arXiv subjects

P. P. Kronberg

Publications and source records attributed to P. P. Kronberg.

16 recordsLinked to original sources

arXiv2025

A two-step strategy to identify episodic sources of gravitational waves and high energy neutrinos in starburst galaxies

Supermassive black hole mergers with spin-flips accelerate energetic particles through their precessing relativistic jets, producing high energy neutrinos and finally gravitational waves. In star formation massive stars come in pairs, triplets and quadruplets, allowing second generation mergers of the remnants with discrepant spin directions. The Gravitational Wave (GW) data support such a scenario. Earlier we suggested that stellar mass black hole mergers (visible in M82) with an associated spin-flip analogously allow the acceleration of energetic particles, with ensuing high energy neutrinos and high energy photons, and finally producing gravitational waves. At cosmic distances only the gravitational waves and the neutrinos remain detectable. Here we generalize the argument to starburst and normal galaxies throughout their cosmic evolution, and show that these galaxies may dominate over Active Galactic Nuclei (AGN) in the flux of ultra-high energy particles observed at Earth. All these sources contribute to the cosmic neutrino background, as well as the gravitational wave background (they detected the lower frequencies). We outline a search strategy to find such episodic sources, which requires to include both luminosity and flux density.

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arXiv2024

Cosmic ray contributions from rapidly rotating stellar mass black holes: Cosmic Ray GeV to EeV proton and anti-proton sources

In Radio Super Novae (RSNe) a magnetic field of $(B \, \times \, r) \, = \, 10^{16.0 \pm 0.12} \, {\rm Gauss \, \times \, cm}$ is observed; these are the same numbers for Blue Super Giant (BSG) star explosions as for Red Super Giant (RSG) star explosions, despite their very different wind properties. The EHT data for M87 as well for low power radio galaxies all show consistency with just this value of the quantity $(B \, \times \, r )$, key for angular momentum and energy transport, and can be derived from the radio jet data. We interpret this as a property of the near surroundings of a black hole (BH) at near maximal rotation, independent of BH mass. In the commonly used green onion model, in which a $2 \, π$ flow changes over to a jet flow we interpret this as a wind emanating from the BH/accretion disk system and its surroundings. Near the BH collisions in the wind can produce a large fraction of anti-protons. In this scenario the cosmic Ray (CR) population from the wind/jet is proposed to be visible as EeV protons and anti-protons in the CR data to EeV energy, with a $E^{-7/3}$ spectrum. This can be connected to a concept of inner and outer Penrose zones in the ergo-region. The observed numbers for the magnetic field imply the Planck time as the governing time scale: A BH rotating near maximum can accept a proton per log bin of energy in an extended spectrum with the associated pions every Planck time.

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arXiv2024

Loaded layer-cake model for cosmic ray interaction around exploding super-giant stars making black holes

The AMS experiment on the International Space Station has provided detailed cosmic ray spectra for various elements, revealing that interactions significantly reduce fluxes up to about 100 GV rigidity. This necessitates revisiting current cosmic ray interaction models. A new model proposed here involves cosmic ray interactions first in the wind shock shell of supergiant stars and second in the OB-Superbubble around supernovae. These stars, including red and blue supergiants, produce black holes and drive electric currents in winds and jets. Variability in these winds creates temporary electric fields that accelerate particles, resulting in steep spectra with synchrotron losses, and analogous hadron spectra produce a flat magnetic irregularity spectrum. This model matches AMS data, explaining cosmic ray spectra below 100 GV. The model predicts a secondary/primary ratio slope of -1/3 and a primary flux reduction below 100 GV relative to a power-law spectrum with slope +2. Key aspects are: a larger interaction column due to heavy element enrichment and a minor secondary contribution even for elements like He, C, and O, as indicated by the $^3$He/$^4$He ratio. This model also accounts for cosmic ray anti-protons, gamma-ray spectra, and high-energy neutrinos, including contributions from ISM-SNe.

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arXiv2018

Supernova explosions of massive stars and cosmic rays

Most cosmic ray particles observed derive from the explosions of massive stars, which commonly produce stellar black holes in their supernova explosions. When two such black holes find themselves in a tight binary system they finally merge in a gigantic emission of gravitational waves, events that have now been detected. After an introduction (section 1) we introduce the basic concept (section 2): Cosmic rays from exploding massive stars with winds always show two cosmic ray components at the same time: (i) the weaker polar cap component only produced by Diffusive Shock Acceleration with a cut-off at the knee, and (ii) the stronger $4 π$ component with a down-turn to a steeper power-law spectrum at the knee, and a final cutoff at the ankle. In section 3 we use the Alpha Magnetic Spectrometer (AMS) data to differentiate these two cosmic ray spectral components. The ensuing secondary spectra can explain anti-protons, lower energy positrons, and other secondary particles. Triplet pair production may explain the higher energy positron AMS data. In section 4 we test this paradigm with a theory of injection based on a combined effect of first and second ionization potential; this reproduces the ratio of Cosmic Ray source abundances to source material abundances. In section 5 we interpret the compact radio source 41.9+58 in the starburst galaxy M82 as a recent binary black hole merger, with an accompanying gamma ray burst. This can also explain the Ultra High Energy Cosmic Ray (UHECR) data in the Northern sky. Thus, by studying the cosmic ray particles, their abundances at knee energies, and their spectra, we can learn about what drives these stars to produce the observed cosmic rays.

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arXiv2017

Detection of microgauss coherent magnetic fields in a galaxy five billion years ago

Magnetic fields play a pivotal role in the physics of interstellar medium in galaxies, but there are few observational constraints on how they evolve across cosmic time. Spatially resolved synchrotron polarization maps at radio wavelengths reveal well-ordered large-scale magnetic fields in nearby galaxies that are believed to grow from a seed field via a dynamo effect. To directly test and characterize this theory requires magnetic field strength and geometry measurements in cosmologically distant galaxies, which are challenging to obtain due to the limited sensitivity and angular resolution of current radio telescopes. Here, we report the cleanest measurements yet of magnetic fields in a galaxy beyond the local volume, free of the systematics traditional techniques would encounter. By exploiting the scenario where the polarized radio emission from a background source is gravitationally lensed by a foreground galaxy at z = 0.439 using broadband radio polarization data, we detected coherent $μ$G magnetic fields in the lensing disk galaxy as seen 4.6 Gyrs ago, with similar strength and geometry to local volume galaxies. This is the highest redshift galaxy whose observed coherent magnetic field property is compatible with a mean-field dynamo origin.

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arXiv2013

Transmission Line Analogy for Relativistic Poynting-Flux Jets

Radio emission, polarization, and Faraday rotation maps of the radio jet of the galaxy 3C 303 have shown that one knot of this jet carries a {\it galactic}-scale electric current and that it is magnetically dominated. We develop the theory of magnetically dominated or Poynting-flux jets by making an analogy of a Poynting jet with a transmission line or waveguide carrying a net current and having a potential drop across it (from the jet's axis to its radius) and a definite impedance which we derive. Time-dependent but not necessarily small perturbations of a Poynting-flux jet are described by the "telegrapher's equations." These predict the propagation speed of disturbances and the effective wave impedance for forward and backward propagating wave components. A localized disturbance of a Poynting jet gives rise to localized dissipation in the jet which may explain the enhanced synchrotron radiation in the knots of the 3C 303 jet, and also in the apparently stationary knot HST-1 in the jet near the nucleus of the nearby galaxy M87. For a relativistic Poynting jet on parsec scales, the reflected voltage wave from an inductive termination or load can lead to a backward propagating wave which breaks down the magnetic insulation of the jet giving $|{\bf E}| /|{\bf B}|\geq 1$. At the threshold for breakdown, $|{\bf E}|/|{\bf B}|=1$, positive and negative particles are directly accelerated in the ${\bf E \times B}$ direction which is approximately along the jet axis. Acceleration can occur up to Lorentz factors $\sim 10^7$. This particle acceleration mechanism is distinct from that in shock waves and that in magnetic field reconnection.

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arXiv2012

New Constraints on the Galactic Halo Magnetic Field using Rotation Measures of Extragalactic Sources Towards the Outer Galaxy

We present a study of the Milky Way disk and halo magnetic field, determined from observations of Faraday rotation measure (RM) towards 641 polarized extragalactic radio sources in the Galactic longitude range 100-117 degs, within 30 degs of the Galactic plane. For |b| < 15 degs, we observe a symmetric RM distribution about the Galactic plane. This is consistent with a disk field in the Perseus arm of even parity across the Galactic mid-plane. In the range 15<|b|<30 degs, we find median rotation measures of -15+/-4 rad/m^2 and -62+/-5 rad/m^2 in the northern and southern Galactic hemispheres, respectively. If the RM distribution is a signature of the large-scale field parallel to the Galactic plane, this suggests that the halo magnetic field toward the outer Galaxy does not reverse direction across the mid-plane. The variation of RM as a function of Galactic latitude in this longitude range is such that RMs become more negative at larger |b|. This is consistent with an azimuthal magnetic field of strength 2 microGauss (7 microGauss) at a height 0.8-2 kpc above (below) the Galactic plane between the local and the Perseus spiral arm. We propose that the Milky Way could possess spiral-like halo magnetic fields similar to those observed in M51.

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arXiv2012

An improved map of the Galactic Faraday sky

We aim to summarize the current state of knowledge regarding Galactic Faraday rotation in an all-sky map of the Galactic Faraday depth. For this we have assembled the most extensive catalog of Faraday rotation data of compact extragalactic polarized radio sources to date. In the map making procedure we use a recently developed algorithm that reconstructs the map and the power spectrum of a statistically isotropic and homogeneous field while taking into account uncertainties in the noise statistics. This procedure is able to identify some rotation angles that are offset by an integer multiple of pi. The resulting map can be seen as an improved version of earlier such maps and is made publicly available, along with a map of its uncertainty. For the angular power spectrum we find a power law behavior with a power law index of -2.14 for a Faraday sky where an overall variance profile as a function of Galactic latitude has been removed, in agreement with earlier work. We show that this is in accordance with a 3D Fourier power spectrum P(k) proportional to k^-2.14 of the underlying field n_e times B_r under simplifying geometrical and statistical assumptions.

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arXiv2012

Relativistic Poynting-Flux Jets as Transmission Lines

Recent radio emission, polarization, and Faraday rotation maps of the radio jet of the galaxy 3C 303 have shown that one knot of this jet has a {\it galactic}-scale electric current of $\sim 3\times 10^{18}$ Ampère flowing along the jet axis (Kronberg et al. 2011). We develop the theory of relativistic Poynting-flux jets which are modeled as a transmission line carrying a DC current $I_0$, having a potential drop $V_0$, and a definite impedance ${\cal Z}_0 =90(u_z/c)Ω$, where $u_z$ is the bulk velocity of the jet plasma. The electromagnetic energy flow in the jet is ${\cal Z}_0 I_0^2$. The observed current in 3C 303 can be used to calculate the electromagnetic energy flow in this magnetically dominated jet. Time-dependent but not necessarily small perturbations of a Poynting-flux jet - possibly triggered by a gas cloud penetrating the jet - are described by "telegrapher's equations," which predict the propagation speed of disturbances and the effective wave impedance ${\cal Z}$. The disturbance of a Poynting jet by the cloud gives rise to localized dissipation in the jet which may explain the enhanced synchrotron radiation in the knots of the 3C 303 jet, and in the apparently stationary knot HST-1 in the jet from the nucleus of the galaxy M87 (Biretta et al. 1999).

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arXiv2011

Deriving global structure of the Galactic Magnetic Field from Faraday Rotation Measures of extragalactic sources

We made use of the two latest sets of Rotational Measures (RMs) of extra-galactic radio sources, namely the NRAO VLA Sky Survey otation Measures Catalogue, and a compilation by Kronberg&Newton-McGee(2011), to infer the global structure of the Galactic Magnetic Field (GMF). We have checked that these two data sets are consistent with each other. Motivated by clear patterns in the observed distribution of RMs over the sky, we considered GMF models consisting of the two components: disk (spiral or ring) and halo. The parameters of these components were determined by fitting different model field geometries to the observed RMs. We found that the model consisting of a symmetric (with respect to the Galactic plane) spiral disk and anti-symmetric halo fits the data best, and reproduces the observed distribution of RMs over the sky very well. We confirm that ring disk models are disfavored. Our results favor small pitch angles around -5 degrees and an increased vertical scale of electron distribution, in agreement with some previous studies. Based on our fits, we identify two benchmark models suitable for studies of cosmic ray propagation, including the ultra-high energies.

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arXiv2010

A Survey of Extragalactic Faraday Rotation at High Galactic Latitude: The Vertical Magnetic Field of the Milky Way towards the Galactic Poles

We present a study of the vertical magnetic field of the Milky Way towards the Galactic poles, determined from observations of Faraday rotation toward more than 1000 polarized extragalactic radio sources at Galactic latitudes |b| > 77 degs, using the Westerbork Radio Synthesis Telescope and the Australia Telescope Compact Array. We find median rotation measures (RMs) of 0.0 +/- 0.5 rad/m^2 and +6.3 +/- 0.7 rad/m^2 toward the north and south Galactic poles, respectively, demonstrating that there is no coherent vertical magnetic field in the Milky Way at the Sun's position. If this is a global property of the Milky Way's magnetism, then the lack of symmetry across the disk rules out pure dipole or quadrupole geometries for the Galactic magnetic field. The angular fluctuations in RM seen in our data show no preferred scale within the range ~ 0.1 to 25 degs. The observed standard deviation in RM of ~ 9 rad/m^2 then implies an upper limit of ~1microGauss on the strength of the random magnetic field in the warm ionized medium at high Galactic latitudes.

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arXiv2007

A Global Probe of Cosmic Magnetic Fields to High Redshifts

Faraday rotation (RM) probes of magnetic fields in the universe are sensitive to cosmological and evolutionary effects as $z$ increases beyond $\sim $1 because of the scalings of electron density and magnetic fields, and the growth in the number of expected intersections with galaxy-scale intervenors, $d$N/$dz$. In this new global analysis of an unprecedented large sample of RM's of high latitude quasars extending out to $z\sim $3.7 we find that the distribution of RM broadens with redshift in the 20 $-$ 80 rad m$^{-2}$ range range, despite the (1 +$z$)$^{-2}$ wavelength dilution expected in the observed Faraday rotation. Our results indicate that the Universe becomes increasingly ``Faraday-opaque'' to sources beyond $z \sim$ 2, that is, as $z$ increases progressively fewer sources are found with a ``small'' RM in the observer's frame. This is in contrast to sources at $z \la$1. They suggest that the environments of galaxies were significantly magnetized at high redshifts, with magnetic field strengths that were at least as strong within a few Gyr of the Big Bang as at the current epoch. We separately investigate a simple unevolving toy model in which the RM is produced by MgII absorber systems, and find that it can approximately reproduce the observed trend with redshift. An additional possibility is that the intrinsic RM associated with the radio sources was much higher in the past, and we show that this is not a trivial consequence of the higher radio luminosities of the high redshift sources.

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arXiv2007

Discovery of new faint radio emission on 8$\arcdeg$ to 3$\arcmin$ scales in the Coma field, and some Galactic and extragalactic implications

We present a deep, 8$\degr$ diameter, 0.4 GHz radio image using a first time combination of the NAIC Arecibo 305-m telescope in Puerto Rico, and the wide-angle interferometer at the Dominion Radio Astrophysical Observatory at Penticton, Canada. Our observations are centered on the Coma Cluster of galaxies in the ``Great Wall'' of galaxies near the North Galactic Pole. The complementary nature of these two instruments enables us to produce a distortion-free image that is sensitive to radiation on scales from 8$\degr$ down to that of an individual galaxy halo at the 100 Mpc distance of the Great Wall. Newly revealed patches of distributed radio ``glow'' are seen well above the detection limit. One prominent such area coincides with groupings of radio galaxies near the Coma cluster, and indicates intergalactic IGM magnetic fields in the range 0.2 to 0.4 $μ$G on scales of up to $\sim$ 4 Mpc. Other patches of diffuse emission, not previously explored at these high latitudes on arcminute scales, probably contain Galactic ``cirrus''. A striking anticorrelation is found between low-level diffuse radio glow and some regions of enhanced optical galaxy surface density, suggesting that cosmological Large Scale Structure (LSS), normally defined by the baryonic (or dark) matter density, is not {\it uniquely} traced by faint continuum radio glow. Rather, intergalactic diffuse synchrotron radiation represents IGM magnetic and Cosmic ray energy density, instead of matter density. The diffuse, arcminute-level structures over a large region of sky are potentially important pathfinders to CMB foreground radiation on high multipole scales.

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arXiv2001

Magnetic Energy of the Intergalactic Medium from Galactic Black Holes

A quantitative analysis of two radio source samples having opposite extremes of ambient gas density leads to important new conclusions about the magnetic energy in the IGM. We conclude that giant sources in rarefied IGM environments, which contain magnetic energies E_B ~ 10^60-61 ergs, can be viewed as important "calorimeters" of the minimum energy a black hole (BH) accretion disk system injects into the IGM. In contrast to the radiation energy released by BH accretion, most of the magnetic energy is "trapped" initially in a volume, up to ~10^73 cm^3, around the host galaxy. But since these large, Mpc scale radio lobes are still overpressured after the AGN phase, their subsequent expansion and diffusion will magnetize a large fraction of the entire IGM. This suggests that the energy stored in intergalactic magnetic fields will have a major, as yet underestimated effect on the evolution of subsequently forming galaxies. Comparison with the second sample, consisting of sources within 150 kpc of rich cluster cores, shows that the minimum magnetic energy E_B can be a strongly variable fraction of the inferred accretion energy E_acc, and that it depends on the ambient IGM environment. AGNs inject significant energy as PdV work on the thermal ICM gas, and their magnetic energy, even ignoring the contribution from stellar and starburst outflows, is sufficient to account for that recently found beyond the inner cores of galaxy clusters. Other loss processes in the course of the lobe expansion are considered. We conclude that the aggregate IGM magnetic energy derived purely from galactic black holes since the first epoch of significant galaxy BH formation is sufficiently large that it will have an important influence on the process of both galaxy and visible structure formation on scales up to ~ 1Mpc.

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arXiv2000

A New Radio - X-Ray Probe of Galaxy Cluster Magnetic Fields

Results are presented of a new VLA-ROSAT study that probes the magnetic field strength and distribution over a sample of 16 ``normal'' low redshift (z < 0.1) galaxy clusters. The clusters span two orders of magnitude in X-ray luminosity, and were selected to be free of (unusual) strong radio cluster halos, and widespread cooling flows. Consistent with these criteria, most clusters show a relaxed X-ray morphology and little or no evidence for recent merger activity. Analysis of the rotation measure (RM) data shows cluster-generated Faraday RM excess out to ~0.5 Mpc from cluster centers. The results, combined with RM imaging of cluster-embedded sources and ROSAT X-ray profiles indicates that the hot intergalactic gas within these ``normal'' clusters is permeated with a high filling factor by magnetic fields at levels of <|B|> = 5-10 (l/10 kpc)^{-1/2} microGauss, where l is the field correlation length. These results lead to a global estimate of the total magnetic energy in clusters, and give new insight into the ultimate energy origin, which is likely gravitational. These results also shed some light on the cluster evolutionary conditions that existed at the onset of cooling flows.

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arXiv1996

Cosmic Ray Protons and Magnetic Fields in Clusters of Galaxies and their Cosmological Consequences

The masses of clusters of galaxies estimated by gravitational lensing exceed in many cases the mass estimates based on hydrostatic equilibrium. This may suggest the existence of nonthermal pressure. We ask if radio galaxies can heat and support the cluster gas with injected cosmic ray protons and magnetic field densities, which are permitted by Faraday rotation and gamma ray observations of clusters of galaxies. We conclude that they are powerful enough to do this within a cluster radius of roughly 1 Mpc. If present, nonthermal pressures could lead to a revised estimate of the ratio of baryonic mass to total mass, and the apparent baryonic overdensity in clusters would disappear. In consequence, $Ω_{\rm cold}$, the clumping part of the cosmological density $Ω_{o}$, would be larger than $0.4\,h_{50}^{-1/2}$.

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