Einstein Probe Detects Mysterious X-ray Flare with Record-Long Emission
Fast Evolving X-ray Transients (FEXTs) are intense bursts of soft X-ray emissions that can last for minutes to hours with a wide range of luminosities. Due to their enigmatic nature, FEXTs have been a importance for scientists. Einstein Probe (EP) is one of the crucial space telescopes for the search and investigation of FEXTs. An international team of astronomers using the Einstein Probe reports the discovery of a new peculiar fast-evolving X-transient. The newfound transient exhibits an unprecedentedly long-lasting X-ray emission.
A Puzzling Long-Lived X-ray Transient
The finding was detailed in a paper published May 12 on the arXiv preprint server. According to the published paper, the newfound peculiar FEXT, dubbed EP241021a, was detected on Oct 21, 2024, with the help of EP’s wide-field X-ray telescope (WXT). EP241021a was identified by WXT as an intense flare, which lasted for approximately 92 seconds and reached a luminosity of about one quindecillion erg/s. The X-ray spectrum of the flare was found to be relatively hard with a photon index of 1.8.
The team of astronomers, led by Xinwen Shu of the Anhui Normal University in China, has concluded that EP241021a is an extremely unusual transient mainly due to its extended emission period. Follow-up observations of the flare up to 79 days after its detection revealed that its X-ray light curve shows a nearly plateau phase for the first 7 days, which is followed by a steep decline during the period of about 30 days. Afterward, the X-ray emission rapidly drops under the detection level.
The researchers also detected significant multiwavelength signals associated with EP241021a. About 1.8 days after the initial X-ray detection, optical emissions were also detected. This emission is likely connected to the flare’s afterglow.
Possible origins
The origin of FEXTs is puzzling. Astronomers try to explain their origin take into account several scenarios; for instance, stellar flares, supernova shock breakouts, or long gamma-ray bursts (GRBs).
Trying to explain the origin of EP241021a, the authors of the paper favor two scenarios. These are: a magnetar engine, involving a highly magnetized neutron star, or a jetted tidal disruption event (TDE), where a star is consumed by a black hole.
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Astronomers international team has employed various satellites and telescopes for performing multiwavelength observations of a supernova remnant known as SNR J0450.4-7050. The result that scientists got after an observational campaign, published on June 18, 2025, on the preprint server arXiv, gained new insights into the properties of this remnant, and observed that it is much larger than thought in the past. Supernova remnants (SNRs) are expanded structures resulting from the explosion of a supernova. It usually lasts for several hundred thousand years before the time it disperses into the interstellar medium.
Multiwavelength Observations Reveal New Details of SNR J0450.4-7050
As per the study by NASA, observations by the scientists indicate that SNRs contain the ejected expansion of material from the explosion and other interstellar material swept by the passage of the shockwave from the star that exploded. SNR studies beyond the Milky Way are important for comprehending the feedback in different evolutionary phases and gaining valuable insights into the local ISM. The Large Magellanic Cloud is the galaxy that has its SNR population explored in depth.
Importance of Studying Supernova Remnants Beyond the Milky Way
The recent observations reveal that SNR J0450.4-7050, a large supernova remnant in the LMC having physical dimensions of 332 by 244 light years, is estimated to have the remnants of around 45,000 years old. Scientists named it Veliki, which means large in Serbian. It also showcases the complex filamentary morphology with different inner and outer shell structures.
Discovery of Veliki: A Large, Aged Remnant in the Large Magellanic Cloud
An astronomer’s group led by Zachary J. Smeaton decided to take a closer observation of SNR J0450.4−7050 by the Australian Square Kilometre Array Pathfinder and MeerKAT radio telescope. The SNR showed a high radial surface brightness with one of the lowest average radio spectral indices, with similar remnants.
Unusual Radio Properties Suggest Veliki is a Fully Radiative SNR
These unusual features, according to the scientists, give the prediction that Veliki is mainly a radiative SNR with a high shock compression ratio. This states about the non-thermal spectrum and higher surface brightness and emissions. Further observations of the surrounding environment are needed to confirm the hypothesis with an understanding of the remnants’ nature in a better way.
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