High energy gamma rays from nebulae associated with extragalactic microquasars and ultra-luminous X-ray sources

Uchiyama

Arakawa

et al. 2017

ApJ

On both observational and theoretical grounds, the disk of our Galaxy should be accreting cool gas with temperature 10 5 K via the halo at a rate ∼ 1 M ⊙ yr −1 . At least some of this accretion is mediated by high velocity clouds (HVCs), observed to be traveling in the halo with velocities of a few 100 km s −1 and occasionally impacting the disk at such velocities, especially in the outer regions of the Galaxy. We address the possibility of particle acceleration in shocks triggered by such HVC accretion events, and the detectability of consequent non-thermal emission in the radio to gamma-ray bands and high-energy neutrinos. For plausible shock velocities ∼ 300 km s −1 and magnetic field strengths ∼ 0.3 − 10 µG, electrons and protons may be accelerated up to ∼ 1 − 10 TeV and ∼ 30 − 10 3 TeV, respectively, in sufficiently strong adiabatic shocks during their lifetime of ∼ 10 6 yr. The resultant pion decay and inverse Compton gamma-rays may be the origin of some unidentified Galactic GeV-TeV sources, particularly the "dark" source HESS J1503-582 that is spatially coincident with anomalous HI structure known as "forbidden-velocity wings". Correlation of their locations with star-forming regions may be weak, absent, or even opposite. Non-thermal radio and X-ray emission from primary and/or secondary electrons may be detectable with deeper observations. The contribution of HVC accretion to Galactic cosmic rays is subdominant, but could be non-negligible in the outer Galaxy. As the thermal emission induced by HVC accretion is likely difficult to detect, observations of such phenomena may offer a unique perspective on probing gas accretion onto the Milky Way and other galaxies.

Section: Neutral Particles and Radiative Regimementioning

confidence: 91%

Cosmic Rays and Non-thermal Emission Induced by Accretion of Cool Gas onto the Galactic Disk

Uchiyama

Arakawa

et al. 2017

ApJ

“…The emission mechanism for this second component is still under debate. However, CTA is expected to increase the number of these sources as well with its improved sensitivity [107,108], and will potentially lead to the serendipitous discovery of new source populations in the VHE sky [109][110][111][112]. to develop his research.…”

Section: Resultsmentioning

confidence: 99%

Cherenkov telescope array extragalactic survey discovery potential and the impact of axion-like particles and secondary gamma rays

Franco

Cotter

2017

Astroparticle Physics

Self Cite

The Cherenkov Telescope Array (CTA) is about to enter construction phase and one of its main key science projects is to perform an unbiased survey in search of extragalactic sources. We make use of both the latest blazar gamma-ray luminosity function and spectral energy distribution to derive the expected number of detectable sources for both the planned Northern and Southern arrays of the CTA observatory. We find that a shallow, wide survey of about 0.5 hour per field of view would lead to the highest number of blazar detections. Furthermore, we investigate the effect of axionlike particles and secondary gamma rays from propagating cosmic rays on the source count distribution, since these processes predict different spectral shape from standard extragalactic background light attenuation. We can generally expect more distant objects in the secondary gamma-ray scenario, while axion-like particles do not significantly alter the expected distribution. Yet, we find that, these results strongly depend on the assumed magnetic field strength during the propagation. We also provide source count predictions for the High Altitude Water Cherenkov observatory (HAWC), the Large High Altitude Air Shower Observatory (LHAASO) and a novel proposal of a hybrid detector.

“…These expanding nebulae provide suitable conditions for particle production and CR acceleration, especially through a sequence of processes triggered by an initial hadronic interaction. It was shown in Inoue et al [416] that nebulae with fast expansion velocities 120 km s −1 are capable of accelerating charged particles up to ∼100 TeV, making them viable UHE CR sources.…”

Section: Ss433mentioning

confidence: 99%

Cosmic Ray Processes in Galactic Ecosystems

Owen

et al. 2023

Galaxies

Self Cite

Galaxy evolution is an important topic, and our physical understanding must be complete to establish a correct picture. This includes a thorough treatment of feedback. The effects of thermal–mechanical and radiative feedback have been widely considered; however, cosmic rays (CRs) are also powerful energy carriers in galactic ecosystems. Resolving the capability of CRs to operate as a feedback agent is therefore essential to advance our understanding of the processes regulating galaxies. The effects of CRs are yet to be fully understood, and their complex multi-channel feedback mechanisms operating across the hierarchy of galaxy structures pose a significant technical challenge. This review examines the role of CRs in galaxies, from the scale of molecular clouds to the circumgalactic medium. An overview of their interaction processes, their implications for galaxy evolution, and their observable signatures is provided and their capability to modify the thermal and hydrodynamic configuration of galactic ecosystems is discussed. We present recent advancements in our understanding of CR processes and interpretation of their signatures, and highlight where technical challenges and unresolved questions persist. We discuss how these may be addressed with upcoming opportunities.