scholarly journals Understanding the origin of the positron annihilation line and the physics of supernova explosions

2021 ◽  
Author(s):  
F. Frontera ◽  
E. Virgilli ◽  
C. Guidorzi ◽  
P. Rosati ◽  
R. Diehl ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Large Scale ◽  
Gamma Ray ◽  
Nuclear Astrophysics ◽  
High Energy ◽  
Radioactive Isotopes ◽  
Fusion Reactions ◽  
Dark Matter Annihilation ◽  
Annihilation Line ◽  
Supernova Explosions

AbstractNuclear astrophysics, and particularly nuclear emission line diagnostics from a variety of cosmic sites, has remained one of the least developed fields in experimental astronomy, despite its central role in addressing a number of outstanding questions in modern astrophysics. Radioactive isotopes are co-produced with stable isotopes in the fusion reactions of nucleosynthesis in supernova explosions and other violent events, such as neutron star mergers. The origin of the 511 keV positron annihilation line observed in the direction of the Galactic Center is a 50-year-long mystery. In fact, we still do not understand whether its diffuse large-scale emission is entirely due to a population of discrete sources, which are unresolved with current poor angular resolution instruments at these energies, or whether dark matter annihilation could contribute to it. From the results obtained in the pioneering decades of this experimentally-challenging window, it has become clear that some of the most pressing issues in high-energy astrophysics and astro-particle physics would greatly benefit from significant progress in the observational capabilities in the keV-to-MeV energy band. Current instrumentation is in fact not sensitive enough to detect radioactive and annihilation lines from a wide variety of phenomena in our and nearby galaxies, let alone study the spatial distribution of their emission. In this White Paper (WP), we discuss how unprecedented studies in this field will become possible with a new low-energy gamma-ray space experiment, called ASTENA (Advanced Surveyor of Transient Events and Nuclear Astrophysics), which combines new imaging, spectroscopic and polarization capabilities. In a separate WP (Guidorzi et al. 39), we discuss how the same mission concept will enable new groundbreaking studies of the physics of Gamma–Ray Bursts and other high-energy transient phenomena over the next decades.

scholarly journals Modeling Gamma-Ray SEDs and Angular Extensions of Extreme TeV Blazars from Intergalactic Proton-Initiated Cascades in Contemporary Astrophysical EGMF Models

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 220
Author(s):  
Emil Khalikov
Keyword(s):  
Gamma Rays ◽  
Large Scale ◽  
Gamma Ray ◽  
High Energy ◽  
Cascade Model ◽  
Point Sources ◽  
Spectral Energy ◽  
Observation Data ◽  
Cherenkov Telescopes ◽  
The Universe

The intrinsic spectra of some distant blazars known as “extreme TeV blazars” have shown a hint at an anomalous hardening in the TeV energy region. Several extragalactic propagation models have been proposed to explain this possible excess transparency of the Universe to gamma-rays starting from a model which assumes the existence of so-called axion-like particles (ALPs) and the new process of gamma-ALP oscillations. Alternative models suppose that some of the observable gamma-rays are produced in the intergalactic cascades. This work focuses on investigating the spectral and angular features of one of the cascade models, the Intergalactic Hadronic Cascade Model (IHCM) in the contemporary astrophysical models of Extragalactic Magnetic Field (EGMF). For IHCM, EGMF largely determines the deflection of primary cosmic rays and electrons of intergalactic cascades and, thus, is of vital importance. Contemporary Hackstein models are considered in this paper and compared to the model of Dolag. The models assumed are based on simulations of the local part of large-scale structure of the Universe and differ in the assumptions for the seed field. This work provides spectral energy distributions (SEDs) and angular extensions of two extreme TeV blazars, 1ES 0229+200 and 1ES 0414+009. It is demonstrated that observable SEDs inside a typical point spread function of imaging atmospheric Cherenkov telescopes (IACTs) for IHCM would exhibit a characteristic high-energy attenuation compared to the ones obtained in hadronic models that do not consider EGMF, which makes it possible to distinguish among these models. At the same time, the spectra for IHCM models would have longer high energy tails than some available spectra for the ALP models and the universal spectra for the Electromagnetic Cascade Model (ECM). The analysis of the IHCM observable angular extensions shows that the sources would likely be identified by most IACTs not as point sources but rather as extended ones. These spectra could later be compared with future observation data of such instruments as Cherenkov Telescope Array (CTA) and LHAASO.

Transient Gamma Ray Spectrometer Observations of Gamma‐Ray Lines from Novae. I. Limits on the Positron Annihilation Line in Five Individual Novae

1999 ◽  
Vol 522 (1) ◽  
pp. 424-432 ◽  
Author(s):  
M. J. Harris ◽  
J. E. Naya ◽  
B. J. Teegarden ◽  
T. L. Cline ◽  
N. Gehrels ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Gamma Ray ◽  
Annihilation Line ◽  
Gamma Ray Spectrometer

scholarly journals The H.E.S.S. Galactic plane survey

2018 ◽  
Vol 612 ◽  
pp. A1 ◽  
Author(s):  
◽  
H. Abdalla ◽  
A. Abramowski ◽  
F. Aharonian ◽  
F. Ait Benkhali ◽  
...  
Keyword(s):  
Supernova Remnants ◽  
Large Scale ◽  
Gamma Ray ◽  
Galactic Center ◽  
Galactic Plane ◽  
High Energy ◽  
High Angular Resolution ◽  
Data Set ◽  
Cherenkov Telescopes ◽  
Spatial Coverage

We present the results of the most comprehensive survey of the Galactic plane in very high-energy (VHE) γ-rays, including a public release of Galactic sky maps, a catalog of VHE sources, and the discovery of 16 new sources of VHE γ-rays. The High Energy Spectroscopic System (H.E.S.S.) Galactic plane survey (HGPS) was a decade-long observation program carried out by the H.E.S.S. I array of Cherenkov telescopes in Namibia from 2004 to 2013. The observations amount to nearly 2700 h of quality-selected data, covering the Galactic plane at longitudes from ℓ = 250° to 65° and latitudes |b|≤ 3°. In addition to the unprecedented spatial coverage, the HGPS also features a relatively high angular resolution (0.08° ≈ 5 arcmin mean point spread function 68% containment radius), sensitivity (≲1.5% Crab flux for point-like sources), and energy range (0.2–100 TeV). We constructed a catalog of VHE γ-ray sources from the HGPS data set with a systematic procedure for both source detection and characterization of morphology and spectrum. We present this likelihood-based method in detail, including the introduction of a model component to account for unresolved, large-scale emission along the Galactic plane. In total, the resulting HGPS catalog contains 78 VHE sources, of which 14 are not reanalyzed here, for example, due to their complex morphology, namely shell-like sources and the Galactic center region. Where possible, we provide a firm identification of the VHE source or plausible associations with sources in other astronomical catalogs. We also studied the characteristics of the VHE sources with source parameter distributions. 16 new sources were previously unknown or unpublished, and we individually discuss their identifications or possible associations. We firmly identified 31 sources as pulsar wind nebulae (PWNe), supernova remnants (SNRs), composite SNRs, or gamma-ray binaries. Among the 47 sources not yet identified, most of them (36) have possible associations with cataloged objects, notably PWNe and energetic pulsars that could power VHE PWNe.

scholarly journals The signature of large scale structures on the very high energy gamma ray sky

2007 ◽  
Vol 2007 (04) ◽  
pp. 013-013 ◽  
Author(s):  
A Cuoco ◽  
S Hannestad ◽  
T Haugbølle ◽  
G Miele ◽  
P D Serpico ◽  
...  
Keyword(s):  
Large Scale ◽  
Gamma Ray ◽  
High Energy ◽  
Large Scale Structures ◽  
High Energy Gamma ◽  
Very High Energy ◽  
Energy Gamma ◽  
Scale Structures ◽  
Very High

scholarly journals Studying stellar explosions with Athena

2015 ◽  
Vol 11 (A29B) ◽  
pp. 243-243
Author(s):  
P. O'Brien ◽  
P. Jonker
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Gamma Ray Bursts ◽  
Spectral Energy ◽  
Intermediate Mass ◽  
Tidal Disruption ◽  
X Ray ◽  
Cosmic Vision ◽  
Esa Cosmic Vision ◽  
Supernova Explosions

AbstractAthena is the second large mission selected in the ESA Cosmic Vision plan. With its large collecting area, high spectral-energy resolution (X-IFU instrument) and impressive grasp (WFI instrument), Athena will truly revolutionise X-ray astronomy. The most prodigious sources of high-energy photons are often transitory in nature. Athena will provide the sensitivity and spectral resolution coupled with rapid response to enable the study of the dynamic sky. Potential sources include: distant Gamma-Ray Bursts to probe the reionisation epoch and find missing baryons in the cosmic web; tidal disruption events to reveal dormant supermassive and intermediate-mass black holes; and supernova explosions to understand progenitors and their environments. We illustrate Athenas capabilities and show how it will be able to constrain the nature of explosive transients including gas metallicity and dynamics.

scholarly journals The supernova–gamma-ray burst–jet connection

2013 ◽  
Vol 371 (1992) ◽  
pp. 20120275 ◽  
Author(s):  
Jens Hjorth
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Theoretical Framework ◽  
Gamma Ray Bursts ◽  
Discussion Paper ◽  
Gamma Ray Burst ◽  
Supernova Explosions ◽  
Observational Status ◽  
Radioactive Heating

The observed association between supernovae and gamma-ray bursts represents a cornerstone in our understanding of the nature of gamma-ray bursts. The collapsar model provides a theoretical framework for this connection. A key element is the launch of a bipolar jet (seen as a gamma-ray burst). The resulting hot cocoon disrupts the star, whereas the 56 Ni produced gives rise to radioactive heating of the ejecta, seen as a supernova. In this discussion paper, I summarize the observational status of the supernova–gamma-ray burst connection in the context of the ‘engine’ picture of jet-driven supernovae and highlight SN 2012bz/GRB 120422A—with its luminous supernova but intermediate high-energy luminosity—as a possible transition object between low-luminosity and jet gamma-ray bursts. The jet channel for supernova explosions may provide new insights into supernova explosions in general.

scholarly journals Interpreting Crab Nebula’s synchrotron spectrum: two acceleration mechanisms

2019 ◽  
Vol 489 (2) ◽  
pp. 2403-2416 ◽  
Author(s):  
Maxim Lyutikov ◽  
Tea Temim ◽  
Sergey Komissarov ◽  
Patrick Slane ◽  
Lorenzo Sironi ◽  
...  
Keyword(s):  
Spectral Index ◽  
Large Scale ◽  
Gamma Ray ◽  
Lorentz Factor ◽  
Peak Frequency ◽  
High Energy ◽  
X Rays ◽  
High Energy Electrons ◽  
Astrophysical Objects ◽  
Different Populations

ABSTRACT We outline a model of the Crab pulsar wind nebula with two different populations of synchrotron emitting particles, arising from two different acceleration mechanisms: (i) Component-I due to Fermi-I acceleration at the equatorial portion of the termination shock, with particle spectral index pI ≈ 2.2 above the injection break corresponding to γwindσwind ∼ 105, peaking in the ultraviolet (UV, γwind ∼ 102 is the bulk Lorentz factor of the wind, σwind ∼ 103 is wind magnetization); and (ii) Component-II due to acceleration at reconnection layers in the bulk of the turbulent Nebula, with particle index pII ≈ 1.6. The model requires relatively slow but highly magnetized wind. For both components, the overall cooling break is in the infrared at ∼0.01 eV, so that the Component-I is in the fast cooling regime (cooling frequency below the peak frequency). In the optical band, Component-I produces emission with the cooling spectral index of αo ≈ 0.5, softening towards the edges due to radiative losses. Above the cooling break, in the optical, UV, and X-rays, Component-I mostly overwhelms Component-II. We hypothesize that acceleration at large-scale current sheets in the turbulent nebula (Component-II) extends to the synchrotron burn-off limit of ϵs ∼ 100 MeV. Thus in our model acceleration in turbulent reconnection (Component-II) can produce both hard radio spectra and occasional gamma-ray flares. This model may be applicable to a broader class of high-energy astrophysical objects, like active galactic nuclei and gamma-ray burst jets, where often radio electrons form a different population from the high-energy electrons.

scholarly journals PROBING THE CENTRAL BLACK HOLE IN M87 WITH GAMMA-RAYS

2012 ◽  
Vol 27 (28) ◽  
pp. 1230030 ◽  
Author(s):  
FRANK M. RIEGER ◽  
FELIX AHARONIAN
Keyword(s):  
Black Hole ◽  
Large Scale ◽  
Gamma Ray ◽  
High Sensitivity ◽  
High Energy ◽  
X Rays ◽  
Central Black Hole ◽  
Central Engine ◽  
Very High Energy ◽  
Observational Status

Recent high-sensitivity observation of the nearby radio galaxy M87 has provided important insights into the central engine that drives the large-scale outflows seen in radio, optical and X-rays. This review summarizes the observational status achieved in the high energy (HE < 100 GeV) and very high energy (VHE > 100 GeV) gamma-ray domains, and discusses the theoretical progress in understanding the physical origin of this emission and its relation to the activity of the central black hole.

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