THE COSMOLOGICAL IMPACT OF LUMINOUS TeV BLAZARS. I. IMPLICATIONS OF PLASMA INSTABILITIES FOR THE INTERGALACTIC MAGNETIC FIELD AND EXTRAGALACTIC GAMMA-RAY BACKGROUND

By A. Broderick, P. Chang, C. Pfrommer. 2011

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Inverse Compton cascades (ICCs) initiated by energetic gamma rays (E ≳ 100 GeV) enhance the GeV emission from bright, extragalactic TeV sources. The absence of this emission from bright TeV blazars has been used to constrain the intergalactic magnetic field (IGMF), and the stringent limits placed on the unresolved extragalactic gamma-ray background (EGRB) by Fermi have been used to argue against a large number of such objects at high redshifts. However, these are predicated on the assumption that inverse Compton scattering is the primary energy-loss mechanism for the ultrarelativistic pairs produced by the annihilation of the energetic gamma rays on extragalactic background light photons. Here, we show that for sufficiently bright TeV sources (isotropic-equivalent luminosities ≳ 1042 erg s−1) plasma beam instabilities, specifically the “oblique” instability, present a plausible mechanism by which the energy of these pairs can be dissipated locally, heating the intergalactic medium. Since these instabilities typically grow on timescales short in comparison to the inverse Compton cooling rate, they necessarily suppress the ICCs. As a consequence, this places a severe constraint on efforts to limit the IGMF from the lack of a discernible GeV bump in TeV sources. Similarly, it considerably weakens the Fermi limits on the evolution of blazar populations. Specifically, we construct a TeV-blazar luminosity function from those objects currently observed and find that it is very well described by the quasar luminosity function at z ∼ 0.1, shifted to lower luminosities and number densities, suggesting that both classes of sources are regulated by similar processes. Extending this relationship to higher redshifts, we show that the magnitude and shape of the EGRB above ∼10 GeV are naturally reproduced with this particular example of a rapidly evolving TeV-blazar luminosity function.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/e331e4baba871f233ea3c88c337ca7dd218e7d53

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Citations in the corpus

Simulations of magnetic fields in isolated disc galaxies (2012, background): “There have even been claims of an indirect detection of magnetic fields in cosmic voids (Neronov & Vovk 2010), although the robustness of this result is debated (Broderick et al. 2012).”
Planck 2015 results: XIX. Constraints on primordial magnetic fields (2015, unknown): “…is a deflection of the electron-positron pairs owing to the presence of a diffuse magnetic field (see Neronov & Vovk 2010; Taylor et al. 2011; Tavecchio et al. 2011; Vovk et al. 2012; and Neronov et al. 2013b for details on this explanation; and see Broderick et al. 2012 for alternative scenarios).”
The Search for Spatial Extension in High-latitude Sources Detected by the Fermi Large Area Telescope (2018, background): “The cascade is not suppressed by the dissipation of energy of the e+e− beam into plasma instabilities (the efficiency of these instabilities is a matter of ongoing debate; see, e.g., Broderick et al. (2012); Sironi & Giannios (2014); Menzler & Schlickeiser (2015); and Chang et al. (2016)).”
Modified Gravity-GADGET: A new code for cosmological hydrodynamical simulations of modified gravity models (2013, background): “The effects on the temperature PDF, e.g. the 15% shift in the peak temperature, may, however, be rather small compared to uncertainties in the heating efficiency due to helium II reionization (see e.g. McQuinn et al. 2009) or the effects of a recently suggested additional heating of the IGM by TeV-b”
Cosmological Magnetic Fields: Their Generation, Evolution and Observation (2013, methodology): “The calculation of the growth rate of plasma instabilities by Broderick et al (2012) was performed in linear approximation, i.e. not taking into account back reaction of the beam perturbations on the growth rate.”