An amazing source of energy studied by astronomers

An amazing source of energy studied by astronomers

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Regional significance map of LHAASO J2108+5157 using ~2400 days of data taken by HAWC. Credit: Kumar et al., 2023.

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Regional significance map of LHAASO J2108+5157 using ~2400 days of data taken by HAWC. Credit: Kumar et al., 2023.

Astronomers from the University of Maryland and Michigan Technological University, have examined the mysterious source of gamma-rays known as LHAASO J2108 + 5157. The results of the study, published on August 31 in the pre-print server arXivit can help us uncover the true source.

Sources emitting gamma rays with photon energies between 100 GeV and 100 TeV are called very high energy (VHE) gamma-ray sources, while those with photon energies greater than 0.1 PeV are known as ultra-high energy sources. high (UHE) gamma-ray. The nature of these sources is not well understood; therefore, astronomers are constantly looking for new objects of this type to reveal their characteristics, which may shed more light on their general characteristics.

A team of astronomers led by the University of Maryland’s Sajan Kumar decided to take a closer look at one UHE gamma-ray source designated LHAASO J2108+5157. It is a point-like source with an extension of less than 0.39 degrees, known to be associated with a molecular cloud. [MML2017]4607—is about 10,700 light years away.

Previous observations of LHAASO J2108+5157 did not identify X-ray counterparts and it was found that the closest X-ray source is the eclipsing binary RX J2107.3+5202 with a separation of about 0.3 degrees. Because no powerful pulsars or supernova remnants have been found so far in the area of ​​LHAASO J2108 + 5157, it is difficult to determine the origin of the gamma-ray emission as it can be explained either by hadronic or leptonic models.

Therefore, Kumar’s team observed LHAASO J2108 + 5157 with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) and the High-Altitude Water Cherenkov Observatory (HAWC) for more light in the gamma-rays of HE is released.

The observation did not find any significant emission near the position of LHAASO J2108 + 5158. Astronomers also performed a spectral analysis of the circular region with a radius of 0.09 degrees around the position of LHAASO J2108 + 5157, measuring the flux variation with upper limits of 1.0 , 3.98, and 15.38 TeV energies—in agreement with previous studies.

The upper limits obtained exclude the hadronic model and suggest a leptonic origin for the emission from a few TeV to hundreds of TeV energies. However, researchers have noted that a new molecular cloud has recently been identified in the area of ​​LHAASO J2108 + 5157, which sheds more light on the origin of the gamma-ray emission.

“The morphology of the new cloud is very consistent with the LHAASO J2108 + 5157 gamma-ray emission up to 2 GeV from Fermi-LAT and the emission detected by LHAASO. This makes it possible that the gamma rays are produced by -hadronic channel and molecular. The cloud as the main target of cosmic ray particles accelerated by unknown PeVatrons,” the astronomers concluded.

They added that future observations with CTA and analysis in the X-ray band are needed to fully understand the nature of LHAASO J2108 + 5157.

More information:
Sajan Kumar et al, VERITAS and HAWC observations of the unknown source LHAASO J2108+5157, arXiv (2023). DOI: 10.48550/arxiv.2309.00089

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