Gamma-Ray Astrophysics with High Sensitivity

Dear Colleagues,

Since the discovery of gamma-ray bursts in the 1960s, more and more sensitive gamma-ray instruments have been built to work on the ground and in space, nurturing the development of gamma-ray astrophysics, which involves the study of relativistic particles and fascinating objects like active galactic nuclei, pulsars, binaries, supernova remnants, and extreme astrophysical environments around these objects.

The ever-improved sensitivity and angular resolution of various gamma-ray astronomical detectors have greatly advanced the field of gamma-ray astrophysics and made it a fully mature branch of astrophysics in the last decade. Recently, this has culminated in the publication of source catalogs, especially in the GeV and TeV energy bands. The Data Release 4 of the fourth Fermi-LAT catalog (4FGL-DR4) now contains more than 7000 sources detected at GeV energies; in the TeV energy band, more than 300 sources are included in the TeVCat, as of August, 2024. At the highest energies, the LHAASO instruments have opened the PeV observing window, and surprisingly or not, many leptonic and hadronic PeVatrons do exist in our galaxy. This recent development highlights the intimate relationship of gamma-ray astronomy and the origin of cosmic rays. The CTA array with its supreme sensitivity and angular resolution will certainly add much to our knowledge in this quest.

On the other hand, the lack of sensitive instruments in the MeV energy band since COMPTEL has hindered the development of MeV astrophysics, which is important in studying the cosmic nucleons. Therefore, the discovery space in the MeV band remains huge and the next generation of instruments are much awaited to fill the gap.

This Special Issue seeks to make a milestone in the field, by including articles written by top researchers in the field of gamma-ray astronomy from MeV to PeV energy. Original works about important scientific discoveries, instrumentation, innovative detection and analysis techniques, and current status and future prospects of the field, are invited. We anticipate that this Special Issue will serve to advance our understanding of the universe seen at the gamma-rays with higher and higher sensitivity.

Prof. Dr. Pak Hin Thomas Tam
Guest Editor

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• instrumentations
• gamma-ray detection techniques
• source catalogs
• gamma-ray astrophysics