Evidence of Cosmic-Ray Excess from Local Giant Molecular Clouds

Baghmanyan, Vardan; Peron, Giada; Casanova, S.; Aharonian, F.; Zanin, R.

doi:10.3847/2041-8213/abb5f8

Cited by 25 publications

(38 citation statements)

References 29 publications

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“…The emission enhancement associated with the clouds makes it possible to precisely locate along a given line of sight where the CR population produces the emission. Molecular clouds are thus used to perform a sort of tomography, and obtain a three-dimensional view of the CR distribution in the Galaxy (Issa & Wolfendale 1981;Aharonian & Atoyan 1996;Aharonian 2001;Casanova et al 2010a;Aharonian et al 2020;Baghmanyan et al 2020).…”

Section: Molecular Clouds Close To Middle-aged Snrs: the Case Of W44mentioning

confidence: 99%

On particle acceleration and transport in plasmas in the Galaxy: theory and observations

Amato

Casanova

2021

J. Plasma Phys.

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Accelerated particles are ubiquitous in the Cosmos and play a fundamental role in many processes governing the evolution of the Universe at all scales, from the sub-AU scale relevant for the formation and evolution of stars and planets to the Mpc scale involved in Galaxy assembly. We reveal the presence of energetic particles in many classes of astrophysical sources thanks to their production of non-thermal radiation, and we detect them directly at the Earth as cosmic rays. In the last two decades both direct and indirect observations have provided us a wealth of new, high-quality data about cosmic rays and their interactions both in sources and during propagation, in the Galaxy and in the Solar System. Some of the new data have confirmed existing theories about particle acceleration and propagation and their interplay with the environment in which they occur. Some others have brought about interesting surprises, whose interpretation is not straightforward within the standard framework and may require a change of paradigm in terms of our ideas about the origin of cosmic rays of different species or in different energy ranges. In this article, we focus on cosmic rays of galactic origin, namely with energies below a few petaelectronvolts, where a steepening is observed in the spectrum of energetic particles detected at the Earth. We review the recent observational findings and the current status of the theory about the origin and propagation of galactic cosmic rays.

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Section: Molecular Clouds Close To Middle-aged Snrs: the Case Of W44mentioning

confidence: 99%

On particle acceleration and transport in plasmas in the Galaxy: theory and observations

Amato

Casanova

2021

J. Plasma Phys.

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“…In such a situation, we need alternative ways to probe the past activity of pevatrons, and therefore attempt to do archaeology of pevatrons 1 . The signature of the extinct pevatron could for instance be found through deeper studies of SNR shocks (e.g., extrapolating backwards the shock dynamics), by probing the surrounding molecular clouds (MC) of the pevatron candidates, for instance through gamma rays observations of MCs in the vicinty of pevatron candidates [101][102][103], or through the study of the radiation of secondary particles produced around pevatrons [104].…”

Section: Archeology Of Pevatronsmentioning

confidence: 99%

The Hunt for Pevatrons: The Case of Supernova Remnants

Cristofari

2021

Universe

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The search for Galactic pevatrons is now a well-identified key science project of all instruments operating in the very-high-energy domain. Indeed, in this energy range, the detection of gamma rays clearly indicates that efficient particle acceleration is taking place, and observations can thus help identify which astrophysical sources can energize particles up to the ~PeV range, thus being pevatrons. In the search for the origin of Galactic cosmic rays (CRs), the PeV range is an important milestone, since the sources of Galactic CRs are expected to accelerate PeV particles. This is how the central scientific goal that is ’solving the mystery of the origin of CRs’ has often been distorted into ’finding (a) pevatron(s)’. Since supernova remnants (SNRs) are often cited as the most likely candidates for the origin of CRs, ’finding (a) pevatron(s)’ has often become ’confirming that SNRs are pevatrons’. Pleasingly, the first detection(s) of pevatron(s) were not associated to SNRs. Moreover, all clearly detected SNRs have yet revealed to not be pevatrons, and the detection from VHE gamma rays from regions unassociated with SNRs, are reminding us that other astrophysical sites might well be pevatrons. This short review aims at highlighting a few important results on the search for Galactic pevatrons.

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“…We use a technique similar to what is followed in [4,6,8,10] to construct spatial templates for the pion decay emission. We use the dust 353 GHz opacity map which is a tracer of both molecular and atomic gas, and realize a rectangular cutout (Figure 2) around the ellipse that represents the cloud extension, with = 0.22°, = 0.48°, and position_angle = 166°as given in the clouds catalog [11].…”

Section: A Sinhamentioning

confidence: 99%

Search for enhanced TeV gamma ray emission from Giant Molecular Clouds using H.E.S.S.

Sinha

Baghmanyan²,

Peron³

et al. 2021

Proceedings of 37th International Cosmic Ray Conference — PoS(ICRC2021)

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Cosmic Ray (CR) interactions with the dense gas inside Giant Molecular Clouds (GMCs) produce neutral pions, which in turn decay into gamma rays. Thus, the gamma ray emission from GMCs is a direct tracer of the cosmic ray density and the matter density inside the clouds. Detection of enhanced TeV emission from GMCs, i.e., an emission significantly larger than what is expected from the average Galactic cosmic rays illuminating the cloud, can imply a variation in the local cosmic ray density, due to, for example, the presence of a recent accelerator in proximity to the cloud. Such gamma-ray observations can be crucial in probing the cosmic ray distribution across our Galaxy, but are complicated to perform with present generation Imaging Atmospheric Cherenkov Telescopes (IACTs). These studies require differentiating between the strong cosmic-ray induced background, the large scale diffuse emission, and the emission from the clouds, which is difficult to the small field of view of present generation IACTs. In this contribution, we use H.E.S.S. data collected over 16 years to search for TeV emission from GMCs in the inner molecular galacto-centric ring of our Galaxy. We implement a 3D FoV likelihood technique, and simultaneously model the hadronic background, the galactic diffuse emission and the emission expected from known VHE sources to probe for excess TeV gamma ray emission from GMCs.

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Evidence of Cosmic-Ray Excess from Local Giant Molecular Clouds

Cited by 25 publications

References 29 publications

On particle acceleration and transport in plasmas in the Galaxy: theory and observations

On particle acceleration and transport in plasmas in the Galaxy: theory and observations

The Hunt for Pevatrons: The Case of Supernova Remnants

Search for enhanced TeV gamma ray emission from Giant Molecular Clouds using H.E.S.S.

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