Astronomers have found a mysterious new cosmic explosion that has never been observed before. According to the scientists, the burst EP240408a was detected for the first time by the Einstein Probe, an X-ray space telescope, on April 8, 2024. Early in the observations, scientists believed it was a typical gamma-ray burst, but this explosion does not fit into any known cosmic explosion.
Observations of the explosion in various wavelengths - ultraviolet, optical, infrared, radio, X-ray, and gamma-ray - show that it is quite peculiar.
The leading theory was proposed in a study published in the Astrophysical Journal Letters; according to it, EP240408a may be the product of a white dwarf being torn apart by a medium-sized black hole. This destruction has created a powerful jet of material directly aimed at Earth, allowing for a view that is otherwise impossible - the violent end of a star. It is stretching the boundaries of our knowledge in high-energy astrophysics.
"EP240408a ticks some of the boxes for several different kinds of phenomena, but it doesn't tick all of the boxes for anything," said Brendan O'Connor, a McWilliams Postdoctoral Fellow at Carnegie Mellon's McWilliams Center for Cosmology and Astrophysics and lead author of the study.
High-energy transients are brief bursts of high-energy radiation detected within or outside of our galaxy. Most are often determined to be gamma-ray bursts. In EP240408a's case, its properties are distinct from any previously known high-energy transient.
In addition to being detected by the Einstein Probe, follow-up observations with the Neutron star Interior Composition Explorer (NICER) and the Neil Gehrels Swift Observatory revealed a fading X-ray transient. The X-ray behavior was unprecedented, falling in an intermediate regime of both duration and luminosity where other transients had not been observed, which provided a crucial hint toward its origin.
However, it was not detected by the Very Large Array, a radio astronomy observatory operated by the US National Science Foundation. Observations from the Very Large Array at 11 days, 158 days and 258 days after EP240408a's initial discovery indicated no radio emission from the source.
"When we see something this bright for this long in X-rays, it usually has an extremely luminous radio counterpart," O'Connor said. "And here we see nothing, which is very peculiar."
