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Artist's design of a burst of gamma rays. A jet of fast moving material is propelled outward through the spherical shell of material ejected after the initial explosion of a massive star and its subsidence in a black hole. Credit: Bill Saxton, NRAO / AUI / NSF
Astronomers have compared data from a vast ongoing survey of the sky using the very large Karl G. Jansky Network (VLA) of the National Science Foundation with previous survey data likely to have allowed the first discovery of the burst of a powerful burst of gamma rays producing no gamma ray. detectable rays on Earth. The unprecedented discovery of this "orphan" gamma-ray explosion (ORB) provides essential clues to understanding the consequences of these very energetic events.
"GRBs emit their gamma rays in the form of tightly focused beams, in which case we think that the beams were directed away from the Earth, so gamma ray telescopes did not see this event. have discovered, it is the radio show that has followed the magnitude of the explosion, acting in time. as much as we expect for a GRB, "said Casey Law, of University of California, Berkeley.
While they were looking for data from the earliest observation period for the VLA Sky Survey (VLASS) at the end of 2017, astronomers noted that an object appearing in the images of the first time of observation for the VLA Sky Survey (VLASS) at the end of 2017 a previous VLA survey of 1994 did not appear in the VLASS images. They then searched for additional data from the VLA and other radio telescopes. They discovered that observations of the object's position in the sky dating back to 1975 did not detect it until its first appearance on a 1993 VLA image.
The object then appeared in several images made with the VLA and the Westerbork telescope in the Netherlands from 1993 to 2015. This object, christened FIRST J1419 + 3940, lies on the outskirts of a galaxy at over 280 million light years from Earth.
"It is a small galaxy with a formation of active stars, similar to others in which we have seen the type of GRB resulting from the explosion. a very massive star, "said Law.
A series of radio images of FIRST J1419 + 3940 from 1993 to 2017 shows its slow fading. Credit: Law et al., Bill Saxton, NRAO / AUI / NSF
The power of radio broadcasts of J1419 + 3940 and its slow evolution over time support the idea that it is the remanence of such a sebum, said the scientists. They suggested that the explosion and explosion of gamma rays would have been observed at some point in 1992 or 1993.
However, after looking in gamma observatory databases, "we did not find any convincing candidate to detect a detected GRB in this galaxy," said Law.
Although there are other possible explanations for the behavior of the object, the scientists said that a GRB was most likely.
"It's exciting, and not just because it's probably the first 'orphan' to be discovered, it's also the oldest of the well-located GRBs, and the long period in which it has been observed means that it can give us new information about the remanence of GRB, "said Law.
"Until now, we had never seen how the remanence of the GRB behaved at such a late time," said Brian Metzger of Columbia University, co-author of the report. study. "If a neutron star is responsible for the GRB's power supply and it's still active, it could give us an unprecedented opportunity to see this activity as the ejector expands." The explosion of the supernova finally becomes transparent. "
The animation of images from 1993 to 2017 shows a radio broadcast from an alleged "orphan" gamma burst that fades over time. Credit: Law et al., Bill Saxton, NRAO / AUI / NSF
"I am delighted to see this discovery, which is expected to be the first among many others that will come from the unique investment made by the National Radio Astronomy Observatory (NRAO) and the National Science Foundation in VLASS," he said. said NRAO director Tony Beasley.
VLASS is the largest VLA history observation project. Begun in 2017, the survey will use 5,500 hours of observation over seven years. The sounding will make three full sky sweeps visible from the VLA, about 80% of the sky. The first images of the first round of observations are now available to astronomers.
VLASS follows two previous sky surveys conducted with the VLA. The NRAO VLA Sky Survey (NVSS), like the VLASS, was a complete survey of the sky conducted from 1993 to 1996, and the FIRST survey (Fuzzy images of Radio Sky at twenty centimeters) focused on a smaller part of the sky more Detailed. 1993 to 2002. Astronomers discovered FIRST J1419 + 3940 by comparing a 1994 image from the FIRST survey to the 2017 VLASS data.
From 2001 to 2012, the VLA underwent a major upgrade, significantly increasing its sensitivity or ability to reproduce faint objects. The upgrade made possible a new, improved survey with a rich scientific advantage. Previous studies have been cited more than 4,500 times in scientific papers and scientists expect VLASS to be a valuable resource for research in the coming years.
Law and his colleagues publish their findings in the Astrophysical Journal Letters.
Explore further:
VLA begins a vast project of cosmic discovery
More information:
"Discovery of luminous extragalactic transient spike, several decades" FIRST J141918.9 + 394036, "C. J. Law et al., 2018, forthcoming Astrophysical Journal Letters, Pre-printing: arxiv.org/abs/1808.08964
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