Abstract
The apparent position of jet base (core) in radio-loud active galactic nuclei changes with frequency because of synchrotron self-absorption. Studying this ‘core shift’ effect enables us to ...reconstruct properties of the jet regions close to the central engine. We report here results from core shift measurements in AGNs observed with global VLBI at 2 and 8 GHz at epochs from 1994 to 2016. Our sample contains 40 objects observed at least 10 times during that period. The core shift is determined using a new automatic procedure introduced to minimize possible biases. The resulting multiple epoch measurements of the core position are employed for examining temporal variability of the core shift. We argue that the core shift variability is a common phenomenon, as established for 33 of 40 AGNs we study. Our analysis shows that the typical offsets between the core positions at 2 and 8 GHz are about 0.5 mas and they vary in time. Typical variability of the individual core positions is about 0.3 mas. The measurements show a strong dependence between the core position and its flux density, suggesting that changes in both are likely related to the nuclear flares injecting denser plasma into the flow. We determine that density of emitting relativistic particles significantly increases during these flares, while relative magnetic field changes less and in the opposite direction.
We prove that a resonance enhancement of neutrino oscillations in magnetic field is possible due to transition magnetic moments and demonstrate that this resonance is strictly connected to the ...neutrino polarization. To study the main properties of this resonance, we obtain the probabilities of transitions between neutrino states with definite flavor and helicity in inhomogeneous electromagnetic field in the adiabatic approximation. Since the resonance is present only when the adiabaticity condition is fulfilled, we also obtain and discuss this condition.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We obtain a relativistically covariant wave equation for neutrinos in dense matter and electromagnetic field, which describes both flavor oscillations and neutrino spin rotation. Using this equation ...we construct a quasiclassical theory of these phenomena. We obtain the probabilities of arbitrary spin-flavor transitions assuming the external conditions to be constant. We demonstrate that the resonance behavior of the transition probabilities is possible only when the neutrino flavor states cannot be described as superpositions of the mass eigenstates. We discover that a resonance, which is similar to the Mikheev–Smirnov–Wolfenstein resonance, takes place for neutrinos in magnetic field due to the transition magnetic moments. This resonance gives an opportunity to determine, whether neutrinos are Dirac or Majorana particles.
Jet ejection by accreting black holes is a mass invariant mechanism unifying stellar and supermassive black holes (SMBHs) that should also apply for intermediate-mass black holes (IMBHs), which are ...thought to be the seeds from which SMBHs form. We present the detection of an off-nuclear IMBH of ∼5 × 104 M⊙ located in an unusual spiral arm of the galaxy NGC 2276 based on quasi-simultaneous Chandra X-ray observations and European VLBI Network (EVN) radio observations. The IMBH, NGC2276-3c, possesses a 1.8 pc radio jet that is oriented in the same direction as large-scale (∼650 pc) radio lobes and whose emission is consistent with flat to optically thin synchrotron emission between 1.6 and 5 GHz. Its jet kinetic power (4 × 1040 erg s−1) is comparable to its radiative output and its jet efficiency (≥46 per cent) is as large as that of SMBHs. A region of ∼300 pc along the jet devoid of young stars could provide observational evidence of jet feedback from an IMBH. The discovery confirms that the accretion physics is mass invariant and that seed IMBHs in the early Universe possibly had powerful jets that were an important source of feedback.
The existing CMS endcap calorimeters will be replaced with a High Granularity Calorimeter (HGCAL) for operation at the High Luminosity (HL) LHC . Radiation hardness and excellent physics performance ...will be achieved by utilising silicon pad sensors and SiPM-on-scintillator tiles with high longitudinal and transverse segmentation. One of the major challenges of the HL-LHC will be the high pileup environment, with interaction vertices spread not only in position, but also in time. In order to efficiently reject particles originating from pileup, precision timing information of the order of 30 ps will be of great benefit. In order to meet such performance goals, the HGCAL will provide timing measurements for individual hits with signals above 12 fC (equivalent to 3–10 MIPs), such that clusters resulting from particles with pT>5 GeV should have a timing resolution better than 30 ps. Given the complexity and size of the system, this poses a particular challenge to the readout electronics as well as to the calibration and reconstruction procedures. We present the challenges for the front-end electronics design, results from prototype tests in laboratory and beam environments, as well as anticipated timing performance from simulation.
Context.
Very long baseline interferometry (VLBI) is a radio-astronomical technique whereby the correlated signal from various baselines is combined into an image of the highest possible angular ...resolution. Due to the sparsity of the measurements, this imaging procedure constitutes an ill-posed inverse problem. For decades, the CLEAN algorithm has been the standard choice in VLBI studies, despite it bringing on some serious disadvantages and pathologies that are brought on by the requirements of modern frontline VLBI applications.
Aims.
We developed a novel multiscale CLEAN deconvolution method (DoB-CLEAN) based on continuous wavelet transforms that address several pathologies in CLEAN imaging. We benchmarked this novel algorithm against CLEAN reconstructions on synthetic data and reanalyzed BL Lac observations of RadioAstron with DoB-CLEAN.
Methods.
The DoB-CLEAN method approaches the image via multiscalar and multidirectional wavelet dictionaries. Two different dictionaries were used: 1) a difference of elliptical spherical Bessel functions dictionary fitted to the
uv
-coverage of the observation that is used to sparsely represent the features in the dirty image; 2) a difference of elliptical Gaussian wavelet dictionary that is well suited to represent relevant image features cleanly. The deconvolution was performed by switching between the dictionaries.
Results.
DoB-CLEAN achieves a super-resolution compared to CLEAN and remedies the spurious regularization properties of CLEAN. In contrast to CLEAN, the representation via basis functions has a physical meaning. Hence, the computed deconvolved image still fits the observed visibilities, in contrast to CLEAN.
Conclusions.
State-of-the-art multiscalar imaging approaches seem to outperform single-scalar standard approaches in VLBI and are well suited to maximize the extraction of information in ongoing frontline VLBI applications.
Context. Velocity measurements made from multiple-epoch astronomical images of evolving objects with optically thin continuum emission (e.g. as relativistic jets or expanding supernova shells) may be ...confused as a result of the overlap of semi-transparent features moving at different speeds. Aims. Multi-scale wavelet decomposition can be effectively applied to identify and track such overlapping features, provided that their respective structural responses can be separated over the spatial scales used for the decomposition. Methods. We developed a new method that combines the stacked cross-correlation with the wavelet-based image segmentation and evaluation (WISE) technique of decomposition of two-dimensional structures, to separate and track dominant spatial responses of overlapping evolving features. Results. The method is tested on a set of simulated images of a stratified relativistic jet, demonstrating the robust detection of both the faster spine and the slower sheath speeds. The method is applied to mutliple-epoch images from the MOJAVE survey, revealing two different superluminal streams inside the jet in 3C 273 and the acceleration of the flow in 3C 120. Conclusions. The method can be applied to densely monitored objects with composite structural evolution such as the parsec-scale jet in M 87 or heavily resolved expanding supernova shells.
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the ...rotational energy from a Kerr black hole, which could be the case for NGC 1052, to launch these jets. This requires magnetic fields on the order of 103G to 104G. We imaged the vicinity of the SMBH of the AGN NGC 1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the magnetic field at 1 Schwarzschild radius to lie between 200 G and ~ 8.3 × 104 G consistent with Blandford & Znajek models.
T-Violation in Neutrino Oscillations Lobanov, A. E.; Chukhnova, A. V.
Journal of experimental and theoretical physics,
09/2022, Letnik:
135, Številka:
3
Journal Article
Recenzirano
We analyze the T-invariance violation in probabilities of flavor transitions and neutrino spin rotation in a dense medium in an electromagnetic field. Since the electromagnetic field and the ...potentials of interaction with the medium appear in the wave equation for the neutrino, the model considered here is a theory with Lorentz-invariance violation. For such models, the conditions for the CPT theorem are not satisfied, and T-invariance violation is not necessarily a consequence of CP invariance violation. We have obtained the sufficient condition for T-invariance violation, which implies that T-symmetry can be violated not only because of the presence of a CP-violating phase in the mixing matrix, but also due to simultaneous influence of the medium and the electromagnetic field. We have obtained the probabilities of spin–flavor transitions of the neutrino in the three-flavor model with account for neutrino diagonal magnetic moments and the interaction with the medium only via neutral currents. Studying the explicit form of the probabilities, we conclude that the transition probabilities for right-handed antineutrinos in a medium consisting of antiparticles differ from the transition probabilities for left-handed neutrinos in a medium of particles only in the sign of the T-violating term.
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