Fig 15 - uploaded by A. Eungwanichayapant
Content may be subject to copyright.
Source publication
We study the formation of giant electron-positron pair halos around the powerful high energy extragalactic sources. We investigate the dependence of radiation of pair halos, in particular the spectral and angular distributions on the energy spectrum of the primary gamma rays, the redshift of the source, and the flux of the extragalactic background...
Similar publications
The developed electronic control module of an electromagnetic hammer for destruction of boulders is described and studied in the article. The possibility of using an inductive slot sensor for both controlling electromagnets and for measuring dynamic and energy characteristics is demonstrated. During the research of the possibility of controlling th...
Citations
... A pair halo refers to the case where a strong IGMF (10 −12 -10 −9 G) isotropizes a large fraction of high-energy charged particles in the cascade, causing them to accumulate around the source. The reprocessed emission arriving at the observer is consequently extremely time-delayed, on the order of hundreds of years (Eungwanichayapant and Aharonian, 2009). ...
... In addition to analytical approximations, there are an abundance of numerical simulations, which treat the cascade process and magnetic-field structure with varying levels of detail (Abramowski et al., 2014, Alves Batista et al., 2016, Archambault, S. and others , 2017, Arlen et al., 2014, Eungwanichayapant and Aharonian, 2009, Finke et al., 2015, Fitoussi et al., 2017, Kachelriess et al., 2012, Taylor et al., 2011. Numerical simulations, although often computationally intensive, provide more accurate predictions of the cascade spectrum and angular extension, and the ratio of cascade to total emission (cascade fraction). ...
In this chapter, we discuss the contributions of gamma-ray astronomy at TeV energies to our understanding of the visible content and structure of the universe. We start from the present epoch with the second most intense electromagnetic background field after the CMB: the extragalactic background light (EBL). The EBL is composed of all the light emitted by stars and galaxies since the beginning of reionization, including light absorbed and re-emitted by dust. As such, the EBL traces the history of radiating matter in the universe. We then further dive into the large voids of the universe to study the large-scale magnetic fields that should permeate them. These fields could originate from the onset of structure formation or early phase transitions, bringing us back to the infancy of the universe. We conclude by looking back to the elusive Planck time scale, where the standard models of cosmology and particle physics are no longer applicable. Observations with current-generation gamma-ray astronomy experiments have now started to scratch the surface of cosmology, as we will show in this chapter.
... Very High Energy (VHE) gamma-rays from extra-galactic sources such as Active Galactic Nuclei (AGNs) have been considered as an origin of an electron-positron pair halo [1][2][3]. The detailed explanation of the model were published many years ago [4,5]. ...
Interactions between Very High Energy (VHE) gamma-rays from Active Galactic Nuclei (AGNs) and infrared photons from the Extragalactic Background Light (EBL) can start electromagnetic cascades. If the extragalactic magnetic field near a host galaxy is strong enough (∼1 µ G), the cascades would develop isotropically around the AGN. As a result, the electron/positron pairs created along the development of the cascades would create an X-ray halo via synchrotron radiation process. It is believed that the VHE gamma-ray spectra from the AGNs could be approximated by a power-law model which is truncated at high energy end (i.e. maximum energy). In this work we studied the X-ray Spectral Energy Distribution (SED) of the halo generated from the AGN spectra with different power indices and maximum energy levels. The results showed that the SEDs were slightly higher and broader, as they were obtaining higher flux if the power indices were lower. On the other hand, the SEDs were sensitive to the maximum energy levels between 100-300 TeV. More flux could be obtained from the higher maximum energy. However, we found that the SED becomes insensitive to the varied parameters when the maximum energy and the power index are > 500 TeV and < 1.5, respectively.
... Only the spectral energy distributions (SEDs) of the γ-rays from pair halos were computed in that work. Later on, the angular distribution of the γ-rays from the pair halos was calculated by Eungwanichayapant & Aharonian (2009). Most work on the e ± pair halos has focused on radiation in the gamma band. ...
... The angular distance θ from the central source is another important observable quantity from the pair halos. To compute the distribution of the angular distance with high statistical accuracy and limited numerical expense, the utilization of spherical symmetry of pair halos in Eungwanichayapant & Aharonian (2009), in which the pair halos look the same in all directions, is still a good strategy. Then we created an observer sphere with radius d s covering the AGN in our simulation. ...
It was previously suggested that e± pair halos could be observed in γ-rays. Searching for pair halos is a challenging topic in γ-ray astronomy that has not yet yielded a convincing detection for an individual object. Here we propose that X-ray observations could reveal the existence of e± pair halos. To support our suggestion, we computed the observed energy and spatial distribution of X-ray photons from the pair halos and check the feasibility of pair halo detection by current and future X-ray observatories. The results show that current X-ray missions could register a positive signal for the pair halos created under some conditions. For a magnetic field (B) of ∼1 μG, the X-ray could be observable for a seed gamma-ray energy of Eg >~ 50 TeV. If Eg ~ 100 TeV, the observable range of B would be B>~300 nG.
... Therefore, the intrinsic spectrum should be well described by a power law with the observed GeV spectral index reported in the Fermi-LAT 4-Year Point Source Catalog ( Acero et al. 2015). An exponential cutoff was set in 10 TeV to ensure a sufficient amount of VHE gamma-rays (Eungwanichayapant & Aharonian 2009). ...
Intergalactic space is believed to contain nonzero magnetic fields (the Intergalactic Magnetic Field: IGMF), which at scales of megaparsecs would have intensities below 10⁻⁹ G. Very high energy (VHE > 100 GeV) gamma-rays coming from blazars can produce e⁺e⁻ pairs when interacting with the extragalactic background light (EBL) and the cosmic microwave background, generating an electromagnetic cascade of megaparsec scale. The IGMF may produce a detectable broadening of the emission beam that could lead to important constrains both on the IGMF intensity and its coherence length. Using the Monte Carlo-based Elmag code, we simulate the electromagnetic cascade corresponding to two detected TeV sources: PKS 2155-304 visible from the south and H1426+428 visible from the north. Assuming an EBL model and intrinsic spectral properties of the sources, we obtain the spectral and angular distribution of photons when they arrive at Earth. We include the response of the next generation Cherenkov telescopes by using simplified models for Cherenkov Telescope Array (CTA)-south and CTA-north based on a full simulation of each array performance. Combining the instrument properties with the simulated source fluxes, we calculate the telescope point-spread function for null and non-null IGMF intensities and develop a method to test the statistical feasibility of detecting IGMF imprints by comparing the resulting angular distributions. Our results show that for the analyzed source PKS 2155-304 corresponding to the southern site, CTA should be able to detect IGMF with intensities stronger than 10-14.5 G within an observation time of ∼100 hr. © 2018. The American Astronomical Society. All rights reserved.
... Therefore, the intrinsic spectrum should be well described by a power law with the observed GeV spectral index reported in the Fermi LAT 4-Year Point Source Catalog (Acero et al. 2015). An exponential cutoff was set in 10 TeV to ensure a sufficient amount of VHE gamma rays (Eungwanichayapant & Aharonian 2009). ...
Intergalactic space is believed to contain non-zero magnetic fields (the Intergalactic Magnetic Field: IGMF) which at scales of Mpc would have intensities below G. Very high energy (VHE 100 GeV) gamma rays coming from blazars can produce ee pairs when interacting with the Extragalactic Background Light (EBL) and the Cosmic Microwave Background, generating an electromagnetic cascade of Mpc scale. The IGMF may produce a detectable broadening of the emission beam that could lead to important constrains both on the IGMF intensity and its coherence length. Using the Monte Carlo-based Elmag code, we simulate the electromagnetic cascade corresponding to two detected TeV sources: PKS 2155-304 visible from the South and H1426+428 visible from the North. Assuming an EBL model and intrinsic spectral properties of the sources we obtain the spectral and angular distribution of photons when they arrive at Earth. We include the response of the next generation Cherenkov telescopes by using simplified models for CTA (Cherenkov Telescope Array)-south and CTA-north based on a full simulation of each array performance. Combining the instrument properties with the simulated source fluxes, we calculate the telescope point spread function for null and non-null IGMF intensities and develop a method to test the statistical feasibility of detecting IGMF imprints by comparing the resulting angular distributions. Our results show that for the analysed source PKS 2155-304 corresponding to the southern site, CTA should be able to detect IGMF with intensities stronger than 10G within an observation time of 100 hours.
... Brüggen et al. 2005;Brüggen 2013)-and thus the pairs are quickly isotropized. These are the typical conditions for the formation of giant pair halos (Aharonian et al. 1994;Eungwanichayapant & Aharonian 2009). However, studies of the point spread function (PSF) in the H.E.S.S. and VERITAS images of our targets seem to exclude the presence of extended emission (Abramowski et al. 2014;Archambault et al. 2017). ...
... However, studies of the point spread function (PSF) in the H.E.S.S. and VERITAS images of our targets seem to exclude the presence of extended emission (Abramowski et al. 2014;Archambault et al. 2017). Furthermore, the spectrum should be softer than observed below 200 GeV and the intrinsic primary flux is required to be ∼ 100× higher than the flux from EBL-correction alone, because of the re-isotropization (Eungwanichayapant & Aharonian 2009). This would increase dramatically the energy requirements of the source, both in luminosity and peak energy of the primary emission, making the problem of explaining the emitted SED even worse. ...
Hard-TeV BL Lacs are a new type of blazars characterized by a hard intrinsic TeV spectrum, locating the peak of their gamma-ray emission in the spectral energy distribution (SED) above 2-10 TeV. Such high energies are problematic for the Compton emission, using a standard one-zone leptonic model. We study six examples of this new type of BL Lacs in the hard X-ray band with the NuSTAR satellite. Together with simultaneous observations with the SWIFT satellite, we fully constrain the peak of the synchrotron emission in their SED, and test the leptonic synchrotron self-Compton (SSC) model. We confirm the extreme nature of 5 objects also in the synchrotron emission. We do not find evidence of additional emission components in the hard X-ray band. We find that a one-zone SSC model can in principle reproduce the extreme properties of both peaks in the SED, from X-ray up to TeV energies, but at the cost of i) extreme electron energies with very low radiative efficiency, ii) conditions heavily out of equipartition (by 3 to 5 orders of magnitude), and iii) not accounting for the simultaneous UV data, which then should belong to a different emission component, possibly the same as the far-IR (WISE) data. We find evidence of this separation of the UV and X-ray emission in at least two objects. In any case, the TeV electrons must not "see" the UV or lower-energy photons, even if coming from different zones/populations, or the increased radiative cooling would steepen the VHE spectrum.
... Brüggen et al. 2005;Brüggen 2013)-and thus the pairs are quickly isotropized. These are the typical conditions for the formation of giant pair halos (Aharonian et al. 1994;Eungwanichayapant & Aharonian 2009). However, studies of the point spread function (PSF) in the H.E.S.S. and VERITAS images of our targets seem to exclude the presence of extended emission (Abramowski et al. 2014;Archambault et al. 2017). ...
... However, studies of the point spread function (PSF) in the H.E.S.S. and VERITAS images of our targets seem to exclude the presence of extended emission (Abramowski et al. 2014;Archambault et al. 2017). Furthermore, the spectrum should be softer than observed below 200 GeV and the intrinsic primary flux is required to be ∼ 100× higher than the flux from EBL-correction alone, because of the re-isotropization (Eungwanichayapant & Aharonian 2009). This would increase dramatically the energy requirements of the source, both in luminosity and peak energy of the primary emission, making the problem of explaining the emitted SED even worse. ...
Hard-TeV BL Lacs are a new type of blazars characterized by a hard intrinsic TeV spectrum, locating the peak of their gamma-ray emission in the spectral energy distribution (SED) above 2-10 TeV. Such high energies are problematic for the Compton emission, using a standard one-zone leptonic model. We study six examples of this new type of BL Lacs in the hard X-ray band with the NuSTAR satellite. Together with simultaneous observations with the SWIFT satellite, we fully constrain the peak of the synchrotron emission in their SED, and test the leptonic synchrotron self-Compton (SSC) model. We confirm the extreme nature of 5 objects also in the synchrotron emission. We do not find evidence of additional emission components in the hard X-ray band. We find that a one-zone SSC model can in principle reproduce the extreme properties of both peaks in the SED, from X-ray up to TeV energies, but at the cost of i) extreme electron energies with very low radiative efficiency, ii) conditions heavily out of equipartition (by 3 to 5 orders of magnitude), and iii) not accounting for the simultaneous UV data, which then should belong to a different emission component, possibly the same as the far-IR (WISE) data. We find evidence of this separation of the UV and X-ray emission in at least two objects. In any case, the TeV electrons must not "see" the UV or lower-energy photons, even if coming from different zones/populations, or the increased radiative cooling would steepen the VHE spectrum.
... Les nouveaux photons gamma diffusés peuvent alors être émis dans la direction de l'observateur. Ceci induit la formation d'une source étendue autour de la source ponctuelle (Aharonian et al. 1994;Eungwanichayapant and Aharonian 2009). ...
... La mesure dépend aussi de la bande d'énergie considérée. Des halos de paires doivent être observables sur les blazars comme sur les sursauts gamma dans différentes bandes d'énergie gamma (Eungwanichayapant and Aharonian 2009) et même potentiellement dans la bande X (1 -10 keV) (Coppi 1998). La complexité d'observer des halos réside aussi dans la capacité à pouvoir distinguer le halo lié à la cascade du bruit de fond. ...
... ◮ Eungwanichayapant and Aharonian (2009) propose un code qui considère que les leptons sont isotropisés avant interaction (c'est-à-dire émis dans toutes les directions) ce qui crée une zone de cascades étendue. Ceci est valide pour des amplitudes du champ magnétique extragalactique comprise entre 10 −12 G et 10 −7 G. Comme la zone où se développe la cascade est assez restreinte, le spectre du fond diffus extragalactique est considéré comme ne variant pas sur l'ensemble du développement de la cascade (pas de prise en compte de l'évolution cosmologique du spectre). ...
Cette thèse vise à étudier le phénomène dit de « cascades électromagnétiques cosmologiques ». Ces cascadessont typiquement générées dans le milieu intergalactique par l’absorption de rayons gamma sur les photons du fond optique / UV et par la production de paires électron / positron associés. Ces leptons eux-mêmes interagissent avec les photons du fond diffus cosmologique via diffusion inverse Compton pour produire de nouveaux rayons gamma qui eux même peuvent s’annihiler, générant à partir d’un unique photon primaire toute une gerbe de photons et de particules secondaires. D’un point de vue observationnel, le développement de cette cascade introduit trois effets : une déformation du spectre à haute énergie, un retard temporel dans l’arrivée des rayons gamma et une extension de la taille apparente de la source.Les cascades électromagnétiques cosmologiques ont commencé à être étudiées dans les années soixante. Mais ce n’est qu’à partir des années 2010 avec l’arrivée du satellite Fermi (entre autres) et des observations dans la bande au GeV et au TeV que la discipline a explosé. Le phénomène est particulièrement important. D’une part il altère le spectre observé des sources rendant difficile la compréhension de la physique de ces dernières. D’autre part les cascades se développant dans le milieu extragalactique, elles sont très sensibles à la composition de ce dernier (fond diffus de photons, champ magnétique). Or ce milieu étant très ténu, il est difficile à étudier. Les cascades deviennent alors une formidable sonde pour accéder à sa compréhension et pouvoir en comprendre l’origine qui remonte au commencement de l’Univers.Pourtant les cascades cosmologiques sont un phénomène complexe faisant intervenir des interactions difficiles à modéliser (sections efficaces complexes) et le transport de particules dans un Univers en expansion (cosmologie). Face à cette complexité les expressions analytiques sont vite limitées et le passage au numérique devient inévitable. Dans le cadre de cette thèse un code de simulation Monte Carlo a donc été développé visant à reproduire aussi précisément que possible le phénomène des cascades. Ce code a été testé et validé en le confrontant aux expressions analytiques.Grâce à ce code, le rôle des différents paramètres physiques impactant le développement de la cascade a été étudié de manière systématique. Cette étude a permis de mieux comprendre la physique du phénomène. En particulier, l’impact des propriétés du milieu extragalactique (fond diffus extragalactique, champ magnétique extragalactique) sur les observables a été mis en évidence.Finalement, une seconde étude a été menée pour mesurer la contribution des cascades au fond gamma extragalactique. Des travaux récents montrent qu’une grande partie de l’émission diffuse à très haute énergie provient de sources ponctuelles non résolues (blazars en particulier). Ces sources gamma (résolues et non résolues) doivent en principe initier des cascades qui peuvent contribuer au fond diffus. En partant d’une modélisation de l’émission des blazars à différents redshifts, l’absorption et la contribution des cascades ont alors été calculées à l’aide du code Monte Carlo. Les résultats montrent que la contribution des cascades au fond gamma extragalactique pourrait violer les limites Fermi mais l’excès doit encore être confirmé.
... First, the source spectrum is altered because each high energy TeV photon is reprocessed into thousands of GeV photons (Protheroe 1986;Roscherr & Coppi 1998;Aharonian et al. 2002;Neronov & Vovk 2010). Second, due to the deflection of leptons by the EGMF, new gamma-rays are emitted along different lines of sight, so that a point source may appear as extended (Aharonian et al. 1994;Eungwanichayapant & Aharonian 2009). Third, as leptons are deflected, cascade photons travel a longer distance and arrive with a significant time delay, as compared to unabsorbed, primary photons (Kronberg 1995;Plaga 1995;Ichiki et al. 2008;Murase et al. 2008;Takahashi et al. 2008). ...
TeV photons from extragalactic sources are absorbed in the intergalactic medium and initiate electromagnetic cascades. These cascades offer a unique tool to probe the properties of the universe at cosmological scales. We present a new Monte Carlo code dedicated to the physics of such cascades. This code has been tested against both published results and analytical approximations, and is made publicly available. Using this numerical tool, we investigate the main cascade properties (spectrum, halo extension, time delays), and study in detail their dependence on the physical parameters (extra-galactic magnetic field, extra-galactic background light, source redshift, source spectrum and beaming emission). The limitations of analytical solutions are emphasised. In particular, analytical approximations account only for the first generation of photons and higher branches of the cascade tree are neglected.
... A general model for the shape of cascade spectra was developed in Zdziarski (1988). A more recent model can be found in Eungwanichayapant & Aharonian (2009) and is depicted as the grey curve in Fig. 3. Although predictions at the high-energy end of the cascade strongly depend on the cutoff energy of the injection spectrum, an index of ∼2 is expected in the energy range just before the secondary flux drops rapidly. ...
... In the publication by Eungwanichayapant & Aharonian (2009), a study of the formation of PHs was conducted. In particular, the authors investigated the spectral and angular distributions of PHs in relation to the redshift of the central source, the spectral shape of the primary γ-rays and the flux of the EBL. ...
... For the Primack et al. (2001) EBL model, the differential angular distribution of a PH at z ≈ 0.13 and E γ > 100 GeV, which best suits our data, was taken from Fig. 6 of Eungwanichayapant & Aharonian (2009) and is used here to derive limits on a possible PH flux. The effect of the slight differences between the assumed redshift in the model and the actual redshifts of the analysed sources is smaller than the effect of different EBL models and will therefore be neglected. ...
Context: Very-high-energy (VHE; E>100 GeV) {\gamma}-ray emission from blazars
inevitably gives rise to electron-positron pair production through the
interaction of these {\gamma}-rays with the Extragalactic Background Light
(EBL). Depending on the magnetic fields in the proximity of the source, the
cascade initiated from pair production can result in either an isotropic halo
around an initially beamed source or a magnetically broadened cascade flux.
Aims: Both extended pair halo (PH) and magnetically broadened cascade (MBC)
emission from regions surrounding the blazars 1ES 1101-232, 1ES 0229+200 and
PKS 2155-304 were searched for, using VHE {\gamma}-ray data taken with the High
Energy Stereoscopic System (H.E.S.S.), and high energy (HE; 100 MeV<E<100 GeV)
{\gamma}-ray data with the Fermi Large Area Telescope (LAT). Methods: By
comparing the angular distributions of the reconstructed gamma-ray events to
the angular profiles calculated from detailed theoretical models, the presence
of PH and MBC was investigated. Results: Upper limits on the extended emission
around 1ES 1101-232, 1ES 0229+200 and PKS 2155-304 are found to be at a level
of few percent of the Crab nebula flux above 1 TeV, depending on the assumed
photon index of the cascade emission. Assuming strong Extra-Galactic Magnetic
Field (EGMF) values, > 10G, this limits the production of pair halos
developing from electromagnetic cascades. For weaker magnetic fields, in which
electromagnetic cascades would result in magnetically broadened cascades, EGMF
strengths in the range (0.3 - 3)G were excluded for PKS
2155-304 at the 99% confidence level, under the assumption of a 1 Mpc coherence
length.
