Four new X-ray supernova remnants detected in the galaxy NGC 7793
Tomasz Nowakowski
astronomy writer
Robert Egan
associate editor
Using NASA's Chandra spacecraft and ESA's XMM-Newton satellite, astronomers have investigated the galaxy NGC 7793, searching for supernova remnants (SNRs). As a result, they discovered four new X-ray SNRs in this galaxy. The findings were June 10 on the arXiv pre-print server.
SNRs are diffuse, expanding nebulae of gas and dust resulting from a supernova explosion. They usually last several hundred thousand years before dispersing into the interstellar medium (ISM).
Detecting X-ray SNRs in other galaxies is crucial for understanding their feedback in different evolutionary phases and gaining insights into their local ISM. However, SNRs beyond the Local Group are rarely found, mainly due to the limited sensitivity of current X-ray instruments.
NGC 7793 is a flocculent spiral galaxy at a distance of some 12 million light years. The galaxy is an excellent place to search for new X-ray supernova remnants as it hosts a large number of optical SNRs. That is why a team of astronomers led by Maria Kopsacheili of the Institute of Space Sciences (ICE-CSIC) in Barcelona, Spain, decided to look for X-ray SNRs in this galaxy using Chandra and XMM-Newton.
"To identify X-ray SNRs, we utilized Chandra's spatial resolution and analyzed all available archival data of NGC 7793, totaling 229.9 ks over 19 years. After data reduction, we performed source detection and analysis, searching for X-ray sources coinciding with optical SNRs. We also used XMM-Newton for spectral analysis of the confirmed and candidate SNRs," the researchers explained.
All in all, the observations identified dozens of X-ray sources in NGC 7793, and five of them—designated X11, X13, X15, X25 and X38—turned out to coincide with optical SNRs with offsets smaller than 1.3 arcseconds. X15 was previously reported as an X-ray SNR, while the remaining four were detected for the first time.
The newfound X-ray SNRs in NGC 7793 have X-ray luminosities between 0.88 and 5.49 undecillion erg/s. They all exhibit soft X-ray emission, positioning them in the soft region of the color-color diagrams, and show no significant short- or long-term variability.
The astronomers noted that the spectra of X11 and X15 show soft emission typical of hot plasma (with temperatures exceeding 2.5 million K) with strong oxygen and neon lines. Moreover, the spectra showcase strong emission lines from K-shell transitions of various elements.
The study also detected two new candidate X-ray SNRs in NGC 7793, designated X23 and X42. The researchers explained that although these two sources have not been detected in optical wavelengths, they classified them as SNR candidates due to their soft, non-variable X-ray emission.
"We do not have any strong evidence against the scenario of X23 and X42 to be SNRs, and hence we can consider them as candidate SNRs," the authors of the paper concluded.
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More information: Kopsacheili et al, New X-ray Supernova Remnants in NGC 7793, arXiv (2025).
Journal information: arXiv
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