Matched-filtering Line Search Methods Applied to Suzaku Data

TL;DR

This paper introduces a matched-filtering line search method applied to Suzaku X-ray data, effectively detecting or constraining emission and absorption lines in AGN and magnetar spectra, with implications for understanding their physical properties.

Contribution

The study develops and applies a matched-filtering approach for line searches in Suzaku data, providing new upper limits on spectral features in magnetars and confirming previous AGN findings.

Findings

Consistent detection of known AGN outflows at ~3σ level.

No significant line features found in magnetar spectra.

Upper limits on line equivalent widths are a few eV to hundreds of eV.

Abstract

A detailed search for emission and absorption lines and assessing their upper limits are performed for Suzaku data. The method utilizes a matched-filtering approach to maximize the signal-to-noise ratio for a given energy resolution, which could be applicable to many types of line search. We first applied it to well-known AGN spectra that have been reported to have ultra-fast outflows, and find that our results are consistent with previous findings at the ~3{\sigma} level. We proceeded to search for emission and absorption features in the two bright magnetars 4U 0142+61 and 1RXS J1708-4009, applying the filtering method to Suzaku data. We found that neither source showed any significant indication of line features, even using long Suzaku observations and dividing their spectra into spin phases. The upper limits on the equivalent width of emission/absorption lines are constrained to be a few eV at ~1 keV, and a few hundreds of eV at ~10 keV. This strengthens previous reports that persistently bright magnetars do not show proton cyclotron absorption features in soft X-rays and, even if they exist, they would be broadened or much weaker than below the detection limit of X-ray CCD.