Origin Of Galactic Cosmic Rays Research Articles

The Cryogenic AntiCoincidence Detector for ATHENA X-IFU: The Project Status

The ATHENA observatory is the second large class ESA mission to be launched on 2031 at L2 orbit. One of the two onboard instruments is X-IFU, a TES-based kilo-pixel array able to perform simultaneous high-grade energy spectroscopy (FWHM 2.5 eV@7 keV) and imaging over the 5′ field of view. The X-IFU sensitivity is degraded by primary particle background of both solar and galactic cosmic ray (GCR) origins, and by secondary electrons produced by primaries, interacting with the materials surrounding the detector: These particles cannot be distinguished by the scientific photons, thus degrading the instrument performance. Results from studies regarding the GCR component performed by Geant4 simulations address the necessity to use background reduction techniques to enable the study of several key science topics. This is feasible by combining an active Cryogenic AntiCoincidence detector (CryoAC) and a passive electron shielding to reach the required residual particle background of 0.005 cts/cm2/s/keV inside the 2–10 keV scientific energy band. The CryoAC is a four-pixel detector made of Si-suspended absorbers sensed by a network of IrAu TESes and placed at a distance < 1 mm below the TES array. Here we will provide an overview of the CryoAC program, starting with some details on the background assessment having impacts on the CryoAC design; then, we continue with its design concept including electronics and the Demonstration Model results, to conclude with programmatic aspects.

Measurement of the knees of proton and H&He spectra below 1 PeV

Galactic Cosmic ray (CR) origin is still a mystery. Measuring the knees of the CR spectra for individual species is a very important approach to solve the problem. ARGO-YBJ and LHAASO-WFCTA[1] combined experiment made the first step by measuring the spectrum of hydrogen plus helium nuclei and finding the knee around 0.7 PeV[2]. A significant boost is expected by using LHAASO experiment[3] to measure the spectra and their knees for pure proton and other species in few years. The key is to separate the specific species from all CR samples. In this paper, a multi variate analysis (MVA) approach for the CR composition analysis in LHAASO experiment is discussed. Preliminary results of the analysis and expectations are presented.

Observation of Very-High-Energy Cosmic Rays with the Tibet Air Shower Experiment—Quest for the Galactic Cosmic Ray Origin—

Observation of Very-High-Energy Cosmic Rays with the Tibet Air Shower Experiment—Quest for the Galactic Cosmic Ray Origin—

Anisotropies of different mass compositions of cosmic rays

The spectral hardenings of cosmic ray nuclei above ∼ 200 GV followed by softenings around 10 TV, the knee of the all-particle spectrum around PeV energies, as well as the pattern change of the amplitude and phase of the large-scale anisotropies around 100 TeV indicate the complexities of the origin and transportation of Galactic cosmic rays. It has been shown that nearby source(s) are most likely to be the cause of such spectral features of both the spectra and the anisotropies. In this work, we study the anisotropy features of different mass composition (or mass groups) of cosmic rays in this nearby source model. We show that even if the spectral features from the nearby source component is less distinctive compared with the background component from e.g., the population of distant sources, the anisotropy features are more remarkable to be identified. Measurements of the anisotropies of each mass composition (group) of cosmic rays by the space experiments such as DAMPE and HERD and the ground-based experiments such as LHAASO in the near future are expected to be able to critically test this scenario.

The origin of Galactic cosmic rays: Challenges to the standard paradigm

A critical review of the standard paradigm for the origin of Galactic cosmic rays (CRs) is presented. Recent measurements of local and far-away CRs reveal unexpected behaviors, which challenge the commonly accepted scenario. These recent findings are discussed, together with long-standing open issues. Despite the progress made thanks to ever-improving observational techniques and theoretical investigations, at present our understanding of the origin and of the behavior of CRs remains incomplete. We believe it is still unclear whether a modification of the standard paradigm, or rather a radical change of the paradigm itself is needed in order to interpret all the available data on CRs within a self-consistent scenario.

Indication of nearby source signatures of cosmic rays from energy spectra and anisotropies

The origin of Galactic cosmic rays (GCRs) remains a mystery after more than one century of their discovery. The diffusive propagation of charged particles in the turbulent Galactic magnetic field makes us unable to trace back to their acceleration sites. Nevertheless, nearby GCR source(s) may leave imprints on the locally measured energy spectra and the anisotropies of the arrival direction. In this work we propose a simple but natural description of the GCR production and propagation, within a two-zone disk-halo diffusion scenario together with a nearby source, to understand the up-to-date precise measurements of the energy spectra and anisotropies of GCRs. We find that a common energy scale of ∼100 TeV appears in both energy spectra of protons and helium nuclei measured recently by CREAM and large-scale anisotropies detected by various experiments. These results indicate that one or more local sources are very likely important contributors to GCRs below 100 TeV . This study provides a probe to identify source(s) of GCRs by means of joint efforts of spectral and anisotropy measurements.

Gamma-ray astronomy as a milestone in the cosmic ray origin issue

During the last years, high-energy astrophysics has not been considered at the same level as other scientific disciplines. In doing so, there is a very high risk neglecting the $$\gamma $$-ray energy band that has a strong importance to solve some still open issues. This paper is focused, in particular, on the galactic cosmic ray origin issue, and it shows how only a coexistence of low-energy (MeV–GeV) and high-energy (GeV–TeV) $$\gamma $$-ray instruments can allow us to solve this century-old issue.

The Origin of the Most Energetic Galactic Cosmic Rays: Supernova Explosions into Massive Star Plasma Winds

We propose that the high energy Cosmic Ray particles up to the upturn commonly called the ankle, from around the spectral turn-down commonly called the knee, mostly come from Blue Supergiant star explosions. At the upturn, i.e., the ankle, Cosmic Rays probably switch to another source class, most likely extragalactic sources. To show this we recently compiled a set of Radio Supernova data where we compute the magnetic field, shock speed and shock radius. This list included both Blue and Red Supergiant star explosions; both data show the same magnetic field strength for these two classes of stars despite very different wind densities and velocities. Using particle acceleration theory at shocks, those numbers can be transformed into characteristic ankle and knee energies. Without adjusting any free parameters both of these observed energies are directly indicated by the supernova data. In the next step in the argument, we use the Supernova Remnant data of the starburst galaxy M82. We apply this analysis to Blue Supergiant star explosions: The shock will race to their outer edge with a magnetic field that is observed to follow over several orders of magnitude B ( r ) × r ∼ c o n s t . , with in fact the same magnetic field strength for such stellar explosions in our Galaxy, and other galaxies including M82. The speed is observed to be ∼0.1 c out to about 10 16 cm radius in the plasma wind. The Supernova shock can run through the entire magnetic plasma wind region at full speed all the way out to the wind-shell, which is of order parsec scale in M82. We compare and identify the Cosmic Ray spectrum in other galaxies, in the starburst galaxy M82 and in our Galaxy with each other; we suggest how Blue Supergiant star explosions can provide the Cosmic Ray particles across the knee and up to the ankle energy range. The data from the ISS-CREAM (Cosmic Ray Energetics and Mass Experiment at the International Space Station) mission will test this cosmic ray concept which is reasonably well grounded in two independent radio supernova data sets. The next step in developing our understanding will be to obtain future more accurate Cosmic Ray data near to the knee, and to use unstable isotopes of Cosmic Ray nuclei at high energy to probe the “piston” driving the explosion. We plan to incorporate these data with the physics of the budding black hole which is probably forming in each of these stars.

Evolution of High-energy Particle Distribution in Supernova Remnants

Abstract Supernova remnants (SNRs) have been considered to be the dominant contributors to Galactic cosmic rays. However, the relation between high-energy particles trapped in SNRs and cosmic rays observed at the Earth remains obscure. In this paper, we fit the spectral energy distributions of 35 SNRs with a simple one-zone emission model and analyze correlations of model parameters to uncover the evolution of high-energy particle distribution in SNRs. We find that (1) the particle distribution in general can be described by a broken power-law function with a high-energy cutoff for all SNRs; (2) the low-energy spectrum becomes harder and the break energy decreases with aging of SNRs, (3) for most middle-age SNRs, the energy loss timescale of electrons at the high-energy cutoff is approximately equal to the age of the corresponding remnant implying quenching of very-high-energy electron acceleration; for young SNRs, this energy loss timescale is shorter than the age of SNRs implying continuous electron acceleration at the cutoff energy; and for a few old age SNRs, the energy loss timescale is longer than the corresponding age, which may suggest escaping of higher energy particles from SNRs. Finally, we comment on the implications of these results on the SNR origin of Galactic cosmic rays.

Measurement of Low-Energy Cosmic Rays via the Neutral Iron Line

There has been little information of Galactic low-energy cosmic rays (LECRs) so far because observations of LECRs in the solar system are affected by solar modulation and there is no effective way of indirect measurement. When LECRs in the MeV energy band collide with neutral iron atoms in the interstellar medium, uorescent X-rays at 6.4 keV are produced via inner-shell ionization of neutral iron atoms. We investigate the 6.4 keV line in supernova remnants (SNRs) as a prime candidate for the Galactic cosmic-ray origin. The line emission is discovered from 11 SNRs. The spectra and morphologies suggest that the 6.4 keV line is produced by LECRs interacting with cold gas. The proton energy density is estimated to be 10–100 eV cm−3. Furthermore, we measure the distribution of the 6.4 keV line emission near the Galactic center. The intensity profile is very similar to that of molecular clouds. The most plausible origin of the enhancement is the LECR proton bombardment. The energy density of MeV protons is estimated to be ∼ 80 eV cm−3. Since the diffusion length of MeV protons is short, they should be produced in situ. Surprisingly, there is no SNR in the vicinity, and thus another mechanism such as the stochastic acceleration would possibly work.

Gamma-Ray Production in the Extended Halo of the Galaxy and Possible Implications for the Origin of Galactic Cosmic Rays

Various studies have implied the existence of a gaseous halo around the Galaxy extending out to 100 kpc. Galactic cosmic rays (CRs) that propagate to the halo, either by diffusion or by convection with the possibly existing large-scale Galactic wind, can interact with the gas therein and produce gamma-rays via proton-proton collision. We calculate the cosmic ray distribution in the halo and the gamma-ray flux, and explore the dependence of the result on model parameters such as diffusion coefficient, CR luminosity, CR spectral index. We find that the current measurement of isotropic gamma-ray background at $\lesssim$TeV with Fermi Large Area Telescope already approaches a level that can provide interesting constraints on the properties of Galactic cosmic ray (e.g., with CR luminosity $L_{CR}\leq 10^{41}$erg/s). We also discuss the possibilities of the Fermi bubble and IceCube neutrinos originating from the proton-proton collision between cosmic rays and gas in the halo, as well as the implication of our results for the baryon budget of the hot circumgalactic medium of our Galaxy. Given that the isotropic gamma-ray background is likely to be dominated by unresolved extragalactic sources, future telescopes may extract more individual sources from the IGRB, and hence put even more stringent restriction on the relevant quantities (such as Galactic cosmic ray luminosity and baryon budget in the halo) in the presence of a turbulent halo that we consider.

The GRAND project and GRANDProto300 experiment

The Giant Array for Neutrino Detection (GRAND) is a proposal for a giant observatory of ultra-high energy cosmic particles (neutrinos, cosmic rays and gamma rays). It will be composed of twenty subarrays of 10 000 antennas each, totaling a detection area of 200 000 km2. GRAND will reach unprecedented sensitivity to neutrinos allowing to detect cosmogenic neutrinos while its sub-degree angular resolution will also make it possible to hunt for point sources and possibly start neutrino astronomy. Combined with its gigantic exposure to ultra-high energy cosmic rays and gamma rays, GRAND will be a powerful tool to solve the century-long mistery of the nature and origin of the particles with highest energy in the Universe. On the path to GRAND, the GRANDProto300 experiment will be deployed in 2020 over a total area of 200 km2. It primarly aims at validating the detection concept of GRAND, but also proposes a rich science program centered on a precise and complete measurement of the air showers initiated by cosmic rays with energies between 1016.5and 1018eV, a range where we expect to observe the transition between the Galactic and extra-galactic origin of cosmic rays.

Measurement of knees of the spectra of heavy nuclei above 10 PeV with LHAASO

Measuring the knees of the cosmic ray spectra for individual species is a very important approach to solve the problem of the origin of ultra high energy galactic cosmic rays. The knee of the iron spectrum is implied to be above 10 PeV from previous experiments, such as ARGO-YBJ and LHAASO-WFCTA. LHAASO is a suitable size for measurements with the required precision. The key is to separate iron nuclei from all cosmic ray samples. In this paper, we identify a couple of variables that are sensitive to the composition of showers recorded by the detector arrays in LHAASO. A multi variate analysis is proposed for the separation. The efficiency and purity of the selection for demanded species are optimized by well configuring the LHAASO array using the LHAASO simulation tools.

Particle Acceleration by Supernova Shocks and Spallogenic Nucleosynthesis of Light Elements

In this review, we first reassess the supernova remnant paradigm for the origin of Galactic cosmic rays in the light of recent cosmic-ray data acquired by the Voyager 1 spacecraft. We then describe the theory of light-element nucleosynthesis by nuclear interaction of cosmic rays with the interstellar medium and outline the problem of explaining the measured beryllium abundances in old halo stars of low metallicity with the standard model of the Galactic cosmic-ray origin. We then discuss the various cosmic-ray models proposed in the literature to account for the measured evolution of the light elements in the Milky Way, and point out the difficulties that they all encounter. It seems to us that, among all possibilities, the superbubble model provides the most satisfactory explanation for these observations.

The Cosmic Ray Energy Spectrum between 2 PeV and 2 EeV Observed with the TALE Detector in Monocular Mode

Abstract We report on a measurement of the cosmic ray energy spectrum by the Telescope Array Low-Energy Extension (TALE) air fluorescence detector (FD). The TALE air FD is also sensitive to the Cherenkov light produced by shower particles. Low-energy cosmic rays, in the PeV energy range, are detectable by TALE as Cherenkov events. Using these events, we measure the energy spectrum from a low energy of ∼2 PeV to an energy greater than 100 PeV. Above 100 PeV, TALE can detect cosmic rays using air fluorescence. This allows for the extension of the measurement to energies greater than a few EeV. In this paper, we describe the detector, explain the technique, and present results from a measurement of the spectrum using ∼1000 hr of observation. The observed spectrum shows a clear steepening near 1017.1 eV, along with an ankle-like structure at 1016.2 eV. These features present important constraints on the origin of galactic cosmic rays and on propagation models. The feature at 1017.1 eV may also mark the end of the galactic cosmic ray flux and the start of the transition to extragalactic sources.

Elemental Composition at the Cosmic-Ray Source Derived from the ACE-CRIS Instrument. I. 6C to 28Ni

Abstract We report new elemental source abundances from 6C to 28Ni for galactic cosmic rays, using observations from the Cosmic Ray Isotope Spectrometer (CRIS) on board the NASA Advanced Composition Explorer spacecraft. Abundances were calculated using CRIS energy spectra at energies below 550 MeV/nucleon from the 1997–98 and 2009–10 solar-minimum periods, as well as from the 2001–03 solar-maximum period. These new results, when combined with results for heavier elements reported in a forthcoming paper, are consistent with a model of galactic cosmic-ray origin where nuclei found in interstellar grains are accelerated preferentially over those found in interstellar gas, with this acceleration happening in OB associations.

Where do the ultra-high energy cosmic rays come from?

Cosmic rays are the only sample of matter coming from outer space. They carry rich information about particle physics, high-energy astrophysics, composition and evolution of the Universe. The highest energy of cosmic rays detected so far is about 3×10 20 eV. How are the cosmic rays accelerated?What kind of astronomic sources do the cosmic rays originate from?Are the fundamental physics laws still valid in such high-energy scales? are all important scientific problems waiting to be addressed. To answer these questions, various space and ground experiments have been carried out to explore the nature of cosmic rays in a multi-messenger approach. The past few decades have witnessed great achievements in high-energy cosmic ray, gamma ray, neutrino observations, and detection of gravitational wave. (1) The cosmic ray spectra, composition, and anisotropy have been measured with unprecedented precision leading to better understanding of cosmic ray acceleration and transport and stricter constraints on properties of potential candidates of dark matter particles, and the dipole anisotropy of ultrahigh energy cosmic rays indicates that they have an extragalactic origin. (2) Space borne experiments have discovered more than 3000 sources in the GeV range, and the ground based experiments have uncovered more than 200 sources at TeV energies. Most of these sources are high-energy electron accelerators, and a few of them are identified as the accelerators of cosmic ray nuclei. Diffuse gamma-ray emission associated with galactic disks and jets and/or outbursts of Active Galactic Nuclei is also measured with better spatial and energy resolutions, which can be used to study cosmic ray transport in the interstellar/galactic/cluster medium. (3) With the IceCube experiment, about 100 high-energy neutrino events have been recorded and their isotropic distribution suggests an extragalactic origin. (4) The first gravitational wave event with simultaneous multi-wavelength observations has been detected opening the epoch of gravitational wave astronomy. Strong gravitational wave events represent the most catastrophic energy release in the Universe and can be important cosmic ray sources. These new results established the foundation to address the origin of cosmic rays and to develop theories of particle acceleration and transport. The study of cosmic ray transport has gone beyond the diffusion approximation to study the effect of magnetic field fluctuations on small scale anisotropy of cosmic rays and comprehensive numerical modelings of cosmic ray transport in the Galaxy are advanced with multi-wavelength observations. Diffusive particle acceleration by strong shocks of supernova remnants (SNRs) is also advanced based on multi-wavelength observations and cosmic ray measurements. The scenario of SNR origin of Galactic cosmic rays is being quantified with testable predictions. Although there are still uncertainties in amplification of magnetic field by cosmic rays and cosmic ray scattering by turbulent plasmas, sophisticated numerical codes are being developed to address these issues. Successful construction and operation of new generation cosmic ray and gamma-ray experiments will open a new chapter of the astro-particle physics study.

Spatially resolved spectroscopy of non-thermal X-rays in RX J1713.7−3946 with Chandra

Abstract The young shell-type supernova remnant (SNR) RX J1713.7−3946 has been studied as a suitable target to test the SNR paradigm for the origin of Galactic cosmic rays. We present a spatially resolved spectroscopy of the non-thermal X-ray emission in RX J1713.7−3946 with Chandra. In order to obtain X-ray properties of the filamentary structures and their surrounding regions, we divide the southeastern (SE), southwestern (SW), and northwestern (NW) parts of the SNR into subregions on the typical order of several 10" and extract spectra from each subregion. Their photon indices are significantly different among the subregions, with a range of 1.8 &amp;lt; Γ &amp;lt; 3. In the SE part, the clear filaments are harder (Γ ∼ 2.0) than the surrounding regions. This is a common feature often observed in young SNRs and naturally interpreted as a consequence of synchrotron cooling. On the other hand, the bright filamentary regions do not necessarily coincide with the hardest regions in the SW and NW parts. We also find the SW filamentary region is relatively rather soft (Γ ∼ 2.7). In addition, we find that hard regions with photon indices of 2.0–2.2 exist around the bright emission although the hard regions lie in the downstream region and the bright emission does not appear to be the blast wave shock front. Both the aforementioned characteristic regions in SW are located close to peaks of the interstellar gas. We discuss possible origins of the spatial variation of the photon indices, paying particular attention to the shock–cloud interactions.

On the search for Galactic supernova remnant PeVatrons with current TeV instruments

The supernova remnant hypothesis for the origin of Galactic cosmic rays has passed several tests, but the firm identification of a supernova remnant pevatron, considered to be a decisive step to prove the hypothesis, is still missing. While a lot of hope has been placed in next-generation instruments operating in the multi-TeV range, it is possible that current gamma-ray instruments, operating in the TeV range, could pinpoint these objects or, most likely, identify a number of promising targets for instruments of next generation. Starting from the assumption that supernova remnants are indeed the sources of Galactic cosmic rays, and therefore must be pevatrons for some fraction of their lifetime, we investigate the ability of current instruments to detect such objects, or to identify the most promising candidates.

The supernova remnant W49B as seen with H.E.S.S. and Fermi-LAT

The supernova remnant (SNR) W49B originated from a core-collapse supernova that occurred between one and four thousand years ago, and subsequently evolved into a mixed-morphology remnant, which is interacting with molecular clouds (MC). Gamma-ray observations of SNR-MC associations are a powerful tool to constrain the origin of Galactic cosmic rays, as they can probe the acceleration of hadrons through their interaction with the surrounding medium and subsequent emission of non-thermal photons. We report the detection of a γ-ray source coincident with W49B at very high energies (VHE; E &gt; 100 GeV) with the H.E.S.S. Cherenkov telescopes together with a study of the source with five years of Fermi-LAT high-energy γ-ray (0.06–300 GeV) data. The smoothly connected, combined source spectrum, measured from 60 MeV to multi-TeV energies, shows two significant spectral breaks at 304 ± 20 MeV and 8.4−2.5+2.2 GeV; the latter is constrained by the joint fit from the two instruments. The detected spectral features are similar to those observed in several other SNR-MC associations and are found to be indicative of γ-ray emission produced through neutral-pion decay.