic expansion in the small parameter epsilon =H/R (the ratio of disk thickness to its radial dimension) of the equations of viscous hydrodynamics. The equation of state was assumed to be polytropic. For all values alpha< 0.685 of the viscosity parameter, we find significant backflow in the midplane of the disk occuring at all radii larger than a certain value; however, in the inner regions of the disk the fluid always flows toward the accreting object. The region of backflow is separated from the region of inflow by a surface flaring outwards from a circular locus of stagnation points situated in the midplane of the disk.
The central engine of gamma-ray bursters
W. Kluzniak,M. Ruderman
Physics , 1997, DOI: 10.1086/311622
Abstract: GRBs are thought to arise in relativistic blast-wave shocks at distances of 10 to 1000 AU from the point where the explosive energy is initially released. To account for the observed duration and variability of the gamma-ray emission in most GRBs, a central engine powering the shocks must remain active for several seconds to many minutes but must strongly fluctuate in its output on much shorter timescales. We show how a neutron star differentially rotating at millisecond periods (DROMP) could be such an engine. A magnetized DROMP would repeatedly wind up toroidal magnetic fields to about 10**17 G and only release the corresponding magnetic energy, when each buoyant magnetic field torus floats up to, and breaks through, the stellar surface. The resulting rapid sub-bursts, separated by relatively quiescent phases, repeat until the kinetic energy of differential rotation is exhausted by these events. Calculated values of the energy released and of the various timescales are in agreement with observations of GRBs. The baryon loading in each sub-burst may also be consistent with theoretical requirements for a blast wave capable of giving the X-ray, optical and radio afterglows recently observed from cosmological distances. DROMPs could be created in several kinds of astrophysical events; some of these would be expected to occur at about the observed GRB rate. The requisite differential rotation could be imparted to neutron stars as they are born or at the end of their existence: some DROMPs may be created close to star forming regions while others may arise far from galaxies.
Relativistic effects on coronal ejection in variable X-ray sources
B. Mishra,W. Kluzniak
Physics , 2013,
Abstract: Optically thin coronae around neutron stars suffering an X-ray burst can be ejected as a result of rapid increase in stellar luminosity. In general relativity (GR), radiation pressure from the central luminous star counteracts gravitational attraction more strongly than in Newtonian physics. However, motion near the neutron star is very effectively impeded by the radiation field. We discuss coronal ejection in a general relativistic calculation of the motion of a test particle in a spherically symmetric radiation field. At every radial distance from the star larger than that of the ISCO, and any initial luminosity of the star, there exists a luminosity change which leads to coronal ejection. The luminosity required to eject from the system the inner parts of the optically thin neutron-star corona is very high in the presence of radiation drag and always close to the Eddington luminosity. Outer parts of the corona, at a distance of ~20 $R_G$ or more, will be ejected by a sub-Eddington outburst. Mildly fluctuating luminosity will lead to dissipation in the plasma and may explain the observed X-ray temperatures of coronae in low mass X-ray binaries (LMXBs). At large radial distances from the star ($3\cdot 10^3 R_G$ or more) the results do not depend on whether or not Poynting-Robertson drag is included in the calculation.
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