7,971 research outputs found
Multi-wavelength INTEGRAL NEtwork (MINE) observations of the microquasar GRS 1915+105
We present the international collaboration MINE (Multi-lambda Integral
NEtwork) aimed at conducting multi-wavelength observations of X-ray binaries
and microquasars simultaneously with the INTEGRAL gamma-ray satellite. We will
focus on the 2003 March-April campaign of observations of the peculiar
microquasar GRS 1915+105 gathering radio, IR and X-ray data. The source was
observed 3 times in the plateau state, before and after a major radio and X-ray
flare. It showed strong steady optically thick radio emission corresponding to
powerful compact jets resolved in the radio images, bright near-infrared
emission, a strong QPO at 2.5 Hz in the X-rays and a power law dominated
spectrum without cutoff in the 3-300 keV range. We compare the different
observations, their multi-wavelength light curves, including JEM-X, ISGRI and
SPI, and the parameters deduced from fitting the spectra obtained with these
instruments on board INTEGRAL.Comment: 4 pages, 9 fig., Proc. of the 5th INTEGRAL Workshop (Feb. 16-20
2004), to be published by ES
Simultaneous multi-wavelength observations of microquasars (the MINE collaboration)
We present the international collaboration MINE (Multi-lambda INTEGRAL
NEtwork) aimed at conducting multi-wavelength observations of microquasars
simultaneously with the INTEGRAL satellite. The first results on GRS 1915+105
are encouraging and those to come should help us to understand the physics of
the accretion and ejection phenomena around a compact object.Comment: 2 p, 3 fig., proc. of the IAU Coll. 194, ``Compact Binaries in the
Galaxy and Beyond'', Nov. 2003, La Paz, Mexico, to be published in the Conf.
Series of Revista Mexicana de Astronomia y Astrofisica, Eds. G. Tovmassian &
E. Sio
Study of several factors affecting crew escape trajectories from the Space Shuttle Orbiter at low-subsonic speeds
Factors affecting the bailout characteristics from the space shuttle orbiter at low-subsonic speeds were investigated. In the 12-foot low-speed tunnel and the 4 by 7-meter tunnel with 0.03-scale models. The effect of crew-model exit velocity, body position, and body weight were studied with egress from the main side hatch with the orbiter upright and from the upper cabin hatch with the orbiter inverted. Crew model drag and flow field measurements around the orbiter were estimated. The high-angle-of-attack trim characteristics of the orbiter was determined by force tests in an attempt to improve bailout conditions. A computer simulation was made to evaluate the maneuver necessary to attain the high-angle-of-attack trim
Sco X-1: The Evolution and Nature of the Twin Compact Radio Lobes
The radio components associated with the LMXB Sco X-1 have been monitored
with extensive VLBI imaging at 1.7 and 5.0 GHz over four years, including a
56-hour continuous VLBI observation in 1999 June. We often detected one strong
and one weak compact radio component, moving in opposite directions from the
radio core. We suggest that the moving components are radio lobes generated by
the disruption of energy flow in a twin-beam from the binary system. The
average lifetime of a lobe-pair, the space motion of the lobes and the measured
energy flow in the beam are discussed in arXiv:astro-ph/0104325. The lobe has a
flux density that is variable over a time-scale of one hour, a measured minimum
size of 1 mas (2.8 au), and is extended perpendicular to its motion. This short
electron radiative lifetime may be caused by synchrotron losses if the lobe
magnetic field is 300 G, or by adiabatic expansion of the electrons as soon as
they are produced at the working surface. The lobes also show periods of slow
expansion and a steepening radio spectrum, perhaps related to the
characteristics of the beam energy flow. The radio morphology for Sco X-1 is
more simple than for most other Galactic jet sources. The lobes of Sco X-1 are
similar to hot-spots found in many extragalactic double sources. Scaling the
phenomena observed in Sco X-1 to extragalactic sources implies hot-spot
variability time-scales of 10^4 yr and hot-spot lifetimes of 10^5 yr. The
recurrent formation of lobes in Sco X-1 probably does not occur for
extragalactic radio sources.Comment: 22 pages of text + 16 figures. ApJ, in pres
Cherenkov Radiation from Pairs and Its Effect on Induced Showers
We calculate the Cherenkov radiation from an pair at small
separations, as occurs shortly after a pair conversion. The radiation is
reduced (compared to that from two independent particles) when the pair
separation is smaller than the wavelength of the emitted light. We estimate the
reduction in light in large electromagnetic showers, and discuss the
implications for detectors that observe Cherenkov radiation from showers in the
Earth's atmosphere, as well as in oceans and Antarctic ice.Comment: Final version, with minor changes, to appear in PRD. 5 pages with 4
figure
Building a patient safety toolkit for use in general practice
Despite 340 000 000 primary care consultations annually in the UK, most of the literature on patient safety has focused on hospital-based services. To improve safety in primary care settings, we must know what methods, tools and indicators are available to measure and monitor patient safety. In collaboration with patient safety experts at the University of Dundee, we were able to identify a number of existing tools, and many of these were adopted for use in the Patient Safety Toolkit
ISO observations of a sample of Compact Steep Spectrum and GHz Peaked Spectrum Radio Galaxies
We present results from observations obtained with ISOPHOT, on board the ISO
satellite, of a representative sample of seventeen CSS/GPS radio galaxies and
of a control sample of sixteen extended radio galaxies spanning similar ranges
in redshift (0.2 = 10^26 W/Hz).
The observations have been performed at lambda = 60, 90, 174 and 200 microns.
Seven of the CSS/GPS sources have detections >= 3 sigma at one or more
wavelengths, one of which is detected at >= 5 sigma. By co-adding the data we
have obtained average flux densities at the four wavelengths. We found no
evidence that the FIR luminosities of the CSS/GPS sources are significantly
different from those of the extended objects and therefore there is not any
support for CSS/GPS sources being objects "frustrated" by an abnormally dense
ambient medium. The two samples were then combined, providing FIR information
on a new sample of radio galaxies at intermediate redshifts. We compare this
information with what previously known from IRAS and discuss the average
properties of radio galaxies in the redshift range 0.2 - 0.8. The FIR emission
cannot be accounted for by extrapolation of the synchrotron radio spectrum and
we attribute it to thermal dust emission. The average FIR luminosity is >=
6*10^11 L_sun. Over the observed frequency range the infrared spectrum can be
described by a power law with spectral index alpha >~1.0 +/- 0.2. Assuming the
emission to be due to dust, a range of temperatures is required, from >=80 K to
\~25 K. The dust masses required to explain the FIR emission range from 5*10^5
M_sun for the hotter component up to 2*10^8 M_sun for the colder one.
(abridged)Comment: Astronomy & Astrophysics, in press, 16 pages, 2 Figure
Coherent Vector Meson Photoproduction with Nuclear Breakup in Relativistic Heavy Ion Collisions
Relativistic heavy ions are copious sources of virtual photons. The large
photon flux gives rise to a substantial photonuclear interaction probability at
impact parameters where no hadronic interactions can occur. Multiple
photonuclear interactions in a single collision are possible. In this letter,
we use mutual Coulomb excitation of both nuclei as a tag for moderate impact
parameter collisions. We calculate the cross section for coherent vector meson
production accompanied by mutual excitation, and show that the median impact
parameter is much smaller than for untagged production. The vector meson
rapidity and transverse momentum distribution are very different from untagged
exclusive vector meson production.Comment: 14 pages, including 4 figure
Evidence for Ordered Magnetic Fields in the Quasar Environment
At a distance of 20 pc from the purported supermassive black hole powering
quasars, temperatures and densities are inferred from optical observations to
be ~10**4 K and ~10**4 cm**-3. Here we present Very Long Baseline
Interferometry radio observations revealing organized magnetic fields on the
parsec scale in the hot plasma surrounding the quasar OQ172 (1442+101). These
magnetic fields rotate the plane of polarization of the radio emission coming
from the core and inner jet of the quasar. The derived rotation measure (RM) is
40,000 rad m**-2 in the rest frame of the quasar. Only 10 mas (a projected
distance of 68 pc) from the nucleus the jet absolute values of RM fall to less
than 100 rad m**-2.Comment: in press at ApJ Letters, 12 page LaTeX document includes 4 postscript
figure
Stoics against stoics in Cudworth's "A Treatise of Freewill"
In his 'A Treatise of Freewill', Ralph Cudworth argues against Stoic determinism by drawing on what he takes to be other concepts found in Stoicism, notably the claim that some things are ‘up to us’ and that these things are the product of our choice. These concepts are central to the late Stoic Epictetus and it appears at first glance as if Cudworth is opposing late Stoic voluntarism against early Stoic determinism. This paper argues that in fact, despite his claim to be drawing on Stoic doctrine, Cudworth uses these terms with a meaning first articulated only later, by the Peripatetic commentator Alexander of Aphrodisias
- …