2,532 research outputs found
X-ray Emission Properties of Large Scale Jets, Hotspots and Lobes in Active Galactic Nuclei
We examine a systematic comparison of jet-knots, hotspots and radio lobes
recently observed with Chandra and ASCA. This report will discuss the origin of
their X-ray emissions and investigate the dynamics of the jets. The data was
compiled at well sampled radio (5GHz) and X-ray frequencies (1keV) for more
than 40 radio galaxies. We examined three models for the X-ray production:
synchrotron (SYN), synchrotron self-Compton (SSC) and external Compton on CMB
photons (EC). For the SYN sources -- mostly jet-knots in nearby low-luminosity
radio galaxies -- X-ray photons are produced by ultrarelativistic electrons
with energies 10-100 TeV that must be accelerated in situ. For the other
objects, conservatively classified as SSC or EC sources, a simple formulation
of calculating the ``expected'' X-ray fluxes under an equipartition hypothesis
is presented. We confirmed that the observed X-ray fluxes are close to the
expected ones for non-relativistic emitting plasma velocities in the case of
radio lobes and majority of hotspots, whereas considerable fraction of
jet-knots is too bright at X-rays to be explained in this way. We examined two
possibilities to account for the discrepancy in a framework of the
inverse-Compton model: (1) magnetic field is much smaller than the
equipartition value, and (2) the jets are highly relativistic on kpc/Mpc
scales. We concluded, that if the inverse-Compton model is the case, the X-ray
bright jet-knots are most likely far from the minimum-power condition. We also
briefly discuss the other possibility, namely that the observed X-ray emission
from all of the jet-knots is synchrotron in origin.Comment: 20 pages, 10 figures, accepted for publication in the Astrophysical
Journal, vol.62
ets-2 is a target for an akt (Protein kinase B)/jun N-terminal kinase signaling pathway in macrophages of motheaten-viable mutant mice
Ras-mediated phosphorylation of a conserved threonine residue enhances the transactivation activities of c-Ets1 and c-Ets2
The Ras oncogene products regulate the expression of genes in transformed cells, and members of the Ets family of transcription factors have been implicated in this process. To determine which Ets factors are the targets of Ras signaling pathways, the abilities of several Ets factors to activate Ras-responsive enhancer (RRE) reporters in the presence of oncogenic Ras were examined. In transient transfection assay, reporters containing RREs composed of Ets-AP-1 binding sites could be activated 30-fold in NIH 3T3 fibroblasts and 80-fold in the macrophage-like line RAW264 by the combination of Ets1 or Ets2 and Ras but not by several other Ets factors that were tested in the assay. Ets2 and Ras also superactivated an RRE composed of Ets-Ets binding sites, but the Ets-responsive promoter of the c-fms gene was not superactivated. Mutation of a threonine residue to alanine in the conserved amino-terminal regions of Ets1 and Ets2 (threonine 38 and threonine 72, respectively) abrogated the ability of each of these proteins to superactivate reporter gene expression. Phosphoamino acid analysis of radiolabeled Ets2 revealed that Ras induced normally absent threonine-specific phosphorylation of the protein. The Ras-dependent increase in threonine phosphorylation was not observed in Ets2 proteins that had the conserved threonine 72 residue mutated to alanine or serine. These data indicate that Ets1 and Ets2 are specific nuclear targets of Ras signaling events and that phosphorylation of a conserved threonine residue is a necessary molecular component of Ras-mediated activation of these transcription factors
Spectroscopic Survey of {\gamma} Doradus Stars I. Comprehensive atmospheric parameters and abundance analysis of {\gamma} Doradus stars
We present a spectroscopic survey of known and candidate \,Doradus
stars. The high-resolution, high signal-to-noise spectra of 52 objects were
collected by five different spectrographs. The spectral classification,
atmospheric parameters (\teff, , ), and chemical
composition of the stars were derived. The stellar spectral and luminosity
classes were found between G0-A7 and IV-V, respectively. The initial values for
\teff\ and \logg\ were determined from the photometric indices and spectral
energy distribution. Those parameters were improved by the analysis of hydrogen
lines. The final values of \teff, \logg\ and were derived from the iron
lines analysis. The \teff\ values were found between 6000\,K and 7900\,K, while
\logg\,values range from 3.8 to 4.5\,dex. Chemical abundances and
values were derived by the spectrum synthesis method. The values were
found between 5 and 240\,km\,s. The chemical abundance pattern of
\,Doradus stars were compared with the pattern of non-pulsating stars.
It turned out that there is no significant difference in abundance patterns
between these two groups. Additionally, the relations between the atmospheric
parameters and the pulsation quantities were checked. A strong correlation
between the and the pulsation periods of \,Doradus variables
was obtained. The accurate positions of the analysed stars in the H-R diagram
have been shown. Most of our objects are located inside or close to the blue
edge of the theoretical instability strip of \,Doradus.Comment: 18 pages, 13 figure
INTEGRAL observations of TeV plerions
Amongst the sources seen in very high gamma-rays several are associated with
Pulsar Wind Nebulae (``TeV plerions''). The study of hard X-ray/soft gamma-ray
emission is providing an important insight into the energetic particle
population present in these objects. The unpulsed emission from pulsar/pulsar
wind nebula systems in the energy range accessible to the INTEGRAL satellite is
mainly synchrotron emission from energetic and fast cooling electrons close to
their acceleration site. Our analyses of public INTEGRAL data of known TeV
plerions detected by ground based Cherenkov telescopes indicate a deeper link
between these TeV plerions and INTEGRAL detected pulsar wind nebulae. The newly
discovered TeV plerion in the northern wing of the Kookaburra region
(G313.3+0.6 powered by the middle aged PSR J1420-6048) is found to have a
previously unknown INTEGRAL counterpart which is besides the Vela pulsar the
only middle aged pulsar detected with INTEGRAL. We do not find an INTEGRAL
counterpart of the TeV plerion associated with the X-ray PWN ``Rabbit''
G313.3+0.1 which is possibly powered by a young pulsar.Comment: 4 pages, 6 figures, proceedings of conference "The Multi-Messenger
Approach to High-Energy Gamma-ray Sources" Barcelona/Spain (2006
Repetitions in infinite palindrome-rich words
Rich words are characterized by containing the maximum possible number of
distinct palindromes. Several characteristic properties of rich words have been
studied; yet the analysis of repetitions in rich words still involves some
interesting open problems. We address lower bounds on the repetition threshold
of infinite rich words over 2 and 3-letter alphabets, and construct a candidate
infinite rich word over the alphabet with a small critical
exponent of . This represents the first progress on an open
problem of Vesti from 2017.Comment: 12 page
Permutable entire functions satisfying algebraic differential equations
It is shown that if two transcendental entire functions permute, and if one
of them satisfies an algebraic differential equation, then so does the other
one.Comment: 5 page
High Energy gamma-rays From FR I Jets
Thanks to Hubble and Chandra telescopes, some of the large scale jets in
extragalactic radio sources are now being observed at optical and X-ray
frequencies. For the FR I objects the synchrotron nature of this emission is
surely established, although a lot of uncertainties - connected for example
with the particle acceleration processes involved - remain. In this paper we
study production of high energy gamma-rays in FR I kiloparsec-scale jets by
inverse-Compton emission of the synchrotron-emitting electrons. We consider
different origin of seed photons contributing to the inverse-Compton
scattering, including nuclear jet radiation as well as ambient, stellar and
circumstellar emission of the host galaxies. We discuss how future detections
or non-detections of the evaluated gamma-ray fluxes can provide constraints on
the unknown large scale jet parameters, i.e. the magnetic field intensity and
the jet Doppler factor. For the nearby sources Centaurus A and M 87, we find
measurable fluxes of TeV photons resulting from synchrotron self-Compton
process and from comptonisation of the galactic photon fields, respectively. In
the case of Centaurus A, we also find a relatively strong emission component
due to comptonisation of the nuclear blazar photons, which could be easily
observed by GLAST at energy ~10 GeV, providing important test for the
unification of FR I sources with BL Lac objects.Comment: 39 pages, 6 figures included. Modified version, accepted for
publication in Astrophysical Journa
Opposing actions of c-ets/PU.1 and c-myb protooncogene products in regulating the macrophage-specific promoters of the human and mouse colony-stimulating factor-1 receptor (c-fms) genes
The receptor for macrophage colony stimulating factor (CSF-1), the c- fms gene product, is a key determinant in the differentiation of monocytic phagocytes. Dissection of the human and mouse c-fms proximal promoters revealed opposing roles for nuclear protooncogenes in the transcriptional regulation of this gene. On the one hand, c-ets-1, c- ets-2, and the macrophage-specific factor PU.1, but not the ets-factor PEA3, trans-activated the c-fms proximal promoter. On the other hand c- myb repressed proximal promoter activity in macrophages and blocked the action of c-ets-1 and c-ets-2. Basal c-fms promoter activity was almost undetectable in the M1 leukaemia line, which expressed high levels of c- myb, but was activated as cells differentiated in response to leukemia inhibitory factor and expressed c-fms mRNA. The repressor function of c- myb depended on the COOH-terminal domain of the protein. We propose that ets-factors are necessary for the tissue-restricted expression of c-fms and that c-myb acts to ensure correct temporal expression of c- fms during myeloid differentiation
The Electron Energy Distribution in the Hotspots of Cygnus A: Filling the Gap with the Spitzer Space Telescope
Here we present Spitzer Space Telescope imaging of Cyg A with the Infrared
Array Camera, resulting in the detection of the high-energy tails or cut-offs
in the synchrotron spectra for all four hotspots of this archetype radio
galaxy. When combined with the other data collected from the literature, our
observations allow for detailed modeling of the broad-band emission for the
brightest spots A and D. We confirm that the X-ray flux detected previously
from these features is consistent with the synchrotron self-Compton radiation
for the magnetic field intensity 170 muG in spot A, and 270 muG in spot D. We
also find that the energy density of the emitting electrons is most likely
larger by a factor of a few than the energy density of the hotspots' magnetic
field. We construct energy spectra of the radiating ultrarelativistic
electrons. We find that for both hotspots A and D these spectra are consistent
with a broken power-law extending from at least 100 MeV up to 100 GeV, and that
the spectral break corresponds almost exactly to the proton rest energy of 1
GeV. We argue that the shape of the electron continuum reflects two different
regimes of the electron acceleration process at mildly relativistic shocks,
rather than resulting from radiative cooling and/or absorption effects. In this
picture the protons' inertia defines the critical energy for the hotspot
electrons above which Fermi-type acceleration processes may play a major role,
but below which the operating acceleration mechanism has to be of a different
type. At energies >100 GeV, the electron spectra cut-off/steepen again, most
likely as a result of spectral aging due to radiative loss effects. We discuss
several implications of the presented analysis for the physics of extragalactic
jets.Comment: 29 pages, 8 figures and 2 tables included. Accepted for publication
in Ap
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