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An international team of astronomers has employed various satellites and ground-based telescopes to perform multiwavelength observations of a supernova remnant known as SNR J0450.4−7050. Results of the observational campaign, June 18 on the pre-print server arXiv, yield new insights into the properties of this remnant, finding that it is much larger than previously thought.

Supernova remnants (SNRs) are diffuse, expanding structures resulting from a supernova explosion, which usually last several hundred thousand years before dispersing into the interstellar medium (ISM). Observations show that SNRs contain ejected material expanding from the explosion and other interstellar material that has been swept up by the passage of the shockwave from the exploded star.

Studies of SNRs beyond the Milky Way are crucial for understanding their feedback in different evolutionary phases and gaining insights into their local ISM. The Large Magellanic Cloud (LMC) is one of the galaxies that has its SNR population explored in detail.

SNR J0450.4−7050 is a large supernova remnant in the LMC with a physical dimension of 332 by 244 light years. The remnant is estimated to be about 45,000 years old and showcases a complex filamentary morphology with distinct inner and outer shell structure.

A group of astronomers led by Zachary J. Smeaton of Western Sydney University in Australia, decided to take a closer look at SNR J0450.4−7050 using mainly the Australian Square Kilometer Array Pathfinder (ASKAP) and MeerKAT radio telescope, but also a set of other ground-based observing facilities and spacecraft.

The new observations detected previously unseen faint filamentary structures extending out of the north and south of SNR J0450.4−7050, increasing the extent of this remnant to 489 by 264 light years. Therefore, Smeaton's team nicknamed the SNR "Veliki", which means "large" in Serbian.

Furthermore, the observations found that Veliki has an unusually high radio surface brightness and has one of the lowest average radio spectral indices, when compared to other SNRs of similar size. A bright hydrogen-alpha shell has also been identified, suggesting predominantly radiative shocks.

Trying to explain the unusual properties of Veliki, the astronomers investigated several theoretical scenarios. According to them, the most plausible explanation is that Veliki is a fully radiative SNR and the flatter spectral index and brighter surface brightness is attributed to a higher compression ratio.

"This is most likely an older, predominantly radiative SNR with a higher shock compression ratio, which gives a flatter non-thermal spectrum, in combination with a thermal (bremsstrahlung) emission contribution," the researchers conclude.

However, further observations of Veliki, especially those focused on its environment, are required in order to confirm this hypothesis and to fully constrain the nature of this remnant.

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