Superstrong photospheric magnetic fields in sunspot penumbrae

TL;DR

This study examines reports of superstrong magnetic fields in sunspot penumbrae, analyzing observational data and simulations to assess the reliability and origins of these extreme magnetic measurements.

Contribution

It provides a detailed analysis of the reliability of superstrong magnetic field detections in sunspot penumbrae using multiple diagnostic and inversion techniques.

Findings

Superstrong fields (>7 kG) are associated with supersonic downflows.

Different inversion methods yield varying magnetic field strengths.

Simulations support the presence of localized strong fields with downflows.

Abstract

Recently, there have been some reports of unusually strong photospheric magnetic fields (which can reach values of over 7 kG) inferred from Hinode SOT/SP sunspot observations within penumbral regions. These superstrong penumbral fields are even larger than the strongest umbral fields on record and appear to be associated with supersonic downflows. The finding of such fields has been controversial since they seem to show up only when spatially coupled inversions are performed. Here, we investigate and discuss the reliability of those findings by studying in detail observed spectra associated with particularly strong magnetic fields at the inner edge of the penumbra of active region 10930. We apply classical diagnostic methods and various inversions with different model atmospheres to the observed Stokes profiles in two selected pixels with superstrong magnetic fields, and compare the results with a magnetohydrodynamic simulation of a sunspot whose penumbra contains localized regions with strong fields (nearly 5 kG at $\tau=1$) associated with supersonic downflows...