Blazar jet physics in the age of Fermi

The impact of the Fermi Gamma-ray Space Telescope on blazar research is reviewed. This includes a brief description of the Fermi Large Area Telescope, a summary of the various classes of extragalactic sources found in the First Large Area Telescope AGN Catalog, and more detailed discussion of the flat spectrum radio quasar 3C454.3 and the BL Lac object PKS 2155-304. Some theoretical studies related to ongoing blazar research with Fermi are mentioned, including implications of gamma-ray observations of radio galaxies on blazar unification scenarios, variability in colliding shells, and whether blazars are sources of ultra-high energy cosmic rays.Comment: Minor corrections and improvements; 11 pages, 2 figures; in Proceedings of IAU Symposium 285, "Jets at all Scales," Buenos Aires, Argentina, 13-17 September, 2010, G.E. Romero, R.A. Sunyaev and T. Belloni, ed

Stark and Zeeman effects on laser cooling of positronium

Theoretical work on laser cooling of Positronium, including effects of external magnetic and electric fields, is reviewed and extended

Theory of high-energy messengers

Knowledge of the distant high-energy universe comes from photons, ultra-high energy cosmic rays (UHECRs), high-energy neutrinos, and gravitational waves. The theory of high-energy messengers reviewed here focuses on the extragalactic background light at all wavelengths, cosmic rays and magnetic fields in intergalactic space, and neutrinos of extragalactic origin. Comparisons are drawn between the intensities of photons and UHECRs in intergalactic space, and the high-energy neutrinos recently detected with IceCube at about the Waxman-Bahcall flux. Source candidates for UHECRs and high-energy neutrinos are reviewed, focusing on star-forming and radio-loud active galaxies. HAWC and Advanced LIGO are just underway, with much anticipation.Comment: 12 pages, 8 figures; invited review for 14th International Congress in Topics in Astroparticle and Underground Physics, Torino, Italy, 7 - 11 September 201

Variability in Blazars

The kinetic energy of bulk relativistic plasma ejected from the central engine of blazars is converted into nonthermal particle energy in the comoving frame through a process of sweeping up material from the surrounding medium. The resulting deceleration of the bulk plasma introduces a number of effects which must be included in blazar modeling. For example, the varying Doppler factor means that model fits must employ time integrations appropriate to the observing times of the detectors. We find that the ratio of the peak synchrotron fluxes reached at two different photon energies is largest when viewing along the jet axis, and becomes smaller at large angles to the jet axis. This effect is important in studies of the statistics of jet sources. Variability due either to bulk plasma deceleration or radiative cooling must be distinguished in order to apply recently proposed tests for beaming from correlated X-ray and TeV observations. The blast-wave physics developed to analyze these problems implies that most of the energy injected in the comoving frame is originally in the form of nonthermal hadrons. Because plasmoid deceleration can produce rapid variability due to a changing Doppler factor, arguments against hadronic blazar models related to the long radiative cooling time scale of hadrons are not compelling.Comment: 13 pages, 3 figures,Invited talk at VERITAS Workshop on TeV Astrophysics of Extragalactic Sources, Cambridge, MA, Oct. 23-24, 1998. In press, Astroparticle Physics, ed. M. Catanese, J. Quinn, T. Weeke

Impact of Fermi-LAT and AMS-02 results on cosmic-ray astrophysics

This article reviews a few topics relevant to Galactic cosmic-ray astrophysics, focusing on the recent AMS-02 data release and Fermi Large Area Telescope data on the diffuse Galactic gamma-ray emissivity. Calculations are made of the diffuse cosmic-ray induced p+p --> pi^0 --> 2 gamma spectra, normalized to the AMS-02 cosmic-ray proton spectrum at ~ 10 - 100 GV, with and without a hardening in the cosmic-ray proton spectrum at rigidities R >~ 300 GV. A single power-law momentum "shock" spectrum for the local interstellar medium cosmic-ray proton spectrum cannot be ruled out from the gamma-ray emissivity data alone without considering the additional contribution of electron bremsstrahlung. Metallicity corrections are discussed, and a maximal range of nuclear enhancement factors from 1.52 to 1.92 is estimated.Origins of the 300 GV cosmic-ray proton and alpha-particle hardening are discussed.Comment: In SuGAR2015, Searching for the sources of Galactic Cosmic Rays, University of Geneva, 21-23 January 2015; eds. E. Prandini & S. Toscano; 6 pages, 3 figure

Curvature Effects in Gamma Ray Burst Colliding Shells

An elementary kinematic model for emission produced by relativistic spherical colliding shells is studied. The case of a uniform blast-wave shell with jet opening angle $\theta_j \gg 1/\Gamma$ is considered, where $\Gamma$ is the Lorentz factor of the emitting shell. The shell, with comoving width $\Delta r^\prime$, is assumed to be illuminated for a comoving time $\Delta t^\prime$ and to radiate a broken power-law $\nu L_\nu$ spectrum peaking at comoving photon energy \e_{pk,0}^{\prime}. Synthetic GRB pulses are calculated, and the relation between energy flux and internal comoving energy density is quantified. Curvature effects dictate that the measured $\nu F_\nu$ flux at the measured peak photon energy \e_{pk} is proportional to \e^3_{pk} in the declining phase of a GRB pulse. Possible reasons for discrepancy with observations are discussed, including adiabatic and radiative cooling processes that extend the decay timescale, a nonuniform jet, or the formation of pulses by external shock processes. A prediction of a correlation between prompt emission properties and times of the optical afterglow beaming breaks is made for a cooling model, which can be tested with Swift.Comment: 13 pages, 5 figures, added back-of-envelope estimate of curvature relation, minor corrections, ApJ, in press, v. 614, 10 Oct 200