50 research outputs found
Radiative models for jets in X-ray binaries
In this work we develop a lepto-hadronic model for the electromagnetic
radiation from jets in microquasars with low-mass companion stars. We present
general results as well as applications to some specific systems, and carefully
analyze the predictions of the model in the gamma-ray band. The results will be
directly tested in the near future with the present and forthcoming space-borne
and terrestrial gamma-ray telescopes.Comment: 10 pages, 6 figures. Short summary of the main results of the
author's PhD Thesis. The full text of the thesis is available for download at
http://fcaglp.unlp.edu.ar/~gvila/thesi
A model for jets of low-mass microquasars
In this work we present a new jet model for the non-thermal broadband
emission of low-mass microquasars. We calculate the contribution of
relativistic particles, primary electrons and protons as well as secondary
muons, charged pions and electron-positron pairs, to the electromagnetic
spectrum of the sources. The distribution in energy of all particle species is
obtained for an extended, inhomogeneous region. We include detailed analysis of
particle energy losses, injection, decay and escape from the acceleration zone.
We also calculate absorption effects due to photon-photon annihilation. As an
application, we consider the case of XTE J1118+480, a well-known low-mass X-ray
binary in the galactic halo, and we present predictions about its high-energy
radiationComment: 7 pages, 6 figures. Proceedings of the 25th Texas Symposium on
Relativistic Astrophysics - TEXAS 2010, December 06-10, 2010, Heidelberg,
German
Leptonic/hadronic models for electromagnetic emission in microquasars: the case of GX 339-4
We present a general self-consistent lepto/hadronic jet model for the
non-thermal electromagnetic emission of microquasars. The model is applied to
the low-mass microquasar (LMMQ) GX 339-4 and predicts its high-energy features.
We assume that both leptons and hadrons are accelerated up to relativistic
energies by diffusive shock acceleration, and calculate their contribution to
the electromagnetic spectrum through all main radiative processes. The
radiative contribution of secondary particles (pions, muons and
electron-positron pairs) is included. We use a set of simultaneous observations
in radio and X-rays to constrain the model parameters and find the best fit to
the data. We obtain different spectral energy distributions that can explain
the observations, and make predictions for the high-energy emission.
Observations with gamma-ray instruments like Fermi can be used to test the
model and determine the proton content of the jets. Finally, we estimate the
positron injection in the surrounding medium. Our findings support the
suggested association between LMMQs and the observed distribution of the 511
keV line flux observed by INTEGRAL.Comment: 13 pages, 7 figures, accepted for publication in MNRA
High-energy signatures of binary systems of supermassive black holes
Context. Binary systems of supermassive black holes are expected to be strong
sources of long gravitational waves prior to merging. These systems are good
candidates to be observed with forthcoming space-borne detectors. Only a few of
these systems, however, have been firmly identified to date.
Aims. We aim at providing a criterion for the identification of some
supermassive black hole binaries based on the characteristics of the
high-energy emission of a putative relativistic jet launched from the most
massive of the two black holes.
Methods. We study supermassive black hole binaries where the less massive
black hole has carved an annular gap in the circumbinary disk, but nevertheless
there is a steady mass flow across its orbit. Such a perturbed disk is hotter
and more luminous than a standard thin disk in some regions. Assuming that the
jet contains relativistic electrons, we calculate its broadband spectral energy
distribution focusing on the inverse Compton up-scattering of the disk photons.
We also compute the opacity to the gamma rays produced in the jet by photon
annihilation with the disk radiation and take into account the effects of the
anisotropy of the target photon field as seen from the jet.
Results. We find that the excess of low-energy photons radiated by the
perturbed disk causes an increment in the external Compton emission from the
jet in the X-ray band, and a deep absorption feature at energies of tens of
TeVs for some sets of parameters. According to our results, observations with
Cherenkov telescopes might help in the identification of supermassive black
hole binaries, especially those black hole binaries that host primaries from
tens to hundreds of million of solar masses.Comment: 12 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
Lepto-hadronic model for the broadband emission of Cygnus X-1
Cygnus X-1 is a well observed microquasar. Broadband observations at all
wavelengths have been collected over the years. The origin of the MeV tail
observed with COMPTEL and INTEGRAL is still under debate and it has mostly been
attributed to the corona, although its high degree of polarization suggests it
is synchrotron radiation from a jet. The origin of the transient emission above
GeV is also unclear. We aim to disentangle the origin of the
broadband spectral energy distribution (SED) of Cygnus X-1, focusing
particularly on the gamma-ray emission, and to gain information on the physical
conditions inside the jets. We develop and apply a lepto-hadronic,
inhomogeneous jet model to the non-thermal SED of Cygnus X-1. We calculate the
contributions to the SED of both protons and electrons accelerated in an
extended region of the jet. We also estimate the radiation of charged
secondaries produced in hadronic interactions, through several radiative
processes. Absorption effects are considered. We produce synthetic maps of the
jets at radio wavelengths. We find two sets of model parameters that lead to
good fits of the SED. One of the models fits all the observations, including
the MeV tail. This model also predicts hadronic gamma-ray emission slightly
below the current upper limits. The flux predicted at 8.4 GHz is in agreement
with the observations available in the literature, although the synthetic
source is more compact than the imaged radio jet. Our results show that the MeV
emission in Cygnus X-1 may be jet synchrotron radiation. This depends mainly on
the strength of the jet magnetic field and the location of the injection region
of the relativistic particles. Our calculations show that there must be
energetic electrons in the jets quite far from the black hole.Comment: Accepted for publication in A&
Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies
Using publicly available Monte Carlo codes as well as compilation of
published data on p--p interactions for proton kinetic energy below 2 GeV, we
parametrize the energy spectra and production rates of -rays by simple
but quite accurate () analytical expressions in a broad range from
the kinematic threshold to PeV energies.Comment: 19 pages, 15 figures, v2 version fixes the cross reference
Non-thermal radiation from Cygnus X-1 corona
Cygnus X-1 was the first X-ray source widely accepted to be a black hole
candidate and remains among the most studied astronomical objects in its class.
The detection of non-thermal radio, hard X-rays and gamma rays reveals the fact
that this kind of objects are capable of accelerating particles up to very high
energies.
In order to explain the electromagnetic emission from Cygnus X-1 in the
low-hard state we present a model of a black hole corona with both relativistic
lepton and hadron content. We characterize the corona as a two-temperature hot
plasma plus a mixed non-thermal population in which energetic particles
interact with magnetic, photon and matter fields. Our calculations include the
radiation emitted by secondary particles (pions, muons and electron/positron
pairs). Finally, we take into account the effects of photon absorption. We
compare the results obtained from our model with data of Cygnus X-1 obtained by
the COMPTEL instrument.Comment: 6 pages, 10 figures, presented as a poster in HEPRO II, Buenos Aires,
Argentina, October 26-30 2009 / accepted for publication in Int. Jour. Mod.
Phys.
Tonic immobility in PTSD : exacerbation of emotional cardiac defense response.
Among defensive behaviors, tonic immobility (TI) is considered the last defensive resort when life is at extreme risk. Post-Traumatic Stress Disorder (PTSD) is the main psychiatric consequence resulting from exposure to traumatic events. Increasing evidence indicate an association between peritraumatic tonic immobilility and severity of PTSD. Cardiac defense response, a reactivity to perceived danger or threat, has been studied by recording heart rate changes that follows the presentation of an unpredictable intense auditory aversive stimulus. The aim of this study was to investigate potential distinctiveness in cardiac defense response among PTSD patients who presented ? compared to those that did not ? TI reaction in the laboratory setting. Patients (N = 17) completed the TI questionnaire for signs of immobility elicited by passive listening to their autobiographical trauma script. After a while, they were exposed to an intense white noise, while electrocardiogram was recorded. The heart rate during the 80 s after the noise, subtracted from baseline, was analyzed. Higher reports of TI to the trauma script were associated with stronger and sustained heart rate accelerations after the noise. The effects on cardiac defense response add to increasing evidence that some PTSD patients are prone to repeated re-experiences of TI, which may implicate in a potentially distinct pathophysiology and even a new PTSD subtype
Pervasive gaps in Amazonian ecological research
Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear un derstanding of how ecological communities respond to environmental change across time and space.3,4
While the increasing availability of global databases on ecological communities has advanced our knowledge
of biodiversity sensitivity to environmental changes,5–7 vast areas of the tropics remain understudied.8–11 In
the American tropics, Amazonia stands out as the world’s most diverse rainforest and the primary source of
Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepre sented in biodiversity databases.13–15 To worsen this situation, human-induced modifications16,17 may elim inate pieces of the Amazon’s biodiversity puzzle before we can use them to understand how ecological com munities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus
crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced
environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple or ganism groups in a machine learning model framework to map the research probability across the Brazilian
Amazonia, while identifying the region’s vulnerability to environmental change. 15%–18% of the most ne glected areas in ecological research are expected to experience severe climate or land use changes by
2050. This means that unless we take immediate action, we will not be able to establish their current status,
much less monitor how it is changing and what is being lostinfo:eu-repo/semantics/publishedVersio