497 research outputs found
Time-domain modelling of Extreme-Mass-Ratio Inspirals for the Laser Interferometer Space Antenna
When a stellar-mass compact object is captured by a supermassive black hole
located in a galactic centre, the system losses energy and angular momentum by
the emission of gravitational waves. Subsequently, the stellar compact object
evolves inspiraling until plunging onto the massive black hole. These EMRI
systems are expected to be one of the main sources of gravitational waves for
the future space-based Laser Interferometer Space Antenna (LISA). However, the
detection of EMRI signals will require of very accurate theoretical templates
taking into account the gravitational self-force, which is the responsible of
the stellar-compact object inspiral. Due to its potential applicability on
EMRIs, the obtention of an efficient method to compute the scalar self-force
acting on a point-like particle orbiting around a massive black hole is being
object of increasing interest. We present here a review of our time-domain
numerical technique to compute the self-force acting on a point-like particle
and we show its suitability to deal with both circular and eccentric orbits.Comment: 4 pages, 2 figures, JPCS latex style. Submitted to JPCS (special
issue for the proceedings of the Spanish Relativity Meeting (ERE2010)
Testing Chern-Simons modified gravity with observations of extreme-mass-ratio binaries
Extreme-Mass-Ratio Inspirals (EMRIs) are one of the most promising sources of
gravitational waves (GWs) for space-based detectors like the Laser
Interferometer Space Antenna (LISA). EMRIs consist of a compact stellar object
orbiting around a massive black hole (MBH). Since EMRI signals are expected to
be long lasting (containing of the order of hundred thousand cycles), they will
encode the structure of the MBH gravitational potential in a precise way such
that features depending on the theory of gravity governing the system may be
distinguished. That is, EMRI signals may be used to test gravity and the
geometry of black holes. However, the development of a practical methodology
for computing the generation and propagation of GWs from EMRIs in theories of
gravity different than General Relativity (GR) has only recently begun. In this
paper, we present a parameter estimation study of EMRIs in a particular
modification of GR, which is described by a four-dimensional Chern-Simons (CS)
gravitational term. We focus on determining to what extent a space-based GW
observatory like LISA could distinguish between GR and CS gravity through the
detection of GWs from EMRIs.Comment: 10 pages, JPCS of the Amaldi 9 and NRDA 201
Are Time-Domain Self-Force Calculations Contaminated by Jost Solutions?
The calculation of the self force in the modeling of the gravitational-wave
emission from extreme-mass-ratio binaries is a challenging task. Here we
address the question of the possible emergence of a persistent spurious
solution in time-domain schemes, referred to as a {\em Jost junk solution} in
the literature, that may contaminate self force calculations. Previous studies
suggested that Jost solutions are due to the use of zero initial data, which is
inconsistent with the singular sources associated with the small object,
described as a point mass. However, in this work we show that the specific
origin is an inconsistency in the translation of the singular sources into jump
conditions. More importantly, we identify the correct implementation of the
sources at late times as the sufficient condition guaranteeing the absence of
Jost junk solutions.Comment: RevTeX. 5 pages, 2 figures. Version updated to match the contents of
the published articl
A Chandra View of the Normal SO Galaxy NGC 1332: II: Solar Abundances in the Hot Gas and Implications for SN Enrichment
We present spectral analysis of the diffuse emission in the normal, isolated,
moderate-Lx S0 NGC 1332, constraining both the temperature profile and the
metal abundances in the ISM. The characteristics of the point source population
and the gravitating matter are discussed in two companion papers. The diffuse
emission comprises hot gas, with an ~isothermal temperature profile (~0.5 keV),
and emission from unresolved point-sources. In contrast with the cool cores of
many groups and clusters, we find a small central temperature peak. We obtain
emission-weighted abundance contraints within 20 kpc for several key elements:
Fe, O, Ne, Mg and Si. The measured iron abundance (Z_Fe=1.1 in solar units;
>0.53 at 99% confidence) strongly excludes the very sub-solar values often
historically reported for early-type galaxies but agrees with recent
observations of brighter galaxies and groups. The abundance ratios, with
respect to Fe, of the other elements were also found to be ~solar, although
Z_o/Z_Fe was significantly lower (<0.4). Such a low O abundance is not
predicted by simple models of ISM enrichment by Type Ia and Type II supernovae,
and may indicate a significant contribution from primordial hypernovae.
Revisiting Chandra observations of the moderate-Lx, isolated elliptical NGC
720, we obtain similar abundance constraints. Adopting standard SNIa and SNII
metal yields, our abundance ratio constraints imply 73+/-5% and 85+/-6% of the
Fe enrichment in NGC 1332 and NGC 720, respectively, arises from SNIa. Although
these results are sensitive to the considerable systematic uncertainty in the
SNe yields, they are in good agreement with observations of more massive
systems. These two moderate-Lx early-type galaxies reveal a consistent pattern
of metal enrichment from cluster scales to moderate Lx/Lb galaxies. (abridged)Comment: 12 pages, 4 figures, accepted for publication in ApJ. Minor changes
to match published versio
The Coronal X-ray Spectrum of the Multiple Weak-Lined T Tauri Star System HD 98800
We present high-resolution X-ray spectra of the multiple (hierarchical
quadruple) weak-lined T Tauri star system HD 98800, obtained with the High
Energy Transmission Gratings Spectrograph (HETGS) aboard the Chandra X-ray
Observatory (CXO). In the zeroth-order CXO/HETGS X-ray image, both principle
binary components of HD 98800 (A and B, separation 0.8'') are detected;
component A was observed to flare during the observation. The infrared excess
(dust disk) component, HD 98800B, is a factor ~4 fainter in X-rays than the
apparently ``diskless'' HD 98800A, in quiescence. The line ratios of He-like
species (e.g., Ne IX, O VII) in the HD 98800A spectrum indicate that the
X-ray-emitting plasma around HD 98800 is in a typical coronal density regime
(log n <~ 11). We conclude that the dominant X-ray-emitting component(s) of HD
98800 is (are) coronally active. The sharp spectral differences between HD
98800 and the classical T Tauri star TW Hya demonstrate the potential utility
of high-resolution X-ray spectroscopy in providing diagnostics of pre-main
sequence accretion processes.Comment: 11 pages, 5 figures; to appear in the Astrophysical Journal (Letters
Evolution and Hydrodynamics of the Very-Broad X-ray Line Emission in SN1987A
Author Manuscript 20 Apr 2012.Observations of SN 1987A by the Chandra High Energy Transmission Grating (HETG) in 1999 and the XMM-Newton Reflection Grating Spectrometer (RGS) in 2003 show very broad (v-b) lines with a full width at half-maximum (FWHM) of order 10[superscript 4] km s[superscript –1]; at these times the blast wave (BW) was primarily interacting with the H II region around the progenitor. Since then, the X-ray emission has been increasingly dominated by narrower components as the BW encounters dense equatorial ring (ER) material. Even so, continuing v-b emission is seen in the grating spectra suggesting that the interaction with H II region material is ongoing. Based on the deep HETG 2007 and 2011 data sets, and confirmed by RGS and other HETG observations, the v-b component has a width of 9300 ± 2000 km s[superscript –1] FWHM and contributes of order 20% of the current 0.5-2 keV flux. Guided by this result, SN 1987A's X-ray spectra are modeled as the weighted sum of the non-equilibrium-ionization emission from two simple one-dimensional hydrodynamic simulations; this "2 × 1D" model reproduces the observed radii, light curves, and spectra with a minimum of free parameters. The interaction with the H II region (ρinit ≈ 130 amu cm[superscript –3], ± 15° opening angle) produces the very broad emission lines and most of the 3-10 keV flux. Our ER hydrodynamics, admittedly a crude approximation to the multi-D reality, gives ER densities of ~10[superscript 4] amu cm[superscript –3], requires dense clumps (×5.5 density enhancement in ~30% of the volume), and predicts that the 0.5-2 keV flux will drop at a rate of ~17% per year once no new dense ER material is being shocked
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