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In January 2024, the Chinese Academy of Sciences and the European Space Agency launched the Einstein Probe to stare at the sky in search of transient events, such as stellar explosions. And in April of 2024, the probe spotted an unusual event that astronomers named EP240408a. On January 27, 2025, Carnegie Mellon University said while the explosion was originally thought to be a gamma-ray burst, it now appears it might represent a rare new class of powerful cosmic explosion.<\/p>\n
Lead author Brendan O\u2019Connor of Carnegie Mellon University said: <\/p>\n
\nEP240408a ticks some of the boxes for several different kinds of phenomena, but it doesn\u2019t tick all the boxes for anything. In particular, the short duration and high luminosity are hard to explain in other scenarios. The alternative is that we are seeing something entirely new!<\/p>\n<\/blockquote>\n
The researchers published their peer-reviewed study on January 27, 2025, in The Astrophysical Journal Letters<\/em>.<\/p>\n
The 2025 EarthSky lunar calendar makes a great gift. Get yours today!<\/p>\n
An unidentified exploding object<\/h3>\n
After the Einstein Probe caught the explosion with its X-ray vision in April, the research team followed up with additional observations using multiple other telescopes, including NuSTAR, Swift, Gemini, Keck, DECam, VLA, ATCA, and NICER. While originally pegged as a gamma-ray burst, the follow-up observations did not agree. In fact, the researchers said the characteristics of EP240408a don\u2019t match those of a standard gamma-ray burst.<\/p>\n
So, what is <\/em>a gamma-ray burst? A gamma-ray burst is a highly energetic explosion that creates a black hole. This explosion can result from two neutron stars merging or a massive star collapsing. Its telltale sign is the powerful jet of gamma rays it emits.<\/p>\n
But the follow-up observations showed a lack of a bright gamma-ray counterpart. So what else could it be?<\/p>\n
A jetted tidal disruption<\/h3>\n
One peculiar characteristic of this explosion is that the Very Large Array (VLA) \u2013 a radio telescope in New Mexico \u2013 did not see the burst. O\u2019Connor said: <\/p>\n
\nWhen we see something this bright for this long in X-rays, it usually has an extremely luminous radio counterpart. And here we see nothing, which is very peculiar.<\/p>\n<\/blockquote>\n
So this eventually led the researchers to consider a jetted tidal disruption. These are rare events that happen when a supermassive black hole rips a star apart. So far, astronomers have only discovered 100 such events.<\/p>\n
The researchers think they might be seeing EP240408a after the initial X-ray outburst but before the formation of the jets that would emit radio waves. O\u2019Connor said: <\/p>\n
\nIt seems to me that this is the most likely explanation for why we aren\u2019t seeing radio emission. Hopefully, eventually, we will see a jet at radio wavelengths, either with the current setup of the VLA or the Next Generation VLA, and we can monitor it for years to come in order to learn even more about this explosion.<\/p>\n<\/blockquote>\n
And if they don\u2019t? Then perhaps we are seeing a whole new class of object!<\/p>\n
Bottom line: Scientists determined a powerful explosion \u2013 named EP240408a \u2013 was not a gamma-ray burst. So what was it? It might have been a jetted tidal disruption, or perhaps it was something completely new!<\/p>\n
Source: Characterization of a Peculiar Einstein Probe Transient EP240408a: An Exotic Gamma-Ray Burst or an Abnormal Jetted Tidal Disruption Event?<\/p>\n
Via Carnegie Mellon University<\/p>\n
Via MIT<\/p>\n
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