高能暂现源 · 每日文献综述

The Large High Altitude Air Shower Observatory (LHAASO) monitors sources within its field of view for up to 7 hr daily, achieving a duty cycle exceeding 98% and an annual point-source sensitivity of 1.5% Crab units (CU) in the very-high-energy (VHE) band. This unbiased sky-survey mode facilitates systematic monitoring and investigation of outburst phenomena. In this paper, we present results from an unprecedented 3 yr monitoring campaign (2021 March─2024 March) of Markarian 421 (Mrk 421) using LHAASO, spanning energies from 0.4 to 20 TeV. We find that the blazar stayed in a quiescent state in 2021 and became active starting in 2022 with a total of 23 VHE outburst events identified, where the highest observed daily significance reaches 20σ with a flux equivalent to approximately 3.3 CU. LHAASO's continuous monitoring suggests the flaring occupancy of Mrk 421 to be around 14%. During long-term monitoring, multiwavelength (MWL) variability and correlation analyses are conducted using complementary data from the Fermi Large Area Telescope, Monitor of All-sky X-ray Image Gas Slit Camera, the Neil Gehrels Swift Observatory X-Ray Telescope, and the Zwicky Transient Facility. A significant correlation (>3σ) is observed between the X-ray and VHE bands with no detectable time lag, while the correlation between the GeV and TeV bands is weaker. The energy spectrum of the TeV emission during the quiescent state is different from that in the active state, implying the existence of two modes of energy dissipation in the blazar jet. Using simultaneous MWL data, we also analyzed both the long-term and outburst-period spectral energy distributions, and discussed the possible origin of the outburst events.

We consider the early binary neutron star inspiral phase as a scenario to probe environmental axion─photon resonant conversion. For this we approximately model the merger site electromagnetic fields as the superposition of two rotating dipolar stellar magnetic fields at the 1000 km scale when both magnetospheres are not largely distorted. We capture the time-sliced near-zone magnetospheric geometry relevant for axion─photon mixing. Plasma effects are incorporated through an effective Goldreich─Julian charge density, used to determine the effective plasma frequency and the location of resonant conversion surfaces. Our results show that axion─photon resonant conversion in binary magnetospheres mostly occurs on extended peanut-shaped surfaces whose global geometry evolves as the binary inspiral evolves. The resulting signal is intrinsically narrowband, with photon frequencies set by the axion mass, and its amplitude is slowly modulated by the inspiral through the changing resonant geometry. We illustrate our findings with benchmark values g<SUB>aγ</SUB> = 10<SUP>−12</SUP> GeV<SUP>−1</SUP> and ρ<SUB>a</SUB> = 10<SUP>23</SUP> GeV cm<SUP>−3</SUP>. As an optimistic benchmark, we consider a Galactic source at D = 10 kpc and compare it with a realistic GW170817-like event at D = 40 Mpc. The corresponding D<SUP>−2</SUP> suppression reduces the flux by ∼10<SUP>−8</SUP>, placing extragalactic signals below the sensitivity of current and planned radio facilities. Our work provides a theoretical and phenomenological framework showing that binary neutron star magnetospheres may support extended resonant axion─photon conversion regions whose geometry and emission correlate with the GW frequency.