1,023 research outputs found
Solutions to the relativistic precession model
The relativistic precession model (RPM) can be used to obtain a precise
measurement of the mass and spin of a black hole when the appropriate set of
quasi periodic oscillations is detected in the power-density spectrum of an
accreting black hole. However, in previous studies the solution of the RPM
equations could be obtained only through numerical methods at a price of an
intensive computational effort. Here we demonstrate that the RPM system of
equations can be solved analytically, drastically reducing the computational
load, now limited to the Monte-Carlo simulation necessary to estimate the
uncertainties. The analytical method not only provides an easy solution to the
RPM system when three oscillations are detected, but in all the cases where the
detection of two simultaneous oscillations is coupled with an independent mass
measurement. We also present a computationally inexpensive method to place
limits on the black hole mass and spin when only two oscillations are observed.Comment: Accepted to MNRAS; 8 pages, 3 figure
Editorial: Feminism, womenâs movements and women in movement
Introduction to Special Issue that engages with the increasingly important, separate yet interrelated themes of feminism, womenâs movements and women in movement in the context of global neoliberalism
Black-hole binaries: life begins at 40 keV
In the study of black-hole transients, an important problem that still needs
to be answered is how the high-energy part of the spectrum evolves from the
low-hard to the high-soft state, given that they have very different
properties. Recent results obtained with RXTE and INTEGRAL have given
inconsistent results. With RXTE, we have found that the high-energy cutoff in
GX 339-4 during the transition first decreases (during the low-hard state),
then increases again across the Hard-Intermediate state, to become unmeasurable
in the soft states (possibly because of statistical limitations). We show
Simbol-X will be able to determine the spectral shape with superb accuracy. As
the high-energy part of the spectrum is relatively less known than the one
below 20 keV, Simbol-X will provide important results that will help out
understanding of the extreme physical conditions in the vicinity of a
stellar-mass black hole.Comment: Proc. "Simbol-X: Focusing on the Hard X-Ray Universe", Paris, 2-5
Dec. 2008, ed. J. Rodriguez and P. Ferrando; 4 pages, 3 figure
Feminism, womenâs movements and women in movement
Non peer reviewedPublisher PD
The Patterns of Yarning
The Patterns of Yarning is a 3-minute digital visualisation that\u27s based on the accompanying sunrise themed sonic yarning audio
On the modulation of low frequency Quasi-Periodic Oscillations in black-hole transients
We studied the properties of the low-frequency quasi-periodic oscillations
detected in a sample of six black hole candidates (XTE J1550-564, H 1743-322,
XTE J1859+226, 4U 1630-47,GX 339-4, XTE J1650-500) observed by the Rossi XTE
satellite. We analyzed the relation between the full width half maximum and the
frequency of all the narrow peaks detected in power density spectra where a
type-C QPO is observed. Our goal was to understand the nature of the modulation
of the signal by comparing the properties of different harmonic peaks in the
power density spectrum. We find that for the sources in our sample the width of
the fundamental and of the first harmonic are compatible with a frequency
modulation, while that of the sub-harmonic is independent of frequency,
possibly indicating the presence of an additional modulation in amplitude. We
compare our results with those obtained earlier from GRS 1915+105 and XTE
J1550-564.Comment: 8 pages, 3 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society Main Journa
A self-lensing binary massive black hole interpretation of quasi-periodic eruptions
Binary supermassive black hole (SMBH) systems result from galaxy mergers, and
will eventually coalesce due to gravitational wave (GW) emission if the binary
separation can be reduced to pc by other mechanisms. Here, we
explore a gravitational self-lensing binary SMBH model for the sharp (duration
hr), quasi-regular X-ray flares -- dubbed quasi-periodic eruptions --
recently observed from two low mass active galactic nuclei: GSN 069 and RX
J1301.9+2747. In our model, the binary is observed edge-on, such that
each SMBH gravitationally lenses light from the accretion disc surrounding the
other SMBH twice per orbital period. The model can reproduce the flare spacings
if the current eccentricity of RX J1301.9+2747 is ,
implying a merger within yrs. However, we cannot reproduce the
observed flare profiles with our current calculations. Model flares with the
correct amplitude are the observed duration, and model flares with
the correct duration are the observed amplitude. Our modelling
yields three distinct behaviours of self-lensing binary systems that can be
searched for in current and future X-ray and optical time-domain surveys: i)
periodic lensing flares, ii) partial eclipses (caused by occultation of the
background mini-disc by the foreground mini-disc), and iii) partial eclipses
with a very sharp in-eclipse lensing flare. Discovery of such features would
constitute very strong evidence for the presence of a supermassive binary, and
monitoring of the flare spacings will provide a measurement of periastron
precession.Comment: Accepted for publication in MNRA
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