21 research outputs found
Symmetries of microcanonical entropy surfaces
Symmetry properties of the microcanonical entropy surface as a function of
the energy and the order parameter are deduced from the invariance group of the
Hamiltonian of the physical system. The consequences of these symmetries for
the microcanonical order parameter in the high energy and in the low energy
phases are investigated. In particular the breaking of the symmetry of the
microcanonical entropy in the low energy regime is considered. The general
statements are corroborated by investigations of various examples of classical
spin systems.Comment: 15 pages, 5 figures include
X-ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies
By combining complementary monitoring observations spanning long, medium and
short time scales, we have constructed power spectral densities (PSDs) of six
Seyfert~1 galaxies. These PSDs span 4 orders of magnitude in temporal
frequency, sampling variations on time scales ranging from tens of minutes to
over a year. In at least four cases, the PSD shows a "break," a significant
departure from a power law, typically on time scales of order a few days. This
is similar to the behavior of Galactic X-ray binaries (XRBs), lower mass
compact systems with breaks on time scales of seconds. NGC 3783 shows tentative
evidence for a doubly-broken power law, a feature that until now has only been
seen in the (much better-defined) PSDs of low-state XRBs. It is also
interesting that (when one previously-observed object is added to make a small
sample of seven), an apparently significant correlation is seen between the
break time scale and the putative black hole mass , while none
is seen between break time scale and luminosity. The data are consistent with
the linear relation T = M_{\rm BH}/10^{6.5} \Msun; extrapolation over 6--7
orders of magnitude is in reasonable agreement with XRBs. All of this
strengthens the case for a physical similarity between Seyfert~1s and XRBs.Comment: 27 pages, 13 figures. Accepted for publication in ApJ. Typo correcte
A model for double notches and bifurcated components in radio profiles of pulsars and magnetars - Evidence for the parallel acceleration maser in pulsar magnetosphere
Averaged pulse profiles of three nearby pulsars: B1929+10, J0437-4715 and
B0950+08 exhibit unusual `double notches'. These W-like looking features
consist of two adjacent V-shaped dips that approach each other at increasing
observation frequency nuobs roughly at a rate sep \propto nuobs^{-1/2}, where
sep is the separation between the notches' minima. We show that basic
properties of the notches, namely their W-like look and the rate of their
converging can be understood within a narrow class of models of coherent radio
emission from pulsars: the free electron maser models based on coherent inverse
Compton scattering of parallel oscillations of ambient electric field. The
observed properties of the pulsars imply that the Fourier spectrum of the
wiggler-like oscillations is narrow and that the broad-band character of the
radio emission reflects the width of the electron energy distribution. Such a
model provides a natural explanation for the frequency-independent separation
between the main pulse and interpulse of B0950+08 as well as for the lack of
radius to frequency mapping in the conal-like emission of J0437-4715. The
frequency behaviour of the main pulse in the profile of the first radio
magnetar XTE J1810-197 can also be explained within this model.Comment: 15 pages, 10 figures, accepted by A&A after minor change
Pulsar shadow as the origin of double notches in radio pulse profiles
We present the model of eclipsing a rotating, spatially extended source of
directional emission by a central absorber, and apply it to the pulsar
magnetosphere. The model assumes the radially extended inward radio emission
along the local direction of the magnetic field, and the pulsar as the
absorber. The geometry of the magnetic field lines of the rotating dipole is
favourable for the double eclipse events, which we identify with the double
notches observed in pulse profiles of nearby pulsars. For pulsars with large
dipole inclinations 70 <~ alpha <~ 110 deg the double notches are predicted to
occur within a narrow phase range of 20 to 30 deg before the main radio peak.
Application of the model to PSR B0950+08 establishes it as a nearly orthogonal
rotator (alpha =~ 75 deg, beta =~ -10 deg) with many pulse components naturally
interpreted in terms of the inward radio emission from a large range of
altitudes. The inward components include the intermittently strong, leading
component of the main pulse, which would traditionally have been interpeted as
a conal emission in the outward direction. The model also identifies the
magnetic field lines along which the radially extended inward radio emission
occurs in B0950+08. These have a narrow range of the footprint parameter s
close to 1.1 (closed field line region, near the last open field lines). We
describe directional characteristics of inward emission from the radially
extended region and compare them with characteristics of extended outward
emission. Our work shows that pulse profiles of at least some pulsars may be a
superposition of both inward and outward emission.Comment: 28 pages, 13 figures, accepted by ApJ, high-quality figures are
available from http://www.ncac.torun.pl/~michalf/inward1_figs