Intergalactic magnetic field spectra from diffuse gamma-rays

Chen, Wenlei; Chowdhury, Borun D.; Ferrer, Francesc; Tashiro, Hiroyuki; Vachaspati, Tanmay

doi:10.1093/mnras/stv308

Cited by 50 publications

(63 citation statements)

References 24 publications

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“…These lower bounds are controversial because of the claims [27][28][29][30][31] that the development of the cascade is suppressed by plasma instabilities that arise from interactions with the intergalactic medium. On the other hand, recent direct observations [32] and PIC simulations [33] of cascades suggest that plasma instabilities are not operative and that the orig-inal bounds hold. We expect that future analyses will clarify the role, if any, of plasma instabilities in the development of the electromagnetic cascade.…”

Section: Introductionmentioning

confidence: 99%

“…More recently, it has been proposed that helicity can leave characteristic parity-odd imprints on the arrival directions of gamma rays that are the result of gamma-rayinduced electromagnetic cascades [32,[38][39][40][41]. In particular, Long & Vachaspati [41] have carried out a thorough analysis of the morphology of the arrival directions of gamma rays using a semi-analytical approach, but without including the stochasticity of the magnetic field or the cascade process.…”

Section: Introductionmentioning

confidence: 99%

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Probing intergalactic magnetic fields with simulations of electromagnetic cascades

et al. 2016

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We determine the effect of intergalactic magnetic fields on the distribution of high energy gamma rays by performing three-dimensional Monte Carlo simulations of the development of gamma-rayinduced electromagnetic cascades in the magnetized intergalactic medium. We employ the so-called "Large Sphere Observer" method to efficiently simulate blazar gamma ray halos. We study magnetic fields with a Batchelor spectrum and with maximal left-and right-handed helicities. We also consider the case of sources whose jets are tilted with respect to the line of sight. We verify the formation of extended gamma ray halos around the source direction, and observe spiral-like patterns if the magnetic field is helical. We apply the Q-statistics to the simulated halos to extract their spiral nature and also propose an alternative method, the S-statistics. Both methods provide a quantative way to infer the helicity of the intervening magnetic fields from the morphology of individual blazar halos for magnetic field strengths B 10 −15 G and magnetic coherence lengths Lc 100 Mpc. We show that the S-statistics has a better performance than the Q-statistics when assessing magnetic helicity from the simulated halos.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Probing intergalactic magnetic fields with simulations of electromagnetic cascades

et al. 2016

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“…CTA observations should be able to either confirm or rule out evidence of a nonzero IGMF (e.g., Essey et al 2011;Chen et al 2015aChen et al , 2015b and improve current limits on its field strength and coherence length by orders of magnitude (e.g., Taylor et al 2011;Arlen et al 2014;Finke et al 2015). Especially if IGMF configurations are realized in nature that lead to either strong or very small deflections of the + -e e pairs, it will be possible to rule out large fractions of the IGMF parameter space.…”

Section: Discussionmentioning

confidence: 99%

“…In the approximation that the Doppler factor is equal to the bulk Lorentz factor G L of the emitting plasma, this implies q G~-10 2 . These parameters cover the evidencesfor a nonzero IGMF (Chen et al 2015a(Chen et al , 2015b, as well as scenarios for astrophysical or primordial origins of the IGMF (e.g., Durrer & Neronov 2013). …”

Section: Cascade Simulationsmentioning

confidence: 99%

Sensitivity of the Cherenkov Telescope Array to the Detection of Intergalactic Magnetic Fields

Meyer

Conrad

Dickinson

2016

ApJ

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Very high energy (VHE; energy E100 GeV) γ-rays originating from extragalactic sources undergo pair production with low-energy photons of background radiation fields. These pairs can inverse-Compton-scatter background photons, initiating an electromagnetic cascade. The spatial and temporal structure of this secondary γ-ray signal is altered as the + -e e pairs are deflected in an intergalactic magnetic field (IGMF). We investigate how VHE observations with the future Cherenkov Telescope Array, with its high angular resolution and broad energy range, can potentially probe the IGMF. We identify promising sources and simulate γ-ray spectra over a wide range of values of the IGMF strength and coherence length using the publicly available ELMAG MonteCarlo code. Combining simulated observations in a joint likelihood approach, we find that current limits on the IGMF can be significantly improved. The projected sensitivity depends strongly on the time a source has been γ-ray active and on the emitted maximum γ-ray energy.

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“…Such magnetic fields violate parity since the handedness of the field is related to the preference of matter over antimatter. Evidence for helical cosmological magnetic fields has recently been discovered [58,59], suggesting that they may have been produced during the decay of monopoles-on-strings.…”

Section: Observational Constraintsmentioning

confidence: 99%

Monopoles on strings

Kibble

Vachaspati

2015

J. Phys. G: Nucl. Part. Phys.

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Abstract. In cosmological scenarios based on grand unification, string theory or braneworlds, many kinds of topological or non-topological defects, including monopoles and cosmic strings, are predicted to be formed in the early universe. Here we review specifically the physics of composite objects involving monopoles tied to strings. There is a wide variety of these, including for example "dumbbells" and "necklaces", depending on how many strings attach to each monopole and on the extent to which the various fluxes are confined to the strings. We also briefly survey the prospects for observing such structures, the existing observational limits, and potential evidence for a cosmological role.

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Intergalactic magnetic field spectra from diffuse gamma-rays

Cited by 50 publications

References 24 publications

Probing intergalactic magnetic fields with simulations of electromagnetic cascades

Probing intergalactic magnetic fields with simulations of electromagnetic cascades

Sensitivity of the Cherenkov Telescope Array to the Detection of Intergalactic Magnetic Fields

Monopoles on strings

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