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Abstract In extreme scattering events, the brightness of a compact radio source drops significantly, as light is refracted out of the line of sight by foreground plasma lenses. Despite recent efforts, the nature of these lenses has remained a puzzle, because any roughly round lens would be so highly overpressurized relative to the interstellar medium that it could only exist for about a year. This, combined with a lack of constraints on distances and velocities, has led to a plethora of theoretical models. We present observations of a dramatic double-lensing event in pulsar PSR B0834+06 and use a novel phase-retrieval technique to show that the data can be reproduced remarkably well with a two-screen model: one screen with many small lenses and another with a single, strong one. We further show that the latter lens is so strong that it would inevitably cause extreme scattering events. Our observations show that the lens moves slowly and is highly elongated on the sky. If similarly elongated along the line of sight, as would arise naturally from a sheet of plasma viewed nearly edge-on, no large overpressure is required and hence the lens could be long-lived.
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This content will become publicly available on August 29, 2026
Transient Blurring of the Scintillation Arc of Pulsar B1737+13
Abstract For many pulsars, the scattering structures responsible for scintillation are typically dominated by a single, thin screen along the line of sight, which persists for years or decades. In recent years, an increasing number of doubly lensed events have been observed, where a secondary lens crosses the line of sight. This causes additional or distorted scintillation arcs over timescales ranging from days to months. In this work, we report such a transient event for pulsar B1737+13 and propose a possible lensing geometry including the distance to both lenses and the orientation of the main screen. Using phase retrieval techniques to separate the two lenses in the wavefield, we report the curvature and rate of motion of features associated with the secondary lens as it passed through the line of sight. By fitting the annual variation of the curvature, we report a possible distance and orientation for the main screen. The distance of the secondary lens is found by mapping the secondary feature onto the sky and tracking its position over time for different distances. We validate this method using B0834+06, for which the screen solutions are known through VLBI, and successfully recover the correct solution for the secondary feature. With the identified lensing geometry, we are able to estimate the size of the secondary lens, 1–3 au. Although this is an appropriate size for a structure that could cause an extreme scattering event, we do not have conclusive evidence for or against that possibility.
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- Award ID(s):
- 2009759
- PAR ID:
- 10635986
- Publisher / Repository:
- Astrophysical Journal
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 990
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 91
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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