A very mysterious energy source that has been investigated by astronomers

Astronomers from the University of Maryland and Michigan Technological University have investigated a mysterious high-energy gamma-ray source known as LHAASO J2108+5157. The study results were published on August 31 on a preprint server arXivIt can help us reveal the true nature of this source.

Sources that emit gamma radiation with photon energies in the range of 100 GeV to 100 TeV are called very high energy (VHE) gamma-ray sources, while those with photon energies above 0.1 TeV are known as high-energy gamma-ray sources. Very (UHE). The nature of these sources is still not well understood; Therefore, astronomers are constantly looking for new objects of this type to characterize, which may shed more light on their properties in general.

A team of astronomers led by Sajjan Kumar of the University of Maryland decided to take a closer look at a UHE gamma-ray source called LHAASO J2108+5157. It is a point-like source with an extent of less than 0.39°, and is known to be associated with the molecular cloud [MML2017]4607 – is located about 10,700 light-years away.

Previous observations of LHAASO J2108+5157 did not detect any X-ray counterparts, and the closest X-ray source turned out to be the eclipsing binary RX J2107.3+5202 with a separation of about 0.3 degrees. Since no strong pulsars or supernova remnants have yet been detected near LHAASO J2108+5157, it is difficult to pinpoint the origin of the gamma-ray emission, as this can be explained by either hadron or leptonian models.

Therefore, Kumar’s team observed LHAASO J2108+5157 using the Very Active Radiation Imaging Telescope Array System (VERITAS) and High Altitude Cherenkov Observatory (HAWC) in order to shed more light on the emitted UHE gamma rays.

Observations found no significant emission near the location of LHAASO J2108+5158. The astronomers also performed a spectral analysis of the circular region with a radius of 0.09 degrees around the position of LHAASO J2108+5157, and measured the upper bounds of the differential flux at 1.0, 3.98, and 15.38 TeV energies, which is consistent with previous studies.

The obtained upper bounds exclude the hadron model and suggest a leptonian origin for the emission ranging from a few TeV to hundreds of TeV energies. However, the researchers note that a new molecular cloud has recently been identified near LHAASO J2108+5157, which sheds more light on the origin of the observed gamma-ray emission.

“The shape of this new cloud is closely related to the LHAASO J2108+5157 gamma-ray emission of up to 2 GeV from Fermi-LAT and the emission detected by LHAASO. This raises the possibility of gamma-ray production through the molecular hadron channel. The astronomers concluded, “ “The cloud is the main target of cosmic ray particles that are accelerated by unidentified PeVatrons.”

They added that future observations by the CTA and analysis in the X-ray range are required in order to fully understand the nature of LHAASO J2108+5157.