Even a precessing clock is right twice per orbit -- The super-periods of eRO-QPE2 and challenges for quasi-periodic eruption orbital models
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arXiv
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2026
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| author | Arcodia, R. Miniutti, G. Chakraborty, J. Franchini, A. Giustini, M. Linial, I. Mummery, A. Bertassi, L. Bonetti, M. Kara, E. Merloni, A. Motta, A. Ponti, G. Quintin, E. Soria, R. Baldini, P. Buchner, J. Dotti, M. Fragile, P. C. Ingram, A. Middleton, M. Panagiotou, C. Sesana, A. Yao, P. Rau, A. Vincentelli, F. M. Guolo, M. Saxton, R. |
| author_facet | Arcodia, R. Miniutti, G. Chakraborty, J. Franchini, A. Giustini, M. Linial, I. Mummery, A. Bertassi, L. Bonetti, M. Kara, E. Merloni, A. Motta, A. Ponti, G. Quintin, E. Soria, R. Baldini, P. Buchner, J. Dotti, M. Fragile, P. C. Ingram, A. Middleton, M. Panagiotou, C. Sesana, A. Yao, P. Rau, A. Vincentelli, F. M. Guolo, M. Saxton, R. |
| contents | We present O$-$C (``observed minus calculated'') timing analysis of the quasi-periodic eruption (QPE) source eRO-QPE2 with a multi-mission X-ray campaign, which includes 32 observed eruptions spanning a month (i.e. 325 QPE cycles). In relation to accretion (e.g. disk instability) models, the O-C is consistent with a damped random walk of the QPE recurrence, albeit with highly uncertain parameters. If instead an underlying orbital clock is present, eRO-QPE2 is consistent with a period of $P \sim 2.24$\,h and two hierarchical super-periodic modulations, with periods of $\sim 4.4$\,d ($\sim47$\,P) and $\approx 95$\,d ($\approx 1000$\,P). We found no negative period derivative, with $|\dot{P}| \lesssim 2 \times 10^{-6}$\,s/s at $3σ$. This disfavors high-eccentricity WDs and high-mass/eccentricity IMBHs via GW decay. For disk-collision models, where the $\dot{P}$ from gas drag and the QPE integrated energy provide bounds on the local disk density, a main-sequence star is disfavored as EMRI secondary unless stellar debris streams are present, while stripped stars remain allowed. The correlated odd/even O-C disfavors both disk crossings per orbit being observed. Interpreting the data with one \emph{observed} event per orbit, the short modulation is consistent with apsidal precession for $a \sim 140\,R_g$, $e \approx 0.1$, and $M_{\rm BH} \approx 1.5 \times 10^{5}\,M_\odot$. The longer modulation (much less constrained) is inconsistent with EMRI nodal precession and disk precession is allowed for a limited parameter volume, while there is a solution with a stable hierarchical triple system with an outer massive black hole at $\sim 0.4\,\mathrm{mpc}$ and mass $\sim(0.1-1) \times M_{\rm BH}$. However, no reliable solution can be found with more robust EMRI trajectory models, possibly due to narrow likelihood peaks in a multi-dimensional parameter space with sparse data. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_09788 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Even a precessing clock is right twice per orbit -- The super-periods of eRO-QPE2 and challenges for quasi-periodic eruption orbital models Arcodia, R. Miniutti, G. Chakraborty, J. Franchini, A. Giustini, M. Linial, I. Mummery, A. Bertassi, L. Bonetti, M. Kara, E. Merloni, A. Motta, A. Ponti, G. Quintin, E. Soria, R. Baldini, P. Buchner, J. Dotti, M. Fragile, P. C. Ingram, A. Middleton, M. Panagiotou, C. Sesana, A. Yao, P. Rau, A. Vincentelli, F. M. Guolo, M. Saxton, R. High Energy Astrophysical Phenomena We present O$-$C (``observed minus calculated'') timing analysis of the quasi-periodic eruption (QPE) source eRO-QPE2 with a multi-mission X-ray campaign, which includes 32 observed eruptions spanning a month (i.e. 325 QPE cycles). In relation to accretion (e.g. disk instability) models, the O-C is consistent with a damped random walk of the QPE recurrence, albeit with highly uncertain parameters. If instead an underlying orbital clock is present, eRO-QPE2 is consistent with a period of $P \sim 2.24$\,h and two hierarchical super-periodic modulations, with periods of $\sim 4.4$\,d ($\sim47$\,P) and $\approx 95$\,d ($\approx 1000$\,P). We found no negative period derivative, with $|\dot{P}| \lesssim 2 \times 10^{-6}$\,s/s at $3σ$. This disfavors high-eccentricity WDs and high-mass/eccentricity IMBHs via GW decay. For disk-collision models, where the $\dot{P}$ from gas drag and the QPE integrated energy provide bounds on the local disk density, a main-sequence star is disfavored as EMRI secondary unless stellar debris streams are present, while stripped stars remain allowed. The correlated odd/even O-C disfavors both disk crossings per orbit being observed. Interpreting the data with one \emph{observed} event per orbit, the short modulation is consistent with apsidal precession for $a \sim 140\,R_g$, $e \approx 0.1$, and $M_{\rm BH} \approx 1.5 \times 10^{5}\,M_\odot$. The longer modulation (much less constrained) is inconsistent with EMRI nodal precession and disk precession is allowed for a limited parameter volume, while there is a solution with a stable hierarchical triple system with an outer massive black hole at $\sim 0.4\,\mathrm{mpc}$ and mass $\sim(0.1-1) \times M_{\rm BH}$. However, no reliable solution can be found with more robust EMRI trajectory models, possibly due to narrow likelihood peaks in a multi-dimensional parameter space with sparse data. |
| title | Even a precessing clock is right twice per orbit -- The super-periods of eRO-QPE2 and challenges for quasi-periodic eruption orbital models |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2604.09788 |