64 research outputs found
The X-ray emission of the Intermediate Polar V709 Cas
We present RXTE and BeppoSAX observations of the Intermediate Polar V709 Cas
acquired in 1997 and 1998 respectively. The X-ray emission from 0.1 to 30keV is
dominated by the strong pulsation at the rotational period of the white dwarf
(312.8s) with no sign of orbital or sideband periodicity, thus confirming
previous ROSAT results. However, we detect changes in the power spectra between
the two epochs. While the second harmonic of the spin period is present during
both observations, the first harmonic is absent in 1997. An increase in the
amplitude of the spin pulsation is found between 1997 and 1998 together with a
decrease in the X-ray flux. The average X-ray spectrum from 0.1 to 100keV is
well described by an isothermal plasma at ~27keV plus complex absorption and an
iron K(alpha) fluorescent line, due to reflection from the white dwarf surface.
The rotational pulsation is compatible with complex absorption dominating the
low energy range, while the high energy spin modulation can be attributed to
tall shocks above the accreting poles. The RXTE spectrum in 1997 also shows the
presence of an absorption edge from ionized iron likely located in the
pre-shock accretion flow. The variations along the spin period of the partial
covering absorber and of reflection are compatible with the classical accretion
curtain scenario. The variations in the spin pulse characteristics and X-ray
flux indicate that V709 Cas experiences changes in the mass accretion rate on
timescales from months to years.Comment: 12 pages, A&A Latex, 9 figures, accepted for publication in A&
Interferometric Astrometry with Hubble Space Telescope Fine Guidance Sensor 3:The Parallax of the Cataclysmic Variable TV Columbae
TV Columbae (TV Col) is a 13th magnitude Intermediate Polar (IP) Cataclysmic
Variable (CV), with multiple periods found in the light curves. Past estimates
predicted a distance of 400 parsec to greater than 500 parsec. Recently
completed Hubble Space Telescope (HST) Fine Guidance Sensor (FGS)
interferometric observations allow us to determine the first trigonometric
parallax to TV Col. This determination puts the distance of TV Col at 368
-15+17 parsecs.
CD-32 2376, a 10th magnitude Tycho Catalog star, is a reference star in the
TV Col frame. We find a distance of $127.7 -1+1 parsecs.Comment: 24 pages, 2 figure
Spitzer IRS Spectroscopy of Intermediate Polars: Constraints on Mid-Infrared Cyclotron Emission
We present Spitzer Infrared Spectrograph (IRS) observations of eleven
intermediate polars (IPs). Spectra covering the wavelength range from 5.2 to 14
m are presented for all eleven objects, and longer wavelength spectra are
presented for three objects (AE Aqr, EX Hya, and V1223 Sgr). We also present
new, moderate resolution (R 2000) near-infrared spectra for five of the
program objects. We find that, in general, the mid-infrared spectra are
consistent with simple power laws that extend from the optical into the
mid-infrared. There is no evidence for discrete cyclotron emission features in
the near- or mid-infrared spectra for any of the IPs investigated. If cyclotron
emission is occurring in the 5.2 to 14.0 m bandpass it constitutes less
than 1% of the bolometric luminosity of any of the IPs. We discuss our results
in the context of the standard model for IPs.Comment: 43 pages, including 17 figures, accepted by the Astrophysical Journa
Discovery of extreme particle acceleration in the microquasar Cygnus X-3
The study of relativistic particle acceleration is a major topic of
high-energy astrophysics. It is well known that massive black holes in active
galaxies can release a substantial fraction of their accretion power into
energetic particles, producing gamma-rays and relativistic jets. Galactic
microquasars (hosting a compact star of 1-10 solar masses which accretes matter
from a binary companion) also produce relativistic jets. However, no direct
evidence of particle acceleration above GeV energies has ever been obtained in
microquasar ejections, leaving open the issue of the occurrence and timing of
extreme matter energization during jet formation. Here we report the detection
of transient gamma-ray emission above 100 MeV from the microquasar Cygnus X-3,
an exceptional X-ray binary which sporadically produces powerful radio jets.
Four gamma-ray flares (each lasting 1-2 days) were detected by the AGILE
satellite simultaneously with special spectral states of Cygnus X-3 during the
period mid-2007/mid-2009. Our observations show that very efficient particle
acceleration and gamma-ray propagation out of the inner disk of a microquasar
usually occur a few days before major relativistic jet ejections. Flaring
particle energies can be thousands of times larger than previously detected
maximum values (with Lorentz factors of 105 and 102 for electrons and protons,
respectively). We show that the transitional nature of gamma-ray flares and
particle acceleration above GeV energies in Cygnus X-3 is clearly linked to
special radio/X-ray states preceding strong radio flares. Thus gamma-rays
provide unique insight into the nature of physical processes in microquasars.Comment: 29 pages (including Supplementary Information), 8 figures, 2 tables
version submitted to Nature on August 7, 2009 (accepted version available at
http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature08578.pdf
A High Statistics Search for Ultra-High Energy Gamma-Ray Emission from Cygnus X-3 and Hercules X-1
We have carried out a high statistics (2 Billion events) search for
ultra-high energy gamma-ray emission from the X-ray binary sources Cygnus X-3
and Hercules X-1. Using data taken with the CASA-MIA detector over a five year
period (1990-1995), we find no evidence for steady emission from either source
at energies above 115 TeV. The derived upper limits on such emission are more
than two orders of magnitude lower than earlier claimed detections. We also
find no evidence for neutral particle or gamma-ray emission from either source
on time scales of one day and 0.5 hr. For Cygnus X-3, there is no evidence for
emission correlated with the 4.8 hr X-ray periodicity or with the occurrence of
large radio flares. Unless one postulates that these sources were very active
earlier and are now dormant, the limits presented here put into question the
earlier results, and highlight the difficulties that possible future
experiments will have in detecting gamma-ray signals at ultra-high energies.Comment: 26 LaTeX pages, 16 PostScript figures, uses psfig.sty to be published
in Physical Review
The Large Observatory For X-ray Timing: LOFT
LOFT, the Large Observatory for X-ray Timing, is a new space mission concept devoted to observations of Galactic and extra-Galactic sources in the X-ray domain with the main goals of probing gravity theory in the very strong field environment of black holes and other compact objects, and investigating the state of matter at supra-nuclear densities in neutron stars. The instruments on-board LOFT, the Large area detector and the Wide Field Monitor combine for the first time an unprecedented large effective area (~10 m2 at 8 keV) sensitive to X-ray photons mainly in the 2-30 keV energy range and a spectral resolution approaching that of CCD-based telescopes (down to 200 eV at 6 keV). LOFT is currently competing for a launch of opportunity in 2022 together with the other M3 mission candidates of the ESA Cosmic Vision Progra
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
A giant outburst two years before the core-collapse of a massive star
The death of massive stars produces a variety of supernovae, which are linked
to the structure of the exploding stars. The detection of several precursor
stars of Type II supernovae have been reported, however we do not yet have
direct information on the progenitors of the hydrogen deficient Type Ib and Ic
supernovae. Here we report that the peculiar Type Ib supernova SN2006jc is
spatially coincident with a bright optical transient that occurred in 2004.
Spectroscopic and photometric monitoring of the supernova leads us to suggest
that the progenitor was a carbon-oxygen Wolf-Rayet star embedded within a
helium-rich circumstellar medium. There are different possible explanations for
this pre-explosion transient. It appears similar to the giant outbursts of
Luminous Blue Variables (LBV) of 60-100 solar mass stars, however the
progenitor of SN2006jc was helium and hydrogen deficient. An LBV-like outburst
of a Wolf-Rayet star could be invoked, but this would be the first
observational evidence of such a phenomenon. Alternatively a massive binary
system composed of an LBV which erupted in 2004, and a Wolf-Rayet star
exploding as SN2006jc, could explain the observations.Comment: 15 pages, 4 figures (supplementary information included). Originally
submitted on Nov. 24, 2006; twice revised. Final version submitted to Natur
Fungal Planet description sheets: 1383â1435
Novel species of fungi described in this study include those from various countries as follows: Australia, Agaricus albofoetidus, Agaricus aureoelephanti and Agaricus parviumbrus on soil, Fusarium ramsdenii from stem cankers of Araucaria cunninghamii, Keissleriella sporoboli from stem of Sporobolus natalensis, Leptosphaerulina queenslandica and Pestalotiopsis chiaroscuro from leaves of Sporobolus natalensis, Serendipita petricolae as endophyte from roots of Eriochilus petricola, Stagonospora tauntonensis from stem of Sporobolus natalensis, Teratosphaeria carnegiei from leaves of Eucalyptus grandis Ă E. camaldulensis and Wongia ficherai from roots of Eragrostis curvula. Canada, Lulworthia fundyensis from intertidal wood and Newbrunswickomyces abietophilus (incl. Newbrunswickomyces gen. nov.)on buds of Abies balsamea. Czech Republic, Geosmithia funiculosa from a bark beetle gallery on Ulmus minor and Neoherpotrichiella juglandicola (incl. Neoherpotrichiella gen. nov.)from wood of Juglans regia. France, Aspergillus rouenensis and Neoacrodontium gallica (incl. Neoacrodontium gen. nov.)from bore dust of Xestobium rufovillosum feeding on Quercus wood, Endoradiciella communis (incl. Endoradiciella gen. nov.)endophyticin roots of Microthlaspi perfoliatum and Entoloma simulans on soil. India, Amanita konajensis on soil and Keithomyces indicus from soil. Israel, Microascus rothbergiorum from Stylophora pistillata. Italy, Calonarius ligusticus on soil. Netherlands , Appendopyricularia juncicola (incl. Appendopyricularia gen. nov.), Eriospora juncicola and Tetraploa juncicola on dead culms of Juncus effusus, Gonatophragmium physciae on Physcia caesia and Paracosmospora physciae (incl. Paracosmospora gen. nov.)on Physcia tenella, Myrmecridium phragmitigenum on dead culm of Phragmites australis, Neochalara lolae on stems of Pteridium aquilinum, Niesslia nieuwwulvenica on dead culm of undetermined Poaceae, Nothodevriesia narthecii (incl. Nothodevriesia gen. nov.) on dead leaves of Narthecium ossifragum and Parastenospora pini (incl. Parastenospora gen. nov.)on dead twigs of Pinus sylvestris. Norway, Verticillium bjoernoeyanum from sand grains attached to a piece of driftwood on a sandy beach. Portugal, Collybiopsis cimrmanii on the base of living Quercus ilex and amongst dead leaves of Laurus and herbs. South Africa , Paraproliferophorum hyphaenes (incl. Paraproliferophorum gen. nov.) on living leaves of Hyphaene sp. and Saccothecium widdringtoniae on twigs of Widdringtonia wallichii. Spain, Cortinarius dryosalor on soil, Cyphellophora endoradicis endophytic in roots of Microthlaspi perfoliatum, Geoglossum laurisilvae on soil, Leptographium gemmatum from fluvial sediments, Physalacria auricularioides from a dead twig of Castanea sativa , Terfezia bertae and Tuber davidlopezii in soil. Sweden, Alpova larskersii, Inocybe alpestris and Inocybe boreogodeyi on soil. Thailand, Russula banwatchanensis, Russula purpureoviridis and Russula lilacina on soil. Ukraine, Nectriella adonidis on over wintered stems of Adonis vernalis. USA, Microcyclus jacquiniae from living leaves of Jacquinia keyensis and Penicillium neoherquei from a minute mushroom sporocarp. Morphological and culture characteristics are supported by DNA barcodes
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