42 research outputs found
Neutron star bulk viscosity, "spin-flip" and GW emission of newly born magnetars
The viscosity-driven "spin-flip" instability in newborn magnetars with
interior toroidal magnetic fields is re-examined. We calculate the bulk
viscosity coefficient () of cold, matter in neutron stars
(NS), for selected values of the nuclear symmetry energy and in the regime
where -equilibration is slower than characteristic oscillation periods.
We show that: i) is larger than previously assumed and the instability
timescale correspondingly shorter; ii) for a magnetically-induced ellipticity
, typically expected in newborn
magnetars, spin-flip occurs for initial spin periods ms, with
some dependence on the NS equation of state (EoS). We then calculate the
detectability of GW signals emitted by newborn magnetars subject to
"spin-flip", by accounting also for the reduction in range resulting from
realistic signal searches. For an optimal range of , and birth spin period ms, we estimate an horizon
of Mpc, and Mpc, for Advanced and third generation
interferometers at design sensitivity, respectively. A supernova (or a
kilonova) is expected as the electromagnetic counterpart of such GW events.
Outside of the optimal range for GW emission, EM torques are more efficient in
extracting the NS spin energy, which may power even brighter EM transients.Comment: 10 pages, 4 figures, accepted for publication in MNRA
Coherent search of continuous gravitational wave signals: extension of the 5-vectors method to a network of detectors
We describe the extension to multiple datasets of a coherent method for the
search of continuous gravitational wave signals, based on the computation of
5-vectors. In particular, we show how to coherently combine different datasets
belonging to the same detector or to different detectors. In the latter case
the coherent combination is the way to have the maximum increase in
signal-to-noise ratio. If the datasets belong to the same detector the
advantage comes mainly from the properties of a quantity called {\it coherence}
which is helpful (in both cases, in fact) in rejecting false candidates. The
method has been tested searching for simulated signals injected in Gaussian
noise and the results of the simulations are discussed.Comment: 9 pages, 2 figures. Journal of Physics: Conference Series, in pres
A method for narrow-band searches of continuous gravitational wave signals
Targeted searches of continuous waves from spinning neutron stars normally
assume that the frequency of the gravitational wave signal is at a given known
ratio with respect to the rotational frequency of the source, e.g. twice for an
asymmetric neutron star rotating around a principal axis of inertia. In fact
this assumption may well be invalid if, for instance, the gravitational wave
signal is due to a solid core rotating at a slightly different rate with
respect to the star crust. In this paper we present a method for {\it
narrow-band} searches of continuous gravitational wave signals from known
pulsars in the data of interferometric detectors. This method assumes source
position is known to high accuracy, while a small frequency and spin-down range
around the electromagnetic-inferred values is explored. Barycentric and
spin-down corrections are done with an efficient time-domain procedure.
Sensitivity and computational efficiency estimates are given and results of
tests done using simulated data are also discussed.Comment: 13 pages; 6 figures; accepted in PR
Distinguishing between dark-matter interactions with gravitational-wave detectors
Ground-based gravitational-wave interferometers could directly probe the
existence of ultralight dark matter ( eV/)
that couples to standard-model particles in the detectors. Recently, many
techniques have been developed to extract a variety of potential dark-matter
signals from noisy gravitational-wave data; however, little effort has gone
into ways to distinguish between types of dark matter that could directly
interact with the interferometers. In this work, we employ the Wiener filter to
follow-up candidate dark-matter interaction signals. The filter captures the
stochastic nature of these signals, and, in simulations, successfully
identifies which type of dark matter interacts with the interferometers. We
apply the Wiener filter to outliers that remained in the LIGO/Virgo/KAGRA
search for dark photons in data from the most recent observing (O3), and show
that they are consistent with noise disturbances. Our proof-of-concept analysis
demonstrates that the Wiener filter can be a powerful technique to confirm or
deny the presence of dark-matter interaction signals in gravitational-wave
data, and distinguish between scalar and vector dark-matter interactions.Comment: 10 pages, 8 figure
Novel directed search strategy to detect continuous gravitational waves from neutron stars in low- and high-eccentricity binary systems
We describe a novel, very fast and robust, directed search incoherent method
for periodic gravitational waves (GWs) from neutron stars in binary systems. As
directed search, we assume the source sky position to be known with enough
accuracy, but all other parameters are supposed to be unknown. We exploit the
frequency-modulation due to source orbital motion to unveil the signal
signature by commencing from a collection of time and frequency peaks. We
validate our pipeline adding 131 artificial continuous GW signals from pulsars
in binary systems to simulated detector Gaussian noise, characterized by a
power spectral density Sh = 4x10^-24 Hz^-1/2 in the frequency interval [70,
200] Hz, which is overall commensurate with the advanced detector design
sensitivities. The pipeline detected 128 signals, and the weakest signal
injected and detected has a GW strain amplitude of ~10^-24, assuming one month
of gapless data collected by a single advanced detector. We also provide
sensitivity estimations, which show that, for a single- detector data covering
one month of observation time, depending on the source orbital Doppler
modulation, we can detect signals with an amplitude of ~7x10^-25. By using
three detectors, and one year of data, we would easily gain more than a factor
3 in sensitivity, translating into being able to detect weaker signals. We also
discuss the parameter estimate proficiency of our method, as well as
computational budget, which is extremely cheap. In fact, sifting one month of
single-detector data and 131 Hz-wide frequency range takes roughly 2.4 CPU
hours. Due to the high computational speed, the current procedure can be
readily applied in ally-sky schemes, sieving in parallel as many sky positions
as permitted by the available computational power
A method to search for long duration gravitational wave transients from isolated neutron stars using the generalized FrequencyHough
We describe a method to detect gravitational waves lasting
emitted by young, isolated neutron stars, such as those that could form after a
supernova or a binary neutron star merger, using advanced LIGO/Virgo data. The
method is based on a generalization of the FrequencyHough (FH), a pipeline that
performs hierarchical searches for continuous gravitational waves by mapping
points in the time/frequency plane of the detector to lines in the
frequency/spindown plane of the source. We show that signals whose spindowns
are related to their frequencies by a power law can be transformed to
coordinates where the behavior of these signals is always linear, and can
therefore be searched for by the FH. We estimate the sensitivity of our search
across different braking indices, and describe the portion of the parameter
space we could explore in a search using varying fast Fourier Transform (FFT)
lengths.Comment: 15 figure
Characterizing Gravitational Wave Detector Networks: From A to Cosmic Explorer
Gravitational-wave observations by the Laser Interferometer
Gravitational-Wave Observatory (LIGO) and Virgo have provided us a new tool to
explore the universe on all scales from nuclear physics to the cosmos and have
the massive potential to further impact fundamental physics, astrophysics, and
cosmology for decades to come. In this paper we have studied the science
capabilities of a network of LIGO detectors when they reach their best possible
sensitivity, called A#, and a new generation of observatories that are factor
of 10 to 100 times more sensitive (depending on the frequency), in particular a
pair of L-shaped Cosmic Explorer observatories (one 40 km and one 20 km arm
length) in the US and the triangular Einstein Telescope with 10 km arms in
Europe. We use a set of science metrics derived from the top priorities of
several funding agencies to characterize the science capabilities of different
networks. The presence of one or two A# observatories in a network containing
two or one next generation observatories, respectively, will provide good
localization capabilities for facilitating multimessenger astronomy and
precision measurement of the Hubble parameter. A network of two Cosmic Explorer
observatories and the Einstein Telescope is critical for accomplishing all the
identified science metrics including the nuclear equation of state,
cosmological parameters, growth of black holes through cosmic history, and make
new discoveries such as the presence of dark matter within or around neutron
stars and black holes, continuous gravitational waves from rotating neutron
stars, transient signals from supernovae, and the production of stellar-mass
black holes in the early universe. For most metrics the triple network of next
generation terrestrial observatories are a factor 100 better than what can be
accomplished by a network of three A# observatories.Comment: 45 pages, 20 figure