72,355 research outputs found
Fast Simulation of Gaussian-Mode Scattering for Precision Interferometry
Understanding how laser light scatters from realistic mirror surfaces is
crucial for the design, com- missioning and operation of precision
interferometers, such as the current and next generation of gravitational-wave
detectors. Numerical simulations are indispensable tools for this task but
their utility can in practice be limited by the computational cost of
describing the scattering process. In this paper we present an efficient method
to significantly reduce the computational cost of optical simulations that
incorporate scattering. This is accomplished by constructing a near optimal
representation of the complex, multi-parameter 2D overlap integrals that
describe the scattering process (referred to as a reduced order quadrature). We
demonstrate our technique by simulating a near-unstable Fabry-Perot cavity and
its control signals using similar optics to those installed in one of the LIGO
gravitational-wave detectors. We show that using reduced order quadrature
reduces the computational time of the numerical simulation from days to minutes
(a speed-up of ) whilst incurring negligible errors. This
significantly increases the feasibility of modelling interferometers with
realistic imperfections to overcome current limits in state-of-the-art optical
systems. Whilst we focus on the Hermite-Gaussian basis for describing the
scattering of the optical fields, our method is generic and could be applied
with any suitable basis. An implementation of this reduced order quadrature
method is provided in the open source interferometer simulation software
Finesse.Comment: 15 pages, 11 figure
Long Term Study of the Double Pulsar J0737-3039 with XMM-Newton: pulsar timing
The relativistic double neutron star binary PSR J0737-3039 shows clear
evidence of orbital phase-dependent wind-companion interaction, both in radio
and X-rays. In this paper we present the results of timing analysis of PSR
J0737-3039 performed during 2006 and 2011 XMM-Newton Large Programs that
collected ~20,000 X-ray counts from the system. We detected pulsations from PSR
J0737-3039A (PSR A) through the most accurate timing measurement obtained by
XMM-Newton so far, the spin period error being of 2x10^-13 s. PSR A's pulse
profile in X-rays is very stable despite significant relativistic spin
precession that occurred within the time span of observations. This yields a
constraint on the misalignment between the spin axis and the orbital momentum
axis Delta_A ~6.6^{+1.3}_{-5.4} deg, consistent with estimates based on radio
data. We confirmed pulsed emission from PSR J0737-3039B (PSR B) in X-rays even
after its disappearance in radio. The unusual phenomenology of PSR B's X-ray
emission includes orbital pulsed flux and profile variations as well as a loss
of pulsar phase coherence on time scales of years. We hypothesize that this is
due to the interaction of PSR A's wind with PSR B's magnetosphere and
orbital-dependent penetration of the wind plasma onto PSR B closed field lines.
Finally, the analysis of the full XMM-Newton dataset provided evidences of
orbital flux variability (~7%) for the first time, involving a bow-shock
scenario between PSR A's wind and PSR B's magnetosphere.Comment: Comments: 16 Pages, 6 Figures. Accepted for publication in
Astrophysical Journal (Draft Version
X-ray Variability Characteristics of the Seyfert 1 Galaxy NGC 3783
We have characterized the energy-dependent X-ray variability properties of
the Seyfert~1 galaxy NGC 3783 using archival XMM-Newton and Rossi X-ray Timing
Explorer data. The high-frequency fluctuation power spectral density function
(PSD) slope is consistent with flattening towards higher energies. Light curve
cross correlation functions yield no significant lags, but peak coefficients
generally decrease as energy separation of the bands increases on both short
and long timescales. We have measured the coherence between various X-ray bands
over the temporal frequency range of 6e-8 to 1e-4 Hz; this range includes the
temporal frequency of the low-frequency power spectral density function (PSD)
break tentatively detected by Markowitz et al. and includes the lowest temporal
frequency over which coherence has been measured in any AGN to date. Coherence
is generally near unity at these temporal frequencies, though it decreases
slightly as energy separation of the bands increases. Temporal
frequency-dependent phase lags are detected on short time scales; phase lags
are consistent with increasing as energy separation increases or as temporal
frequency decreases. All of these results are similar to those obtained
previously for several Seyfert galaxies and stellar-mass black hole systems.
Qualitatively, these results are consistent with the variability models of
Kotov et al. and Lyubarskii, wherein the X-ray variability is due to inwardly
propagating variations in the local mass accretion rate.Comment: Accepted for publication in The Astrophysical Journal, 2005, vol.
635, p. 180; version 2 has minor grammatical changes; 23 pages; uses
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