7,159 research outputs found
What caused the GeV flare of PSR B1259-63 ?
PSR B1259-63 is a gamma-ray binary system composed of a high spindown pulsar
and a massive star. Non-thermal emission up to TeV energies is observed near
periastron passage, attributed to emission from high energy e+e- pairs
accelerated at the shock with the circumstellar material from the companion
star, resulting in a small-scale pulsar wind nebula. Weak gamma-ray emission
was detected by the Fermi/LAT at the last periastron passage, unexpectedly
followed 30 days later by a strong flare, limited to the GeV band, during which
the luminosity nearly reached the spindown power of the pulsar. The origin of
this GeV flare remains mysterious. We investigate whether the flare could have
been caused by pairs, located in the vicinity of the pulsar, up-scattering
X-ray photons from the surrounding pulsar wind nebula rather than UV stellar
photons, as usually assumed. Such a model is suggested by the geometry of the
interaction region at the time of the flare. We compute the gamma-ray
lightcurve for this scenario, based on a simplified description of the
interaction region, and compare it to the observations. The GeV lightcurve
peaks well after periastron with this geometry. The pairs are inferred to have
a Lorentz factor ~500. They also produce an MeV flare with a luminosity ~1e34
erg/s prior to periastron passage. A significant drawback is the very high
energy density of target photons required for efficient GeV emission. We
propose to associate the GeV-emitting pairs with the Maxwellian expected at
shock locations corresponding to high pulsar latitudes, while the rest of the
non-thermal emission arises from pairs accelerated in the equatorial region of
the pulsar wind termination shock.Comment: 6 pages, 3 figures, accepted for publication in A&
Metacognition and headache: which Is the role in childhood and adolescence?
Headache, in particular migraine, is one of the most frequent neurological symptoms in
children and adolescents and it affects about 60% of children and adolescents all over
the world. Headache can affect several areas of childâs functioning, such as school,
physical activities, peer, and family relationship. The global and severe burden of this
disease requires a multidisciplinary strategy and an effective treatment addressed all
of the patientâs needs and based on cutting-edge scientific research. In recent years,
research has focused on cognitive factors specifically in functions called metacognitive
processes. Metacognition can be defined as the knowledge, beliefs, and cognitive
processes involved in monitoring, control, and assessment of cognition. Metacognition
seems to be closely related to the ability of theory of mind, the ability to infer, and reason
about the mental states of other people in order to predict and explain own behavior.
Recent studies found a relationship between metacognitive skills and anxiety, depression,
motivation, academic performance, human social interactions, and stress symptoms.
This relationship is very interesting for headache treatment, because these factors are
the most commonly reported triggers in this disorder and there is a high comorbidity
with anxiety and depression in children and adolescents with headache. So, headache
and these comorbidities, in particular anxiety and depression, may have in common
persistent and maladaptive patterns of thinking which are related to maladaptive metacognitive
beliefs. Further research should assess metacognitive processes of children
and adolescents with headache in order to increase their ability to control their own
cognitive processes and consequently monitor factors which may trigger the attacks
Headache and alexithymia in children and adolescents: what Is the connection?
Background: Headache is one of the most common complaints in children and adolescents and comorbidity rates are very high and the major associated diseases are depression, anxiety, atopic disorders, sleep, and behavioral disorders. In recent years, it has been highlighted that difficulties regulating emotions such as alexithymia have also been associated with diagnosis of somatization. Methods: We carried out a mini review analyzing the relation between alexithymia and primary headache (e.g., migraine and tension type headache) in children and adolescents by synthesizing the relevant studies in the literature on PubMed, PsycINFO, and Google Scholar. Search terms were "alexithymia" combined with the "primary headache," "migraine," "tension type headache," "children," and "adolescents." Results: All analyzed studies found higher levels of alexithymia in children and adolescents with headache than control groups but there are different opinions about the relationship between headache and alexithymia. For example, some studies suggest that the association between headache and alexithymia in children may be due to an incomplete development of emotive competency or a general immature cognitive development, instead other studies found a correlation between headache symptoms, insecure attachment, and alexithymia. There seems to be also differences between children with migraine compared to those with tension type headache (TTH). Conclusion: There are some studies on adults suffering from headache or migraine and alexithymia, but there is only a moderate amount of research on pediatric age with different opinions and theories about this relationship. Further studies on children and adolescents are necessary to effectively understand this relationship and to help children to reduce headache and improve emotional consciousness
What can Simbol-X do for gamma-ray binaries?
Gamma-ray binaries have been uncovered as a new class of Galactic objects in
the very high energy sky (> 100 GeV). The three systems known today have hard
X-ray spectra (photon index ~ 1.5), extended radio emission and a high
luminosity in gamma-rays. Recent monitoring campaigns of LSI +61 303 in X-rays
have confirmed variability in these systems and revealed a spectral hardening
with increasing flux. In a generic one-zone leptonic model, the cooling of
relativistic electrons accounts for the main spectral and temporal features
observed at high energy. Persistent hard X-ray emission is expected to extend
well beyond 10 keV. We explain how Simbol-X will constrain the existing models
in connection with Fermi Space Telescope measurements. Because of its
unprecedented sensitivity in hard X-rays, Simbol-X will also play a role in the
discovery of new gamma-ray binaries, giving new insights into the evolution of
compact binaries.Comment: 4 pages, 1 figure, Proceedings of the 2nd International Simbol-X
symposium held in Paris, 2-5 December 200
Don't judge a book by its cover. factitious disorder imposed on children-report on 2 cases
Factitious Disorder Imposed on Another (FDIA), also known as Munchausen Syndrome by Proxy (MSbP) is a very serious form of child abuse. The perpetrator, usually the mother, invents symptoms or causes real ones in order to make her child appear sick. Usually this is due to a maladaptive disorder or to an excessive of attention-seeking on her part. We report here two new cases of FDIA. The first one is a 9-year-old boy with a history of convulsive episodes, reduced verbal production, mild psychomotor disorder and urological problems who underwent several invasive procedures and hospitalizations before a diagnosis of FDIA was made. The second is a 12 year-old girl with headache, abdominal pain, lipothymic episodes, seizures and a gait impairment, who was hospitalized in several hospitals before an FDIA was diagnosed
Energy loss in calorimeters using muon spectrometer information at the 2004 ATLAS Combined Test Beam.
In 2004 an ATLAS Combined Test Beam (CTB) was performed in the CERN North area. A complete slice of the barrel detector and of the muon end-cap was tested, with the following goals: pre-commission the final elements and study the combined detector performance. In this note a combined analysis using calorimeter and muon spectrometer information, based on data samples collected during this test, is presented
One-dimensional pair cascade emission in gamma-ray binaries
In gamma-ray binaries such as LS 5039 a large number of electron-positron
pairs are created by the annihilation of primary very high energy (VHE)
gamma-rays with photons from the massive star. The radiation from these
particles contributes to the total high energy gamma-ray flux and can initiate
a cascade, decreasing the effective gamma-ray opacity in the system. The aim of
this paper is to model the cascade emission and investigate if it can account
for the VHE gamma-ray flux detected by HESS from LS 5039 at superior
conjunction, where the primary gamma-rays are expected to be fully absorbed. A
one-dimensional cascade develops along the line-of-sight if the deflections of
pairs induced by the surrounding magnetic field can be neglected. A
semi-analytical approach can then be adopted, including the effects of the
anisotropic seed radiation field from the companion star. Cascade equations are
numerically solved, yielding the density of pairs and photons. In LS 5039, the
cascade contribution to the total flux is large and anti-correlated with the
orbital modulation of the primary VHE gamma-rays. The cascade emission
dominates close to superior conjunction but is too strong to be compatible with
HESS measurements. Positron annihilation does not produce detectable 511 keV
emission. This study provides an upper limit to cascade emission in gamma-ray
binaries at orbital phases where absorption is strong. The pairs are likely to
be deflected or isotropized by the ambient magnetic field, which will reduce
the resulting emission seen by the observer. Cascade emission remains a viable
explanation for the detected gamma-rays at superior conjunction in LS 5039.Comment: 8 pages, 7 figures, 1 table, accepted for publication in Astronomy
and Astrophysic
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