Exploring the Emission Mechanisms of Mrk 180 with Long-term X-Ray and γ-Ray Data

Abstract

Markarian (Mrk) 180 is a BL Lacertae object located at a redshift of 0.045 and is a potential candidate for high-energy cosmic-ray acceleration. We have analyzed the Fermi Large Area Telescope (Fermi-LAT) γ-ray data of Mrk 180 collected over a period of 12.8 yr and found no significant enhancement in the flux from the long-term γ-ray light curve. We have also analyzed Swift X-ray, ultraviolet, and optical, and X-ray Multi-Mirror Mission (XMM-Newton) data to construct the multiwavelength spectral energy distribution (SED). The SED has been modeled with one-zone pure leptonic and lepto-hadronic scenarios to explain the underlying physics of multiwavelength emission. The pure leptonic model and the two lepto-hadronic models, viz., (i) line-of-sight interactions of ultrahigh-energy cosmic rays (UHECRs; E ≳ 1017 eV) with the cosmic background radiation and (ii) the interactions of relativistic protons with the cold protons in the jet, have been compared in our work. Moreover, an earlier study has associated Mrk 180 with the Telescope Array (TA) hotspot of UHECRs at E > 57 EeV. This speculation motivates us to check whether ultrahigh-energy protons and iron nuclei can reach the Earth from Mrk 180. After comparing the results of our simulation with the current observational data, we find that Mrk 180 is unlikely to be a source of the UHECR events contributing to the TA hotspot for conservative strengths of extragalactic magnetic fields.