75,947 research outputs found
Deep Learning for Real-time Gravitational Wave Detection and Parameter Estimation: Results with Advanced LIGO Data
The recent Nobel-prize-winning detections of gravitational waves from merging
black holes and the subsequent detection of the collision of two neutron stars
in coincidence with electromagnetic observations have inaugurated a new era of
multimessenger astrophysics. To enhance the scope of this emergent field of
science, we pioneered the use of deep learning with convolutional neural
networks, that take time-series inputs, for rapid detection and
characterization of gravitational wave signals. This approach, Deep Filtering,
was initially demonstrated using simulated LIGO noise. In this article, we
present the extension of Deep Filtering using real data from LIGO, for both
detection and parameter estimation of gravitational waves from binary black
hole mergers using continuous data streams from multiple LIGO detectors. We
demonstrate for the first time that machine learning can detect and estimate
the true parameters of real events observed by LIGO. Our results show that Deep
Filtering achieves similar sensitivities and lower errors compared to
matched-filtering while being far more computationally efficient and more
resilient to glitches, allowing real-time processing of weak time-series
signals in non-stationary non-Gaussian noise with minimal resources, and also
enables the detection of new classes of gravitational wave sources that may go
unnoticed with existing detection algorithms. This unified framework for data
analysis is ideally suited to enable coincident detection campaigns of
gravitational waves and their multimessenger counterparts in real-time.Comment: 6 pages, 7 figures; First application of deep learning to real LIGO
events; Includes direct comparison against matched-filterin
Gamma-Ray Burst Dust Echoes Revisited: Expectations at Early Times
Gamma-ray burst (GRB) dust echoes were first proposed as an alternative
explanation for the supernova-like (SN-like) components to the afterglows of
GRB 980326 and GRB 970228. However, the spectroscopic identification of Type Ic
SN 2003dh associated with GRB 030329, as well as the identification of SN-like
components to the afterglows of other GRBs, appears to have confirmed the
GRB/SN paradigm. However, the likely progenitors of Type Ic SNe are Wolf-Rayet
WC stars, and late-type WC stars have been observed to be surrounded by dust,
at a distance of 10^14 -- 10^15 cm from the star. Consequently, we revisit the
possibility of GRB dust echoes, not on a timescale of weeks after the burst but
on a timescale of minutes to hours. We find that if the optical flash is
sufficiently bright and the jet sufficiently wide, GRB afterglows may be
accompanied by chromatic variations on this timescale. From these signatures,
such model parameters as the inner radius of the dust distribution, the initial
opening angle of the jet, etc., may be deduced. With rapid and regular
localizations of GRBs by HETE-2, Integral, and now Swift, and new and improved
robotic telescope systems, these early-time GRB dust echoes may soon be
detected. We describe one such robotic telescope system, called PROMPT, that
the University of North Carolina at Chapel Hill is building at the Cerro Tololo
Inter-American Observatory in greater detail.Comment: Accepted to The Astrophysical Journal, 15 pages, 5 figures, LaTe
Lensing and high-z supernova surveys
Gravitational lensing causes the distribution of observed brightnesses of
standard candles at a given redshift to be highly non-gaussian. The
distribution is strongly, and asymmetrically, peaked at a value less than the
expected value in a homogeneous Robertson-Walker universe. Therefore, given any
small sample of observations in an inhomogeneous universe, the most likely
observed luminosity is at flux values less than the Robertson-Walker value.
This paper explores the impact of this systematic error due to lensing upon
surveys predicated on measuring standard candle brightnesses. We re-analyze
recent results from the high-z supernova team (Riess et al. 1998), both when
most of the matter in the universe is in the form of compact objects
(represented by the empty-beam expression, corresponding to the maximal case of
lensing), and when the matter is continuously distributed in galaxies. We find
that the best-fit model remains unchanged (at Omega_m=0, Omega_Lambda=0.45),
but the confidence contours change size and shape, becoming larger (and thus
allowing a broader range of parameter space) and dropping towards higher values
of matter density, Omega_m (or correspondingly, lower values of the
cosmological constant, Omega_Lambda). These effects are slight when the matter
is continuously distributed. However, the effects become considerably more
important if most of the matter is in compact objects. For example, neglecting
lensing, the Omega_m=0.5, Omega_Lambda=0.5 model is more than 2 sigma away from
the best fit. In the empty-beam analysis, this cosmology is at 1 sigma.Comment: 11 pages, 3 ps figures. uses aaspp4.sty. accepted to ApJ Letters.
includes analysis of lensing due to matter continuously distributed in
galaxie
Evidence for Circumburst Extinction of Gamma-Ray Bursts with Dark Optical Afterglows and Evidence for a Molecular Cloud Origin of Gamma-Ray Bursts
First, we show that the gamma-ray bursts with dark optical afterglows (DOAs)
cannot be explained by a failure to image deeply enough quickly enough, and
argue that circumburst extinction is the most likely solution. If so, many DOAs
will be ``revived'' with rapid follow up and NIR searches in the HETE-2 and
Swift eras. Next, we consider the effects of dust sublimation and
fragmentation, and show that DOAs occur in clouds of size R > 10L_{49}^{1/2} pc
and mass M > 3x10^5L_{49} M_{sun}, where L is the luminosity of the optical
flash. Stability considerations show that such clouds cannot be diffuse, but
must be molecular. Consequently, we compute the expected column density
distribution of bursts that occur in Galactic-like molecular clouds, and show
that the column density measurements from X-ray spectra of afterglows, DOAs and
otherwise, satisfy this expectation in the source frame.Comment: Invited Review. To appear in Procs. of Gamma-Ray Burst and Afterglow
Astronomy 2001: A Workshop Celebrating the First Year of the HETE Mission, 8
pages, 8 figures, LaTe
Using gravitational-wave standard sirens
Gravitational waves (GWs) from supermassive binary black hole (BBH) inspirals
are potentially powerful standard sirens (the GW analog to standard candles)
(Schutz 1986, 2002). Because these systems are well-modeled, the space-based GW
observatory LISA will be able to measure the luminosity distance (but not the
redshift) to some distant massive BBH systems with 1-10% accuracy. This
accuracy is largely limited by pointing error: GW sources generally are poorly
localized on the sky. Localizing the binary independently (e.g., through
association with an electromagnetic counterpart) greatly reduces this
positional error. An electromagnetic counterpart may also allow determination
of the event's redshift. In this case, BBH coalescence would constitute an
extremely precise (better than 1%) standard candle visible to high redshift. In
practice, gravitational lensing degrades this precision, though the candle
remains precise enough to provide useful information about the
distance-redshift relation. Even if very rare, these GW standard sirens would
complement, and increase confidence in, other standard candles.Comment: 10 pages, 8 figures. ApJ, in pres
Interstellar Ti II in the Milky Way and Magellanic Clouds
We discuss several sets of Ti II absorption-line data, which probe a variety
of interstellar environments in our Galaxy and in the Magellanic Clouds.
Comparisons of high-resolution (FWHM ~ 1.3-1.5 km/s) Ti II spectra of Galactic
targets with corresponding high-resolution spectra of Na I, K I, and Ca II
reveal both similarities and differences in the detailed structure of the
absorption-line profiles -- reflecting component-to-component differences in
the ionization and depletion behaviour of those species. Moderate-resolution
(FWHM ~ 3.4-4.5 km/s) spectra of more heavily reddened Galactic stars provide
more extensive information on the titanium depletion in colder, denser clouds
-- where more than 99.9 per cent of the Ti may be in the dust phase.
Moderate-resolution (FWHM ~ 4.5-8.7 km/s) spectra of stars in the Magellanic
Clouds suggest that the titanium depletion is generally much less severe in the
LMC and SMC than in our Galaxy [for a given N(H_tot), E(B-V), or molecular
fraction f(H_2)] -- providing additional evidence for differences in depletion
patterns in those two lower-metallicity galaxies. We briefly discuss possible
implications of these results for the interpretation of gas-phase abundances in
QSO absorption-line systems and of variations in the D/H ratio in the local
Galactic ISM.Comment: 56 pages, 26 figures, accepted to MNRA
Decay of protons and neutrons induced by acceleration
We investigate the decay of accelerated protons and neutrons. Calculations
are carried out in the inertial and coaccelerated frames. Particle
interpretation of these processes are quite different in each frame but the
decay rates are verified to agree in both cases. For sake of simplicity our
calculations are performed in a two-dimensional spacetime since our conclusions
are not conceptually affected by this.Comment: 18 pages (REVTEX), 3 figure
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