Astronomers using data from the eROSITA X-ray telescope aboard the Spektrum-Roentgen-Gamma (SRG) observatory have detected the largest supernova remnant ever discovered with X-rays.
This image from the SRG/eROSITA all-sky survey shows SNR Hoinga (marked); the large bright source in the lower quadrant of the image is from SNR Vela; the image colors are correlated with the energies of the detected X-ray photons; red represents the 0.3-0.6 keV energy range, green 0.6-1.0 keV and blue 1.0-2.3 keV. Image credit: SRG / eROSITA / Becker et al., doi: 10.1051/0004-6361/202040156.
“Our aim is to combine expertise across multiple wavelengths, from radio to X-ray, to search for hundreds of supernova remnants (SNRs),” said co-author Dr. Natasha Hurley-Walker, an astronomer at the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR).
“The eROSITA telescope is 25 times more sensitive than its predecessor ROSAT so we expected to discover new SNRs in coming years, but were pleasantly surprised to have one appear straight away.”
Designated G249.5+24.5 and nicknamed Hoinga, the newly-detected SNR is among the largest SNRs discovered at wavelengths other than the radio waves.
“Adding to our excitement, Hoinga is the largest SNR ever discovered via X-rays, in terms of apparent size: about 90 times larger than the full Moon,” Dr. Hurley-Walker said.
“An enduring mystery surrounding SNRs was the shortfall between the expected number of them in our Galaxy and the number actually identified through past surveys.”
“We expect there to be about 1,200 SNRs in our Galaxy, however only about 300 have been found so far,” she added.
“By sifting through archival radio data we discovered Hoinga had been sitting there waiting to be discovered in surveys up to ten years old, but because it was high above the plane of the Milky Way, it was missed.”
“SNRs are not typically expected to be found at high Galactic latitudes so these areas are not usually the focus of surveys, meaning there may be even more of these overlooked remnants out there waiting to be discovered.”
“The radio observations made it possible for us to work out that it is a middle-aged remnant relatively close to Earth, calculations that would have been far less accurate with the X-ray data alone.”
The results were published in the journal Astronomy & Astrophysics.
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W. Becker et al. 2021. Hoinga: A supernova remnant discovered in the SRG/eROSITA All-Sky Survey eRASS1. A&A, in press; doi: 10.1051/0004-6361/202040156
