Lecture 5 Multi-wavelength cosmic background And TeV emission suppression Cross-section for pair production in Photon-photon collisions TeV and multi-wavelength spectra of blazars

Radiogalaxy IC 310 (80 Mpc) TeV emitting region is ~100 Schwarzschild radii Blazar-like behavior Aleksic et al., MAGIC Collab. 2014

Starburst galaxy NGC 253 (3 Mpc) Gamma-ray emission from starbursts Is due to hadronic interactions With dense interstellar matter: “calorimetry” of cosmic rays Lacki et al. 2011 Abramowski et al. 2012

Multiwavelength Cosmic Background

Stecker et al. 1992, ApJ, 390, L49

Infrared intergalactic background Albert et al. 2008

3C 279 (z = 0.54) MAGIC (top) and optical R-ban (bottom) light curves of the FSRQ 3C 279 (z = 0.54) from February to March 2006. The long-term baseline for the optical flux is at 3 mJy. Until recently, 3C279 was the most distant TeV emitter with spectroscopically measured redshift. Announced in 2014 and 2015: S3 0218+35, z = 0.944 PKS1441+25, z = 0.939 Light curves. MAGIC (top) and optical R-band data (bottom) obtained for 3C 279 from February to March 2006. The long-term baseline for the optical flux is at 3 mJy. MAGIC Collaboration, Albert et al. Science 2008;320:1752-1754

Spectrum of 3C 279 measured by MAGIC Spectrum of 3C 279 measured by MAGIC. The gray area includes the combined statistical (1σ) and systematic errors, and underlines the marginal significance of detections at high energy. The dotted line shows compatibility of the measured spectrum with a power law of photon index α = 4.1. The blue and red triangles are measurements corrected on the basis of the two models for EBL density. z = 0.54 Spectrum of 3C 279 measured by MAGIC. The gray area includes the combined statistical (1σ) and systematic errors, and underlines the marginal significance of detections at high energy. The dotted line shows compatibility of the measured spectrum with a power law of photon index α = 4.1. The blue and red triangles are measurements corrected on the basis of the two models for EBL density, discussed in the text. Albert et al. 2008

Spectral energy distribution Light curves TeV blazar Mkn421 (z = 0.031), Campaign of April 1998 Spectral energy distribution Maraschi et al. 1999

Multiwavelength observations of Mkn421 (z = 0.031) in 2008 May 24 - Jun 23 Donnarumma et al. 2009

Multi-wavelength campaign on the blazar Mkn421 (2009 Jan 19 - Jun 1) Abdo et al. 2011

Mkn501 (z = 0.034) Tavecchio et al. 2001 Albert et al. 2007 May – Jul 2005 Tavecchio et al. 2001 Albert et al. 2007

Blazar PKS2155-304 Observed with HESS Atmospheric Cerenkov Telescope Aharonian et al. 2009 Days Days

Spectrum of 3C 279 measured by MAGIC. Spectrum of 3C 279 measured by MAGIC. The gray area includes the combined statistical (1σ) and systematic errors, and underlines the marginal significance of detections at high energy. The dotted line shows compatibility of the measured spectrum with a power law of photon index α = 4.1. The blue and red triangles are measurements corrected on the basis of the two models for EBL density. z = 0.54 Spectrum of 3C 279 measured by MAGIC. The gray area includes the combined statistical (1σ) and systematic errors, and underlines the marginal significance of detections at high energy. The dotted line shows compatibility of the measured spectrum with a power law of photon index α = 4.1. The blue and red triangles are measurements corrected on the basis of the two models for EBL density, discussed in the text. Albert et al. 2008

What is the observational evidence that blazars and GRBs are highly relativistic sources with strong special relativity aberration effects? Large luminosities Non-thermal spectra superluminal motions (blazars, but also micro-QSO) Gamma-ray transparency

Compactness Compactness arguments hold for both blazars and GRBs (Cavallo & Rees 1978): the opacity tau_gg is much larger than 1 for the OBSERVED Luminosities, sizes of emitting region (i.e. variability Times) and frequencies. If one corrects for relativistic Aberration and replaces these quantities with the intrinsic ones, one obtains tau_gg opacities less Than 1 (i.e. transparent to gamma-rays). See Compactnes argument for blazars in Maraschi et al. (1992). In GRBs one has fluences instead of fluxes. See Cavallo & Rees (1978).

C.M. Urry & P. Padovani 1995 Unified Schemes for Radio-Loud Active Galactic Nuclei PASP, 107, 803 G.B. Rybicki & A.P. Lightman 1979 Radiation Processes in Astrophysics G. Cavallo & M. J. Rees 1978 A qualitative study of cosmic fireballs and gamma-ray bursts MNRAS, 183, 359 L. Maraschi, G. Ghisellini, & A. Celotti 1992 A jet model for the gamma-ray emitting blazar 3C279 ApJ, 397, L5 I.F. Mirabel & L.F. Rodriguez 1999 Sources of Relativistic Jets in the Galaxy Annual Review of Astronomy & Astrophysics 37, 409

Reviews on TeV Astronomy: Elihu Boldt The Extreme Universe: Some Views From Here Closing lecture, 3rd INTEGRAL Workshop: The Extreme Universe, Taormina, September 14-18 1998 Astrophysical Letters & Communications Vol. 37, 1999 arXiv:astro-ph/9902040 Reviews on TeV Astronomy: http://tevcat.uchicago.edu/reviews.html