Balmer Filaments in Tycho's Supernova Remnant: An Interplay between Cosmic-ray and Broad-neutral Precursors

We present H spectroscopic observations and detailed modeling of the Balmer filaments in the supernova remnant (SNR) Tycho (SN 1572). We used GH FaS (Galaxy H Fabry-Pérot Spectrometer) on the William Herschel Telescope with a 3 4 × 3 4 field of view, 0 2 pixel scale, and instr = 8.1 km s−1 resolution at 1″ seeing for ∼10 hr, resulting in 82 spatial−spectral bins that resolve the narrow H line in the entire SN 1572 northeastern rim. For the first time, we can therefore mitigate artificial line broadening from unresolved differential motion and probe H emission parameters in varying shock and ambient medium conditions. Broad H line remains unresolved within spectral coverage of 392 km s−1. We employed Bayesian inference to obtain reliable parameter confidence intervals and to quantify the evidence for models with multiple line components. The median H narrow-line (NL) FWHM of all bins and models is W NL = ( 54.8 1.8 ) km s−1 at the 95% confidence level, varying within [35, 72] km s−1 between bins and clearly broadened compared to the intrinsic (thermal) 20 km s−1. Possible line splits are accounted for, significant in 18 % of the filament, and presumably due to remaining projection effects. We also find widespread evidence for intermediate-line emission of a broad-neutral precursor, with a median W IL = ( 180 14 ) km s−1 (95% confidence). Finally, we present a measurement of the remnant's systemic velocity, V LSR = − 34 km s−1, and map differential line-of-sight motions. Our results confirm the existence and interplay of shock precursors in Tycho's remnant. In particular, we show that suprathermal NL emission is near-universal in SN 1572, and that, in the absence of an alternative explanation, collisionless SNR shocks constitute a viable acceleration source for Galactic TeV cosmic-ray protons.