Gamma-ray flares from black hole coronae

We present results of a study of non-thermal, time-dependent particle injection in a corona around an accreting black hole. We model the spectral energy distribution of high-energy flares in this scenario. We consider particle interactions with magnetic, photon and matter fields in the black hole magnetosphere. Transport equations are solved for all species of particles and the electromagnetic output is predicted. Photon annihilation is taken into account for the case of systems with early-type donor stars.Comment: 7 pages, 7 figures. Accepted for publication in the Proceedings of the 25th Texas Symposium on Relativistic Astrophysics, held in Heidelberg, December 06-10, 201

Gravitational Lensing of Neutrino from Collapsars

We study neutrino emission from long gamma-ray bursts. The collapse of very massive stars to black holes, and the consequent jet formation, are expected to produce high-energy neutrinos through photomeson production. Such neutrinos can escape from the source and travel up to the Earth. We focus on the case of Population III progenitors for gamma-ray bursts. Neutrinos can be the only source of information of the first stars formed in the universe. The expected signal is rather weak, but we propose that gravitational lensing by nearby supermassive black holes might enhance the neutrino emission in some cases. We implement a Monte Carlo analysis to ponder the statistical significance of this scenario. We suggest that an observational strategy based on gravitational lensing could lead to the detection of neutrinos from the re-ionization era of the universe with current instrumentation.Comment: 5 pages, 3 figures. Accepted for publication in the Proceedings of the First Argentine-Brazilian Meeting on Gravitation, Astrophysics and Cosmology, held in Foz do Igua\c{c}u, October, 201

A revision of the Neotropical predaceous midges of Brachypogon (Brachypogon) Kieffer (Diptera: Ceratopogonidae)

This revision of the Neotropical predaceous midges of the genus Brachypogon (Brachypogon) Kieffer, recognizes 18 extant species, including the following 12 new species: Brachypogon (B.) apunctipennis, bifidus, bimaculatus, ecuadorensis, ethelae, insularis, monicae, pseudoparaensis, schmitzi, spatuliformis, telesfordi, and woodruffi. Two species groups are recognized, the fuscivenosus and impar groups. The hitherto unknown male of B. paraensis Wirth & Blanton is described and illustrated, and the female of that species as well as both sexes of B. impar (Johannsen) and B. fuscivenosus (Lutz) are redescribed and illustrated. Diagnoses are provided for previously described species, as well as a key for the recognition of all Neotropical species. New records of B. impar are from Brazil, Colombia, and Argentina

A model for the polarization of the high-energy radiation from accreting black holes: the case of XTE J1118+480

The high-energy emission ($400$ keV $- 2$ MeV) of Cygnus X-1 --the most well-studied Galactic black hole-- was recently found to be strongly polarized. The origin of this radiation is still unknown. In this work, we suggest that it is the result of non-thermal processes in the hot corona around the accreting compact object, and study the polarization of high-energy radiation expected for black hole binaries. Two contributions to the total magnetic field are taken into account in our study, a small scale random component related to the corona, and an ordered magnetic field associated with the accretion disk. The degree of polarization of gamma-ray emission for this particular geometry is estimated, as well as the angle of the polarization vector. We obtain that the corona+disk configuration studied in this work can account for the high degree of polarization of gamma-rays detected in galactic black holes without the need of a relativistic jet; specific predictions are made for sources in a low-hard state. In particular, the model is applied to the transient source \xtee; we show that if a new outburst of \xte is observed, then its gamma-ray polarization should be measurable by future instruments, such as ASTRO-H or the proposed ASTROGAM.Comment: 8 pages, 6 figures, accepted for publication in A&

Primordial black hole evolution in two-fluid cosmology

Several processes in the early universe might lead to the formation of primordial black holes with different masses. These black holes would interact with the cosmic plasma through accretion and emission processes. Such interactions might have affected the dynamics of the universe and generated a considerable amount of entropy. In this paper we investigate the effects of the presence of primordial black holes on the evolution of the early universe. We adopt a two-fluid cosmological model with radiation and a primordial black hole gas. The latter is modelled with different initial mass functions taking into account the available constraints over the initial primordial black hole abundances. We find that certain populations with narrow initial mass functions are capable to produce significant changes in the scale factor and the entropy.Comment: 8 pages, 7 figures. Modified to match the published versio

Dependence of the electronic structure of self-assembled InGaAs/GaAs quantum dots on height and composition

While electronic and spectroscopic properties of self-assembled In_{1-x}Ga_{x}As/GaAs dots depend on their shape, height and alloy compositions, these characteristics are often not known accurately from experiment. This creates a difficulty in comparing measured electronic and spectroscopic properties with calculated ones. Since simplified theoretical models (effective mass, k.p, parabolic models) do not fully convey the effects of shape, size and composition on the electronic and spectroscopic properties, we offer to bridge the gap by providing accurately calculated results as a function of the dot height and composition. Prominent results are the following. (i) Regardless of height and composition, the electron levels form shells of nearly degenerate states. In contrast, the hole levels form shells only in flat dots and near the highest hole level (HOMO). (ii) In alloy dots, the electrons' ``s-p'' splitting depends weakly on height, while the ``p-p'' splitting depends non-monotonically. In non-alloyed InAs/GaAs dots, both these splittings depend weakly on height. For holes in alloy dots, the ``s-p'' splitting decreases with increasing height, whereas the ``p-p'' splitting remains nearly unchaged. Shallow, non-alloyed dots have a ``s-p'' splitting of nearly the same magnitude, whereas the ``p-p'' splitting is larger. (iii) As height increases, the ``s'' and ``p'' character of the wavefunction of the HOMO becomes mixed, and so does the heavy- and light-hole character. (iv) In alloy dots, low-lying hole states are localized inside the dot. Remarkably, in non-alloyed InAs/GaAs dots these states become localized at the interface as height increases. This localization is driven by the biaxial strain present in the nanostructure.Comment: 14 pages, 12 figure