Geomagnetic field and altitude effects on the performance of future IACT arrays

The performance of IACT's arrays is sensitive to the altitude and geomagnetic field (GF) of the observatory site. Both effects play important role in the region of the sub-TeV gamma-ray measurements. We investigate the influence of GF on detection rates and the energy thresholds for five possible locations of the future CTA observatory using the Monte Carlo simulations. We conclude that the detection rates of gamma rays and the energy thresholds of the arrays can be fitted with linear functions of the altitude and the component of the GF perpendicular to the shower axis core. These results can be directly extrapolated for any possible localization of the CTA. In this paper we also show the influence of both geophysical effects on the images of shower and gamma/hadron separation.Comment: 4 pages, 6 figures, two-column. Contribution to ICRC 2013 proceeding

Gamma-rays from binary system with energetic pulsar and Be star with aspherical wind: PSR B1259-63/SS2883

At least one massive binary system containing an energetic pulsar, PSR B1259-63/SS2883, has been recently detected in the TeV gamma-rays by the HESS telescopes. These gamma-rays are likely produced by particles accelerated in the vicinity of the pulsar and/or at the pulsar wind shock, in comptonization of soft radiation from the massive star. However, the process of gamma-ray production in such systems can be quite complicated due to the anisotropy of the radiation field, complex structure of the pulsar wind termination shock and possible absorption of produced gamma-rays which might initiate leptonic cascades. In this paper we consider in detail all these effects. We calculate the gamma-ray light curves and spectra for different geometries of the binary system PSR B1259-63/SS2883 and compare them with the TeV gamma-ray observations. We conclude that the leptonic IC model, which takes into account the complex structure of the pulsar wind shock due to the aspherical wind of the massive star, can explain the details of the observed gamma-ray light curve.Comment: 12 pages, 11 figures, accepted for publication in MNRA

Energetics of Tev Blazars and Physical Constraints on their Emission Regions

Using multi-frequency spectra from TeV blazars in quiescent states, we obtain the physical parameters of the emission region of blazars within the framework of the one-zone synchrotron self-Compton (SSC) model. We numerically calculate the steady-state energy spectra of electrons by self-consistently taking into account the effects of radiative cooling with a proper account of the Klein-Nishina effects. Here electrons are assumed to be injected with a power-law spectrum and to escape on a finite time scale, which naturally leads to the existence of a break energy scale. Although we do not use time variabilities but utilize a model of electron escape to constrain the size of the emission region, the resultant size turns out to be similar to that obtained based on time variabilities. Through detailed comparison of the predicted emission spectra with observations, we find that for Mrk 421, Mrk 501, and PKS 2155--304, the energy density of relativistic electrons is about an order of magnitude larger than that of magnetic fields with an uncertainty within a factor of a few.Comment: Accepted for publication in Ap

Analyzing the Multiwavelength Spectrum and Variability of BL Lacertae During the July 1997 Outburst

The multiwavelength spectrum of BL Lacertae during its July 1997 outburst is analyzed in terms of different variations of the homogeneous leptonic jet model for the production of high-energy radiation from blazars. We find that a two-component gamma-ray spectrum, consisting of a synchrotron self-Compton and an external Compton component, is required in order to yield an acceptable fit to the broadband spectrum. Our analysis indicates that in BL Lac, unlike other BL Lac objects, the broad emission line region plays an important role for the high-energy emission. Several alternative blazar jet models are briefly discussed. In the appendix, we describe the formalism in which the process of Comptonization of reprocessed accretion disk photons is treated in the previously developed blazar jet simulation code which we use.Comment: Now accepted for publication in The Astronomical Journal. Significantly extended discussion w.r.t. original version. 3 Figures included using epsf.sty, rotate.st

Tryptophan metabolism and bacterial commensals prevent fungal dysbiosis in Arabidopsis roots

In nature, roots of healthy plants are colonized by multikingdom microbial communities that include bacteria, fungi, and oomycetes. A key question is how plants control the assembly of these diverse microbes in roots to maintain host–microbe homeostasis and health. Using microbiota reconstitution experiments with a set of immunocompromised Arabidopsis thaliana mutants and a multikingdom synthetic microbial community (SynCom) representative of the natural A. thaliana root microbiota, we observed that microbiota-mediated plant growth promotion was abolished in most of the tested immunocompromised mutants. Notably, more than 40% of between-genotype variation in these microbiota-induced growth differences was explained by fungal but not bacterial or oomycete load in roots. Extensive fungal overgrowth in roots and altered plant growth was evident at both vegetative and reproductive stages for a mutant impaired in the production of tryptophan-derived, specialized metabolites (cyp79b2/b3). Microbiota manipulation experiments with single- and multikingdom microbial SynComs further demonstrated that 1) the presence of fungi in the multikingdom SynCom was the direct cause of the dysbiotic phenotype in the cyp79b2/b3 mutant and 2) bacterial commensals and host tryptophan metabolism are both necessary to control fungal load, thereby promoting A. thaliana growth and survival. Our results indicate that protective activities of bacterial root commensals are as critical as the host tryptophan metabolic pathway in preventing fungal dysbiosis in the A. thaliana root endosphere

On the rapid TeV flaring activity of Markarian 501

Aims: We investigate the one-zone SSC model of TeV blazars in the presence of electron acceleration. In this picture electrons reach a maximum energy where acceleration saturates from a combination of synchrotron and inverse Compton scattering losses. Methods: We solve the spatially averaged kinetic equations which describe the simultaneous evolution of particles and photons, obtaining the multi-wavelength spectrum as a function of time. Results: We apply the model to the rapid flare of Mrk 501 of July 9, 2005 as this was observed by the MAGIC telescope and obtain the relevant parameters for the pre-flare quasi steady state and the ones during the flare. We show that a hard lag flare can be obtained with parameters which lie well within the range already accepted for this source. Especially the choice of a high value of the Doppler factor seems to be necessary.Comment: 4 pages, 4 figures, to appear in A&A (Letters

Phase diagram of neutron-rich nuclear matter and its impact on astrophysics

Dense matter as it can be found in core-collapse supernovae and neutron stars is expected to exhibit different phase transitions which impact the matter composition and equation of state, with important consequences on the dynamics of core-collapse supernova explosion and on the structure of neutron stars. In this paper we will address the specific phenomenology of two of such transitions, namely the crust-core solid-liquid transition at sub-saturation density, and the possible strange transition at super-saturation density in the presence of hyperonic degrees of freedom. Concerning the neutron star crust-core phase transition at zero and finite temperature, it will be shown that, as a consequence of the presence of long-range Coulomb interactions, the equivalence of statistical ensembles is violated and a clusterized phase is expected which is not accessible in the grand-canonical ensemble. A specific quasi-particle model will be introduced to illustrate this anomalous thermodynamics and some quantitative results relevant for the supernova dynamics will be shown. The opening of hyperonic degrees of freedom at higher densities corresponding to the neutron stars core modifies the equation of state. The general characteristics and order of phase transitions in this regime will be analyzed in the framework of a self-consistent mean-field approach.Comment: Invited Talk given at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS