1,914 research outputs found
Gamma-Ray Pulsars: Beaming Evolution, Stats and Unident. EGRET Sources
We compute the variation of the beaming fraction with the efficiency of high
energy gamma-ray production in the outer gap pulsar model of Romani and
Yadigaroglu. This allows us to correct the fluxes observed for pulsars in the
EGRET band and to derive a simple estimate of the variation of efficiency with
age. Integration of this model over the population of young neutron stars gives
the expected number of gamma-ray pulsars along with their distributions in age
and distance. This model also shows that many of the unidentified EGRET plane
sources should be pulsars, and predicts the gamma-ray fluxes of known radio
pulsars. The contribution of unresolved pulsars to the background flux in the
EGRET band is found to be about 5 %. For an animation of our pulsar model see
http://geminga.stanford.edu/users/ion/home.html .Comment: 6 pages, all in postscript, with figures Animation of pulsar model at
http://geminga.stanford.edu/users/ion/home.htm
-Ray Pulsars: Emission Zones and Viewing Geometries
There are now a half dozen young pulsars detected in high energy photons by
the Compton GRO, showing a variety of emission efficiencies and pulse profiles.
We present here a calculation of the pattern of high energy emission on the sky
in a model which posits -ray production by charge depleted gaps in the
outer magnetosphere. This model accounts for the radio to -ray pulse
offsets of the known pulsars, as well as the shape of the high energy pulse
profiles. We also show that of emitting young radio pulsars will not
be detected due to beaming effects, while the number of
radio-selected -ray pulsars will be viewed only high energies. Finally
we compute the polarization angle variation and find that the previously
misunderstood optical polarization sweep of the Crab pulsar arises naturally in
this picture. These results strongly support an outer-magnetosphere location
for the ray emission.Comment: 17 pages Latex with aaspp macros and PostScript figures. mpeg
simulations available at
http://geminga.stanford.edu/home/ion/pulsar/frames.htm
Control of Fusarium head blight and accumulation of deoxynivalenol in durum wheat grain, semolina and bran
To verify the effects of E.B.I. fungicides on Fusarium head blight and to determine the deoxynivalenol (DON) content in grain, semolina and bran, three separate trials were carried out in fields near Bologna (Italy) on susceptible durum wheat varieties artificially inoculated with F. graminearum and F. culmorum, responsible of this disease. Treatments with bromuconazole, prochloraz, tebuconazole applied in the field had significantly reduced the FHB disease incidence and severity by 56% and 73% respectively and the numbers of kernels infected by F. graminearum and F. culmorum by 66.6%. These products reduced also DON content in kernels, semolina and bran, compared to the non treated samples. The correlation (r) between DON and the incidence of F. graminearum and F. culmorum infected kernels was in the Original Sample (OS) 0.90
X-ray Emission from the Guitar Nebula
We have detected weak soft X-ray emission from the Pulsar Wind Nebula trailing the high velocity star PSR 2224+65 (the `Guitar Nebula'). This X-ray flux gives evidence of \gamma~10^7 eV particles in the pulsar wind and constrains the properties of the post-shock flow. The X-ray emission is most easily understood if the shocked pulsar wind is partly confined in the nebula and if magnetic fields in this zone can grow to near equipartition values
The Gamma-Ray Blazar Content of the Northern Sky
Using survey data, we have re-evaluated the correlation of flat spectrum
radio sources with EGRET sources in the Northern sky. A likelihood analysis
incorporating the radio and X-ray properties and the Gamma-ray source
localization is used to gauge the reliability of associations and to search for
counterparts of previously unidentified EGRET sources. Above |b|=10deg, where
the classification is complete, we find that 70% of the Northern EGRET sources
have counterparts similar to the bright EGRET blazars. For several of these we
identify known blazar counterparts more likely than the earlier proposed 3EG
association; for ~20 we have new identifications. Spectroscopic confirmation of
these candidates is in progress and we have found flat spectrum radio quasars
and BL Lac counterparts with redshifts as high as 4. We also find strong
evidence for a set of 28 objects with no plausible counterpart like the known
EGRET Blazars. These thus represent either a new extragalactic population or a
population of Galactic objects with a large scale height. The survey has been
extended into the plane, where we find several new blazar candidates; the bulk
of the sources are, however, Galactic. Looking ahead to the GLAST era we
predict that several of the present 3EG sources are composite and that higher
resolution data will break these into multiple Blazar IDs.Comment: 13 pages, 6 figures, submitted to Ap
Simultaneous Absolute Timing of the Crab Pulsar at Radio and Optical Wavelengths
The Crab pulsar emits across a large part of the electromagnetic spectrum.
Determining the time delay between the emission at different wavelengths will
allow to better constrain the site and mechanism of the emission. We have
simultaneously observed the Crab Pulsar in the optical with S-Cam, an
instrument based on Superconducting Tunneling Junctions (STJs) with s time
resolution and at 2 GHz using the Nan\c{c}ay radio telescope with an instrument
doing coherent dedispersion and able to record giant pulses data. We have
studied the delay between the radio and optical pulse using simultaneously
obtained data therefore reducing possible uncertainties present in previous
observations. We determined the arrival times of the (mean) optical and radio
pulse and compared them using the tempo2 software package. We present the most
accurate value for the optical-radio lag of 255 21 s and suggest the
likelihood of a spectral dependence to the excess optical emission asociated
with giant radio pulses.Comment: 8 pages; accepted for publication in Astronomy and Astrophysic
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