Scientists use H.E.S.S. An observatory in Namibia has detected the most energetic gamma rays ever emitted from a dead star called a pulsar. The energy of these gamma rays is 20 teraelectronvolts, about ten trillion times the energy of visible light. This observation is unlikely to be consistent with the theory of the generation of such pulsed gamma rays, the international research team reports in the journal Nature Astronomy. Pulsars are the remains of stars that have exploded spectacularly in supernovae. The explosion left behind a small dead star only 20 km in diameter, spinning extremely fast and with an extremely large magnetic field. H.E.S.S. Scientist Emma de Oña Wilhelmi, co-author of the publication, is working at DESY.

Pulsars emit rotating beams of electromagnetic radiation, somewhat like cosmic lighthouses. If their beam sweeps across our solar system, we see flashes of radiation at regular time intervals. These flashes, also called pulses of radiation, can be searched for in different energy bands of the electromagnetic spectrum. Scientists think that the source of this radiation are fast electrons produced and accelerated in the pulsar’s magnetosphere, while traveling towards its periphery. The magnetosphere is made up of plasma and electromagnetic fields that surround and co-rotate with the star. “On their outward journey, the electrons acquire energy and release it in the form of the observed radiation beams,” says Bronek Rudak from the Nicolaus Copernicus Astronomical Center (CAMK PAN) in Poland, also a co-author.

Pulsar Vela, located in the southern sky in the constellation Vela (Sail of the Ship), is the brightest pulsar in the radio band of the electromagnetic spectrum and the most persistent source of cosmic gamma rays in the gigaelectronvolt (GeV) range ) ). . It rotates about eleven times per second. However, above a few GeV, its emission stops suddenly, possibly because electrons reach the end of the pulsar’s magnetosphere and escape. But that’s not the end of the story: thanks to extensive observations with H.E.S.S., a new radiation component at a higher energy level was discovered, with energies of up to several tens of teraelectronvolts (TeV). “This energy level is about 200 times more than all the radiation this object has ever detected before,” said co-author Christo Venter of North West University in South Africa. This very high energy component appears at the same phase range as that observed in the GeV range. However, to reach these energies, the electrons may have to travel even further from the magnetosphere, but the rotational emission pattern must be preserved.

“This result challenges our previous knowledge of pulsars and requires a rethink of how these natural accelerators work,” said Arache Djannati-Atai of the Astroparticle & Astronomical Laboratory. Cosmology (APC) in France, who led the study, explains. “The traditional theory that particles are accelerated along magnetic field lines inside or slightly outside the magnetosphere cannot fully explain our observations. Perhaps we are witnessing particle acceleration through a process called magnetic reconnection outside the lightweight cylinder, which somehow preserves the rotational pattern? But even this scenario has difficulty explaining how such intense radiation is generated. Whatever the explanation, along with its other superlatives, the Vela pulsar now officially holds the record for the most intense gamma-ray pulsar discovered to date. “This discovery opens a new observational window for detecting other pulsars in the range of tens of teraelectronvolts with current and future gamma-ray telescopes, paving the way for a better understanding of acceleration processes extremes in highly magnetic astrophysical objects.” Djanati-Atai said.

source: https://www.nature.com/articles/s41550-023-02052-3