PACHA: Probing AGN Coronae with High-redshift AGN
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| Natura: | Preprint |
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2026
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| author | Zhao, Xiurui Kammoun, Elias Ajello, Marco Jiang, Yanfei Lanzuisi, Giorgio Lohfink, Anne Marchesi, Stefano Bertola, Elena Boorman, Peter G. Civano, Francesca Comisso, Luca Coppi, Paolo Cox, Isaiah S. Elvis, Martin Gilli, Roberto Harrison, Fiona A. Silver, Ross Stern, Daniel Torres-Albà, Nuria Yang, Qian Zhang, Lizhong |
| author_facet | Zhao, Xiurui Kammoun, Elias Ajello, Marco Jiang, Yanfei Lanzuisi, Giorgio Lohfink, Anne Marchesi, Stefano Bertola, Elena Boorman, Peter G. Civano, Francesca Comisso, Luca Coppi, Paolo Cox, Isaiah S. Elvis, Martin Gilli, Roberto Harrison, Fiona A. Silver, Ross Stern, Daniel Torres-Albà, Nuria Yang, Qian Zhang, Lizhong |
| contents | The X-ray emission of active galactic nuclei (AGN) is generally attributed to inverse Compton scattering of accretion-disk photons by hot electrons in a compact corona. In local AGN, directly constraining coronal properties is challenging because the high-energy cutoff often lies beyond the NuSTAR bandpass. High-redshift, luminous quasars enable systematic constraints on the high-energy cutoff, as cosmological redshift shifts the spectal cutoff into the observable hard X-ray band. We present first results from the ``Probing the AGN Coronae with High-redshift AGN'' (PACHA) project, based on quasi-simultaneous NuSTAR and XMM-Newton observations of 13 radio-quiet AGN at $z>1$. We constrain the high-energy cutoff and coronal temperature at 90\% confidence level for 10 and 9 sources, respectively. The sample exhibits a mean cutoff energy of $E_{\rm cut}=80.8\pm8.1$ keV and a mean coronal temperature of $kT_{\rm e}=18.4\pm1.6$ keV, both significantly lower than those measured in local {\it Swift}-BAT AGN, while the mean optical depth ($τ=4.8\pm0.3$) is significantly higher. The uncertainties are at 1~$σ$. Combining our high-redshift sample with local AGN, we find a potential anti-correlation between cutoff energy and both X-ray luminosity and black hole mass, with no significant dependence on Eddington ratio. Within a hybrid coronal framework, the inferred temperatures lie well below the pair-production limits for purely thermal coronae, indicating a substantial efficient Compton cooling and/or non-thermal electron component. The detection of low coronal temperatures in high-luminosity AGN is broadly consistent with predictions from recent radiation MHD simulations that consider purely thermal electron populations, implying that non-thermal electrons may not be the primary drivers of the observed coronal properties in these systems. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_11286 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | PACHA: Probing AGN Coronae with High-redshift AGN Zhao, Xiurui Kammoun, Elias Ajello, Marco Jiang, Yanfei Lanzuisi, Giorgio Lohfink, Anne Marchesi, Stefano Bertola, Elena Boorman, Peter G. Civano, Francesca Comisso, Luca Coppi, Paolo Cox, Isaiah S. Elvis, Martin Gilli, Roberto Harrison, Fiona A. Silver, Ross Stern, Daniel Torres-Albà, Nuria Yang, Qian Zhang, Lizhong High Energy Astrophysical Phenomena Astrophysics of Galaxies The X-ray emission of active galactic nuclei (AGN) is generally attributed to inverse Compton scattering of accretion-disk photons by hot electrons in a compact corona. In local AGN, directly constraining coronal properties is challenging because the high-energy cutoff often lies beyond the NuSTAR bandpass. High-redshift, luminous quasars enable systematic constraints on the high-energy cutoff, as cosmological redshift shifts the spectal cutoff into the observable hard X-ray band. We present first results from the ``Probing the AGN Coronae with High-redshift AGN'' (PACHA) project, based on quasi-simultaneous NuSTAR and XMM-Newton observations of 13 radio-quiet AGN at $z>1$. We constrain the high-energy cutoff and coronal temperature at 90\% confidence level for 10 and 9 sources, respectively. The sample exhibits a mean cutoff energy of $E_{\rm cut}=80.8\pm8.1$ keV and a mean coronal temperature of $kT_{\rm e}=18.4\pm1.6$ keV, both significantly lower than those measured in local {\it Swift}-BAT AGN, while the mean optical depth ($τ=4.8\pm0.3$) is significantly higher. The uncertainties are at 1~$σ$. Combining our high-redshift sample with local AGN, we find a potential anti-correlation between cutoff energy and both X-ray luminosity and black hole mass, with no significant dependence on Eddington ratio. Within a hybrid coronal framework, the inferred temperatures lie well below the pair-production limits for purely thermal coronae, indicating a substantial efficient Compton cooling and/or non-thermal electron component. The detection of low coronal temperatures in high-luminosity AGN is broadly consistent with predictions from recent radiation MHD simulations that consider purely thermal electron populations, implying that non-thermal electrons may not be the primary drivers of the observed coronal properties in these systems. |
| title | PACHA: Probing AGN Coronae with High-redshift AGN |
| topic | High Energy Astrophysical Phenomena Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2603.11286 |