scholarly journals The Role of Flare Stars in Cosmic-ray Origin

1995 ◽  
Vol 151 ◽  
pp. 185-192
Author(s):  
Maurice M. Shapiro
Keyword(s):  
Alternative Hypothesis ◽  
Cosmic Ray ◽  
Optical Data ◽  
Seed Particles ◽  
Cosmic Ray Acceleration ◽  
The Galaxy ◽  
Flare Stars ◽  
Far Ultraviolet ◽  
Ultraviolet Observations

AbstractSupernovae and their expanding shock fronts are evidently the main agents of cosmic-ray acceleration. The thermal gas in the interstellar medium has been regarded as the reservoir of seed particles destined to become cosmic-ray nuclei. This assumption is, however, at variance with the source composition of galactic cosmic iays. In an alternative hypothesis, the seed particles are injected into the interstellar material as suprathermal seed ions, and it has been surmised that flare stars provide the initial boost. We find that the dMe and dKe stars are probably the principal sources of cosmic-ray seed particles. Most stars in the Galaxy are red dwarfs and many of these flares much more powerfully and frequently than solar flares. Augmenting the optical data, recent X-ray and far-ultraviolet observations now permit a better estimate of the energy budget. Altogether, dMe and dKe stars seem to be the most promising class of cosmic-ray injectors.

scholarly journals Dust in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 57-62
Author(s):  
Paul Hodge
Keyword(s):  
Heavy Element ◽  
Magellanic Clouds ◽  
Dust Content ◽  
Optical Observations ◽  
Optical Data ◽  
Star Forming ◽  
Element Abundances ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Far Ultraviolet

The dust content of the Magellanic Clouds can be studied using optical, ultraviolet, infrared and, indirectly, radio wavelength data. All recent studies show that the dust content is lower than that of the Milky Way Galaxy for both Clouds and that the optical properties of the dust are different. At ultraviolet wavelengths, the 2165 Å “bump” in the extinction curve is significantly smaller than in the Galaxy (this now appears NOT to be a consequence of the lower heavy element abundances) and the far ultraviolet (shortward of ˜2000 Å) extinction is greater than in the Galaxy (this IS likely to be a consequence of the lower heavy element abundances). New optical data on background galaxies suggest that the total extinction in the central parts of both the LMC and the SMC is approximately 1.5 magnitudes. High local extinction values are derived from uv and optical observations of star-forming regions, where a spatial correlation with CO detections is sometimes, but not always, found.

scholarly journals Flare Stars Database

1994 ◽  
Vol 161 ◽  
pp. 380-382
Author(s):  
M. Tsvetkov ◽  
M. Chukova ◽  
K. Tsvetkova
Keyword(s):  
Wide Field ◽  
Flare Activity ◽  
The Galaxy ◽  
Statistical Regularities ◽  
Ceti Type ◽  
Formation And Evolution ◽  
Flare Stars ◽  
Machine Readable

The important role of flare stars (UV Ceti type variables) in astrophysics is due to the fact that the flare activity is not only typical for red stars with small masses but is a necessary stage during their evolution. The flare star search in stellar aggregates has led to the accumulation of rich observational material allowing us to look for statistical regularities in star formation and evolution. At present, there are more than 1500 known flare stars in the Galaxy; these were discovered mainly during the last 30 years. Most results of the long term monitoring with wide-field telescopes are listed in existing catalogues of flare stars in stellar aggregates and in the solar neighbourhood. These catalogues and their machine-readable versions were the basis for the present database of flare stars in the Galaxy.

scholarly journals Reaching thermal noise at ultra-low radio frequencies

2020 ◽  
Vol 642 ◽  
pp. A85 ◽  
Author(s):  
F. de Gasperin ◽  
G. Brunetti ◽  
M. Brüggen ◽  
R. van Weeren ◽  
W. L. Williams ◽  
...  
Keyword(s):  
Thermal Noise ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Galaxy Cluster ◽  
Cosmic Ray ◽  
Radio Halo ◽  
Cosmic Ray Acceleration ◽  
The Galaxy ◽  
Background Turbulence ◽  
Post Shock

Context. Ultra-low frequency observations (< 100 MHz) are particularly challenging because they are usually performed in a low signal-to-noise ratio regime due to the high sky temperature and because of ionospheric disturbances whose effects are inversely proportional to the observing frequency. Nonetheless, these observations are crucial for studying the emission from low-energy populations of cosmic rays. Aims. We aim to obtain the first thermal-noise limited (∼1.5 mJy beam−1) deep continuum radio map using the Low Frequency Array’s Low Band Antenna (LOFAR LBA) system. Our demonstration observation targeted the galaxy cluster RX J0603.3+4214 (known as the Toothbrush cluster). We used the resulting ultra-low frequency (39–78 MHz) image to study cosmic-ray acceleration and evolution in the post shock region considering the presence of a radio halo. Methods. We describe the data reduction we used to calibrate LOFAR LBA observations. The resulting image was combined with observations at higher frequencies (LOFAR 150 MHz and VLA 1500 MHz) to extract spectral information. Results. We obtained the first thermal-noise limited image from an observation carried out with the LOFAR LBA system using all Dutch stations at a central frequency of 58 MHz. With eight hours of data, we reached an rms noise of 1.3 mJy beam−1 at a resolution of 18″ × 11″. Conclusions. The procedure we developed is an important step towards routine high-fidelity imaging with the LOFAR LBA. The analysis of the radio spectra shows that the radio relic extends to distances of 800 kpc downstream from the shock front, larger than what is allowed by electron cooling time. Furthermore, the shock wave started accelerating electrons already at a projected distance of < 300 kpc from the crossing point of the two clusters. These results may be explained by electrons being re-accelerated downstream by background turbulence, possibly combined with projection effects with respect to the radio halo.

scholarly journals Self-Confined Cosmic Rays

1985 ◽  
Vol 107 ◽  
pp. 341-354
Author(s):  
Donat G. Wentzel
Keyword(s):  
Cosmic Rays ◽  
Solar Flares ◽  
Supernova Remnants ◽  
Cosmic Ray ◽  
Clusters Of Galaxies ◽  
Galactic Wind ◽  
Cosmic Ray Acceleration ◽  
The Galaxy ◽  
Particle Speed ◽  
Ray Density

Cosmic rays do not stream freely through the galaxy, contrary to earlier expectations. Streaming cosmic rays are slowed down by the emission of resonant Alfven waves that scatter the cosmic rays. The theory of self-confinement explains the isotropy of the bulk of the cosmic rays but not of cosmic rays above 103 Gev; it has been a stimulus to the theory for cosmic-ray acceleration at supernova shocks; and, on inclusion of diffusion in a galactic wind, it may explain the uniform cosmic-ray density out to 18 kpc in our galaxy. Rapidly streaming electrons in clusters of galaxies, in supernova remnants, and near solar flares are accomodated by the theory when it is expanded to include the effects of hot plasmas and other wave modes. A “resonance gap” may prevent the turning backwards of streaming particles and thus allow streaming near the particle speed.

scholarly journals Supernova Remnants and the ISM: Constraints from Cosmic-Ray Acceleration

1988 ◽  
Vol 101 ◽  
pp. 325-329
Author(s):  
Amri Wandel
Keyword(s):  
Supernova Remnants ◽  
Weak Shock ◽  
Cosmic Ray ◽  
Box Model ◽  
Effective Density ◽  
Moderate Amount ◽  
Supersonic Expansion ◽  
Cosmic Ray Acceleration ◽  
The Galaxy ◽  
Consistent Solution

AbstractSupernova remnants can reaccelerate cosmic rays and modify their distribution during the cosmic ray propagation in the galaxy. Cosmic ray observations (in particular the boron-to-carbon data) strongly limit the permitted amount of reacceleration, which is used to set an upper limit on the expansion of supernova remnants, and a lower limit on the effective density of the ISM swept up by supernova shocks. The constraint depends on the theory of cosmic ray propagation: the standard Leaky Box model requires a high effective density, > 1cm−3, and is probably inconsistent with the present picture of the ISM. Modifying the Leaky Box model to include a moderate amount of weak-shock reacceleration, a self consistent solution is found, where the effective density in this solution is ≈ 0.1 cm−3, which implies efficient evaporation of the warm ISM component by young supernova remnants, during most of their supersonic expansion.

scholarly journals Cosmic rays from the nearby starburst galaxy NGC 253: the effect of a low-luminosity active galactic nucleus

2020 ◽  
Vol 494 (2) ◽  
pp. 2109-2116 ◽  
Author(s):  
E M Gutiérrez ◽  
G E Romero ◽  
F L Vieyro
Keyword(s):  
Black Hole ◽  
Cosmic Ray ◽  
High Energy ◽  
Starburst Galaxy ◽  
Active Nucleus ◽  
Accretion Flow ◽  
Supermassive Black Hole ◽  
Cosmic Ray Acceleration ◽  
The Galaxy ◽  
Dynamo Mechanism

ABSTRACT NGC 253 is a nearby starburst galaxy in the Sculptor group located at a distance of ∼3.5 Mpc that has been suggested by some authors as a potential site for cosmic ray acceleration up to ultrahigh energies. Its nuclear region is heavily obscured by gas and dust, which prevents establishing whether or not the galaxy harbours a supermassive black hole coexisting with the starburst. Some sources have been proposed in the literature as candidates for an active nucleus. In this work, we aim at determining the implications that the presence of a supermassive black hole at the nucleus of NGC 253 might have on cosmic ray acceleration. With this aim, we model the accretion flow on to the putative active nucleus, and we evaluate the feasibility of particle acceleration by the black hole dynamo mechanism. As a by-product, we explore the potential contribution from non-thermal particles in the accretion flow to the high-energy emission of the galaxy. We found that in the three most plausible nucleus candidates, the emission of the accretion flow would inhibit the black hole dynamo mechanism. To rule out completely the influence that a putative nucleus in NGC 253 might have in cosmic ray acceleration, a better clarification concerning the true nature of the nucleus is needed.

scholarly journals Shock waves in the magnetized cosmic web: the role of obliquity and cosmic ray acceleration

2020 ◽  
Vol 496 (3) ◽  
pp. 3648-3667 ◽  
Author(s):  
S Banfi ◽  
F Vazza ◽  
D Wittor
Keyword(s):  
Large Scale ◽  
Cosmic Ray ◽  
Adaptive Mesh ◽  
Relativistic Electrons ◽  
Particle In Cell ◽  
Large Scale Structures ◽  
Cosmic Ray Acceleration ◽  
Mesh Resolution ◽  
Local Shear

ABSTRACT Structure formation shocks are believed to be the largest accelerators of cosmic rays in the Universe. However, little is still known about their efficiency in accelerating relativistic electrons and protons as a function of their magnetization properties, i.e. of their magnetic field strength and topology. In this work, we analysed both uniform and adaptive mesh resolution simulations of large-scale structures with the magnetohydrodynamical grid code enzo, studying the dependence of shock obliquity with different realistic scenarios of cosmic magnetism. We found that shock obliquities are more often perpendicular than what would be expected from a random 3D distribution of vectors, and that this effect is particularly prominent in the proximity of filaments, due to the action of local shear motions. By coupling these results to recent works from particle-in-cell simulations, we estimated the flux of cosmic ray protons in galaxy clusters, and showed that in principle the riddle of the missed detection of hadronic γ-ray emission by the Fermi-LAT can be explained if only quasi-parallel shocks accelerate protons. On the other hand, for most of the cosmic web the acceleration of cosmic ray electrons is still allowed, due to the abundance of quasi-perpendicular shocks. We discuss quantitative differences between the analysed models of magnetization of cosmic structures, which become more significant at low cosmic overdensities.

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