ABSTRACT
Theoretical models for the production of relativistic jets from active galactic nuclei predict that jet power arises from the spin and mass of the central supermassive black hole, as well as from the magnetic field near the event horizon. The physical mechanism underlying the contribution from the magnetic field is the torque exerted on the rotating black hole by the field amplified by the accreting material. If the squared magnetic field is proportional to the accretion rate, then there will be a correlation between jet power and accretion luminosity. There is evidence for such a correlation, but inadequate knowledge of the accretion luminosity of the limited and inhomogeneous samples used prevented a firm conclusion. Here we report an analysis of archival observations of a sample of blazars (quasars whose jets point towards Earth) that overcomes previous limitations. We find a clear correlation between jet power, as measured through the γ-ray luminosity, and accretion luminosity, as measured by the broad emission lines, with the jet power dominating the disk luminosity, in agreement with numerical simulations. This implies that the magnetic field threading the black hole horizon reaches the maximum value sustainable by the accreting matter.
ABSTRACT
Mrk 421 was observed for about 2 days with BeppoSAX in 1998 April as part of a worldwide multiwavelength campaign. A large, well-defined flare was observed in X-rays. The same flare was observed simultaneously at TeV energies by the Whipple Observatory gamma-ray telescope. These data provide (1) the first evidence that the X-ray and TeV intensities are well correlated on timescales of hours and (2) the first exactly simultaneous X-ray and TeV spectra. The results imply that the X-ray and TeV photons derive from the same region and from the same population of relativistic electrons. The physical parameters deduced from a homogeneous synchrotron self-Compton model for the spectral energy distribution yield electron cooling times close to the observed variability timescales.
ABSTRACT
THE presence of rotating neutron stars in binary systems is revealed by the existence of X-ray pulsators which are generally associated with massive companions. The evolutionary history of these systems is now relatively clear (see ref. 1 and refs therein). The X-ray phase, which corresponds to accretion on the neutron star of a strong stellar wind \M approximately 10(-6) M(\circ) yr(-1), is preceded by a much longer quiet state, where the primary is unevolved, possibly with a weak wind, \M approximately 10(-9) M(\circ) yr(-1) and the rotational energy loss of the neutron star inhibits accretion. However, with the only exception of PSR1913 + 16, radio pulsars are not found in binary systems. Here, motivated by the recent discovery of gamma-ray emission from slow pulsars(2,3), we suggest (gamma)-ray observations as a way of detecting binaries in the quiet state and compare the expected number with the COS B results. We refer to the review of van den Heuvel(1) where, as a representative case, a system of initial mass 20 + 8 M(\circ) and orbital period 4.7 d is considered. After the first stage of mass exchange and the supernova explosion, one has a neutron star with an unevolved companion of 22.7 M(\circ). The period is now P = 12.6 d. The primary remains on the main sequence (quiet stage) for t(ms) = 3.6 x 10(6)yr. The X-ray phase occurs after the star has left the main sequence, but before it fills its Roche lobe, as an excessive mass transfer absorbs the X-ray emission. Its duration is t(x) approximately 10(4)yr.
