Astronomers recorded an extremely long gamma-ray burst that lasted more than 1000 seconds. The Fermi satellite saw that, for some reason, it had as many as two peaks, strongly spaced in time. According to scientists, the effect of gravitational lensing is to blame for this.
Extremely long gamma-ray burst
Scientists working with the Fermi Space Telescope published a study in which they reported an extremely long gamma-ray burst observed by this device. It was registered for more than 1000 seconds, while most of these events last only a few dozen.
Gamma-ray bursts should not be confused with another rather mysterious phenomenon — fast radio bursts. Both refer to transients, that is, short-term phenomena. The difference is that events like the one observed by Fermi are much more powerful and last longer. That is why they were discovered several decades ago and found their nature.
Most of them occur at a distance of billions of light-years from us and are associated with the death of very massive stars. Most often, it occurs when a black hole forms during a collapse, even before the outer layers of the luminary break down. Although gamma-ray bursts can also form when two neutron stars collide.
Effect of gravitational lensing
However, there was nothing unusual about the star that generated a new record gamma-ray burst. And the supernova formation event was not distinguished by some very strong release of energy. The only thing that scientists noticed were its two peaks, which were very similar to each other but very far apart in time.
And this feature helped them make an assumption about why this gamma-ray burst was so long. It’s just that some large body got in the way of the rays, and its gravitational force led to the formation of the effect of a gravitational lens, or, more simply, distorted the direction of propagation of the rays.
Usually this phenomenon is known for objects which luminosity is more or less constant. It creates circles and crosses, distorting and duplicating their images. However, in the case of short-term events, the gravitational lens may work a little differently.
It can send some of the rays by a longer route, as a result of which they will come to us with a delay. In the case of this particular event, the difference was small, so astronomers saw the burst as one “smeared” event with two peaks in time.
However, nothing prevents a gravitational lens from sending light from a very bright transient in several different ways with a significant delay. In this case, we will observe several events that will occur in the same place.
According to phys.org
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