2,084 research outputs found
Flaring gamma-ray emission from high redshift blazars
High redshift blazars are among the most powerful objects in the Universe.
Although they represent a significant fraction of the extragalactic hard X-ray
sky, they are not commonly detected in gamma-rays. High redshift (z>2) objects
represent <10 per cent of the AGN population observed by Fermi so far, and
gamma-ray flaring activity from these sources is even more uncommon. The
characterization of the radio-to-gamma-ray properties of high redshift blazars
represent a powerful tool for the study of both the energetics of such extreme
objects and the Extragalactic Background Light. We present results of a
multi-band campaign on TXS 0536+145, which is the highest redshift flaring
gamma-ray blazar detected so far. At the peak of the flare the source reached
an apparent isotropic gamma-ray luminosity of 6.6x10^49 erg/s, which is
comparable with the luminosity observed from the most powerful blazars. The
physical properties derived from the multi-wavelength observations are then
compared with those shown by the high redshift population. In addition
preliminary results from the high redshift flaring blazar PKS 2149-306 will be
discussed.Comment: 2014 Fermi Symposium proceedings - eConf C14102.
Investigating powerful jets in radio-loud Narrow Line Seyfert 1s
We report results on multiband observations from radio to gamma-rays of the
two radio-loud narrow-line Seyfert 1 (NLSy1) galaxies PKS 2004-447 and
J1548+3511. Both sources show a core-jet structure on parsec scale, while they
are unresolved at the arcsecond scale. The high core dominance and the high
variability brightness temperature make these NLSy1 galaxies good gamma-ray
source candidates. Fermi-LAT detected gamma-ray emission only from PKS
2004-447, with a gamma-ray luminosity comparable to that observed in blazars.
No gamma-ray emission is observed for J1548+3511. Both sources are variable in
X-rays. J1548+3511 shows a hardening of the spectrum during high activity
states, while PKS 2004-447 has no spectral variability. A spectral steepening
likely related to the soft excess is hinted below 2 keV for J1548+3511, while
the X-ray spectra of PKS 2004-447 collected by XMM-Newton in 2012 are described
by a single power-law without significant soft excess. No additional absorption
above the Galactic column density or the presence of an Fe line is detected in
the X-ray spectra of both sources.Comment: 16 pages, 8 figures, accepted for publication in MNRA
A negative effect of a pathogen on its vector? A plant pathogen increases the vulnerability of its vector to attack by natural enemies
Plant pathogens that are dependent on arthropod vectors for transmission from host to host may enhance their own success by promoting vector survival and/or performance. The effect of pathogens on vectors may be direct or indirect, with indirect effects mediated by increases in host quality or reductions in the vulnerability of vectors to natural enemies. We investigated whether the bird cherry-oat aphid Rhopalosiphum padi, a vector of cereal yellow dwarf virus (CYDV) in wheat, experiences a reduction in rates of attack by the parasitoid wasp Aphidius colemani when actively harboring the plant pathogen. We manipulated the vector status of aphids (virus carrying or virus free) and evaluated the impact on the rate of attack by wasps. We found that vector status did not influence the survival or fecundity of aphids in the absence of parasitoids. However, virus-carrying aphids experienced higher rates of parasitism and greater overall population suppression by parasitoid wasps than virus-free aphids. Moreover, virus-carrying aphids were accepted as hosts by wasps more often than virus-free aphids, with a greater number of wasps stinging virus-carrying aphids following assessment by antennal palpations than virus-free aphids. Therefore, counter to the prevailing idea that persistent vector-borne pathogens enhance the performance of their vectors, we found that infectious aphids actively carrying a plant pathogen experience greater vulnerability to natural enemies. Our results suggest that parasitoids may contribute to the successful biological control of CYDV by disproportionately impacting virus-carrying vectors, and thus reducing the proportion of vectors in the population that are infectious
A negative effect of a pathogen on its vector? A plant pathogen increases the vulnerability of its vector to attack by natural enemies
Plant pathogens that are dependent on arthropod vectors for transmission from host to host may enhance their own success by promoting vector survival and/or performance. The effect of pathogens on vectors may be direct or indirect, with indirect effects mediated by increases in host quality or reductions in the vulnerability of vectors to natural enemies. We investigated whether the bird cherry-oat aphid Rhopalosiphum padi, a vector of cereal yellow dwarf virus (CYDV) in wheat, experiences a reduction in rates of attack by the parasitoid wasp Aphidius colemani when actively harboring the plant pathogen. We manipulated the vector status of aphids (virus carrying or virus free) and evaluated the impact on the rate of attack by wasps. We found that vector status did not influence the survival or fecundity of aphids in the absence of parasitoids. However, virus-carrying aphids experienced higher rates of parasitism and greater overall population suppression by parasitoid wasps than virus-free aphids. Moreover, virus-carrying aphids were accepted as hosts by wasps more often than virus-free aphids, with a greater number of wasps stinging virus-carrying aphids following assessment by antennal palpations than virus-free aphids. Therefore, counter to the prevailing idea that persistent vector-borne pathogens enhance the performance of their vectors, we found that infectious aphids actively carrying a plant pathogen experience greater vulnerability to natural enemies. Our results suggest that parasitoids may contribute to the successful biological control of CYDV by disproportionately impacting virus-carrying vectors, and thus reducing the proportion of vectors in the population that are infectious
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