EGMF Constraints from Simultaneous GeV-TeV Observations of Blazars

By A. Taylor, I. Vovk, Andrii Y. Neronov. 2011

277 citations recorded by the source corpus.

Attenuation of the TeV gamma-ray flux from distant blazars through pair production with extragalactic background light leads to the development of electromagnetic cascades and subsequent, lower energy, GeV secondary gamma-ray emission. Due to the deflection of VHE cascade electrons by extragalactic magnetic fields (EGMF), the spectral shape of this arriving cascade gamma-ray emission is dependent on the strength of the EGMF. Thus, the spectral shape of the GeV-TeV emission from blazars has the potential to probe the EGMF strength along the line of sight to the object. We investigate constraints on the EGMF derived from observations of blazars for which TeV observations simultaneous with those by the Fermi telescope were reported. We study the dependence of the EGMF bound on the hidden assumptions it rests upon. We select blazar objects for which simultaneous Fermi/LAT GeV and Veritas, MAGIC or HESS TeV emission have been published. We model the development of electromagnetic cascades along the gamma-ray beams from these sources using Monte Carlo simulations, including the calculation of the temporal delay incurred by cascade photons, relative to the light propagation time of direct gamma-rays from the source. Constraints on EGMF could be derived from the simultaneous GeV-TeV data on the blazars RGB J0710+591, 1ES 0229+200, and 1ES 1218+304. The measured source flux level in the GeV band is lower than the expected cascade component calculated under the assumption of zero EGMF. Assuming that the reason for the suppression of the cascade component is the extended nature of the cascade emission, we find that B>10^{-15} G (assuming EGMF correlation length of ~1 Mpc) is consistent with the data. Alternatively, the assumption that the suppression of the cascade emission is caused by the time delay of the cascade photons the data are consistent with B>10^{-17} G for the same correlation length.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/d7a2a70fed1f2908cf0849d0e0ce2c8bde19d626

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In Nuclear and High Energy Physics

1. F. Tavecchio
2. G. Ghisellini
3. C. Dermer
4. J. Biteau
5. Luigi Foschini
6. A. Reimer
7. Kohta Murase
8. E. Orlando

Citations in the corpus

• TIME DELAY OF CASCADE RADIATION FOR TeV BLAZARS AND THE MEASUREMENT OF THE INTERGALACTIC MAGNETIC FIELD (2010, methodology): “A simple semi-analytic approach is used to derive minimum values, for comparison with numerical models (Dolag et al. 2011; Taylor et al. 2011).”
• Extreme TeV blazars and the intergalactic magnetic field (2010, methodology): “A complete, self-consistent treatment of the cascades could be done with Monte Carlo simulations (e.g. Coppi & Aharonian 1997, Elyiv et al. 2009, Dolag et al. 2009, 2011, Neronov et al. 2010, Taylor et al. 2011).”
• Planck 2015 results: XIX. Constraints on primordial magnetic fields (2015, unknown): “Constraints on the GeV emission provide lower limits on the amplitude of intergalactic fields of the order of 10−18–10−15 G (Tavecchio et al. 2010; Taylor et al. 2011; Dermer et al. 2011; Vovk et al. 2012), if this scenario is correct.”
• The Search for Spatial Extension in High-latitude Sources Detected by the Fermi Large Area Telescope (2018, methodology): “…to an excess in the GeV regime of γ-ray spectra, and the non-observation of this feature has been used to derive lower limits on the IGMF strength—or conversely, on the filling factor of the IGMF (Neronov & Vovk 2010; Dolag et al. 2011; Tavecchio et al. 2011; Taylor et al. 2011; Vovk et al. 2012).”
• BLAZARS AS ULTRA-HIGH-ENERGY COSMIC-RAY SOURCES: IMPLICATIONS FOR TeV GAMMA-RAY OBSERVATIONS (2011, background): “On the other hand, the void IGMF cannot be below ∼ 10−18 G Mpc1/2 due to constraints fromFermi (e.g., Dolag et al. 2011; Dermer et al. 2011; Tavecchio et al. 2011; Taylor et al. 2011; Ahlers & Salvado 2011).”