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P. Thévenet

Publications and source records attributed to P. Thévenet.

2 recordsLinked to original sources
arXiv2026

Searching for Nearby Supermassive Black Hole Binaries with GRAVITY

We present a systematic interferometric search for close supermassive black hole (SMBH) binaries in 20 nearby type 1 active galactic nuclei (AGN) observed with VLTI/\grav. We investigate parsec-scale asymmetric emission by modeling the squared visibilities and closure phases with a single circular Gaussian component plus a background point source for the central AGN, and searching for additional compact companions through grid-based binary models. The robustness of the search is validated using injection-recovery simulations and point-spread-function diagnostics. Several features are identified in the initial significance maps, but only one candidate out of 20 shows a persistent compact asymmetry, corresponding to an observed incidence of $5\%$. If NGC~3783 is interpreted as a binary AGN, we derive a Poissonian one-sided $1σ$ upper limit of $f_{\rm bin}<16.5\%$ for GRAVITY-detectable binaries among bright nearby AGN (K<12.5) at separations of $\sim1$-$100$~pc. Conversely, if the observed asymmetry in NGC~3783 is associated with asymmetric circumnuclear dust emission, the corresponding upper limit on the binary fraction is $f_{\rm bin}<9.2\%$. We compare these results with predictions from the Horizon-AGN simulation, finding comparable binary fractions. We also noted that the expected fraction strongly depends on the assumed distribution of individual SMBH accretion rates within binaries, which is currently unresolved in cosmological models. Our results demonstrate the potential of infrared interferometry to identify parsec-scale binary AGN candidates and motivate future GRAVITY+ observations to expand the sample and follow up known candidates, helping to confirm their nature and distinguish genuine binaries from asymmetric nuclear structures.

astro-ph.GA↗
arXiv2026

Improving constraints on the Yukawa correction at the Galactic Center with multiple stellar orbits

We investigate the presence of a Yukawa-like correction ($\propto \, αe^{- r/λ}$) to Newtonian gravity at the Galactic Center, using a multi-star fitting code, including the newly discovered star S$301$, to improve the constraints obtained using S$2$ orbit alone. We perform a Markov Chain Monte Carlo analysis using the astrometric and spectroscopic data of stars S$2$, S$55$, S$29$, S$38$ and S$301$ collected by GRAVITY, GRAVITY$^+$, NACO and SINFONI instruments, covering the period from $1992$ to $2025$. Compared to GRAVITY Collaboration 2025 (Paper I), in which only S$2$ was fitted, the tightest bound on the Yukawa coupling is again reached at $λ= 3\cdot10^{13}\,\rm m\ (\sim 200\,AU)$, where we find $|α| < 6 \cdot10^{-4}$, an improvement of roughly a factor five. The addition of S$301$ extends the constraint to short ranges that were inaccessible to S$2$, yielding $|α| < 0.004$ at $λ=10^{12}\,\rm m$ and $|α| < 0.006$ at $λ=5\cdot 10^{11}\,\rm m$, while S$29$, with its larger apoapsis, gives $|α| < 0.1$ at $λ\sim 2\cdot10^{15}\,\rm m$. The latter two represent the tightest limits at these scale lengths on a Yukawa correction obtained to date around a supermassive black hole.

astro-ph.GA↗