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Minimum size of the millimeter-wave emission region in RXJ1131-1231

Ascertain the minimum physical size of the millimeter-wave emission region in the lensed quasar RXJ1131-1231 at redshift z = 0.658, beyond the current constraint that only a 95th-percentile upper limit of R_{1/2} < 2.4 × 10^{-4} pc (≈50 AU) is obtained from microlensing analysis of ALMA and R-band data.

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Background

The authors derive an upper limit on the half-light radius of the mm-wave source via Bayesian comparison of observed flux ratios to microlensing simulations, under assumptions about source profiles and stellar surface density in the lens. While a stringent upper bound is obtained, the data do not constrain the lower bound, leaving the true size undetermined within that limit.

A precise measurement of the minimum size would further tighten constraints on coronal models, magnetic field strengths, and emission mechanisms.

References

While we cannot constrain the minimum size of the mm-wave emission with the current data, we obtain a 95th-percentile upper limit of R_{1/2} < 2.4 × 10{-4} pc, equivalent to 50 AU.

— Detection of millimeter-wave coronal emission in a quasar at cosmological distance using microlensing (2503.13313 - Rybak et al., 17 Mar 2025) in Section 3.1 (Microlensing analysis)