57 research outputs found
Extending the WMAP Bound on the Size of the Universe
Clues to the shape of our Universe can be found by searching the CMB for
matching circles of temperature patterns. A full sky search of the CMB, mapped
extremely accurately by NASA's WMAP satellite, returned no detection of such
matching circles and placed a lower bound on the size of the Universe at 24
Gpc. This lower bound can be extended by optimally filtering the WMAP power
spectrum. More stringent bounds can be placed on specific candidate topologies
by using a a combination statistic. We use optimal filtering and the
combination statistic to rule out the infamous "soccer ball universe'' model.Comment: 9 pages, 16 figure
Characterizing the Gravitational Wave Signature from Cosmic String Cusps
Cosmic strings are predicted to form kinks and cusps that travel along the
string at close to the speed of light. These disturbances are radiated away as
highly beamed gravitational waves that produce a burst like pulse as the cone
of emission sweeps past an observer. Gravitational wave detectors such as the
Laser Interferometer Space Antenna (LISA) and the Laser Interferometer
Gravitational wave Observatory (LIGO) will be capable of detecting these bursts
for a wide class of string models. Such a detection would illuminate the fields
of string theory, cosmology, and relativity. Here we develop template based
Markov Chain Monte Carlo (MCMC) techniques that can efficiently detect and
characterize the signals from cosmic string cusps. We estimate how well the
signal parameters can be recovered by the advanced LIGO-Virgo network and the
LISA detector using a combination of MCMC and Fisher matrix techniques. We also
consider joint detections by the ground and space based instruments. We show
that a parallel tempered MCMC approach can detect and characterize the signals
from cosmic string cusps, and we demonstrate the utility of this approach on
simulated data from the third round of Mock LISA Data Challenges (MLDCs).Comment: 10 pages, 10 figure
GW150914: First search for the electromagnetic counterpart of a gravitational-wave event by the TOROS collaboration
We present the results of the optical follow-up conducted by the TOROS
collaboration of the first gravitational-wave event GW150914. We conducted
unfiltered CCD observations (0.35-1 micron) with the 1.5-m telescope at Bosque
Alegre starting ~2.5 days after the alarm. Given our limited field of view
(~100 square arcmin), we targeted 14 nearby galaxies that were observable from
the site and were located within the area of higher localization probability.
We analyzed the observations using two independent implementations of
difference-imaging algorithms, followed by a Random-Forest-based algorithm to
discriminate between real and bogus transients. We did not find any bona fide
transient event in the surveyed area down to a 5-sigma limiting magnitude of
r=21.7 mag (AB). Our result is consistent with the LIGO detection of a binary
black hole merger, for which no electromagnetic counterparts are expected, and
with the expected rates of other astrophysical transients.Comment: ApJ Letters, in pres
Getting Ready for LISA: The Data, Support and Preparation Needed to Maximize US Participation in Space-Based Gravitational Wave Science
The NASA LISA Study Team was tasked to study how NASA might support US
scientists to participate and maximize the science return from the Laser
Interferometer Space Antenna (LISA) mission. LISA is gravitational wave
observatory led by ESA with NASA as a junior partner, and is scheduled to
launch in 2034. Among our findings: LISA science productivity is greatly
enhanced by a full-featured US science center and an open access data model. As
other major missions have demonstrated, a science center acts as both a locus
and an amplifier of research innovation, data analysis, user support, user
training and user interaction. In its most basic function, a US Science Center
could facilitate entry into LISA science by hosting a Data Processing Center
and a portal for the US community to access LISA data products. However, an
enhanced LISA Science Center could: support one of the parallel independent
processing pipelines required for data product validation; stimulate the high
level of research on data analysis that LISA demands; support users unfamiliar
with a novel observatory; facilitate astrophysics and fundamental research;
provide an interface into the subtleties of the instrument to validate
extraordinary discoveries; train new users; and expand the research community
through guest investigator, postdoc and student programs. Establishing a US
LISA Science Center well before launch can have a beneficial impact on the
participation of the broader astronomical community by providing training,
hosting topical workshops, disseminating mock catalogs, software pipelines, and
documentation. Past experience indicates that successful science centers are
established several years before launch; this early adoption model may be
especially relevant for a pioneering mission like LISA.Comment: 93 pages with a lovely cover page thanks to Bernard Kelly and
Elizabeth Ferrar
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
The Mock LISA Data Challenges: from Challenge 3 to Challenge 4
The Mock LISA Data Challenges are a program to demonstrate LISA data-analysis
capabilities and to encourage their development. Each round of challenges
consists of one or more datasets containing simulated instrument noise and
gravitational waves from sources of undisclosed parameters. Participants
analyze the datasets and report best-fit solutions for the source parameters.
Here we present the results of the third challenge, issued in Apr 2008, which
demonstrated the positive recovery of signals from chirping Galactic binaries,
from spinning supermassive--black-hole binaries (with optimal SNRs between ~ 10
and 2000), from simultaneous extreme-mass-ratio inspirals (SNRs of 10-50), from
cosmic-string-cusp bursts (SNRs of 10-100), and from a relatively loud
isotropic background with Omega_gw(f) ~ 10^-11, slightly below the LISA
instrument noise.Comment: 12 pages, 2 figures, proceedings of the 8th Edoardo Amaldi Conference
on Gravitational Waves, New York, June 21-26, 200
- …