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Register a new userCIELO-RGS: a catalogue of soft X-ray ionized emission lines
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High-resolution X-ray spectroscopy has advanced our understanding of the hot Universe by revealing physical properties like kinematics, temperature, and abundances of the astrophysical plasmas. Despite the technical and scientific achievements, the lack of scientific products at a level higher than count spectra is hampering full scientific exploitation of high-quality data. This paper introduces the Catalogue of Ionized Emission Lines Observed by the Reflection Grating Spectrometer (CIELO-RGS) onboard the XMM-Newton space observatory. The CIELO-RGS catalogue aims to facilitate the exploitation of emission features in the public RGS spectra archive, in particular, to perform the correlation between X-ray spectral diagnostics parameters with measurements at other wavelengths. This paper focuses on the methodology of catalogue generation, describing the automated line detection algorithm. A moderate sample (~2400 observations) of high-quality RGS spectra available at XMM-Newton Science Archive is used as our starting point. A list of potential emission lines is selected based on a multi-scale peak detection algorithm in a uniform and automated way without prior assumption on the underlying astrophysical model. The candidate line list is validated via spectral fitting with simple continuum and line profile models. We also compare the catalogue content with published literature results on a small number of exemplary sources. We generate a catalogue of emission lines ~12000 detected in ~1600 observations toward stars, X-ray binaries, supernovae remnants, active galactic nuclei, and groups and clusters of galaxies. For each line, we report the observed wavelength, broadening, energy and photon flux, and equivalent width, etc.
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We report on robust measurements of elemental abundances of the Type IIn supernova SN 1978K, based on the high-resolution X-ray spectrum obtained with the Reflection Grating Spectrometer (RGS) onboard XMM-Newton. The RGS clearly resolves a number of emission lines, including N Ly$alpha$, O Ly$alpha$, O Ly$beta$, Fe XVII, Fe XVIII, Ne He$alpha$ and Ne Ly$alpha$ for the first time from SN 1978K. The X-ray spectrum can be represented by an absorbed, two-temperature thermal emission model, with temperatures of $kT sim 0.6$ keV and $2.7$ keV. The elemental abundances are obtained to be N $=$ $2.36_{-0.80}^{+0.88}$, O $=$ $0.20 pm{0.05}$, Ne $=$ $0.47 pm{0.12}$, Fe $=$ $0.15_{-0.02}^{+0.01}$ times the solar values. The low metal abundances except for N show that the X-ray emitting plasma originates from the circumstellar medium blown by the progenitor star. The abundances of N and O are far from CNO-equilibrium abundances expected for the surface composition of a luminous blue variable, and resemble the H-rich envelope of less-massive stars with masses of 10-25 M$_odot$. Together with other peculiar properties of SN 1978K, i.e., a low expansion velocity of 500-1000 km s$^{-1}$ and SN IIn-like optical spectra, we propose that SN 1978K is a result of either an electron-capture SN from a super asymptotic giant branch star, or a weak Fe core-collapse explosion of a relatively low-mass ($sim$10 M$_odot$) or high-mass ($sim$20-25 M$_odot$) red supergiant star. However, these scenarios can not naturally explain the high mass-loss rate of the order of $dot{M} sim 10^{-3} rm{M_{odot} yr^{-1}}$ over $gtrsim$1000 yr before the explosion, which is inferred by this work as well as many other earlier studies. Further theoretical studies are required to explain the high mass-loss rates at the final evolutionary stages of massive stars.
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