406 research outputs found
Detection of variable VHE gamma-ray emission from the extra-galactic gamma-ray binary LMC P3
Context. Recently, the high-energy (HE, 0.1-100 GeV) -ray emission
from the object LMC P3 in the Large Magellanic Cloud (LMC) has been discovered
to be modulated with a 10.3-day period, making it the first extra-galactic
-ray binary.
Aims. This work aims at the detection of very-high-energy (VHE, >100 GeV)
-ray emission and the search for modulation of the VHE signal with the
orbital period of the binary system.
Methods. LMC P3 has been observed with the High Energy Stereoscopic System
(H.E.S.S.); the acceptance-corrected exposure time is 100 h. The data set has
been folded with the known orbital period of the system in order to test for
variability of the emission. Energy spectra are obtained for the orbit-averaged
data set, and for the orbital phase bin around the VHE maximum.
Results. VHE -ray emission is detected with a statistical
significance of 6.4 . The data clearly show variability which is
phase-locked to the orbital period of the system. Periodicity cannot be deduced
from the H.E.S.S. data set alone. The orbit-averaged luminosity in the
TeV energy range is erg/s. A luminosity of erg/s is reached during 20% of the orbit. HE and VHE
-ray emissions are anti-correlated. LMC P3 is the most luminous
-ray binary known so far.Comment: 5 pages, 3 figures, 1 table, accepted for publication in A&
Detailed spectral and morphological analysis of the shell type SNR RCW 86
Aims: We aim for an understanding of the morphological and spectral
properties of the supernova remnant RCW~86 and for insights into the production
mechanism leading to the RCW~86 very high-energy gamma-ray emission. Methods:
We analyzed High Energy Spectroscopic System data that had increased
sensitivity compared to the observations presented in the RCW~86 H.E.S.S.
discovery publication. Studies of the morphological correlation between the
0.5-1~keV X-ray band, the 2-5~keV X-ray band, radio, and gamma-ray emissions
have been performed as well as broadband modeling of the spectral energy
distribution with two different emission models. Results:We present the first
conclusive evidence that the TeV gamma-ray emission region is shell-like based
on our morphological studies. The comparison with 2-5~keV X-ray data reveals a
correlation with the 0.4-50~TeV gamma-ray emission.The spectrum of RCW~86 is
best described by a power law with an exponential cutoff at TeV and a spectral index of ~. A static
leptonic one-zone model adequately describes the measured spectral energy
distribution of RCW~86, with the resultant total kinetic energy of the
electrons above 1 GeV being equivalent to 0.1\% of the initial kinetic
energy of a Type I a supernova explosion. When using a hadronic model, a
magnetic field of ~100G is needed to represent the measured data.
Although this is comparable to formerly published estimates, a standard
E spectrum for the proton distribution cannot describe the gamma-ray
data. Instead, a spectral index of ~1.7 would be required, which
implies that ~erg has been transferred into
high-energy protons with the effective density cm^-3. This
is about 10\% of the kinetic energy of a typical Type Ia supernova under the
assumption of a density of 1~cm^-3.Comment: accepted for publication by A&
Characterizing the gamma-ray long-term variability of PKS 2155-304 with H.E.S.S. and Fermi-LAT
Studying the temporal variability of BL Lac objects at the highest energies
provides unique insights into the extreme physical processes occurring in
relativistic jets and in the vicinity of super-massive black holes. To this
end, the long-term variability of the BL Lac object PKS 2155-304 is analyzed in
the high (HE, 100 MeV 200 GeV)
gamma-ray domain. Over the course of ~9 yr of H.E.S.S observations the VHE
light curve in the quiescent state is consistent with a log-normal behavior.
The VHE variability in this state is well described by flicker noise
(power-spectral-density index {\ss}_VHE = 1.10 +0.10 -0.13) on time scales
larger than one day. An analysis of 5.5 yr of HE Fermi LAT data gives
consistent results ({\ss}_HE = 1.20 +0.21 -0.23, on time scales larger than 10
days) compatible with the VHE findings. The HE and VHE power spectral densities
show a scale invariance across the probed time ranges. A direct linear
correlation between the VHE and HE fluxes could neither be excluded nor firmly
established. These long-term-variability properties are discussed and compared
to the red noise behavior ({\ss} ~ 2) seen on shorter time scales during
VHE-flaring states. The difference in power spectral noise behavior at VHE
energies during quiescent and flaring states provides evidence that these
states are influenced by different physical processes, while the compatibility
of the HE and VHE long-term results is suggestive of a common physical link as
it might be introduced by an underlying jet-disk connection.Comment: 11 pages, 16 figure
The exceptionally powerful TeV gamma-ray emitters in the Large Magellanic Cloud
The Large Magellanic Cloud, a satellite galaxy of the Milky Way, has been
observed with the High Energy Stereoscopic System (H.E.S.S.) above an energy of
100 billion electron volts for a deep exposure of 210 hours. Three sources of
different types were detected: the pulsar wind nebula of the most energetic
pulsar known N 157B, the radio-loud supernova remnant N 132D and the largest
non-thermal X-ray shell - the superbubble 30 Dor C. The unique object SN 1987A
is, surprisingly, not detected, which constrains the theoretical framework of
particle acceleration in very young supernova remnants. These detections reveal
the most energetic tip of a gamma-ray source population in an external galaxy,
and provide via 30 Dor C the unambiguous detection of gamma-ray emission from a
superbubble.Comment: Published in Science Magazine (Jan. 23, 2015). This ArXiv version has
the supplementary online material incorporated as an appendix to the main
pape
Expression of Toll-Like Receptors in the Developing Brain
Toll-like receptors (TLR) are key players of the innate and adaptive immune response in vertebrates. The original protein Toll in Drosophila melanogaster regulates both host defense and morphogenesis during development. Making use of real-time PCR, in situ hybridization, and immunohistochemistry we systematically examined the expression of TLR1â9 and the intracellular adaptor molecules MyD88 and TRIF during development of the mouse brain. Expression of TLR7 and TLR9 in the brain was strongly regulated during different embryonic, postnatal, and adult stages. In contrast, expression of TLR1â6, TLR8, MyD88, and TRIF mRNA displayed no significant changes in the different phases of brain development. Neurons of various brain regions including the neocortex and the hippocampus were identified as the main cell type expressing both TLR7 and TLR9 in the developing brain. Taken together, our data reveal specific expression patterns of distinct TLRs in the developing mouse brain and lay the foundation for further investigation of the pathophysiological significance of these receptors for developmental processes in the central nervous system of vertebrates
Dynamic Regulation of Oct1 during Mitosis by Phosphorylation and Ubiquitination
Transcription factor Oct1 regulates multiple cellular processes. It is known to be phosphorylated during the cell cycle and by stress, however the upstream kinases and downstream consequences are not well understood. One of these modified forms, phosphorylated at S335, lacks the ability to bind DNA. Other modification states besides phosphorylation have not been described.We show that Oct1 is phosphorylated at S335 in the Oct1 DNA binding domain during M-phase by the NIMA-related kinase Nek6. Phospho-Oct1 is also ubiquitinated. Phosphorylation excludes Oct1 from mitotic chromatin. Instead, Oct1(pS335) concentrates at centrosomes, mitotic spindle poles, kinetochores and the midbody. Oct1 siRNA knockdown diminishes the signal at these locations. Both Oct1 ablation and overexpression result in abnormal mitoses. S335 is important for the overexpression phenotype, implicating this residue in mitotic regulation. Oct1 depletion causes defects in spindle morphogenesis in Xenopus egg extracts, establishing a mitosis-specific function of Oct1. Oct1 colocalizes with lamin B1 at the spindle poles and midbody. At the midbody, both proteins are mutually required to correctly localize the other. We show that phospho-Oct1 is modified late in mitosis by non-canonical K11-linked polyubiquitin chains. Ubiquitination requires the anaphase-promoting complex, and we further show that the anaphase-promoting complex large subunit APC1 and Oct1(pS335) interact.These findings reveal mechanistic coupling between Oct1 phosphorylation and ubquitination during mitotic progression, and a role for Oct1 in mitosis
Constraints on the intergalactic magnetic field using Fermi-LAT and H.E.S.S. blazar observations
Magnetic fields in galaxies and galaxy clusters are believed to be the result
of the amplification of intergalactic seed fields during the formation of
large-scale structures in the universe. However, the origin, strength, and
morphology of this intergalactic magnetic field (IGMF) remain unknown. Lower
limits on (or indirect detection of) the IGMF can be obtained from observations
of high-energy gamma rays from distant blazars. Gamma rays interact with the
extragalactic background light to produce electron-positron pairs, which can
subsequently initiate electromagnetic cascades. The -ray signature of
the cascade depends on the IGMF since it deflects the pairs. Here we report on
a new search for this cascade emission using a combined data set from the Fermi
Large Area Telescope and the High Energy Stereoscopic System. Using
state-of-the-art Monte Carlo predictions for the cascade signal, our results
place a lower limit on the IGMF of G for a coherence
length of 1 Mpc even when blazar duty cycles as short as 10 yr are assumed.
This improves on previous lower limits by a factor of 2. For longer duty cycles
of () yr, IGMF strengths below G
( G) are excluded, which rules out specific models for IGMF
generation in the early universe.Comment: 20 pages, 7 figures, 4 tables. Accepted for publication in ApJ
Letters. Auxiliary data is provided in electronic format at
https://zenodo.org/record/801431
HESS J1809193: a halo of escaped electrons around a pulsar wind nebula?
Context. HESS J1809193 is an unassociated very-high-energy -ray
source located on the Galactic plane. While it has been connected to the nebula
of the energetic pulsar PSR J18091917, supernova remnants and molecular
clouds present in the vicinity also constitute possible associations. Recently,
the detection of -ray emission up to energies of 100 TeV with the
HAWC observatory has led to renewed interest in HESS J1809193.
Aims. We aim to understand the origin of the -ray emission of HESS
J1809193.
Methods. We analysed 93.2 h of data taken on HESS J1809193 above 0.27 TeV
with the High Energy Stereoscopic System (H.E.S.S.), using a multi-component,
three-dimensional likelihood analysis. In addition, we provide a new analysis
of 12.5 yr of Fermi-LAT data above 1 GeV within the region of HESS J1809193.
The obtained results are interpreted in a time-dependent modelling framework.
Results. For the first time, we were able to resolve the emission detected
with H.E.S.S. into two components: an extended component that exhibits a
spectral cut-off at 13 TeV, and a compact component that is located close
to PSR J18091917 and shows no clear spectral cut-off. The Fermi-LAT analysis
also revealed extended -ray emission, on scales similar to that of the
extended H.E.S.S. component.
Conclusions. Our modelling indicates that based on its spectrum and spatial
extent, the extended H.E.S.S. component is likely caused by inverse Compton
emission from old electrons that form a halo around the pulsar wind nebula. The
compact component could be connected to either the pulsar wind nebula or the
supernova remnant and molecular clouds. Due to its comparatively steep
spectrum, modelling the Fermi-LAT emission together with the H.E.S.S.
components is not straightforward. (abridged)Comment: 14 pages, 10 figures. Accepted for publication in A&A. Corresponding
authors: Vikas Joshi, Lars Mohrman
A deep spectromorphological study of the -ray emission surrounding the young massive stellar cluster Westerlund 1
Young massive stellar clusters are extreme environments and potentially
provide the means for efficient particle acceleration. Indeed, they are
increasingly considered as being responsible for a significant fraction of
cosmic rays (CRs) accelerated within the Milky Way. Westerlund 1, the most
massive known young stellar cluster in our Galaxy is a prime candidate for
studying this hypothesis. While the very-high-energy -ray source HESS
J1646-458 has been detected in the vicinity of Westerlund 1 in the past, its
association could not be firmly identified. We aim to identify the physical
processes responsible for the -ray emission around Westerlund 1 and
thus to better understand the role of massive stellar clusters in the
acceleration of Galactic CRs. Using 164 hours of data recorded with the High
Energy Stereoscopic System (H.E.S.S.), we carried out a deep
spectromorphological study of the -ray emission of HESS J1646-458. We
furthermore employed H I and CO observations of the region to infer the
presence of gas that could serve as target material for interactions of
accelerated CRs. We detected large-scale ( diameter) -ray
emission with a complex morphology, exhibiting a shell-like structure and
showing no significant variation with -ray energy. The combined energy
spectrum of the emission extends to several tens of TeV, and is uniform across
the entire source region. We did not find a clear correlation of the
-ray emission with gas clouds as identified through H I and CO
observations. We conclude that, of the known objects within the region, only
Westerlund 1 can explain the bulk of the -ray emission. Several CR
acceleration sites and mechanisms are conceivable, and discussed in detail.
(abridged)Comment: 15 pages, 9 figures. Corresponding authors: L. Mohrmann, S. Ohm, R.
Rauth, A. Specoviu
A MeerKAT, e-MERLIN, H.E.S.S. and Swift search for persistent and transient emission associated with three localised FRBs
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