高能暂现源 · 每日文献综述

We present a timing analysis of the high-cadence optical light curve of the high-redshift flat-spectrum radio quasar PKS 0805 - 07 obtained during TESS Sector 34 (MJD = 59230.90─59239.90). We search for short-timescale quasi-periodic oscillations (QPOs) using complementary time-series techniques, including the Lomb─Scargle periodogram (LSP) and the weighted wavelet Z-transform (WWZ), and evaluate their significance against red-noise variability using Monte Carlo simulations. The LSP reveals a dominant modulation at <mml:math><mml:mrow><mml:mi>f</mml:mi><mml:mo>≍</mml:mo><mml:mn>0.6</mml:mn><mml:mspace></mml:mspace><mml:msup><mml:mrow><mml:mi>d</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math> (P ≍ 1.7 d) exceeding the 99.99% confidence level, while the WWZ independently recovers a consistent timescale at the ∼ 99.9% level and shows that the signal is temporally localized rather than persistent across the full light curve. The modulation spans ∼ 5 coherent cycles, indicating a transient quasi-periodic feature. However, the detected significance only marginally exceeds the highest confidence threshold in the WWZ analysis, and the limited number of coherent cycles is insufficient for a firm confirmation. We discuss possible physical interpretations of the candidate modulation. In a disk-based scenario, orbital motion of a hotspot near the innermost stable circular orbit implies a black hole mass of M<SUB>BH</SUB> ∼ 7.2 × 10<SUP>8</SUP> M<SUB>⊙</SUB>, consistent with typical FSRQ values. Alternatively, magnetohydrodynamic kink instabilities in the relativistic jet can naturally produce day-scale variability for standard blazar parameters and account for the transient character of the signal. Compact SMBH binary and tidal disruption event scenarios are also considered but found to be disfavoured by the jet-dominated nature of the source, the optical rather than X-ray character of the modulation, and the black hole mass well above the regime associated with confirmed QPE host galaxies. We conclude that the candidate modulation is consistent with a compact, short-lived structure embedded within stochastic jet variability, and that high-cadence multiwavelength monitoring will be essential to confirm its recurrence and constrain its physical origin.

Stellar clusters preserve crucial information on the formation and evolutionary processes that shaped the Milky Way (MW) as we see it today. However, several MW clusters still lack sufficient data to constrain their metallicity, ages, and, in some cases, even their basic kinematic properties. We present low-resolution MODS at LBT spectroscopy for five such systems (i.e. Koposov 1, Koposov 2, Muñoz 1, Pfleiderer 2, and RLGC2) from which we derive systemic heliocentric radial velocities (V<SUB>sys</SUB>) with typical uncertainties of ≤10 km s<SUP>−1</SUP>, and metallicities based on the equivalent widths of the infrared Ca II triplet measured in red giant branch members. For Pfleiderer 2 and RLGC2, we provide the first spectroscopic determinations of their systemic velocities and metallicities, for which we find V<SUB>sys</SUB> = 6 ± 5 km s<SUP>−1</SUP> and −313 ± 6 km s<SUP>−1</SUP>, and [Fe/H] = −0.75 ± 0.09 dex and −2.33 ± 0.13 dex, respectively. For the other three clusters, we find results that are consistent with the existing literature. Thanks to our new spectroscopic measurements, we were able to perform an orbital analysis to investigate their origin. We find that Pfleiderer 2 likely formed within the MW, RLGC2 is dynamically associated to the Gaia─Sausage─Enceladus accretion event, and Koposov 1 was likely stripped from the Sagittarius dwarf spheroidal while Muñoz 1 is only tentatively associated with the latter system. Koposov 2, at a high orbital energy, does not show a clear association with any known progenitor system.