Lensing point-spread function of coherent astrophysical sources and non-trivial wave effects

Abstract

Most research on astrophysical lensing has been conducted using the geometric optics framework, where there exists a clear concept of lensing images. However, wave optics effects can be important for coherent sources, e.g. pulsars, fast raio bursts, and gravitational waves observed at long wavelengths. There, the concept of lensing images needs an extension. We introduce the concept of the `lensing point-spread function' (LPSF), the smoothed flux density distribution of a coherent point source after being lensed, as a generalization of the lensing image concept at finite frequencies. The frequency-dependent LPSF captures the gradual change of the flux density distribution of the source from discrete geometric images at high frequencies to a smooth distribution at low frequencies. It complements other generalizations of lensing images, notably the imaginary images and the Lefschetz thimbles. Being a footprint of a lensing system, the LPSF is useful for theoretical studies of lensing. Using the LPSF, we identify a frequency range with non-trivial wave effects, where both geometric optics and perturbative wave optics fail, and determine this range to be $|\kappa {|}^{-1}\lesssim \nu \lesssim 10$, with $\kappa$ and $\nu$ being the dimensionless lens amplitude and the reduced observing frequency, respectively. Observation of LPSFs with non-trivial wave effects requires either very close-by lenses or very large observing wavelengths. The potential possibilities are the lensing of gravitational waves, the plasma lensing of Milky Way pulsars, and lensing by the solar gravitational lens.

Published in ApJ, comments are welcome

References in corpus (37)

• Observation of Gravitational Waves from a Binary Black Hole Merger
• A bright millisecond radio burst of extragalactic origin
• The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background
• Search for an isotropic gravitational-wave background with the Parkes Pulsar Timing Array
• Searching for the nano-Hertz stochastic gravitational wave background with the Chinese Pulsar Timing Array Data Release I
• A Population of Fast Radio Bursts at Cosmological Distances
• The second data release from the European Pulsar Timing Array III. Search for gravitational wave signals
• Faint Scattering Around Pulsars: Probing the Interstellar Medium on Solar System Size Scales
• Lensing of Fast Radio Bursts by Plasma Structures in Host Galaxies
• 100 Microarcsecond Resolution VLBI Imaging of Anisotropic Interstellar Scattering towards Pulsar B0834+06
• Interpretation of parabolic arcs in pulsar secondary spectra
• Theory of Parabolic Arcs in Interstellar Scintillation Spectra
• The Gaussian Plasma Lens in Astrophysics. Refraction
• Effects of plasma on gravitational lensing
• The Scattering and Intrinsic Structure of Sagittarius A* at Radio Wavelengths
• Deflection of Pulsar Signal Reveals Compact Structures in the Galaxy
• Pulsar emission amplified and resolved by plasma lensing in an eclipsing binary
• Two families of astrophysical diverging lens models
• Refractive Convergent Plasma Lenses explain ESE and pulsar scintillation
• Lensing of gravitational waves: efficient wave-optics methods and validation with symmetric lenses
• Extreme Scattering Events Towards Two Young Pulsars
• 50 pico arcsecond astrometry of pulsar emission
• Weakly Lensed Gravitational Waves: Probing Cosmic Structures with Wave-Optics Features
• The Optics of Refractive Substructure
• Image formation for extended sources with the solar gravitational lens
• Double-lens Scintillometry: The variable scintillation of pulsar B1508+55
• Imaging extended sources with the solar gravitational lens
• Probing wave-optics effects and low-mass dark matter halos with lensing of gravitational waves from massive black holes
• Regimes in astrophysical lensing: refractive optics, diffractive optics, and the Fresnel scale
• Extreme scattering events from axisymmetric plasma lenses
• Two families of elliptical plasma lenses
• Imaginary images and Stokes phenomena in the weak plasma lensing of coherent sources
• Plasma microlensing dynamic spectrum probing fine structures in the ionized interstellar medium
• Measuring lens dimensionality in extreme scattering events through wave optics
• Wave optics of the solar gravity lens
• Acquiring the Lefschetz thimbles: efficient evaluation of the diffraction integral for lensing in wave optics
• Stokes phenomena in lensing

Cited by in corpus (2)

• Acquiring the Lefschetz thimbles: efficient evaluation of the diffraction integral for lensing in wave optics
• Plasma lensing modeling of substructures on pulsar scintillation screens