Production of TeV gamma-radiation in the vicinity of the supermassive black hole in the giant radiogalaxy M87

Although the giant radiogalaxy M 87 harbors many distinct regions of broad-band nonthermal emission, the recently reported fast variability of TeV gamma rays from M 87 on a timescale of days strongly constrains the range of speculations concerning the possible sites and scenarios of particle acceleration responsible for the observed TeV emission. A natural production site of this radiation is the immediate vicinity of the central supermassive mass black hole (BH). Because of the low bolometric luminosity, the nucleus of M 87 is effectively transparent for gamma rays up to energy of 10 TeV, which makes this source an ideal laboratory for study of particle acceleration processes close to the BH event horizon. We critically analyse different possible radiation mechanisms in this region, and argue that the observed very high-energy gamma ray emission can be explained by the inverse Compton emission of ultrarelativistic electron-positron pairs produced through the development of an electromagnetic cascade in the BH magnetosphere. We demonstrate, through detailed numerical calculations of acceleration and radiation of electrons in the magnetospheric vacuum gap, that this ``pulsar magnetosphere like'' scenario can satisfactorily explain the main properties of TeV gamma-ray emission of M 87.Comment: 11 pages, ApJ, in prin

Conformal Symmetries of Adiabatic Modes in Cosmology

We remark on the existence of non-linearly realized conformal symmetries for scalar adiabatic perturbations in cosmology. These conformal symmetries are present for any cosmological background, beyond any slow-roll or quasi-de Sitter approximation. The dilatation transformation shifts the curvature perturbation by a constant, and corresponds to the well-known symmetry under spatial rescaling. We argue that the scalar sector is also invariant under special conformal transformations, which shift the curvature perturbation by a term linear in the spatial coordinates. We discuss whether these conformal symmetries can be extended to include tensor perturbations. Tensor modes introduce their own set of non-linearly realized symmetries. We identify an infinite set of large gauge transformations which maintain the transverse, traceless gauge condition, while shifting the tensor mode non-trivially.Comment: 16 page

Serendipitous discovery of an extended X-ray jet without a radio counterpart in a high-redshift quasar

A recent Chandra observation of the nearby galaxy cluster Abell 585 has led to the discovery of an extended X-ray jet associated with the high-redshift background quasar B3 0727+409, a luminous radio source at redshift z=2.5. This is one of only few examples of high-redshift X-ray jets known to date. It has a clear extension of about 12", corresponding to a projected length of ~100 kpc, with a possible hot spot located 35" from the quasar. The archival high resolution VLA maps surprisingly reveal no extended jet emission, except for one knot about 1.4" from the quasar. The high X-ray to radio luminosity ratio for this source appears consistent with the $\propto (1+z)^{4}$ amplification expected from the inverse Compton radiative model. This serendipitous discovery may signal the existence of an entire population of similar systems with bright X-ray and faint radio jets at high redshift, a selection bias which must be accounted for when drawing any conclusions about the redshift evolution of jet properties and indeed about the cosmological evolution of supermassive black holes and active galactic nuclei in general