69 research outputs found
The Nature of Radio Continuum Emission in the Dwarf Starburst Galaxy NGC 625
We present new multi-frequency radio continuum imaging of the dwarf starburst
galaxy NGC 625 obtained with the Very Large Array. Data at 20, 6, and 3.6 cm
reveal global continuum emission dominated by free-free emission, with only
mild synchrotron components. Each of the major HII regions is detected; the
individual spectral indices are thermal for the youngest regions (showing
strongest H Alpha emission) and nonthermal for the oldest. We do not detect any
sources that appear to be associated with deeply embedded, dense, young
clusters, though we have discovered one low-luminosity, obscured source that
has no luminous optical counterpart and which resides in the region of highest
optical extinction. Since NGC 625 is a Wolf-Rayet galaxy with strong recent
star formation, these radio properties suggest that the youngest star formation
complexes have not yet evolved to the point where their thermal spectra are
significantly contaminated by synchrotron emission. The nonthermal components
are associated with regions of older star formation that have smaller ionized
gas components. These results imply a range of ages of the HII regions and
radio components that agrees with our previous resolved stellar population
analysis, where an extended burst of star formation has pervaded the disk of
NGC 625 over the last ~ 50 Myr. We compare the nature of radio continuum
emission in selected nearby dwarf starburst and Wolf-Rayet galaxies,
demonstrating that thermal radio continuum emission appears to be more common
in these systems than in typical HII galaxies with less recent star formation
and more evolved stellar clusters.Comment: ApJ, in press; 27 pages, 5 figures. Full-resolution version may be
obtained at http://www.astro.umn.edu/~cannon/n625.vla.p
A pilot project to increase health literacy among youth from seasonal farmworker families in rural eastern North Carolina: a qualitative exploration of implementation and impact
Objective
There are substantial health inequalities for seasonal agricultural workers and their families in the United States. One identified inequality is in health literacy. The authors explored the implementation and impact of connecting youth from seasonal farmworker families who participated in a leadership and college pipeline program with Internet access by providing a tablet with a paid cellular data plan and university library–based health literacy training.
Methods
With the support of a National Network of Libraries of Medicine Health Information Outreach Award, we conducted a qualitative, utilization-focused evaluation by conducting semi-structured interviews from December 2017 through February 2018 with middle and high school age participants in the program (n=10). After parental consent and youth assent, we recorded interviews with participants at program activity locations or in their homes. We then utilized inductive thematic analysis with 2 primary coders.
Results
We identified four themes: (1) having access to the Internet can be transformative, (2) access resulted in increased knowledge of and interest in one’s own and others’ health, (3) “Google� is the norm, and (4) participant training increased self-efficacy to determine credible sources and resources.
Conclusion
Providing Internet access and iPads was possible to implement and resulted in increased utilization of health information. The combination of Internet access with training on information literacy was a key factor in achieving these positive outcomes. The findings suggest the importance of ensuring equitable access to the Internet in efforts to improve educational and health outcomes for seasonal farmworkers and their families
On the nature of the intermittent pulsar PSR B1931+24
PSR B1931+24 is the first intermittent radio pulsar discovered to date,
characterized by a 0.8 s pulsation which turns on and off quasi-periodically
every ~35 days, with a duty cycle of ~10%. We present here X-ray and optical
observations of PSR B1931+24 performed with the Chandra X-ray Observatory and
Isaac Newton Telescope, respectively. Simultaneous monitoring from the Jodrell
Bank Observatory showed that this intermittent pulsar was in the radio-on phase
during our observations. We do not find any X-ray or optical counterpart to PSR
B1931+24 translating into an upper limit of ~2x10^{31} erg/s on the X-ray
luminosity, and of g' > 22.6 on the optical magnitude. If the pulsar is
isolated, these limits cannot constrain the dim X-ray and optical emission
expected for a pulsar of that age (~1.6 Myr). We discuss the possibility that
the quasi-periodic intermittent behavior of PSR B1931+24 is due to the presence
of a low mass companion star or gaseous planet, tight with the pulsar in an
eccentric orbit. In order to constrain the parameters of this putative binary
system we re-analysed the pulsar radio timing residuals and we found that (if
indeed hosted in a binary system), PSR B1931+24 should have a very low mass
companion and an orbit of low inclination.Comment: 6 pages; accepted for publication in MNRA
The supergiant fast X-ray transient IGR J18483−0311 in quiescence: XMM-Newton, Swift and Chandra observations
IGR J18483−0311 was discovered with INTEGRAL in 2003 and later classified as a supergiant fast X-ray transient. It was observed in outburst many times, but its quiescent state is still poorly known. Here, we present the results of XMM-Newton, Swift and Chandra observations of IGR J18483−0311. These data improved the X-ray position of the source, and provided new information on the timing and spectral properties of IGR J18483−0311 in quiescence. We report the detection of pulsations in the quiescent X-ray emission of this source, and give for the first time a measurement of the spin-period derivative of this source. In IGR J18483−0311, the measured spin-period derivative of −(1.3 ± 0.3) × 10−9 s s−1 likely results from light travel time effects in the binary. We compare the most recent observational results of IGR J18483−0311 and SAX J1818.6−1703, the two supergiant fast X-ray transients for which a similar orbital period has been measure
Studying the galactic outflow in NGC 1569
We present deep WIYN H-alpha imaging of the dwarf irregular starburst galaxy
NGC 1569, together with WIYN SparsePak spatially-resolved optical spectroscopy
of the galactic outflow. This leads on from our previous detailed analyses of
the state of the ISM in the central regions of this galaxy. Our deep imaging
reveals previously undetected ionized filaments in the outer halo. Through
combining these results with our spectroscopy we have been able to re-define
the spatial extent of the previously catalogued superbubbles, and derive
estimates for their expansion velocities, which we find to be in the range
50-100 km/s. The implied dynamical ages of <25 Myr are consistent with the
recent star- and cluster-formation histories of the galaxy. Detailed
decomposition of the multi-component H-alpha line has shown that within a
distinct region ~700x500 pc in size, roughly centred on the bright super star
cluster A, the profile is composed of a bright, narrow (FWHM <= 70 km/s)
feature with an underlying, broad component (FWHM ~ 150 km/s). Applying the
conclusions found in our previous work regarding the mechanism through which
the broad component is produced, we associate the faint, broad emission with
the interaction of the hot, fast-flowing winds from the young star clusters
with cool clumps of ISM material. This interaction generates turbulent mixing
layers on the surface of the clouds and the evaporation and/or ablation of
material into the outflow. Under this interpretation, the extent of the broad
component region may indicate an important transition point in the outflow,
where ordered expansion begins to dominate over turbulent motion. In this
context, we present a multi-wavelength discussion of the evolutionary state of
the outflow.Comment: 17 pages, 12 figures, 2 tables, accepted for publication in MNRA
The supergiant fast X-ray transient IGRJ18483-0311 in quiescence: XMM-Newton, Swift, and Chandra observations
IGR J18483-0311 was discovered with INTEGRAL in 2003 and later classified as
a supergiant fast X-ray transient. It was observed in outburst many times, but
its quiescent state is still poorly known. Here we present the results of
XMM-Newton, Swift, and Chandra observations of IGRJ18483-0311. These data
improved the X-ray position of the source, and provided new information on the
timing and spectral properties of IGR J18483-0311 in quiescence. We report the
detection of pulsations in the quiescent X-ray emission of this source, and
give for the first time a measurement of the spin-period derivative of this
source. In IGRJ18483-0311 the measured spin-period derivative of
-(1.3+-0.3)x10^(-9) s/s likely results from light travel time effects in the
binary. We compare the most recent observational results of IGRJ18483-0311 and
SAXJ1818.6-1703, the two supergiant fast X-ray transients for which a similar
orbital period has been measured.Comment: Accepted for publication in MNRA
A Hard X-Ray View of Scorpius X-1 with INTEGRAL: Nonthermal Emission?
We present here simultaneous INTEGRAL/RXTE observations of Sco X-1 and in particular a study of the hard X-ray emission of the source and its correlation with the position in the Z track of the X-ray color-color diagram. We find that the hard X-ray (above about 30 keV) emission of Sco X-1 is dominated by a power-law component with a photon index of ~3. The flux in the power-law component slightly decreases when the source moves in the color-color diagram in the sense of increasing inferred mass accretion rate from the horizontal branch to the normal branch/flaring branch vertex. It becomes not significantly detectable in the flaring branch, where its flux has decreased by about an order of magnitude. These results present close analogies to the behavior of GX 17+2, one of the so-called Sco-like Z sources. Finally, the hard power law in the spectrum of Sco X-1 does not show any evidence of a high-energy cutoff up to 100-200 keV, strongly suggesting a nonthermal origin of this component
VLA Observations of the H92alpha line from NGC 5253 and Henize 2-10 : Ionized Gas around Super Star Clusters
We have detected the H92alpha radio recombination line from two dwarf
starburst galaxies, NGC 5253 and He 2-10, using the Very Large Array. Both the
line data as well as the radio continuum data are used to model the properties
of the ionized gas in the centers of these galaxies. We consider a
multi-density model for radio recombination lines and show why previous models,
which were based on the assumption of gas at a single density, are valid in
many situations. The models show that the ionized gas has a density of ~10^4
/cc in both galaxies, with an effective size of 2-10 pc and a total mass of
about 10^4 Msun. The derived production rate of Lyman continuum photons is ~2.5
x 10^{52} /s in both the galaxies and the corresponding mass of stars (assuming
a Salpeter IMF) is ~10^5 msun. The implied stellar density shows that the
observed radio recombination lines arise from ionized gas around super star
clusters (SSCs) in both galaxies (these SSCs have been recently detected
through their radio continuum emission). The existence of ~10^4 Msun of ionized
gas within a few parsecs of an SSC places strict constraints on dynamical
models. Using simple arguments, the parameter space for a few possible models
are derived. The well known radio-FIR correlation also holds for NGC 5253,
although the radio emission from this galaxy is almost completely thermal. It
is shown that NGC 5253 is strong evidence that the component of FIR emission
from warm dust is correlated separately with the component of radio emission
from thermal bremsstrahlung.Comment: 15 pages, 4 figures, 5 tables. Accepted for publication in
Astrophysical Journa
The Large Observatory for x-ray timing
The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final down-selection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supra-nuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m2 effective area, 2-30 keV, 240 eV spectral resolution, 1° collimated field of view) and a WideField Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g. GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the status of the mission at the end of its Phase A study
The LOFT mission concept: a status update
The Large Observatory For x-ray Timing (LOFT) is a mission concept which was proposed to ESA as M3 and M4 candidate in the framework of the Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument and the uniquely large field of view of its wide field monitor, LOFT will be able to study the behaviour of matter in extreme conditions such as the strong gravitational field in the innermost regions close to black holes and neutron stars and the supra-nuclear densities in the interiors of neutron stars. The science payload is based on a Large Area Detector (LAD, >8m2 effective area, 2-30 keV, 240 eV spectral resolution, 1 degree collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g., GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the current technical and programmatic status of the mission
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