高能暂现源 · 每日文献综述

We present the multiwavelength variability of the BL Lac object PKS 0735+178, associated with the high-energy neutrino event IC211208A. The light curves cover the radio (1─230 GHz), optical, and Fermi-LAT <inline-formula><tex-math>$\gamma$</tex-math></inline-formula>-ray bands over a <inline-formula><tex-math>$\sim$</tex-math></inline-formula>30 yr time-scale. The light curves are correlated, with delays from 0 to 1200 d increasing towards lower frequencies, consistent with emission from an opacity-stratified jet. The bright flare after the IC211208A event indicates emission from a compact, optically thick region with enhanced activity and more efficient particle acceleration. Short optical and <inline-formula><tex-math>$\gamma$</tex-math></inline-formula>-ray bursts have been detected very close to the neutrino event, within a few days. The <inline-formula><tex-math>$\sim$</tex-math></inline-formula>12-d lag between the <inline-formula><tex-math>$\gamma$</tex-math></inline-formula>-ray and optical emissions is detected for the first time, suggesting that the emission regions are not co-spatial. A characteristic variability time-scale of <inline-formula><tex-math>$\sim$</tex-math></inline-formula>10─11 yr is robustly detected in the radio─mm bands (<inline-formula><tex-math>${\ge} 3\sigma$</tex-math></inline-formula>), while the optical and <inline-formula><tex-math>$\gamma$</tex-math></inline-formula>-ray data show weaker, shorter period signals. The independent constraints from the VLBI core-shift measurements and radio time delays yield consistent estimates of the jet geometry and disturbance propagation, supporting variability governed by jet propagation effects. The long-term modulation is consistent with a slow variation in energy release at the jet base, while individual flares arise from shocks propagating downstream. Jet precession may contribute to the long-term modulation; however, the required viewing angles are inconsistent with the VLBI constraints, indicating that precession alone cannot explain the observed variability.

IGR J17480-2446 is a low-mass x-ray binary, harboring an exceptional accreting pulsar (a neutron star) with an unusual spin frequency of 11 Hz and a very slow postoutburst crust cooling. The former may imply that it is observed at an early stage of recycling, while the latter was shown to indicate the presence in the outer crust of a low thermal conductivity layer, possibly made of glass. Here we argue that the glass layer formation is a natural result of accretion induced failure of pristine cold crystalline crust. This allows us to determine the mass of the accreted material as <inline-formula><mml:math><mml:mrow><mml:mi>∆</mml:mi><mml:mi>M</mml:mi><mml:mo>≍</mml:mo><mml:mn>2.4</mml:mn><mml:mo>×</mml:mo><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>6</mml:mn></mml:mrow></mml:msup><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub></mml:mrow></mml:math></inline-formula>, confirming a very early accretion stage for this neutron star. An analysis of the spin and thermal state reveals a peculiar set of neutron star birth properties which is commonly associated with "recycled" neutron stars, i.e., those that have been experiencing prolonged periods of accretion from a companion. We speculate that such birth properties may represent the outcome of neutron star formation in an electron-capture supernova.