7,640 research outputs found
GR models of the X-ray spectral variability of MCG--6-30-15
We study in detail the GR models of the X-ray spectral variability for
various geometries of the X-ray source and with various relativistic effects
being the dominant cause of spectral variability. The predicted properties are
compared with the Suzaku observational data of the Seyfert 1 galaxy
MCG--6-30-15. The data disfavor models with the X-ray source (1) moving
vertically on the symmetry axis or (2) corotating with the disc and changing
height not far above the disc surface. The most likely explanation for the
observed variability is given by the model involving the X-ray source located
at a very small, varying distance from a rapidly rotating black hole. This
model predicts some enhanced variations in the red wing of the Fe line, which
are not seen in the Suzaku observations. However, the enhanced variability of
the red wing, while ruled out by the Suzaku data, is consistent with an excess
RMS variability, between 5 and 6 keV, reported for some previous ASCA and XMM
observations. We speculate that the presence or lack of such a feature is
related to the change of the ionization state of the innermost part of the
disc, however, investigation of such effects is currently not possible in our
model (where a neutral disc is assumed). If the model, completed by description
of ionization effects, proves to be fully consistent with the observational
data, it will provide a strong indication that the central black hole in
MCG--6-30-15 rotates rapidly, supporting similar conclusions derived from the
Fe line profile.Comment: 15 pages, accepted for publication in A&
Shot-noise-limited control-loop noise in an interferometer with multiple degrees of freedom
Precise measurements, such as those made with interferometric gravitational-wave detectors, require the measurement device to be properly controlled so that the sensitivity can be as high as possible. Mirrors in the interferometer are to be located at specific operation points to isolate laser noise and to accumulate the signal in resonant cavities. On the other hand, rigid control of an auxiliary degree of freedom may result in imposing sensing noise of the control on the target object as excess force noise. Evaluation of this so-called loop noise is important in order to design a decent control scheme of the measurement device. In this paper, we show the method to calculate the level of loop noise, which has been recently implemented in simulation tools that are broadly used for designing gravitational-wave detectors
Lock acquisition studies for advanced interferometers
This document describes some results of time domain simulation for a Fabry-Perot cavity with Advanced LIGO parameters. Future interferometer will employ a high power laser and high finesse cavities. Lock acquisition of arm cavity will be more difficult due to the optical instabilities which are caused by very high power inside the cavity. According to this simulation, the arm cavity should be locked with very low power, and additional hard/software techniques will be needed to establish the first fringe lock. In this paper, possibility of using a new algorithm called 'Guidelock' and a suspension point interferometer are discussed. After lock is acquired, alignment controls must be engaged before increasing the power. This simulation predicts that alignment optical instabilities show up due to a shift of high power beam axis, and they can be stabilized by proper alignment controls
Length sensing and control strategies for the LCGT interferometer
The optical readout scheme for the length degrees of freedom of the LCGT
interferometer is proposed. The control scheme is compatible both with the
broadband and detuned operations of the interferometer. Interferometer
simulations using a simulation software Optickle show that the sensing noise
couplings caused by the feedback control can be reduced below the target
sensitivity of LCGT with the use of feed forward. In order to improve the duty
cycle of the detector, a robust lock acquisition scheme using auxiliary lasers
will be used.Comment: 13 pages 9 figures. A proceedings paper for Amaldi9 conferenc
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