99 research outputs found
Wind Energy Development on the United States Outer Continental Shelf: Balancing Efficient Development and Environmental Risks in the Shadow of OCSLA
Calls for United States energy independence and concerns about dwindling fossil fuel reserves have drawn national attention to the search for viable sources of alternative energy. One such source is offshore wind power generation. Offshore wind farms have already proven successful in Europe and Australia, but none yet exist off the coasts of the United States. A private proposal to build such a facility off the coast of Massachusetts has faced strong opposition. Debate exists as to whether the Outer Continental Shelf Lands Act permits the federal government to lease areas of the Outer Continental Shelf for alternative energy development. Oil and gas extraction developments authorized under the Act have allowed accelerated development at the expense of the environment. This Note argues that a current proposal to amend the Act to include wind power generation facilities does not address the problems encountered by oil and gas developments, and calls for entirely new legislation
The Host Galaxy and Redshift of the Repeating Fast Radio Burst FRB 121102
The precise localization of the repeating fast radio burst (FRB 121102) has
provided the first unambiguous association (chance coincidence probability
) of an FRB with an optical and persistent radio
counterpart. We report on optical imaging and spectroscopy of the counterpart
and find that it is an extended ()
object displaying prominent Balmer and [OIII] emission lines. Based on the
spectrum and emission line ratios, we classify the counterpart as a
low-metallicity, star-forming, AB mag dwarf galaxy at a
redshift of , corresponding to a luminosity distance of 972 Mpc.
From the angular size, the redshift, and luminosity, we estimate the host
galaxy to have a diameter kpc and a stellar mass of
, assuming a mass-to-light ratio between 2 to
3. Based on the H flux, we estimate the star
formation rate of the host to be and a
substantial host dispersion measure depth .
The net dispersion measure contribution of the host galaxy to FRB 121102 is
likely to be lower than this value depending on geometrical factors. We show
that the persistent radio source at FRB 121102's location reported by Marcote
et al (2017) is offset from the galaxy's center of light by 200 mas and
the host galaxy does not show optical signatures for AGN activity. If FRB
121102 is typical of the wider FRB population and if future interferometric
localizations preferentially find them in dwarf galaxies with low metallicities
and prominent emission lines, they would share such a preference with long
gamma ray bursts and superluminous supernovae.Comment: 12 pages, 3 figures, Published in ApJ Letters. V2: Corrected mistake
in author lis
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
Discovery, Timing, and Multiwavelength Observations of the Black Widow Millisecond Pulsar PSR J1555-2908
We report the discovery of PSR J1555-2908, a 1.79 ms radio and gamma-ray pulsar in a 5.6 hr binary system with a minimum companion mass of 0.052 M ⊙. This fast and energetic ( Ė=3×1035 erg s-1) millisecond pulsar was first detected as a gamma-ray point source in Fermi Large Area Telescope (LAT) sky survey observations. Guided by a steep-spectrum radio point source in the Fermi error region, we performed a search at 820 MHz with the Green Bank Telescope that first discovered the pulsations. The initial radio pulse timing observations provided enough information to seed a search for gamma-ray pulsations in the LAT data, from which we derive a timing solution valid for the full Fermi mission. In addition to the discovery and timing of radio and gamma-ray pulsations, we searched for X-ray pulsations using NICER but no significant pulsations were detected. We also obtained time-series r-band photometry that indicates strong heating of the companion star by the pulsar wind. Material blown off the heated companion eclipses the 820 MHz radio pulse during inferior conjunction of the companion for ≈10% of the orbit, which is twice the angle subtended by its Roche lobe in an edge-on system. © 2022. The Author(s). Published by the American Astronomical Society
The NANOGrav 11-Year Data Set: Arecibo Observatory Polarimetry And Pulse Microcomponents
We present the polarization pulse profiles for 28 pulsars observed with the
Arecibo Observatory by the North American Nanohertz Observatory for
Gravitational Waves (NANOGrav) timing project at 2.1 GHz, 1.4 GHz, and 430 MHz.
These profiles represent some of the most sensitive polarimetric millisecond
pulsar profiles to date, revealing the existence of microcomponents (that is,
pulse components with peak intensities much lower than the total pulse peak
intensity). Although microcomponents have been detected in some pulsars
previously, we present microcomponents for PSRs B1937+21, J1713+0747, and
J2234+0944 for the first time. These microcomponents can have an impact on
pulsar timing, geometry, and flux density determination. We present rotation
measures for all 28 pulsars, determined independently at different observation
frequencies and epochs, and find the Galactic magnetic fields derived from
these rotation measures to be consistent with current models. These
polarization profiles were made using measurement equation template matching,
which allows us to generate the polarimetric response of the Arecibo
Observatory on an epoch-by-epoch basis. We use this method to describe its time
variability, and find that the polarimetric responses of the Arecibo
Observatory's 1.4 and 2.1 GHz receivers vary significantly with time.Comment: 41 pages, 20 figure
Discovery, Timing, and Multiwavelength Observations of the Black Widow Millisecond Pulsar PSR J1555-2908
We report the discovery of PSR J1555-2908, a 1.79 ms radio and gamma-ray
pulsar in a 5.6 hr binary system with a minimum companion mass of 0.052
. This fast and energetic ( erg/s)
millisecond pulsar was first detected as a gamma-ray point source in Fermi LAT
sky survey observations. Guided by a steep spectrum radio point source in the
Fermi error region, we performed a search at 820 MHz with the Green Bank
Telescope that first discovered the pulsations. The initial radio pulse timing
observations provided enough information to seed a search for gamma-ray
pulsations in the LAT data, from which we derive a timing solution valid for
the full Fermi mission. In addition to the radio and gamma-ray pulsation
discovery and timing, we searched for X-ray pulsations using NICER but no
significant pulsations were detected. We also obtained time-series r-band
photometry that indicates strong heating of the companion star by the pulsar
wind. Material blown off the heated companion eclipses the 820 MHz radio pulse
during inferior conjunction of the companion for ~10% of the orbit, which is
twice the angle subtended by its Roche lobe in an edge-on system.Comment: 15 pages, 6 figures, accepted by Ap
Bayesian Solar Wind Modeling with Pulsar Timing Arrays
Using Bayesian analyses we study the solar electron density with the NANOGrav
11-year pulsar timing array (PTA) dataset. Our model of the solar wind is
incorporated into a global fit starting from pulse times-of-arrival. We
introduce new tools developed for this global fit, including analytic
expressions for solar electron column densities and open source models for the
solar wind that port into existing PTA software. We perform an ab initio
recovery of various solar wind model parameters. We then demonstrate the
richness of information about the solar electron density, , that can be
gleaned from PTA data, including higher order corrections to the simple
model associated with a free-streaming wind (which are informative probes of
coronal acceleration physics), quarterly binned measurements of and a
continuous time-varying model for spanning approximately one solar cycle
period. Finally, we discuss the importance of our model for chromatic noise
mitigation in gravitational-wave analyses of pulsar timing data and the
potential of developing synergies between sophisticated PTA solar electron
density models and those developed by the solar physics community.Comment: 22 pages, 7 figures, Submitted to Ap
The NANOGrav 12.5-Year Data Set: Dispersion Measure Mis-Estimation with Varying Bandwidths
Noise characterization for pulsar-timing applications accounts for
interstellar dispersion by assuming a known frequency-dependence of the delay
it introduces in the times of arrival (TOAs). However, calculations of this
delay suffer from mis-estimations due to other chromatic effects in the
observations. The precision in modeling dispersion is dependent on the observed
bandwidth. In this work, we calculate the offsets in infinite-frequency TOAs
due to mis-estimations in the modeling of dispersion when using varying
bandwidths at the Green Bank Telescope. We use a set of broadband observations
of PSR J1643-1224, a pulsar with an excess of chromatic noise in its timing
residuals. We artificially restricted these observations to a narrowband
frequency range, then used both data sets to calculate residuals with a timing
model that does not include short-scale dispersion variations. By fitting the
resulting residuals to a dispersion model, and comparing the ensuing fitted
parameters, we quantify the dispersion mis-estimations. Moreover, by
calculating the autocovariance function of the parameters we obtained a
characteristic timescale over which the dispersion mis-estimations are
correlated. For PSR J1643-1224, which has one of the highest dispersion
measures (DM) in the NANOGrav pulsar timing array, we find that the
infinite-frequency TOAs suffer from a systematic offset of ~22 microseconds due
to DM mis-estimations, with correlations over ~1 month. For lower-DM pulsars,
the offset is ~7 microseconds. This error quantification can be used to provide
more robust noise modeling in NANOGrav's data, thereby increasing sensitivity
and improving parameter estimation in gravitational wave searches.Comment: 15 pages, 7 figure
The NANOGrav 12.5-Year Data Set: Polarimetry and Faraday Rotation Measures from Observations of Millisecond Pulsars with the Green Bank Telescope
In this work, we present polarization profiles for 23 millisecond pulsars
observed at 820 MHz and 1500 MHz with the Green Bank Telescope as part of the
NANOGrav pulsar timing array. We calibrate the data using Mueller matrix
solutions calculated from observations of PSRs B1929+10 and J1022+1001. We
discuss the polarization profiles, which can be used to constrain pulsar
emission geometry, and present both the first published radio polarization
profiles for nine pulsars and the discovery of very low intensity average
profile components ("microcomponents") in four pulsars. Using the Faraday
rotation measures, we measure for each pulsar and use it to calculate the
Galactic magnetic field parallel to the line of sight for different lines of
sight through the interstellar medium. We fit for linear and sinusoidal trends
in time in the dispersion measure and Galactic magnetic field and detect
magnetic field variations with a period of one year in some pulsars, but
overall find that the variations in these parameters are more consistent with a
stochastic origin.Comment: 35 pages, 21 figures. Accepted to Ap
The NANOGrav 12.5-Year Data Set:Dispersion Measure Misestimations with Varying Bandwidths
Noise characterization for pulsar-timing applications accounts for interstellar dispersion by assuming a known frequency dependence of the delay it introduces in the times of arrival (TOAs). However, calculations of this delay suffer from misestimations due to other chromatic effects in the observations. The precision in modeling dispersion is dependent on the observed bandwidth. In this work, we calculate the offsets in infinite-frequency TOAs due to misestimations in the modeling of dispersion when using varying bandwidths at the Green Bank Telescope. We use a set of broadband observations of PSR J1643−1224, a pulsar with unusual chromatic timing behavior. We artificially restricted these observations to a narrowband frequency range, then used both the broad- and narrowband data sets to calculate residuals with a timing model that does not account for time variations in the dispersion. By fitting the resulting residuals to a dispersion model and comparing the fits, we quantify the error introduced in the timing parameters due to using a reduced frequency range. Moreover, by calculating the autocovariance function of the parameters, we obtained a characteristic timescale over which the dispersion misestimates are correlated. For PSR J1643−1224, which has one of the highest dispersion measures (DM) in the NANOGrav pulsar timing array, we find that the infinite-frequency TOAs suffer from a systematic offset of ∼22 μs due to incomplete frequency sampling, with correlations over about one month. For lower-DM pulsars, the offset is ∼7 μs. This error quantification can be used to provide more robust noise modeling in the NANOGrav data, thereby increasing the sensitivity and improving the parameter estimation in gravitational wave searches
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