Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources
The riddle of the origin of Cosmic Rays (CR) has been an open question for over a century. Gamma ray observations above 100 MeV reveal the sites of cosmic ray acceleration to energies where they are unaffected by solar modulation; recent evidence supports the existence of hadronic acceleration in Su...
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MDPI AG
2022-07-01
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| Online Access: | https://www.mdpi.com/2571-8800/5/3/22 |
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| author | Omar Tibolla Sarah Kaufmann Paula Chadwick |
| author_facet | Omar Tibolla Sarah Kaufmann Paula Chadwick |
| author_sort | Omar Tibolla |
| collection | DOAJ |
| description | The riddle of the origin of Cosmic Rays (CR) has been an open question for over a century. Gamma ray observations above 100 MeV reveal the sites of cosmic ray acceleration to energies where they are unaffected by solar modulation; recent evidence supports the existence of hadronic acceleration in Supernova Remnants (SNR), as expected in the standard model of cosmic ray acceleration. Nevertheless, the results raise new questions, and no final answer has been provided thus far. Among the suggested possible alternative accelerators in the Very High Energy (VHE) gamma ray sky, pulsar wind nebulae (PWNe, which together with dark matter are the main candidates to explain the local positron excess as well) are the dominant population among known Galactic sources. However, the most numerous population in absolute terms is represented by unidentified sources (~50% of VHE gamma ray sources). The relationship between PWNe and unidentified sources seems very close; in fact, in a PWN, the lifetime of inverse Compton (IC) emitting electrons not only exceeds the lifetime of its progenitor pulsar, but also exceeds the age of the electrons that emit via synchrotron radiation. Therefore, during its evolution, a PWN can remain bright in IC such that its GeV-TeV gamma ray flux remains high for timescales much larger than the lifetimes of the pulsar and the X-ray PWN. In addition, the shell-type remnant of the supernova explosion in which the pulsar was formed has a much shorter lifetime than the electrons responsible for IC emission. Hence, understanding PWNe and VHE unidentified sources is a crucial piece of the solution to the riddle of the origin of cosmic rays. Both theoretical aspects (with particular emphasis on the ancient pulsar wind nebulae scenario) and their observational proofs are discussed in this paper. Specifically, the scientific cases of HESS J1616-508 and HESS J1813-126 are examined in detail. |
| first_indexed | 2024-03-09T23:38:29Z |
| format | Article |
| id | doaj.art-e8b3df0fa15d40bbb615bfb262098247 |
| institution | Directory Open Access Journal |
| issn | 2571-8800 |
| language | English |
| last_indexed | 2024-03-09T23:38:29Z |
| publishDate | 2022-07-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | J |
| spelling | doaj.art-e8b3df0fa15d40bbb615bfb2620982472023-11-23T16:56:58ZengMDPI AGJ2571-88002022-07-015331833310.3390/j5030022Pulsar Wind Nebulae and Unidentified Galactic Very High Energy SourcesOmar Tibolla0Sarah Kaufmann1Paula Chadwick2Universidad Politécnica de Pachuca, Zempoala CP-43830, Hidalgo, MexicoUniversidad Politécnica de Pachuca, Zempoala CP-43830, Hidalgo, MexicoDepartment of Physics, Durham University, Durham DH1 3LE, UKThe riddle of the origin of Cosmic Rays (CR) has been an open question for over a century. Gamma ray observations above 100 MeV reveal the sites of cosmic ray acceleration to energies where they are unaffected by solar modulation; recent evidence supports the existence of hadronic acceleration in Supernova Remnants (SNR), as expected in the standard model of cosmic ray acceleration. Nevertheless, the results raise new questions, and no final answer has been provided thus far. Among the suggested possible alternative accelerators in the Very High Energy (VHE) gamma ray sky, pulsar wind nebulae (PWNe, which together with dark matter are the main candidates to explain the local positron excess as well) are the dominant population among known Galactic sources. However, the most numerous population in absolute terms is represented by unidentified sources (~50% of VHE gamma ray sources). The relationship between PWNe and unidentified sources seems very close; in fact, in a PWN, the lifetime of inverse Compton (IC) emitting electrons not only exceeds the lifetime of its progenitor pulsar, but also exceeds the age of the electrons that emit via synchrotron radiation. Therefore, during its evolution, a PWN can remain bright in IC such that its GeV-TeV gamma ray flux remains high for timescales much larger than the lifetimes of the pulsar and the X-ray PWN. In addition, the shell-type remnant of the supernova explosion in which the pulsar was formed has a much shorter lifetime than the electrons responsible for IC emission. Hence, understanding PWNe and VHE unidentified sources is a crucial piece of the solution to the riddle of the origin of cosmic rays. Both theoretical aspects (with particular emphasis on the ancient pulsar wind nebulae scenario) and their observational proofs are discussed in this paper. Specifically, the scientific cases of HESS J1616-508 and HESS J1813-126 are examined in detail.https://www.mdpi.com/2571-8800/5/3/22cosmic rayssupernova remnantspulsar wind nebulaehigh energy astrophysicsunidentified high energy sourcesHESS J1616-508 |
| spellingShingle | Omar Tibolla Sarah Kaufmann Paula Chadwick Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources J cosmic rays supernova remnants pulsar wind nebulae high energy astrophysics unidentified high energy sources HESS J1616-508 |
| title | Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources |
| title_full | Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources |
| title_fullStr | Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources |
| title_full_unstemmed | Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources |
| title_short | Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources |
| title_sort | pulsar wind nebulae and unidentified galactic very high energy sources |
| topic | cosmic rays supernova remnants pulsar wind nebulae high energy astrophysics unidentified high energy sources HESS J1616-508 |
| url | https://www.mdpi.com/2571-8800/5/3/22 |
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