高能暂现源 · 每日文献综述

The blazar 3C 454.3 is considered a promising candidate for hosting a supermassive black hole binary (SMBHB) capable of generating gravitational waves in the nanohertz frequency range. Using long-term multifrequency radio observations spanning nearly six decades, we identify a persistent quasi-periodic modulation with a characteristic timescale of 2.3 yr in the observer's frame. Interpreting this variability within a relativistic jet framework and adopting a Lorentz factor of γ = 5 yields an intrinsic orbital period of approximately 31 yr. The derived binary parameters correspond to component masses of M ≍ 2.4 × 10<SUP>10</SUP> M<SUB>⊙</SUB> and m ≍ 6.8 × 10<SUP>9</SUP> M<SUB>⊙</SUB>, separated by a Keplerian distance of a ≍ 4.6 × 10<SUP>17</SUP> cm. Under these conditions, the system is expected to radiate gravitational waves at an observed frequency of f<SUB>GW</SUB> ≍ 1.1 × 10<SUP>−9</SUP> Hz (≍ 2.0 × 10<SUP>−9</SUP> Hz in the source frame), placing it firmly within the sensitivity window of pulsar timing arrays (PTAs). The estimated characteristic strain amplitude is h<SUB>0</SUB> ≍ (7─9) × 10<SUP>−16</SUP>.The binary is predicted to merge on a timescale of approximately 5.7 × 10<SUP>4</SUP> yr. Although gravitational-wave emission drives a secular orbital evolution, the expected period change is extremely small, corresponding to a cumulative shift of only a few days over the full duration of available observations. Such a signal is far below the level that can be extracted from the intrinsically variable, Doppler-boosted electromagnetic emission of the source. These results support the interpretation of 3C 454.3 as a potential nanohertz gravitational-wave emitter and suggest that exceptionally massive SMBHB systems of this type may contribute not only to future PTA continuous-wave detections but also to the large-scale anisotropy of the stochastic gravitational-wave background.

Hierarchical triples are promising environments for producing exotica such as black hole mergers and hot Jupiters, because of the von Zeipel─Lidov─Kozai (ZLK) effect, whereby a distant tertiary can torque an inner binary to high eccentricity over secular timescales. In the double-averaged (DA) approximation to ZLK, this eccentricity excitation is suppressed by apsidal precession due to "short-range forces" (SRFs) like relativity and tidal/rotational bulges. Here, we show that, when the DA approximation breaks down, SRFs often catalyze, rather than suppress, extreme-eccentricity behavior. This occurs because SRFs can drive large, discrete jumps in the binary's effective "adiabatic invariants" during high-eccentricity episodes. These nonadiabatic jumps can dramatically alter the maximum/minimum eccentricity and secular period of astrophysically relevant triples, including some for which SRFs were previously thought irrelevant. Even the angular-momentum component j<SUB>z</SUB> evolves secularly—to our knowledge, this is the first time such evolution has been demonstrated from a test-particle quadrupole-order, three-body mechanism. In short, binaries may explore much more of phase space than is implied by any (semi)analytic ZLK theory of which we are aware. We demonstrate this at the test-particle quadrupole level; in a companion work, we show how even more-extreme behavior occurs when the jumps are combined with octupolar ZLK evolution.

A robust understanding of selection effects in galaxy cluster studies is crucial for both astrophysical and cosmological applications. Examining clusters identified through different observational strategies, even in small numbers, helps to illuminate potential biases inherent to each method. We selected four rich galaxy clusters in the northern hemisphere whose early Swift X-ray Telescope (XRT) observations indicated unusually low central X-ray emission, making them unlikely to be detected in X-ray surveys. Spectroscopic follow-up confirms that all four systems are genuine galaxy clusters, rather than projections of multiple clusters or groups along the line of sight. Their optical richness, estimated using one of the baseline Euclid cluster richness estimators, implies masses of log M<SUB>200</SUB>/M<SUB>⊙</SUB> ∼ 14.6 and independently confirms the absence of additional massive structures along the line of sight. Deep XRT follow-up reveals highly disturbed X-ray morphologies: three clusters exhibit at least two distinct X-ray peaks, while the remaining cluster has an axis ratio exceeding 1.5. Spectroscopy shows that galaxies associated with different parts share the same redshift, demonstrating that these substructures are physically connected rather than chance projections. These clusters display low central X-ray surface brightness and total X-ray luminosities suppressed by roughly one dex for their richness, making them undetectable in X-ray surveys as eROSITA. We estimate ∼20% as a lower limit for the poorly sampled population, albeit based on a small sample. Our results demonstrate that even rich clusters in the northern z &lt; 0.3 Universe can be missed by X-ray selection and that the X-ray variety captured by X-ray surveys underestimates the true cluster diversity.

The dark matter (DM) density profile in the innermost region of the Galaxy remains an open question. In particular, while adiabatic growth of the supermassive black hole Sgr A* at the Galactic Center (GC) can induce a 'spike' in central DM density, the existence of such a spike is still under debate. Here we present new constraints on the spike slope γ<SUB>sp</SUB> using conventional DM indirect detection searches. We first recast existing photon and neutrino line searches, which include the contribution from the GC region, into constraints on the thermally-averaged DM annihilation cross section &lt;σv&gt; in the presence of a DM spike. We then derive new bounds on the spike profile for a generic Weakly Interacting Massive Particle (WIMP) DM scenario, where the thermal freeze-out mechanism fixes the annihilation cross-section at &lt;σv&gt; ∼ (2-3) × 10<SUP>-26</SUP> cm<SUP>3</SUP> s<SUP>-1</SUP>. We find that, for DM annihilation to photons, existing Fermi-LAT and MAGIC data place strong constraints on spike profiles at the GC over a broad range of WIMP DM masses, from 10 GeV to 100 TeV, for photon branching fractions down to ∼ 10<SUP>-2</SUP>, and remain sensitive to values as small as ∼ 10<SUP>-4</SUP> in parts of the parameter space. For the neutrino channel, we use the recent IceCube data to constrain the existence of an extremely steep spike in the 𝒪(1-10) TeV DM mass range. Our analysis can be easily extended to other annihilation channels.

We present a systematic detection and characterization of mesoscale atmospheric gravity waves in Martian clouds using High Resolution Stereo Camera (HRSC) imagery from Mars Express during Martian Years 34─37. Gravity wave packets were identified in the HRSC Cloud Atlas data set, and their morphology (horizontal wavelength, packet width/length, orientation) was measured on map-projected products. Cloud top altitudes were derived from blue-green parallax using HRSC's multi-channel imaging geometry. For a subset of stereo─temporal "brooming" pairs separated by ${\Delta }t\approx 30$ min, horizontal winds were derived by manual feature tracking, enabling direct estimates of observed and intrinsic phase speeds and implied vertical wavelengths at the packet scale. We cataloged 146 packets, of which 114 were morphologically characterized, measured 100 cloud top heights, and 11 had full dynamical characterization. Horizontal wavelengths span 2─117 km with an average of 29 km. Cloud tops show a dominant concentration between ≍15 and 40 km, and a less frequent extension to 60─100 km, with uncertainty ∼3─10 km, and clear spatial and seasonal variability. For the dynamical subset, observed phase speeds are 2.0─8.6 m/s, intrinsic phase speeds are 0.4─6.2 m/s, and implied vertical wavelengths are 0.2─3.4 km. These results demonstrate that HRSC repeat-track imaging enables packet-scale constraints on intrinsic gravity wave drag and mesoscale dynamics in Martian circulation models.

We investigate the behavior of Einstein crystals in noncommutative backgrounds described by the Snyder and Snyder-de Sitter models. Possible novel effects, which may arise in realistic systems such as diamond crystals, are analyzed within a thermodynamical framework. We show that noncommutativity influences the key thermodynamic quantities, including internal energy and specific heat. These corrections can be directly related to modifications of the underlying uncertainty relations, of the generalized uncertainty principle (GUP) and generalized extended uncertainty principle (GEUP) types.