Peter L. Biermann

Detection and imaging of atmospheric radio flashes from cosmic ray air showers.

The nature of ultrahigh-energy cosmic rays (UHECRs) at energies >1020 eV remains a mystery. They are likely to be of extragalactic origin, but should be absorbed within ∼50 Mpc through interactions with the cosmic microwave background. As there are no sufficiently powerful accelerators within this distance from the Galaxy, explanations for UHECRs range from unusual astrophysical sources to exotic string physics. Also unclear is whether UHECRs consist of protons, heavy nuclei, neutrinos or γ-rays. To resolve these questions, larger detectors with higher duty cycles and which combine multiple detection techniques are needed. Radio emission from UHECRs, on the other hand, is unaffected by attenuation, has a high duty cycle, gives calorimetric measurements and provides high directional accuracy. Here we report the detection of radio flashes from cosmic-ray air showers using low-cost digital radio receivers. We show that the radiation can be understood in terms of the geosynchrotron effect. Our results show that it should be possible to determine the nature and composition of UHECRs with combined radio and particle detectors, and to detect the ultrahigh-energy neutrinos expected from flavour mixing.

Synchrotron emission from shock waves in active galactic nuclei

The origin of the sharp near infrared cutoff in the continuous energy distribution of many compact non-thermal sources (BL Lacs, OVVs, red quasars and certain jets) is considered under the assumption that particle acceleration takes place in shocks. This model predicts a highest frequency v* of electron synchrotron emission which depends principally on the shock velocity and the ratio a of photon to magnetic energy density in the acceleration region. For near relativistic flows and reasonable values of a a spectral cutoff is predicted in the range 3 1014 < v < 2 1015 Hz. The model thus leads to 1) near relativistic flows, 2) a gradual steepening of optical continuum spectra as one follows a jet outwards, 3) a correlation between spectral hardening and luminosity, 4) a correlation between optical spectrum and X-ray emission, 5) a possible synchrotron contribution to the X-ray emission in Quasars from secondary particles, and 6) the production of very high energy particles such as observed in cosmic rays, of up to ~1012 GeV.

The Nature of the 10 kilosecond X-ray flare in Sgr A*

The X-ray mission Chandra has observed a dramatic X-ray flare { a brightening by a factor of 50 for only three hours { from Sgr A*, the Galactic Center supermassive black hole. Sgr A* has never shown variability of this amplitude in the radio and we therefore argue that a jump of this order in the accretion rate does not seem the likely cause. Based on our model for jet-dominated emission in the quiescent state of Sgr A*, we suggest that the flare is a consequence of extra electron heating near the black hole. This can either lead to direct heating of thermal electrons to Te 6 10 11 K and signicantly increased synchrotron-self Compton emission, or result from non-thermal particle acceleration with increased synchrotron radiation and electron Lorentz factors up to e > 10 5 . While the former scenario is currently favored by the data, simultaneous VLBI, submm, mid-infrared

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, Ωcold, the clumping part of the cosmological density Ω0, would be larger than 0.4 h -->−1/250.

Arrival directions of the most energetic cosmic rays.

In this Letter we examine the arrival directions of the most energetic cosmic rays

CORRELATION BETWEEN COMPACT RADIO QUASARS AND ULTRAHIGH ENERGY COSMIC RAYS

(Eg2\ifmmode\times\else\texttimes\fi{}{10}^{19}\mathrm{eV})

Maximum energy of cosmic-ray particles accelerated by supernova remnant shocks in stellar wind cavities

detected by several air shower experiments. We find that data taken by different air shower arrays show positive correlations, indicating a nonuniform arrival direction distribution. We also find that the events with energy

A new estimate of the extragalactic radio background and implications for ultra-high-energy γ-ray propagation

g4\ifmmode\times\else\texttimes\fi{}{10}^{19}\mathrm{eV}

The origin of the highest energy cosmic rays

exhibit a correlation with the general direction of the supergalactic plane, where a large number of potential sources are located. If confirmed by data from other experiments our results would support models for the extragalactic origin of the highest energy cosmic rays.

Lateral distribution of the radio signal in extensive air showers measured with LOPES

Some proposals to account for the highest energy cosmic rays predict that they should point to their sources. We study the five highest energy events (E>10^20 eV) and find they are all aligned with compact, radio-loud quasars. The probability that these alignments are coincidental is 0.005, given the accuracy of the position measurements and the rarity of such sources. The source quasars have redshifts between 0.3 and 2.2. If the correlation pointed out here is confirmed by further data, the primary must be a new hadron or one produced by a novel mechanism.