913 research outputs found
Spring Dispersal Patterns of Red-winged Blackbirds, Agelaius phoeniceus, Staging in Eastern South Dakota
Red-winged Blackbirds (Agelaius phoeniceus) are very abundant summer residents throughout the Prairie Pothole Region of central North America. In late summer they assemble in post-breeding flocks that cause significant amounts of agricultural damage, particularly in sunflower fields near natal sites. In April 2001, we aerially color-marked ~370,000 Red-winged Blackbirds near Badger, South Dakota (44°48'N, 97°21'W), to determine if migrants staging here were summer residents in sunflower production areas ~350 km to the northwest. We measured patterns of migratory dispersal by collecting birds in 54 randomly selected blocks in the northcentral U.S. and the Prairie Provinces of Canada. The marked specimens (n = 33) were categorized into three polygons based on analyses of banding and re-sighting data and proximity to concentrated sunflower production. We estimated that 82% of the migrants that had staged in eastern South Dakota resided within or on the periphery of the sunflower growing area. These birds probably stay near their breeding territories until at least late August and cause early damage to sunflower, which comprises the majority of damage. Resident birds in Alberta and most of Saskatchewan (18%) might arrive too late in the damage season to impact the sunflower crop significantly
Low frequency geomagnetic fluctuations (.04 to 25 Hz) on land and on the floor of Monterey Bay
A coil antenna consisting of approximately 6000 turns
of copper wire was utilized to measure the horizontal component
of fluctuations of the earth's magnetic field on the
floor of Monterey Bay in water depth of approximately 50
meters. The results indicate that the power spectral density
of the fluctuations varies from 10nT²/Hz at 0.04 Hz to
10ˉ⁶nT²/Hz at 25 Hz, a monotonic decrease of about 6 dB/
octave, except in the 8-20 Hz region where the Schumann
resonances occur. While the sensitivity of the equipment
was insufficient to measure the vertical component of the
fluctuation we can put an upper limit of 10ˉ³nT²/Hz at 1 Hz
and 10ˉ⁶(nT)²/Hz at 10 Hz on the magnitude of this component.
The same sensor was also used to measure various components
of the field fluctuations at a remote land' site
(Chew's Ridge). In the frequency range observed the general
shape of the spectra was similar to those obtained at
sea. However, a strong azimuthal variation at certain
frequencies was noted in the land data. The possibility
that these directional signals are of man made origin
cannot be excluded at this time.http://archive.org/details/lowfrequencygeom00mcdeLieutenant Commander, United States NavyLieutenant, United States NavyApproved for public release; distribution is unlimited
A Persistent Disk Wind in GRS 1915+105 with NICER
The bright, erratic black hole X-ray binary GRS 1915+105 has long been a
target for studies of disk instabilities, radio/infrared jets, and accretion
disk winds, with implications that often apply to sources that do not exhibit
its exotic X-ray variability. With the launch of NICER, we have a new
opportunity to study the disk wind in GRS 1915+105 and its variability on short
and long timescales. Here we present our analysis of 39 NICER observations of
GRS 1915+105 collected during five months of the mission data validation and
verification phase, focusing on Fe XXV and Fe XXVI absorption. We report the
detection of strong Fe XXVI in 32 (>80%) of these observations, with another
four marginal detections; Fe XXV is less common, but both likely arise in the
well-known disk wind. We explore how the properties of this wind depends on
broad characteristics of the X-ray lightcurve: mean count rate, hardness ratio,
and fractional RMS variability. The trends with count rate and RMS are
consistent with an average wind column density that is fairly steady between
observations but varies rapidly with the source on timescales of seconds. The
line dependence on spectral hardness echoes known behavior of disk winds in
outbursts of Galactic black holes; these results clearly indicate that NICER is
a powerful tool for studying black hole winds.Comment: Accepted for publication in ApJL. Comments welcom
Unexpected late-time temperature increase observed in two neutron star crust cooling sources -- XTE~J1701-462 and EXO~0748-676
Transient LMXBs that host neutron stars (NSs) provide excellent laboratories
for probing the dense matter physics present in NS crusts. During accretion
outbursts in LMXBs, exothermic reactions may heat the NS crust, disrupting the
crust-core equilibrium. When the outburst ceases, the crust cools to restore
thermal equilibrium with the core. Monitoring this evolution allows us to probe
the dense matter physics in the crust. Properties of the deeper crustal layers
can be probed at later times after the end of the outburst. We report on the
unexpected late-time temperature evolution (>2000 days after the end of their
outbursts) of two NSs in LMXBs, XTE J1701-462 and EXO 0748-676. Although both
these sources exhibited very different outbursts (in terms of duration and the
average accretion rate), they exhibit an unusually steep decay of ~7 eV in the
observed effective temperature (occurring in a time span of ~700 days) around
~2000 days after the end of their outbursts. Furthermore, they both showed an
even more unexpected rise of ~3 eV in temperature (over a time period of
~500-2000 days) after this steep decay. This rise was significant at the
2.4{\sigma} and 8.5{\sigma} level for XTE J1701-462 and EXO 0748-676,
respectively. The physical explanation for such behaviour is unknown and cannot
be straightforwardly be explained within the cooling hypothesis. In addition,
this observed evolution cannot be well explained by low-level accretion either
without invoking many assumptions. We investigate the potential pathways in the
theoretical heating and cooling models that could reproduce this unusual
behaviour, which so far has been observed in two crust-cooling sources. Such a
temperature increase has not been observed in the other NS crust-cooling
sources at similarly late times, although it cannot be excluded that this might
be a result of the inadequate sampling obtained at such late times.Comment: accepted for publication by A&A letter
GRO J1655-40: Early Stages of the 2005 Outburst
The black-hole X-ray binary transient GRO J1655-40 underwent an outburst
beginning in early 2005. We present the results of our multi-wavelength
observational campaign to study the early outburst spectral and temporal
evolution, which combines data from X-ray (RXTE, INTEGRAL), radio (VLA) and
optical (ROTSE, SMARTS) instruments. During the reported period the source left
quiescence and went through four major accreting black hole states: low-hard,
hard intermediate, soft intermediate and high-soft. We investigated dipping
behavior in the RXTE band and compare our results to the 1996-1997 case, when
the source was predominantly in the high-soft state, finding significant
differences. We consider the evolution of the low frequency quasi-periodic
oscillations and find that the frequency strongly correlates with the spectral
characteristics, before shutting off prior to the transition to the high-soft
state. We model the broad-band high-energy spectrum in the context of empirical
models, as well as more physically motivated thermal and bulk-motion
Comptonization and Compton reflection models. RXTE and INTEGRAL data together
support a statistically significant high energy cut-off in the energy spectrum
at 100~200 keV during the low-hard state. The RXTE data alone also show it very
significantly during the transition, but cannot see one in the high-soft state
spectra. We consider radio, optical and X-ray connections in the context of
possible synchrotron and synchrotron self-Compton origins of X-ray emission in
low-hard and intermediate states. In this outburst of GRO J1655-40, the radio
flux does not rise strongly with the X-ray flux.Comment: 23 pages, 16 figures, accepted for publication in Ap
Use of Colloidal Gold and Neutron Activation in Correlative Microscopic Labeling and Label Quantitation
Albumin was conjugated to 16 nm gold particles (Alb-Au16) and infused into anesthetized pigs to determine if plasma, tissue and bronchoalveolar lavage (BAL) fluid concentrations of gold could be quantitated by neutron activation (Au198). Additionally, transmission electron microscopy (TEM) of lung and liver samples was evaluated for sites of gold distribution and morphological changes. The minimum concentration of gold detected by neutron activation ranged between 1.4 and 1.9 ppb (ng/gm of sample). No gold was detected in the plasma of pigs prior to Alb-Au16 infusion, while mean post infusion concentrations were 1.037 ± 0.69 ppm (μg/gm plasma, ±SD). The concentrations in the lung and liver were 274.4 ± 0.03 and 88.3 ± 0.04 ppm, respectively. There was no measurable Alb-Au16 in the BAL fluid. TEM showed gold particles within phagolysosomes in pulmonary and hepatic intravascular macrophages. No morphological changes were observed within the two populations of macrophages and no gold particles were observed within the alveolar space. Neutron activation of blood, tissue and BAL fluid samples from pigs administered intravenous Alb-Au16 was sensitive to the ppb concentration. The capability of neutron activation to detect very low concentrations of Au 198, combined with the freedom from contamination, make neutron activation an excellent technique for the study of the distribution and metabolism of a substance in vivo
Taken by strum: ukuleles and participatory music-making in Hamilton, Aotearoa/New Zealand
Ethnographic study of ukulele playing in Hamilton, N
Faraday rotation in the MOJAVE blazars: 3C 273 a case study
Radio polarimetric observations of Active Galactic Nuclei can reveal the
magnetic field structure in the parsec-scale jets of these sources. We have
observed the gamma-ray blazar 3C 273 as part of our multi-frequency survey with
the Very Long Baseline Array to study Faraday rotation in a large sample of
jets. Our observations re-confirm the transverse rotation measure gradient in
3C 273. For the first time the gradient is seen to cross zero which is further
indication for a helical magnetic field and spine-sheath structure in the jet.
We believe the difference to previous epochs is due to a different part of the
jet being illuminated in our observations.Comment: 6 pages, 3 figures. To appear in the proceedings of "Beamed and
Unbeamed Gamma-rays from Galaxies", held in Muonio, Finland, April 11-15,
2011. Journal of Physics: Conference Serie
A transient relativistic radio jet from Cygnus X-1
We report the first observation of a transient relativistic jet from the
canonical black hole candidate, Cygnus X-1, obtained with the Multi-Element
Radio-Linked Interferometer Network (MERLIN). The jet was observed in only one
of six epochs of MERLIN imaging of the source during a phase of repeated X-ray
spectral transitions in 2004 Jan--Feb, and this epoch corresponded to the
softest 1.5-12 keV X-ray spectrum. With only a single epoch revealing the jet,
we cannot formally constrain its velocity. Nevertheless, several lines of
reasoning suggest that the jet was probably launched 0.5-4.0 days before this
brightening, corresponding to projected velocities of 0.2c < v_app < 1.6c, and
an intrinsic velocity of > 0.3c. We also report the occurrence of a major radio
flare from Cyg X-1, reaching a flux density of ~120 mJy at 15 GHz, and yet not
associated with any resolvable radio emission, despite a concerted effort with
MERLIN. We discuss the resolved jet in terms of the recently proposed 'unified
model' for the disc-jet coupling in black hole X-ray binaries, and tentatively
identify the 'jet line' for Cyg X-1. The source is consistent with the model in
the sense that a steady jet appears to persist initially when the X-ray
spectrum starts softening, and that once the spectral softening is complete the
core radio emission is suppressed and transient ejecta / shock observed.
However, there are some anomalies, and Cyg X-1 clearly does not behave like a
normal black hole transient in progressing to the canonical soft / thermal
state once the ejection event has happened.Comment: Accepted for publication in MNRA
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