333 research outputs found
The near-synchronous polar V1432 Apl (RX J1940.1-1025) : accretion geometry and synchronization time scale
No full textThe magnetic Cataclysmic Variable (mCV) V1432 Aq
Combined spectral and temporal analysis of Her X-1 turn on
No full textDer 35 Tage Zyklus im akkretierenden Röntgenpulsar Her X-1 ist einer der
deutlichsten Beobachtungs-Hinweise für eine geneigte, verbogene und
präzedierende Akkretionsscheibe in einem Doppelsternsystem. Im September
1997 wurde die Quelle mit dem Röntgensatelliten RXTE mit hoher zeitlicher
und spektraler Auflösung im Spektralbereich von 2-200 keV beobachtet. Die
Beobachtung mit einer Gesamtlänge von 3 Tagen umfasst einen Turn-On des 35
Tage Präzessions-Zyklus der Akkretionsscheibe. Dies entspricht dem
Zeitraum, zu dem der äußere Rand der Akkretionsscheibe die Sicht auf den
Neutronenstern frei gibt. Diese Arbeit stellt die Ergebnisse einer
zeitlichen und spektralen Analyse der Daten vor.
Das phasengemittelte Kontinuum von Her X-1 während des Turn-On wird gut
durch ein Partial Covering Modell beschrieben. Dieses Modell setzt sich
zusammen aus einer stark absorbierten Power-Law-Komponente (alpha ungefähr
1.0) mit einem exponentiellen Abfall (E_cut ungefähr 21 keV) und einer
zusätzlichen spektralen Komponente mit gleichem Verlauf die nicht
absorbiert ist. Das Spektrum weisst eine Eisenfloureszenzlinie bei ungefähr
6.4 keV auf und zeigt eine schwache Zyklotronresonanzlinie bei 39.9
keV. Die Energieauflösung des PCA von RXTE ist zu niedrig, um eine
systematische Variation der Eisenlinie mit der Zeit zu untersuchen. Aus der
Linienlage der Zyklotronlinie lässt sich direkt eine Magnetfeldstärke von
4.1x10^12 Gauss ableiten.
Die Rotationsperiode des Neutronensterns wurde aus den Daten bestimmt und
ist in guter Übereinstimmung mit den Ergebnissen aus anderen
Beobachtungen. Dies bestätigt die lang anhaltende Spin-Up Phase von Her
X-1, die sich erst vor kurzer Zeit zu einem Spin-Down geändert hat. Eine
Zerlegung des Pulsprofils in die Beiträge der beiden Neutronensternpole
liefert ähnliche Ergebnisse für den Turn-On, wie die für das Pulsprofil im
Main-On. Das beobachtete Pulsprofil wird bei hohen Energien von einem
"Pencil Beam" Anteil dominiert, aber beinhaltet auch Anteile eines "Fan
Beams". Die Änderungen des Pulsprofils und des Anteils an gepulstem Fluss
zu Beginn des Turn-On sind konsistent mit der Form eines Main-On
Pulsprofils, das durch photoelektrische Absorption und Thomson-Streuung
beeinflusst ist.
Die Entwicklung der Wasserstoffsäulendichte N_h und der Covering Fraction
während des Turn-Ons kann durch ein einfaches geometrisches Modell erklärt
werden, das eine Akkretionsscheibenkorona und den äusseren Rand der
Akkretionsscheibe mit einbezieht. Das Modell kann auch die beobachtete
Entwicklung des Pulsprofils in den unterschiedlichen Energiebereichen
erklären. Zusätzlich wurden die zeitliche Signatur einer streuenden
heissen Korona auf gepulste und gerichtete Emission untersucht und die
Ergebnisse dargestellt. Ein Vergleich der Ergebnisse der Simulation mit den
beobachteten Pulsprofilen unterstützt das geometrische Modell des Turn-Ons.The 35 day cycle of the accreting X-ray pulsar Her X-1 provides one of the
best evidences for an inclined, warped, and precessing accretion disk in a
binary system. In 1997 September the source was observed with the X-ray
satellite RXTE with high temporal and spectral resolution in the energy
band of 2-200 keV. The 3 days long observation covers a full turn-on of the
35 day precession cycle of the accretion disk, which is the time when the
outer edge of the disk frees the line of sight to the neutron star. In this
thesis I present results of the temporal and spectral analysis of the data.
The phase averaged continuum spectrum of Her X-1 during the turn-on is well
described by a partial covering model, which combines a heavily absorbed
power-law spectral component (alpha approx. 1.0) with an exponential
cut-off (E_cut approx. 21 keV) and a similar spectral component which is
not affected by absorption. The spectrum shows a strong signature of iron
flourescent emission at approx. 6.4 keV and a weak Cyclotron resonant
scattering feature at 39.9 keV. The energy resolution of the PCA on-board
of RXTE is too low for a systematic study of a variation of the iron line
with time. The energy of the CRSF indicates a magnetic field strength of
4.1x10^12 Gauss which confirms recent findings.
The spin period of the neutron star was determined from the data and is in
agreement with other observations. This confirms the long spin-up period of
Her X-1 which only recently changed to a spin-down. A decomposition of the
pulse profile into the contribution of the two neutron star poles gives
similar results for the turn-on as for the main-on pulse profile. The
observed pulse profile is dominated by a "pencil beam" component at high
energies, but shows a signature of a "fan beam" component as well. The
changes in shape of the pulse profile and the pulsed flux ratio towards the
beginning of the turn-on are consistent with the shape of a main-on pulse
profile which is modified by photoelectric absorption and Thomson
scattering.
The evolution of the absorbing column N_h and the covering fraction during
the turn-on can be explained by a simple geometric model which includes an
accretion disk corona and the influence of the outer accretion disk rim.
This model can also explain the observed pulse evolution in different
energy bands. In addition the temporal signature of a partially ionized
corona on beamed and pulsed emission is simulated and the results
presented. These results in turn are used to simulate the influence of a
scattering hot corona on pulsed emission. Comparing the results of the
simulations with the observed pulse profiles supports the presented
geometric model of the turn-on
Long-term developments in Her X-1: Correlation between the histories of the 35 day turn-on cycle and the 1.24 sec pulse period
No full textOn the statistical significance of excess events: Remarks of caution and the need for a standard method of calculation
No full textMethods for calculating the statistical significance of excess events and the interpretation of the formally derived values are discussed. It is argued that a simple formula for a conservative estimate should generally be used in order to provide a common understanding of quoted values
INTEGRAL broadband spectroscopy of Vela X-1
No full textThe wind-accreting X-ray binary pulsar and cyclotron line source Vela X-1 has been observed extensively during INTEGRAL Core Program observations of the Vela region in June-July and November-December 2003. In the latter set of observations the source showed intense flaring -- see also Staubert et al. (2004), these proceedings.
We present early results on time averaged and time resolved spectra, of both epochs of observations. A cyclotron line feature at ~53 keV is clearly detected in the INTEGRAL spectra and its broad shape is resolved in SPI spectra. The remaining issues in the calibration of the instruments do not allow to resolve the question of the disputed line feature at 20-25 keV.
During the first main flare the average luminosity increases by a factor of \~10, but the spectral shape remains very similar, except for a moderate softening.https://arxiv.org/abs/astro-ph/040605
The multiwavelength variability of 3C 273
No full textAims. We present an update of the 3C 273's database hosted by the ISDC, completed with data from radio to gamma-ray observations over the last 10 years. We use this large data set to study the multiwavelength properties of this quasar, especially focussing on its variability behaviour.Methods. We study the amplitude of the variations and the maximum variability time scales across the broad-band spectrum and correlate the light curves in different bands, specifically with the X-rays, to search for possible connections between the emission at different energies.Results. 3C 273 shows variability at all frequencies, with amplitudes and time scales strongly depending on the energy and being the signatures of the different emission mechanisms. The variability properties of the X-ray band imply the presence of either two separate components (possibly a Seyfert-like and a blazar-like) or at least two parameters with distinct timing properties to account for the X-ray emission below and above ~20 keV. The dominant hard X-ray emission is most probably not due to electrons accelerated by the shock waves in the jet as their variability does not correlate with the flaring millimeter emission, but seems to be associated to long-timescale variations in the optical. This optical component is consistent with being optically thin synchrotron radiation from the base of the jet and the hard X-rays would be produced through inverse Compton processes (SSC and/or EC) by the same electron population. We show evidence that this synchrotron component extends from the optical to the near-infrared domain, where it is blended by emission of heated dust that we find to be located within about 1 light-year from the ultraviolet source
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