Discovery of a 9.67-s pulsar in an ultraluminous X-ray source in NGC 4631 with XMM-Newton
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| Main Authors: | , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866915602149408768 |
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| author | Ducci, L. Mereghetti, S. Pintore, F. Allak, S. Santangelo, A. Sasaki, M. Kavanagh, P. |
| author_facet | Ducci, L. Mereghetti, S. Pintore, F. Allak, S. Santangelo, A. Sasaki, M. Kavanagh, P. |
| contents | Thanks to a recent observation with XMM-Newton, we discovered periodic pulsations at P= 9.6652 +/- 0.0002 s in a new ultraluminous X-ray source (ULX) in the galaxy NGC 4631. This source, dubbed as X-8, shows one of the largest spin-up rates ever observed, dP/dt = (-9.6 +/- 0.5)*1E-8 s/s. These findings indicate that the compact object is a neutron star, and X-8 is a new member of the pulsating ULX class. The 0.3-10 keV luminosity of X-8 is ~3.4E39 erg/s, and its X-ray spectrum can be described by an absorbed disk blackbody or a cut-off power law, similar to what is observed in other pulsating ULXs. We discuss two possible causes for the large spin-up rate: Doppler shift from orbital motion of the neutron star and intrinsic spin-up due to accretion torque. This new ULX pulsar adds a key source to the small known population, and will enable future studies to better constrain the physical mechanisms responsible for their super-Eddington luminosities. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2511_04282 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Discovery of a 9.67-s pulsar in an ultraluminous X-ray source in NGC 4631 with XMM-Newton Ducci, L. Mereghetti, S. Pintore, F. Allak, S. Santangelo, A. Sasaki, M. Kavanagh, P. High Energy Astrophysical Phenomena Thanks to a recent observation with XMM-Newton, we discovered periodic pulsations at P= 9.6652 +/- 0.0002 s in a new ultraluminous X-ray source (ULX) in the galaxy NGC 4631. This source, dubbed as X-8, shows one of the largest spin-up rates ever observed, dP/dt = (-9.6 +/- 0.5)*1E-8 s/s. These findings indicate that the compact object is a neutron star, and X-8 is a new member of the pulsating ULX class. The 0.3-10 keV luminosity of X-8 is ~3.4E39 erg/s, and its X-ray spectrum can be described by an absorbed disk blackbody or a cut-off power law, similar to what is observed in other pulsating ULXs. We discuss two possible causes for the large spin-up rate: Doppler shift from orbital motion of the neutron star and intrinsic spin-up due to accretion torque. This new ULX pulsar adds a key source to the small known population, and will enable future studies to better constrain the physical mechanisms responsible for their super-Eddington luminosities. |
| title | Discovery of a 9.67-s pulsar in an ultraluminous X-ray source in NGC 4631 with XMM-Newton |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2511.04282 |