Gamma-ray studies have proven Isolated, powerful pulsars to be exceptional particle accelerators and antimatter manufacturers. The associated acceleration and radiation processes and the sites where they take place remain the subject of numerous unanswered concerns. In their radiation spectra, all of the gamma-ray pulsars seen so far exhibit severe cutoffs or a break above energies of a few gigaelectronvolts.
Using the High Energy Stereoscopic System’s Cherenkov telescopes, scientists using the H.E.S.S. observatory in Namibia have detected the highest energy gamma rays ever from a pulsar. These gamma rays had an energy of 20 tera-electronvolts, roughly ten trillion times that of visible light. This observation is difficult to explain regarding the theory underlying the generation of such pulsed gamma rays.
This radiation component was found to be coming from the Vela pulsar, the brightest pulsar in the radio band of the electromagnetic spectrum and the brightest persistent source of cosmic gamma rays in the giga-electronvolts (GeV) range. The pulsar is located in the Southern sky in the constellation Vela (sail of the ship).
The radiation from this pulsar is about 200 times more energetic than all radiation ever detected before from this object. The phase intervals for this extremely high-energy component coincide with the one seen in the GeV range. The rotating emission pattern must hold up even if the electrons may have to go further than the magnetosphere to reach these energy.
Arache Djannati-Atai from the Astroparticle & Cosmology (A.P.C.) laboratory in France, who led the research said, “This result challenges our previous knowledge of pulsars and requires a rethinking of how these natural accelerators work. The traditional scheme in which particles are accelerated along magnetic field lines within or slightly outside the magnetosphere cannot sufficiently explain our observations.”
“Perhaps we are witnessing the acceleration of particles through the so-called magnetic reconnection process beyond the light cylinder, which still somehow preserves the rotational pattern? But even this scenario faces difficulties in explaining how such extreme radiation is produced.”
“Whatever the explanation, next to its other superlatives, the Vela pulsar now officially holds the record as the pulsar with the highest-energy gamma rays discovered to date. This discovery opens a new observation window for detection of other pulsars in the tens of teraelectronvolt range with current and upcoming more sensitive gamma-ray telescopes, hence paving the way for a better understanding of the extreme acceleration processes in highly magnetized astrophysical objects.”
Journal Reference:
- The H.E.S.S. Collaboration et al.., Zanin, R., Kerr, M., et al. Discovery of a radiation component from the Vela pulsar reaching 20 teraelectronvolts. Nat Astron (2023). DOI: 10.1038/s41550-023-02052-3