Astrophysicists at the H.E.S.S. Observatory in Namibia, in which researchers from the University of Warsaw are involved, have discovered the highest energy gamma rays ever from the Vela pulsar. The project at UW is coordinated by Prof. Tomasz Bulik from the Astronomical Observatory. The results of the research have been published in the journal Nature Astronomy.

Pulsar Vela. Fot. domena publiczna / Wikimedia Commons

Pulsars are the left-over corpses of stars that spectacularly exploded in a supernova. The explosions leave behind a tiny, dead star with a diameter of just some 20 kilometers, rotating extremely fast and endowed with an enormous magnetic field, stresses Prof. Tomasz Bulik from the UW Astronomical Observatory.

The H.E.S.S. team has detected the highest energy gamma rays ever from a pulsar in collaboration with other scientists working at the H.E.S.S. observatory in Namibia. The energy of these gamma rays clocked in at 20 teraelectronvolts, or about ten trillion times the energy of visible light. As the researchers point out, this observation is difficult to reconcile with the theory of the production of such pulsed gamma rays.

The results of the work of astrophysicists have been published in the paper Discovery of a Radiation Component from the Vela Pulsar Reaching 20 Teraelectronvolts in the prestigious journal Nature Astronomy.

Cosmic lighthouses

Pulsars emit rotating beams of electromagnetic radiation. They can be compared to 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, explains Prof. Tomasz Bulik from UW.

Researchers think that the source of this radiation is fast electrons that travel from the pulsar’s surface to the very end of its magnetosphere. The magnetosphere is made up of plasma and electromagnetic fields that surround and co-rotate with the star.

The Vela pulsar, 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 brightest persistent source of cosmic gamma rays in the gigaelectronvolts (GeV) range. It rotates about eleven times per second. Above a few GeV, however, its radiation ends abruptly. Scientists assume that the electrons reach the end of the pulsar’s magnetosphere and escape from it.

Using observations with H.E.S.S., a new radiation component at even higher energies has been discovered, with energies of up to tens of teraelectronvolts (TeV).

This very high-energy component appears at the same phase intervals as the one observed in the GeV range. To attain these energies, the electrons might have to travel even farther than the magnetosphere, yet the rotational emission pattern needs to remain intact.

The Vela pulsar, apart from its other superlatives, holds the record as the pulsar with the highest-energy gamma rays discovered to date.

The High Energy Stereoscopy System (H.E.S.S.) is an array of five imaging atmospheric Cherenkov telescopes for studying cosmic gamma rays. The telescopes are situated in Namibia, near the Gamsberg mountain. Four H.E.S.S. telescopes began their operation in 2002-2003. The much larger fifth telescope, known as H.E.S.S. II, has been in operation since July 2012.

More than 230 scientists from forty-one institutes in fifteen countries are involved in H.E.S.S. research. The H.E.S.S. team includes astrophysicists from five Polish scientific institutions: the Astronomical Observatory of the University of Warsaw, Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences, Astronomical Observatory of the Jagiellonian University, Henryk Niewodniczański Institute of Nuclear Physics of the Polish Academy of Sciences, and Nicolaus Copernicus University in Toruń. Prof. Rafał Moderski from the Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences coordinates the project at the national level.