Hadronic Processes in Advection-Dominated Accretion Flow as the Origin of TeV Excesses in BL Lac Objects
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arXiv
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| Autores principales: | , , |
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| Formato: | Preprint |
| Publicado: |
2025
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| _version_ | 1866917069021249536 |
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| author | Lian, Ji-Shun Wang, Ze-Rui Zhang, Jin |
| author_facet | Lian, Ji-Shun Wang, Ze-Rui Zhang, Jin |
| contents | The spectral energy distributions (SEDs) of certain BL Lac objects (BL Lacs) exhibit an additional hard $γ$-ray component in the TeV energy range that surpasses the predictions of the one-zone leptonic jet model. The origin of this excess emission remains unclear. In this study, we selected five BL Lacs whose SEDs display a very hard intrinsic spectrum in the TeV band and successfully reproduced their broadband SEDs using a two-zone lepto-hadronic model. Within this framework, the emission observed in the optical, X-ray, GeV $γ$-ray, and sub-TeV $γ$-ray bands is modeled using the synchrotron and synchrotron self-Compton radiation processes of the relativistic electrons in the jets. Meanwhile, the TeV excess is attributed to $γ$-ray emission resulting from the photomeson ($pγ$) process via $π^0$ decay occurring within advection-dominated accretion flows (ADAFs). This scenario requires a hard proton spectrum with a spectral index of $p \sim 1.6-1.7$ and a cutoff energy ranging from 30 to 90 TeV, as well as a relatively large ADAF radius. Such hard proton spectra suggest that the dominant acceleration mechanisms are likely magnetic reconnection and/or stochastic acceleration processes within ADAFs. Additionally, the emission from the cascaded electrons results in a bump in the keV--MeV band; however, it is overwhelmed by the jet emission. Although the hadronuclear ($pp$) process cannot be entirely ruled out, it would necessitate an even harder proton spectrum and a higher cutoff energy compared to the $pγ$ process, making it a less favorable explanation for the observed TeV excess. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_04202 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Hadronic Processes in Advection-Dominated Accretion Flow as the Origin of TeV Excesses in BL Lac Objects Lian, Ji-Shun Wang, Ze-Rui Zhang, Jin High Energy Astrophysical Phenomena Astrophysics of Galaxies The spectral energy distributions (SEDs) of certain BL Lac objects (BL Lacs) exhibit an additional hard $γ$-ray component in the TeV energy range that surpasses the predictions of the one-zone leptonic jet model. The origin of this excess emission remains unclear. In this study, we selected five BL Lacs whose SEDs display a very hard intrinsic spectrum in the TeV band and successfully reproduced their broadband SEDs using a two-zone lepto-hadronic model. Within this framework, the emission observed in the optical, X-ray, GeV $γ$-ray, and sub-TeV $γ$-ray bands is modeled using the synchrotron and synchrotron self-Compton radiation processes of the relativistic electrons in the jets. Meanwhile, the TeV excess is attributed to $γ$-ray emission resulting from the photomeson ($pγ$) process via $π^0$ decay occurring within advection-dominated accretion flows (ADAFs). This scenario requires a hard proton spectrum with a spectral index of $p \sim 1.6-1.7$ and a cutoff energy ranging from 30 to 90 TeV, as well as a relatively large ADAF radius. Such hard proton spectra suggest that the dominant acceleration mechanisms are likely magnetic reconnection and/or stochastic acceleration processes within ADAFs. Additionally, the emission from the cascaded electrons results in a bump in the keV--MeV band; however, it is overwhelmed by the jet emission. Although the hadronuclear ($pp$) process cannot be entirely ruled out, it would necessitate an even harder proton spectrum and a higher cutoff energy compared to the $pγ$ process, making it a less favorable explanation for the observed TeV excess. |
| title | Hadronic Processes in Advection-Dominated Accretion Flow as the Origin of TeV Excesses in BL Lac Objects |
| topic | High Energy Astrophysical Phenomena Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2511.04202 |