The supernova remnant Puppis A as an efficient particle accelerator. The study: “Evidence for protons accelerated and escaped from the Puppis A region using Fermi-LAT observations” of R. Giuffrida (INAF-OAPA/UNIPA/Université de Paris) appeared on A&A

The supernova remnant Puppis A reveals itself as an efficient particle accelerator, through different mechanisms in different regions of the remnant

In the 15th episode of the fourth season of the science fiction series Battlestar Galactica, the automaton Cavil complains about not being able to observe the Universe in X-rays and gamma rays, being limited—like humans—to only the visible band. If he had been able to perceive gamma rays, his vision would have been dazzled by the emission from supernova remnants.

These nebulae, produced by supernova explosions and their interaction with the surrounding medium, are in fact extremely efficient at accelerating particles to relativistic energies. One manifestation of this process is the intense gamma-ray emission observed in most supernova remnants, produced mainly by three mechanisms:

in the leptonic case, gamma rays are generated by relativistic electrons scattering low-energy photons, progressively boosting their energy until gamma radiation is produced;
in the hadronic case, instead, gamma rays originate from interactions and decays of particles such as protons;
an alternative hadronic mechanism, proposed in 2010, suggests that in supernova remnants interacting with nearby clouds, gamma rays may be produced within the clouds themselves, compressed and heated by the incident radiation. In this scenario, the gamma-ray emission is accompanied by strong radio radiation from relativistic particles that have “escaped” the supernova remnant and impacted the cloud, through a process called synchrotron emission (radiation from high-energy particles moving in a magnetic field).

One of the most studied supernova remnants across the electromagnetic spectrum is Puppis A, located about 4300 light-years from the Sun and with an estimated age of about 4000 years. A team led by astrophysicist R. Giuffrida (INAF – Astronomical Observatory of Palermo, University of Palermo, and Université de Paris) analyzed data from a long gamma-ray observational campaign conducted with the Fermi-LAT satellite. Puppis A is known for its asymmetric gamma-ray emission, which points to the presence of different emission mechanisms at work in different regions of the remnant.

The study confirms that in the northeast region, where shock waves traveling through Puppis A interact with a dense surrounding cloud, the gamma-ray emission mechanism remains uncertain despite being hadronic in nature and although it is tied to this interaction. In the opposite region, to the southwest, where the remnant expands into a low-density medium, the gamma-ray emission instead appears as the direct result of relativistic particle acceleration by the magnetic field associated with the shock front—a process commonly observed in supernova remnants.

The results, described in the article “Evidence for protons accelerated and escaped from the Puppis A region using Fermi-LAT observations”, recently published in Astronomy & Astrophysics, confirm the crucial role of supernova remnants in accelerating relativistic particles through complex processes that can vary even within a single remnant depending on local conditions. Astrophysicist M. Miceli of the University of Palermo also contributed to the study.

The cover image (click here to view) shows a map of gamma-ray emission from Puppis A obtained with Fermi-LAT. The white circle marks the region used for spectral analysis, while the green contours outline the X-ray emission observed by the eROSITA satellite.