576 research outputs found
Radio light curves during the passage of cloud G2 near Sgr A*
We calculate radio light curves produced by the bow shock that is likely to
form in front of the G2 cloud when it penetrates the accretion disk of Sgr A*.
The shock acceleration of the radio-emitting electrons is captured
self-consistently by means of first-principles particle-in-cell simulations. We
show that the radio luminosity is expected to reach maximum in early 2013,
roughly a month after the bow shock crosses the orbit pericenter. We estimate
the peak radio flux at 1.4 GHz to be 1.4 - 22 Jy depending on the assumed orbit
orientation and parameters. We show that the most promising frequencies for
radio observations are in the 0.1<nu<1 GHz range, for which the bow shock
emission will be much stronger than the intrinsic radio flux for all the models
considered.Comment: 15 pages, 10 figures, accepted for publication in MNRA
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
Precise Localization of the Soft Gamma Repeater SGR 1627-41 and the Anomalous X-ray Pulsar AXP 1E1841-045 with Chandra
We present precise localizations of AXP 1E1841-045 and SGR 1627-41 with
Chandra. We obtained new infrared observations of SGR 1627-41 and reanalyzed
archival observations of AXP 1E1841-045 in order to refine their positions and
search for infrared counterparts. A faint source is detected inside the error
circle of AXP 1E1841-045. In the case of SGR 1627-41, several sources are
located within the error radius of the X-ray position and we discuss the
likelihood of one of them being the counterpart. We compare the properties of
our candidates to those of other known AXP and SGR counterparts. We find that
the counterpart candidates for SGR 1627-41 and SGR 1806-20 would have to be
intrinsically much brighter than AXPs to have detectable counterparts with the
observational limits currently available for these sources. To confirm the
reported counterpart of SGR 1806-20, we obtained new IR observations during the
July 2003 burst activation of the source. No brightening of the suggested
counterpart is detected, implying that the counterpart of SGR 1806-20 remains
yet to be identified.Comment: 29 pages, 4 figures, accepted for publication in Ap
Characterization of a novel zebrafish (Danio rerio) gene, wdr81, associated with cerebellar ataxia, mental retardation and dysequilibrium syndrome (CAMRQ)
Background: WDR81 (WD repeat-containing protein 81) is associated with cerebellar ataxia, mental retardation and disequilibrium syndrome (CAMRQ2, [MIM 610185]). Human and mouse studies suggest that it might be a gene of importance during neurodevelopment. This study aimed at fully characterizing the structure of the wdr81 transcript, detecting the possible transcript variants and revealing its expression profile in zebrafish, a powerful model organism for studying development and disease. Results: As expected in human and mouse orthologous proteins, zebrafish wdr81 is predicted to possess a BEACH (Beige and Chediak-Higashi) domain, a major facilitator superfamily domain and WD40-repeats, which indicates a conserved function in these species. We observed that zebrafish wdr81 encodes one open reading frame while the transcript has one 5' untranslated region (UTR) and the prediction of the 3' UTR was mainly confirmed along with a detected insertion site in the embryo and adult brain. This insertion site was also found in testis, heart, liver, eye, tail and muscle, however, there was no amplicon in kidney, intestine and gills, which might be the result of possible alternative polyadenylation processes among tissues. The 5 and 18 hpf were critical timepoints of development regarding wdr81 expression. Furthermore, the signal of the RNA probe was stronger in the eye and brain at 18 and 48 hpf, then decreased at 72 hpf. Finally, expression of wdr81 was detected in the adult brain and eye tissues, including but not restricted to photoreceptors of the retina, presumptive Purkinje cells and some neurogenic brains regions. Conclusions: Taken together these data emphasize the importance of this gene during neurodevelopment and a possible role for neuronal proliferation. Our data provide a basis for further studies to fully understand the function of wdr81. © 2015 Doldur-Balli et al
The identification of the optical companion to the binary millisecond pulsar J0610-2100 in the Galactic field
We have used deep V and R images acquired at the ESO Very Large Telescope to
identify the optical companion to the binary pulsar PSR J0610-2100, one of the
black-widow millisecond pulsars recently detected by the Fermi Gamma-ray
Telescope in the Galactic plane. We found a faint star (V~26.7) nearly
coincident (\delta r ~0".28) with the pulsar nominal position. This star is
visible only in half of the available images, while it disappears in the
deepest ones (those acquired under the best seeing conditions), thus indicating
that it is variable. Although our observations do not sample the entire orbital
period (P=0.28 d) of the pulsar, we found that the optical modulation of the
variable star nicely correlates with the pulsar orbital period and describes a
well defined peak (R~25.6) at \Phi=0.75, suggesting a modulation due to the
pulsar heating. We tentatively conclude that the companion to PSR J0610-2100 is
a heavily ablated very low mass star (~ 0.02Msun) that completely filled its
Roche Lobe.Comment: 17 pages, 5 figures - Accepted for pubblication in Ap
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