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Microlensing masses via photon bunching


Saha, Prasenjit (2019). Microlensing masses via photon bunching. Monthly Notices of the Royal Astronomical Society, 486(4):5400-5404.

Abstract

In microlensing of a Galactic star by a brown dwarf or other compact object, the amplified image really consists of two unresolved images with slightly different light traveltimes. The difference (of the order of a microsecond) is GM/c3 times a dimensionless factor depending on the total magnification. Since magnification is well measured in microlensing events, a single time-delay measurement would provide the mass of the lens, without degeneracies. The challenge is to find an observable that varies on submicrosecond time-scales. This paper notes that the narrow-band intensity of the unresolved image pair will show photon bunching (the Hanbury Brown and Twiss effect), and argues that the lensed intensity will have an autocorrelation peak at the lensing time delay. The ultrafast photon-counting technology needed for this type of measurement exists, but the photon numbers required to give sufficient signal-to-noise appear infeasible at present. Preliminary estimates suggest time-delayed photon bunching may be measurable for lensed early-type main-sequence stars at {̃ }10 kpc, with the help of 30 m-class telescopes.

Abstract

In microlensing of a Galactic star by a brown dwarf or other compact object, the amplified image really consists of two unresolved images with slightly different light traveltimes. The difference (of the order of a microsecond) is GM/c3 times a dimensionless factor depending on the total magnification. Since magnification is well measured in microlensing events, a single time-delay measurement would provide the mass of the lens, without degeneracies. The challenge is to find an observable that varies on submicrosecond time-scales. This paper notes that the narrow-band intensity of the unresolved image pair will show photon bunching (the Hanbury Brown and Twiss effect), and argues that the lensed intensity will have an autocorrelation peak at the lensing time delay. The ultrafast photon-counting technology needed for this type of measurement exists, but the photon numbers required to give sufficient signal-to-noise appear infeasible at present. Preliminary estimates suggest time-delayed photon bunching may be measurable for lensed early-type main-sequence stars at {̃ }10 kpc, with the help of 30 m-class telescopes.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Physics Institute
07 Faculty of Science > Institute for Computational Science
Dewey Decimal Classification:530 Physics
Scopus Subject Areas:Physical Sciences > Astronomy and Astrophysics
Physical Sciences > Space and Planetary Science
Uncontrolled Keywords:Space and Planetary Science, Astronomy and Astrophysics
Language:English
Date:11 July 2019
Deposited On:31 Oct 2019 13:49
Last Modified:29 Jul 2020 11:36
Publisher:Oxford University Press
ISSN:0035-8711
OA Status:Green
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1093/mnras/stz1208

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