387 research outputs found
Spatially Resolved [FeII] 1.64 \mu m Emission in NGC 5135. Clues for Understanding the Origin of the Hard X-rays in Luminous Infrared Galaxies
Spatially resolved near-IR and X-ray imaging of the central region of the
Luminous Infrared Galaxy NGC 5135 is presented. The kinematical signatures of
strong outflows are detected in the [FeII]1.64 \mu m emission line in a compact
region at 0.9 kpc from the nucleus. The derived mechanical energy release is
consistent with a supernova rate of 0.05-0.1 yr. The apex of the
outflowing gas spatially coincides with the strongest [FeII] emission peak and
with the dominant component of the extranuclear hard X-ray emission. All these
features provide evidence for a plausible direct physical link between
supernova-driven outflows and the hard X-ray emitting gas in a LIRG. This
result is consistent with model predictions of starbursts concentrated in small
volumes and with high thermalization efficiencies. A single high-mass X-ray
binary (HMXB) as the major source of the hard X-ray emission although not
favoured, cannot be ruled out. Outside the AGN, the hard X-ray emission in NGC
5135 appears to be dominated by the hot ISM produced by supernova explosions in
a compact star-forming region, and not by the emission due to HMXB. If this
scenario is common to U/LIRGs, the hard X-rays would only trace the most
compact (< 100 pc) regions with high supernova and star formation densities,
therefore a lower limit to their integrated star formation. The SFR derived in
NGC 5135 based on its hard X-ray luminosity is a factor of two and four lower
than the values obtained from the 24 \mu m and soft X-ray luminosities,
respectively.Comment: Accepted for Publication in ApJ, 18 pages, 2 figure
Orientation and symmetries of Alexandrov spaces with applications in positive curvature
We develop two new tools for use in Alexandrov geometry: a theory of ramified
orientable double covers and a particularly useful version of the Slice Theorem
for actions of compact Lie groups. These tools are applied to the
classification of compact, positively curved Alexandrov spaces with maximal
symmetry rank.Comment: 34 pages. Simplified proofs throughout and a new proof of the Slice
Theorem, correcting omissions in the previous versio
A metabolite-derived protein modification integrates glycolysis with KEAP1-NRF2 signalling.
Mechanisms that integrate the metabolic state of a cell with regulatory pathways are necessary to maintain cellular homeostasis. Endogenous, intrinsically reactive metabolites can form functional, covalent modifications on proteins without the aid of enzymes1,2, and regulate cellular functions such as metabolism3-5 and transcription6. An important 'sensor' protein that captures specific metabolic information and transforms it into an appropriate response is KEAP1, which contains reactive cysteine residues that collectively act as an electrophile sensor tuned to respond to reactive species resulting from endogenous and xenobiotic molecules. Covalent modification of KEAP1 results in reduced ubiquitination and the accumulation of NRF27,8, which then initiates the transcription of cytoprotective genes at antioxidant-response element loci. Here we identify a small-molecule inhibitor of the glycolytic enzyme PGK1, and reveal a direct link between glycolysis and NRF2 signalling. Inhibition of PGK1 results in accumulation of the reactive metabolite methylglyoxal, which selectively modifies KEAP1 to form a methylimidazole crosslink between proximal cysteine and arginine residues (MICA). This posttranslational modification results in the dimerization of KEAP1, the accumulation of NRF2 and activation of the NRF2 transcriptional program. These results demonstrate the existence of direct inter-pathway communication between glycolysis and the KEAP1-NRF2 transcriptional axis, provide insight into the metabolic regulation of the cellular stress response, and suggest a therapeutic strategy for controlling the cytoprotective antioxidant response in several human diseases
Associated molecular and atomic clouds with X-ray shell of superbubble 30 Doradus C in the LMC
30 Doradus C is a superbubble which emits the brightest nonthermal X- and TeV
gamma-rays in the Local Group. In order to explore detailed connection between
the high energy radiation and the interstellar medium, we have carried out new
CO and HI observations using the Atacama Large MillimeterSubmillimeter Array
(ALMA), Atacama Submillimeter Telescope Experiment, and the Australia Telescope
Compact Array with resolutions of up to 3 pc. The ALMA data of CO( =
1-0) emission revealed 23 molecular clouds with the typical diameters of
6-12 pc and masses of 600-10000 . The comparison with
the X-rays of - at 3 pc resolution shows that X-rays are
enhanced toward these clouds. The CO data were combined with the HI to estimate
the total interstellar protons. Comparison of the interstellar proton column
density and the X-rays revealed that the X-rays are enhanced with the total
proton. These are most likely due to the shock-cloud interaction modeled by the
magnetohydrodynamical simulations (Inoue et al. 2012, ApJ, 744, 71). Further,
we note a trend that the X-ray photon index varies with distance from the
center of the high-mass star cluster, suggesting that the cosmic-ray electrons
are accelerated by one or multiple supernovae in the cluster. Based on these
results we discuss the role of the interstellar medium in cosmic-ray particle
acceleration.Comment: 20 pages, 14 figures, 3 tables, accepted for publication in The
Astrophysical Journa
LOFAR discovery of a double radio halo system in Abell 1758 and radio/X-ray study of the cluster pair
Radio halos and radio relics are diffuse synchrotron sources that extend over Mpc-scales and are found in a number of merger galaxy clusters. They are believed to form as a consequence of the energy that is dissipated by turbulence and shocks in the intra-cluster medium (ICM). However, the precise physical processes that generate these steep synchrotron spectrum sources are still poorly constrained. We present a new LOFAR observation of the double galaxy cluster Abell 1758. This system is composed of A1758N, a massive cluster hosting a known giant radio halo, and A1758S, which is a less massive cluster whose diffuse radio emission is confirmed here for the first time. Our observations have revealed a radio halo and a candidate radio relic in A1758S, and a suggestion of emission along the bridge connecting the two systems which deserves confirmation. We combined the LOFAR data with archival VLA and GMRT observations to constrain the spectral properties of the diffuse emission. We also analyzed a deep archival Chandra observation and used this to provide evidence that A1758N and A1758S are in a pre-merger phase. The ICM temperature across the bridge that connects the two systems shows a jump which might indicate the presence of a transversal shock generated in the initial stage of the merger
Polarization constraints on the X-ray corona in Seyfert Galaxies: MCG-05-23-16
We report on the first observation of a radio-quiet Active Galactic Nucleus
(AGN) using polarized X-rays: the Seyfert 1.9 galaxy MCG-05-23-16. This source
was pointed with the Imaging X-ray Polarimetry Explorer (IXPE) starting on May
14, 2022 for a net observing time of 486 ks, simultaneously with XMM-Newton (58
ks) and NuSTAR (83 ks). A polarization degree smaller than (at the
99% c.l.) is derived in the 2-8 keV energy range, where emission is dominated
by the primary component ascribed to the hot corona. The broad-band spectrum,
inferred from a simultaneous fit to the IXPE, NuSTAR, and XMM-Newton data, is
well reproduced by a power law with photon index and a
high-energy cutoff keV. A comparison with Monte Carlo
simulations shows that a lamp-post and a conical geometry of the corona are
consistent with the observed upper limit, a slab geometry is allowed only if
the inclination angle of the system is less than 50.Comment: 7 pages, 3 figures, 1 table. Submitted to MNRAS Letter
Complex variations of X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431
We report on \ixpe observations of the Be-transient X-ray pulsar LS V +44
17/RX J0440.9+4431 at two luminosity levels during the giant outburst in
January--February 2023. Considering the observed spectral variability and
changes in the pulse profiles, the source was likely caught in super- and
sub-critical states with significantly different emission region geometry,
associated with the presence of accretion columns and hot spots, respectively.
We focus here on the pulse-phase resolved polarimetric analysis and find that
the observed dependencies of the polarization degree and polarization angle
(PA) on pulse phase are indeed drastically different for the two observations.
The observed differences, if interpreted within the framework of the rotating
vector model (RVM), imply dramatic variations of the spin axis inclination and
the position angle and the magnetic colatitude by tens of degrees within just a
few days separating the observations. We suggest that the apparent changes in
the observed PA phase dependence are predominantly related to the presence of a
polarized unpulsed component in addition to the polarized radiation associated
with the pulsar itself. We show that the observed PA phase dependence in both
observations can then be explained with a single set of RVM parameters defining
the pulsar's geometry. We also suggest that the additional polarized component
is likely produced by scattering of the pulsar radiation off the equatorial
disk wind.Comment: 9 pages, 5 figures, submitted to A&
Accretion geometry of the neutron star low mass X-ray binary Cyg X-2 from X-ray polarization measurements
We report spectro-polarimetric results of an observational campaign of the
bright neutron star low-mass X-ray binary Cyg X-2 simultaneously observed by
IXPE, NICER and INTEGRAL. Consistently with previous results, the broad-band
spectrum is characterized by a lower-energy component, attributed to the
accretion disc with 1 keV, plus unsaturated
Comptonization in thermal plasma with temperature keV and
optical depth , assuming a slab geometry. We measure the
polarization degree in the 2-8 keV band per cent and
polarization angle , consistent with the
previous X-ray polarimetric measurements by OSO-8 as well as with the direction
of the radio jet which was earlier observed from the source. While polarization
of the disc spectral component is poorly constrained with the IXPE data, the
Comptonized emission has a polarization degree per cent and a
polarization angle aligned with the radio jet. Our results strongly favour a
spreading layer at the neutron star surface as the main source of the
polarization signal. However, we cannot exclude a significant contribution from
reflection off the accretion disc, as indicated by the presence of the iron
fluorescence line.Comment: 10 pages, 7 figures, accepted for publication in MNRA
IXPE observation confirms a high spin in the accreting black hole 4U 1957+115
We present the results of the first X-ray polarimetric observation of the
low-mass X-ray binary 4U 1957+115, performed with the Imaging X-ray Polarimetry
Explorer in May 2023. The binary system has been in a high-soft spectral state
since its discovery and is thought to host a black hole. The 571 ks
observation reveals a linear polarisation degree of and a
polarisation angle of in the 2-8 keV energy range.
Spectral modelling is consistent with the dominant contribution coming from the
standard accretion disc, while polarimetric data suggest a significant role of
returning radiation: photons that are bent by strong gravity effects and forced
to return to the disc surface, where they can be reflected before eventually
reaching the observer. In this setting, we find that models with a black hole
spin lower than 0.96 and an inclination lower than are disfavoured.Comment: 12 pages, 10 figures, 2 tables, accepted for publication in A&
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