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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
| Published: |
2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2502.17617 |
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| _version_ | 1866909550965161984 |
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| author | Lusso, Elisabeta Casetti, Lapo Romoli, Marco Fossi, Lara Nardini, Emanuele Arra, Emanuele Barsi, Benedetta Calamai, Clarissa Campani, Francesca Capogrosso, Riccardo Tegli, Francesco Chiti Ciantini, Riccardo Demertzi, Eirini Gaitani, Marina A. Giudice, Asia Gori, Alessia Graziani, Lorenzo Macchiarini, Laura Michelagnoli, Marianna Niccolai, Chiara Parenti, Irene Pistolesi, Simone Rago, Martina Romani, Ofelia Sani, Leonardo Sartini, Jacopo Scianni, Matilde Triggianese, Alba Andreuzzi, Gloria Ambrosino, Filippo |
| author_facet | Lusso, Elisabeta Casetti, Lapo Romoli, Marco Fossi, Lara Nardini, Emanuele Arra, Emanuele Barsi, Benedetta Calamai, Clarissa Campani, Francesca Capogrosso, Riccardo Tegli, Francesco Chiti Ciantini, Riccardo Demertzi, Eirini Gaitani, Marina A. Giudice, Asia Gori, Alessia Graziani, Lorenzo Macchiarini, Laura Michelagnoli, Marianna Niccolai, Chiara Parenti, Irene Pistolesi, Simone Rago, Martina Romani, Ofelia Sani, Leonardo Sartini, Jacopo Scianni, Matilde Triggianese, Alba Andreuzzi, Gloria Ambrosino, Filippo |
| contents | Active galactic nuclei (AGN) are known to be variable sources across the entire electromagnetic spectrum, in particular at optical/ultraviolet and X-ray energies. Over the past decades, a growing number of AGN have displayed type transitions: from type 1 to type 2 or viceversa within a few years or even several months. These galaxies have been commonly referred to as changing-look AGN (CLAGN). Here we report on a new CLAGN, NGC 4614, which transitioned from a type 1.9 to a type 2 state. NGC 4614 is a nearly face-on barred galaxy at redshift $z = 0.016$, classified as a low-luminosity AGN. Its central black hole has a mass of about $1.6\times 10^7 M_\odot$ and an Eddington ratio around 1 percent. We recently acquired optical spectra of NGC 4614 at the Telescopio Nazionale Galileo and the data clearly suggest that the broad H$α$ component has strongly dimmed, if not disappeared. A very recent Swift observation confirmed our current optical data, with the AGN weakened by almost a factor of 10 with respect to previous X-ray observations. Indeed, NGC 4614 had been also observed by Swift/XRT 6 times in 2011, when the source was clearly detected in all observations. By fitting the stack of the 2011 Swift observations we obtain a photon index of $Γ=1.3\pm0.3$ and an equivalent hydrogen column density of $N_{\rm H}$=$1.2\pm0.3$ $\times$10$^{22}$ cm$^{-2}$, indicating that NGC 4614 can be moderately absorbed in the X-rays. Although a significant change in the foreground gas absorption that may have obscured the broad line region cannot be entirely ruled out, the most likely explanation for our optical and X-ray data is that NGC 4614 is experiencing a change in the accretion state that reduces the radiative efficiency of the X-ray corona. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2502_17617 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Low-Eddington ratio, changing-look active galactic nuclei: the case of NGC 4614 Lusso, Elisabeta Casetti, Lapo Romoli, Marco Fossi, Lara Nardini, Emanuele Arra, Emanuele Barsi, Benedetta Calamai, Clarissa Campani, Francesca Capogrosso, Riccardo Tegli, Francesco Chiti Ciantini, Riccardo Demertzi, Eirini Gaitani, Marina A. Giudice, Asia Gori, Alessia Graziani, Lorenzo Macchiarini, Laura Michelagnoli, Marianna Niccolai, Chiara Parenti, Irene Pistolesi, Simone Rago, Martina Romani, Ofelia Sani, Leonardo Sartini, Jacopo Scianni, Matilde Triggianese, Alba Andreuzzi, Gloria Ambrosino, Filippo Astrophysics of Galaxies Active galactic nuclei (AGN) are known to be variable sources across the entire electromagnetic spectrum, in particular at optical/ultraviolet and X-ray energies. Over the past decades, a growing number of AGN have displayed type transitions: from type 1 to type 2 or viceversa within a few years or even several months. These galaxies have been commonly referred to as changing-look AGN (CLAGN). Here we report on a new CLAGN, NGC 4614, which transitioned from a type 1.9 to a type 2 state. NGC 4614 is a nearly face-on barred galaxy at redshift $z = 0.016$, classified as a low-luminosity AGN. Its central black hole has a mass of about $1.6\times 10^7 M_\odot$ and an Eddington ratio around 1 percent. We recently acquired optical spectra of NGC 4614 at the Telescopio Nazionale Galileo and the data clearly suggest that the broad H$α$ component has strongly dimmed, if not disappeared. A very recent Swift observation confirmed our current optical data, with the AGN weakened by almost a factor of 10 with respect to previous X-ray observations. Indeed, NGC 4614 had been also observed by Swift/XRT 6 times in 2011, when the source was clearly detected in all observations. By fitting the stack of the 2011 Swift observations we obtain a photon index of $Γ=1.3\pm0.3$ and an equivalent hydrogen column density of $N_{\rm H}$=$1.2\pm0.3$ $\times$10$^{22}$ cm$^{-2}$, indicating that NGC 4614 can be moderately absorbed in the X-rays. Although a significant change in the foreground gas absorption that may have obscured the broad line region cannot be entirely ruled out, the most likely explanation for our optical and X-ray data is that NGC 4614 is experiencing a change in the accretion state that reduces the radiative efficiency of the X-ray corona. |
| title | Low-Eddington ratio, changing-look active galactic nuclei: the case of NGC 4614 |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2502.17617 |