140 research outputs found
The International Pulsar Timing Array: First Data Release
The highly stable spin of neutron stars can be exploited for a variety of (astro)physical investigations. In particular, arrays of pulsars with rotational periods of the order of milliseconds can be used to detect correlated signals such as those caused by gravitational waves. Three such \u27pulsar timing arrays\u27 (PTAs) have been set up around the world over the past decades and collectively form the \u27International\u27 PTA (IPTA). In this paper, we describe the first joint analysis of the data from the three regional PTAs, i.e. of the first IPTA data set. We describe the available PTA data, the approach presently followed for its combination and suggest improvements for future PTA research. Particular attention is paid to subtle details (such as underestimation of measurement uncertainty and long-period noise) that have often been ignored but which become important in this unprecedentedly large and inhomogeneous data set. We identify and describe in detail several factors that complicate IPTA research and provide recommendations for future pulsar timing efforts. The first IPTA data release presented here (and available on-line) is used to demonstrate the IPTA\u27s potential of improving upon gravitational-wave limit
Kinematics, Structure, and Mass Outflow Rates of Extreme Starburst Galactic Outflows
We present results on the properties of extreme gas outflows in massive (10), compact, starburst () galaxies at z = with very high star
formation surface densities ($2000 \,\rm M_{\odot} \
yr^{-1} \ kpc^{-2}820 - 2860
\kmps. High-resolution spectroscopy allows us to measure precise column
densities and covering fractions as a function of outflow velocity and
characterize the kinematics and structure of the cool gas outflow phase (T
\sim^4 K). We find substantial variation in the absorption profiles,
which likely reflects the complex morphology of inhomogeneously-distributed,
clumpy gas and the intricacy of the turbulent mixing layers between the cold
and hot outflow phases. There is not a straightforward correlation between the
bursts in the galaxies' star formation histories and their wind absorption line
profiles, as might naively be expected for starburst-driven winds. The lack of
strong \mgii \ absorption at the systemic velocity is likely an orientation
effect, where the observations are down the axis of a blowout. We infer high
mass outflow rates of \rm \sim-\rm M_{\odot} \, yr^{-1}\eta\sim\eta\sim$20 for two galaxies. While
these values have high uncertainties, they suggest that starburst galaxies are
capable of ejecting very large amounts of cool gas that will substantially
impact their future evolution.Comment: Accepted for publication in The Astrophysical Journa
The star formation history of the Sco-Cen association: Coherent star formation patterns in space and time
We reconstruct the star formation history of the Sco-Cen OB association using
a novel high-resolution age map of the region. We develop an approach to
produce robust ages for Sco-Cen's recently identified 37 stellar clusters using
the \texttt{SigMA} algorithm. The Sco-Cen star formation timeline reveals four
periods of enhanced star formation activity, or bursts, remarkably separated by
about 5 Myr. Of these, the second burst, which occurred 15 million years ago,
is by far the dominant, and most of Sco-Cen's stars and clusters were in place
by the end of this burst. The formation of stars and clusters in Sco-Cen is
correlated, but not linearly, meaning that more stars were formed per cluster
during the peak of star formation rate. Most of the clusters, which are large
enough to have supernova precursors, were formed during the 15 Myr period. Star
and cluster formation activity has been continuously declining since then. We
have clear evidence that Sco-Cen formed from the inside out and contains 100-pc
long correlated chains of contiguous clusters exhibiting well-defined age
gradients, from massive older clusters to smaller young clusters. These
observables suggest an important role for feedback in the formation of about
half of Sco-Cen stars, although follow-up work is needed to quantify this
statement. Finally, we confirm that the Upper-Sco age controversy discussed in
the literature during the last decades is solved: the region toward Upper-Sco,
a benchmark region for planet formation studies, contains not one but up to
nine clusters spanning ages from 3 to 19 Myr.Comment: 19 pages, 14 figures, preliminary version of this work. Comments
welcome. Soon to be submitted to A&
The Green Bank North Celestial Cap Pulsar Survey. IV: Four New Timing Solutions
We present timing solutions for four pulsars discovered in the Green Bank
Northern Celestial Cap (GBNCC) survey. All four pulsars are isolated with spin
periods between 0.26s and 1.84s. PSR J00382501 has a 0.26s
period and a period derivative of ,
which is unusually low for isolated pulsars with similar periods. This low
period derivative may be simply an extreme value for an isolated pulsar or it
could indicate an unusual evolution path for PSR J00382501, such as a
disrupted recycled pulsar (DRP) from a binary system or an orphaned central
compact object (CCO). Correcting the observed spin-down rate for the Shklovskii
effect suggests that this pulsar may have an unusually low space velocity,
which is consistent with expectations for DRPs. There is no X-ray emission
detected from PSR J00382501 in an archival swift observation, which suggests
that it is not a young orphaned CCO. The high dispersion measure of PSR
J1949+3426 suggests a distance of 12.3kpc. This distance indicates that PSR
J1949+3426 is among the most distant 7% of Galactic field pulsars, and is one
of the most luminous pulsars.Comment: 7 pages, 5 figure
The Green Bank Northern Celestial Cap Pulsar Survey II: The Discovery and Timing of Ten Pulsars
We present timing solutions for ten pulsars discovered in 350 MHz searches
with the Green Bank Telescope. Nine of these were discovered in the Green Bank
Northern Celestial Cap survey and one was discovered by students in the Pulsar
Search Collaboratory program in analysis of drift-scan data. Following
discovery and confirmation with the Green Bank Telescope, timing has yielded
phase-connected solutions with high precision measurements of rotational and
astrometric parameters. Eight of the pulsars are slow and isolated, including
PSR J09302301, a pulsar with nulling fraction lower limit of 30\% and
nulling timescale of seconds to minutes. This pulsar also shows evidence of
mode changing. The remaining two pulsars have undergone recycling, accreting
material from binary companions, resulting in higher spin frequencies. PSR
J05572948 is an isolated, 44 \rm{ms} pulsar that has been partially recycled
and is likely a former member of a binary system which was disrupted by a
second supernova. The paucity of such so-called `disrupted binary pulsars'
(DRPs) compared to double neutron star (DNS) binaries can be used to test
current evolutionary scenarios, especially the kicks imparted on the neutron
stars in the second supernova. There is some evidence that DRPs have larger
space velocities, which could explain their small numbers. PSR J1806+2819 is a
15 \rm{ms} pulsar in a 44 day orbit with a low mass white dwarf companion. We
did not detect the companion in archival optical data, indicating that it must
be older than 1200 Myr.Comment: 9 pages, 5 figure
Limits on the Stochastic Gravitational Wave Background from the North American Nanohertz Observatory for Gravitational Waves
We present an analysis of high-precision pulsar timing data taken as part of
the North American Nanohertz Observatory for Gravitational waves (NANOGrav)
project. We have observed 17 pulsars for a span of roughly five years using the
Green Bank and Arecibo radio telescopes. We analyze these data using standard
pulsar timing models, with the addition of time-variable dispersion measure and
frequency-variable pulse shape terms. Sub-microsecond timing residuals are
obtained in nearly all cases, and the best root-mean-square timing residuals in
this set are ~30-50 ns. We present methods for analyzing post-fit timing
residuals for the presence of a gravitational wave signal with a specified
spectral shape. These optimally take into account the timing fluctuation power
removed by the model fit, and can be applied to either data from a single
pulsar, or to a set of pulsars to detect a correlated signal. We apply these
methods to our dataset to set an upper limit on the strength of the
nHz-frequency stochastic supermassive black hole gravitational wave background
of h_c (1 yr^-1) < 7x10^-15 (95%). This result is dominated by the timing of
the two best pulsars in the set, PSRs J1713+0747 and J1909-3744.Comment: To be submitted to Ap
Physical Properties of Massive Compact Starburst Galaxies with Extreme Outflows
© 2021. The Author(s). Published by the American Astronomical Society. This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 licence. https://creativecommons.org/licenses/by/4.0/We present results on the nature of extreme ejective feedback episodes and the physical conditions of a population of massive (M * ∼ 1011 M ⊙), compact starburst galaxies at z = 0.4–0.7. We use data from Keck/NIRSPEC, SDSS, Gemini/GMOS, MMT, and Magellan/MagE to measure rest-frame optical and near-IR spectra of 14 starburst galaxies with extremely high star formation rate surface densities (mean ΣSFR ∼ 2000 M ⊙ yr−1 kpc−2) and powerful galactic outflows (maximum speeds v 98 ∼ 1000–3000 km s−1). Our unique data set includes an ensemble of both emission ([O ii] λλ3726,3729, Hβ, [O iii] λλ4959,5007, Hα, [N ii] λλ6549,6585, and [S ii] λλ6716,6731) and absorption (Mg ii λλ2796,2803, and Fe ii λ2586) lines that allow us to investigate the kinematics of the cool gas phase (T ∼ 104 K) in the outflows. Employing a suite of line ratio diagnostic diagrams, we find that the central starbursts are characterized by high electron densities (median n e ∼ 530 cm−3), and high metallicity (solar or supersolar). We show that the outflows are most likely driven by stellar feedback emerging from the extreme central starburst, rather than by an AGN. We also present multiple intriguing observational signatures suggesting that these galaxies may have substantial Lyman continuum (LyC) photon leakage, including weak [S ii] nebular emission lines. Our results imply that these galaxies may be captured in a short-lived phase of extreme star formation and feedback where much of their gas is violently blown out by powerful outflows that open up channels for LyC photons to escape.Peer reviewedFinal Published versio
Testing Theories of Gravitation Using 21-Year Timing of Pulsar Binary J1713+0747
We report 21-year timing of one of the most precise pulsars: PSR J1713+0747. Its pulse times of arrival are well modeled by a comprehensive pulsar binary model including its three-dimensional orbit and a noise model that incorporates short-and long-timescale correlated noise such as jitter and red noise. Its timing residuals have weighted root mean square similar to 92 ns. The new data set allows us to update and improve previous measurements of the system properties, including the masses of the neutron star (1.31 +/- 0.11 M-circle dot) and the companion white dwarf (0.286 +/- 0.012 M-circle dot) as well as their parallax distance 1.15 +/- 0.03 kpc. We measured the intrinsic change in orbital period, (P) over dot(b)(Int), is -0.20 +/- 0.17 ps s(-1), which is not distinguishable from zero. This result, combined with the measured (P) over dot(b)(Int) of other pulsars, can place a generic limit on potential changes in the gravitational constant G. We found that (G) over dot/G is consistent with zero [(-0.6 +/- 1.1) x 10(-12) yr(-1), 95% confidence] and changes at least a factor of 31 (99.7% confidence) more slowly than the average expansion rate of the universe. This is the best (G) over dot/G limit from pulsar binary systems. The (P) over dot(b)(Int) of pulsar binaries can also place limits on the putative coupling constant for dipole gravitational radiation kappa(D) = (-0.9 +/- 3.3) 10(-4) (95% confidence). Finally, the nearly circular orbit of this pulsar binary allows us to constrain statistically the strong-field post-Newtonian parameters Delta, which describes the violation of strong equivalence principle, and (alpha) over cap (3), which describes a breaking of both Lorentz invariance in gravitation and conservation of momentum. We found, at 95% confidence, Delta <0.01 and (3) <2 x 10(-20) based on PSR J1713+0747
First Discovery of a Fast Radio Burst at 350 MHz by the GBNCC Survey
We report the first discovery of a fast radio burst (FRB), FRB 20200125A, by
the Green Bank Northern Celestial Cap (GBNCC) Pulsar Survey conducted with the
Green Bank Telescope at 350 MHz. FRB 20200125A was detected at a Galactic
latitude of 58.43 degrees with a dispersion measure of 179 pc cm, while
electron density models predict a maximum Galactic contribution of 25 pc
cm along this line of sight. Moreover, no apparent Galactic foreground
sources of ionized gas that could account for the excess DM are visible in
multi-wavelength surveys of this region. This argues that the source is
extragalactic. The maximum redshift for the host galaxy is ,
corresponding to a maximum comoving distance of approximately 750 Mpc. The
measured peak flux density for FRB 20200125A is 0.37 Jy, and we measure a pulse
width of 3.7 ms, consistent with the distribution of FRB widths observed at
higher frequencies. Based on this detection and assuming an Euclidean flux
density distribution of FRBs, we calculate an all-sky rate at 350 MHz of
FRBs sky day above a peak flux
density of 0.42 Jy for an unscattered pulse having an intrinsic width of 5 ms,
consistent with rates reported at higher frequencies. Given the recent
improvements in our single-pulse search pipeline, we also revisit the GBNCC
survey sensitivity to various burst properties. Finally, we find no evidence of
interstellar scattering in FRB 20200125A, adding to the growing evidence that
some FRBs have circumburst environments where free-free absorption and
scattering are not significant.Comment: 15 pages, 6 figures, Submitted to Ap
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