Astronomers detect very high energy gamma ray emission around distant pulsar

Using the Large High-Altitude Air Shower Observatory (LHAASO), an international team of astronomers has detected very high energy (VHE) gamma rays around the pulsar PSR J0248+6021, which may be the pulsar’s halo or a nebula of the pulsar wind. . The discovery was reported in a paper published October 6 on the preprint server. arXiv.

Pulsars are highly magnetized rotating neutron stars that emit a beam of electromagnetic radiation. They are usually detected as short bursts of radio emission; however, some of them are also observed via optical, x-ray and gamma-ray telescopes.

Sources emitting gamma radiation with photon energies between 100 GeV and 100 TeV are called very high energy (VHE) gamma-ray sources, while those with photon energies above 0.1 PeV are called sources ultra-high energy (UHE) gamma rays. The nature of these sources is not yet well understood; therefore, astronomers are constantly searching for new objects of this type to characterize them, which could shed more light on their properties in general.

Discovered in 1997, PSR J0248+6021 is a middle-aged pulsar with a rotation period of approximately 217 milliseconds and a rotational power level of 213 decillion erg/s. The pulsar has an unusually high dispersion measurement of around 370 pc/cm³which is probably due to its location in the dense giant region of ionized atomic hydrogen (HII region), designated W5, at a distance of approximately 6,500 light years.

Today, a team of astronomers led by Zhen Cao of the Chinese Academy of Sciences (CAS) reports the detection of a VHE gamma-ray emission located near the position of PSR J0248+6021. The discovery is based on data from LHAASO’s Water Cherenkov Detector Array (WCDA).

By analyzing WCDA data, Cao’s team identified three gamma-ray sources, two of which are close to PSR J0248+6021 based on their angular distance. One of them was found to be an extended source consistent with 1LHAASO J0249+6022 reported in the first LHAASO catalog, while the other is a point source with an angular distance of about 1.2 degrees from the pulsar.

According to the paper, no clear extended multi-wavelength counterpart of 1LHAASO J0249+6022 has been found from radio to GeV bands. Therefore, the authors of the paper concluded that the most plausible explanation for the detected VHE gamma-ray emission is the inverse Compton process of highly relativistic electrons and positrons injected by PSR J0248+6021.

Astronomers noted that the morphology of the VHE gamma-ray emission suggests that 1LHAASO J0249+6022 is the halo of the TeV pulsar or a pulsar wind nebula associated with PSR J0248+6021.

“It is assumed that these electrons/positrons are either confined in the pulsar wind nebula or have already escaped into the interstellar medium, forming a pulsar halo,” the researchers concluded.

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