Cosmic Ray Signatures Research Articles

Cosmic-ray electron transport in the galaxy M 51

Context. Indirect observations of the cosmic-ray electron (CRE) distribution via synchrotron emission is crucial for deepening the understanding of the CRE transport in the interstellar medium, and in investigating the role of galactic outflows. Aims. In this paper, we quantify the contribution of diffusion- and advection-dominated transport of CREs in the galaxy M51 considering relevant energy loss processes. Methods. We used recent measurement from M 51 that allow for the derivation of the diffusion coefficient, the star formation rate, and the magnetic field strength. With this input, we solved the 3D transport equation numerically including the spatial dependence as provided by the measurements, using the open-source transport framework CRPropa (v3.1). We included 3D transport (diffusion and advection), and the relevant loss processes. Results. We find that the data can be described well with the parameters from recent measurements. For the best fit, it is required that the wind velocity, following from the observed star formation rate, must be decreased by a factor of 5. We find a model in which the inner galaxy is dominated by advective escape and the outer galaxy is composed by both diffusion and advection. Conclusions. Three-dimensional modelling of cosmic-ray transport in the face-on galaxy M51 allows for conclusions about the strength of the outflow of such galaxies by quantifying the need for a wind in the description of the cosmic-ray signatures. This opens up the possibility of investigating galactic winds in face-on galaxies in general.

Unveiling the nature of the unidentified gamma-ray sources 4FGL J1908.6+0915e, HESS J1907+089/HOTS J1907+091, and 3HWC J1907+085 in the sky region of the magnetar SGR 1900+14

ABSTRACT Supernova remnants (SNRs), star formation regions (SFRs), and pulsar wind nebulae (PWNe) are prime candidates for Galactic PeVatrons. The non-thermal high-energy (HE, ε > 100 MeV) and very high-energy (VHE, ε > 100 GeV) γ-ray emission from these sources should be a promising manifestation of acceleration processes. We investigate the possibility to explain the HE and VHE γ-ray emission from the sky region of the magnetar SGR 1900+14 as a signature of cosmic rays accelerated in above-mentioned sources. To this end, we simulate the γ-ray emission from the extended Fermi-LAT HE source 4FGL J1908.6+0915e, the extended VHE H.E.S.S. source candidate HOTS J1907+091, and the point-like HAWC TeV source 3HWC J1907+085, which are spatially coincident with the SNR G42.8+0.6, the magnetar SGR 1900+14, and the star-forming region W49A. The simulations are performed within the hadronic and leptonic models. We show that the observed γ-ray emission from the region of the magnetar SGR 1900+14 can, in principle, include contributions of different intensities from all three types of (potentially confused) sources. The considered in detail cases of a magnetar-connected but still undetected SNR and a PWN are the most promising ones, but with a serious requirement on the energy reserve of radiated CR particles – of the order of $10^{51}d_{\textrm {10kpc}}^{2}$ erg for sources at a distance of d ∼ 10 kpc. Such energy reserve can be provided by the magnetar-related hypernova and/or magnetar wind nebula remnant created by the newborn millisecond magnetar with the large supply of rotational energy Erot ∼ 1052 erg.

Regimes of cosmic-ray diffusion in Galactic turbulence

Cosmic-ray transport in astrophysical environments is often dominated by the diffusion of particles in a magnetic field composed of both a turbulent and a mean component. This process, which is two-fold turbulent mixing in that the particle motion is stochastic with respect to the field lines, needs to be understood in order to properly model cosmic-ray signatures. One of the most important aspects in the modeling of cosmic-ray diffusion is that fully resonant scattering, the most effective such process, is only possible if the wave spectrum covers the entire range of propagation angles. By taking the wave spectrum boundaries into account, we quantify cosmic-ray diffusion parallel and perpendicular to the guide field direction at turbulence levels above 5% of the total magnetic field. We apply our results of the parallel and perpendicular diffusion coefficient to the Milky Way. We show that simple purely diffusive transport is in conflict with observations of the inner Galaxy, but that just by taking a Galactic wind into account, data can be matched in the central 5 kpc zone. Further comparison shows that the outer Galaxy at >5 kpc, on the other hand, should be dominated by perpendicular diffusion, likely changing to parallel diffusion at the outermost radii of the Milky Way.

Monte Carlo simulations for the ANTARES underwater neutrino telescope

Monte Carlo simulations are a unique tool to check the response of a detector and to monitor its performance. For a deep-sea neutrino telescope, the variability of the environmental conditions that can affect the behaviour of the data acquisition system must be considered, in addition to a reliable description of the active parts of the detector and of the features of physics events, in order to produce a realistic set of simulated events. In this paper, the software tools used to produce neutrino and cosmic ray signatures in the telescope and the strategy developed to represent the time evolution of the natural environment and of the detector efficiency are described.

New Physics of Strong Interaction and Dark Universe

The history of dark universe physics can be traced from processes in the very early universe to the modern dominance of dark matter and energy. Here, we review the possible nontrivial role of strong interactions in cosmological effects of new physics. In the case of ordinary QCD interaction, the existence of new stable colored particles such as new stable quarks leads to new exotic forms of matter, some of which can be candidates for dark matter. New QCD-like strong interactions lead to new stable composite candidates bound by QCD-like confinement. We put special emphasis on the effects of interaction between new stable hadrons and ordinary matter, formation of anomalous forms of cosmic rays and exotic forms of matter, like stable fractionally charged particles. The possible correlation of these effects with high energy neutrino and cosmic ray signatures opens the way to study new physics of strong interactions by its indirect multi-messenger astrophysical probes.

Cosmic-ray signatures of dark matter from a flavor dependent gauge symmetry model with neutrino mass mechanism

We propose an extension to the Standard Model accommodating two families of Dirac neutral fermions and Majorana fermions under additional ${U(1)_{e-\mu} \times Z_3\times Z_2}$ symmetries where ${U(1)_{e-\mu}}$ is a flavor dependent gauge symmetry related to the first and second family of the lepton sector, which features a two-loop induced neutrino mass model. The two families are favored by minimally reproducing the current neutrino oscillation data and two mass difference squares and canceling the gauge anomalies at the same time. As a result, we have a prediction for neutrino masses. The lightest Dirac neutral fermion is a dark matter candidate with tree-level interaction restricted to electron, muon and neutrinos, which makes it difficult to detect in direct dark matter search as well as indirect search focusing on the ${\tau}$-channel, such as through ${\gamma}$-rays. It may however be probed by search for dark matter signatures in electron and positron cosmic rays, and allows interpretation of a structure appearing in the CALET electron+positron spectrum around 350-400 GeV as its signature, with a boost factor $\approx$40 Breit-Wigner enhancement of the annihilation cross section.

Ultra-high-energy cosmic rays and neutrinos from tidal disruptions by massive black holes

Tidal disruptions are extremely powerful phenomena that have been designated as candidate sources of ultra-high-energy cosmic rays. The disruption of a star by a black hole can naturally provide protons and heavier nuclei, which can be injected and accelerated to ultra-high energies within a jet. Inside the jet, accelerated nuclei are likely to interact with a dense photon field, leading to a significant production of neutrinos and secondary particles. We model numerically the propagation and interactions of high-energy nuclei in jetted tidal disruption events in order to evaluate consistently their signatures in cosmic rays and neutrinos. We propose a simple model of the light curve of tidal disruption events, consisting of two stages: a high state with bright luminosity and short duration and a medium state, less bright and longer lasting. These two states have different impacts on the production of cosmic rays and neutrinos. In order to calculate the diffuse fluxes of cosmic rays and neutrinos, we model the luminosity function and redshift evolution of jetted tidal disruption events. We find that we can fit the latest ultra-high-energy cosmic-ray spectrum and composition results of the Auger experiment for a range of reasonable parameters. The diffuse neutrino flux associated with this scenario is found to be subdominant, but nearby events can be detected by IceCube or next-generation detectors such as IceCube-Gen2.

Constraints on Leptophilic Dark Matter from the AMS-02 Experiment

Abstract The annihilation of dark matter particles in the Galactic halo of the Milky Way may lead to cosmic ray signatures that can be probed by the AMS-02 experiment, which has measured the composition and fluxes of charged cosmic rays with unprecedented precision. Given the absence of characteristic spectral features in the electron and positron fluxes measured by AMS-02, we derive upper limits on the dark matter annihilation cross section for leptophilic dark matter models. Our limits are based on a new background model that describes all recent measurements of the energy spectra of cosmic-ray positrons and electrons. For thermal dark matter relics, we can exclude dark matter masses below about 100 GeV. We include the radiation of electroweak gauge bosons in the dark matter annihilation process and compute the antiproton signal that can be expected within leptophilic dark matter models.

The race for the pole

One of the very first facts you learn about electromagnetism-long before you walk into your first physics class-is that every magnet has two poles. Cut a bar magnet in half and you wind up with two magnets, each of which has its own north and south poles. And that's true for every single object in our experience that boasts a magnetic field-whether it's the entire Earth or an iron atom. There are no solitary poles. Strangely, though, there is no fundamental reason why that has to be the case. In fact, there are a few good reasons to suspect that there might be single-poled magnetic objects- magnetic monopoles-floating about in the universe. If these particles exist, they are probably quite rare, but that hasn't stopped physicists from looking for them. Here's why: If they exist, they could help answer longstanding questions about the nature of the universe, shedding light on the way fundamental forces of nature are tied together. So over the past few decades, physicists have scoured Antarctic ice and lunar dust and scrutinized rocks culled from ocean beds and polar volcanoes. They've tried to create monopoles in particle colliders and have searched for signatures in cosmic rays that collide with Earth.

New detection technologies for ultra-high energy cosmic rays and neutrinos

Even with an accumulated data set from an integrated six years of lifetime from the Auger experiment, no point sources of charged cosmic rays have be identified at the highest energies. Significantly increased apertures such as promised by the JEMEUSO mission will be required to identify these sources from the cosmic ray signatures themselves. However, in employing water-cherenkov surface detectors as well as fluorescence telescopes, Auger has demonstrated the power provided by the hybrid technology approach. New detection technologies thus provide a valuable tool, in particular for the study of systematic effects.

Cosmic rays and tests of fundamental principles

It is now widely acknowledged that cosmic rays experiments can test possible new physics directly generated at the Planck scale or at some other fundamental scale. By studying particle properties at energies far beyond the reach of any man-made accelerator, they can yield unique checks of basic principles. A well-known example is provided by possible tests of special relativity at the highest cosmic-ray energies. But other essential ingredients of standard theories can in principle be tested: quantum mechanics, uncertainty principle, energy and momentum conservation, effective space-time dimensions, hamiltonian and lagrangian formalisms, postulates of cosmology, vacuum dynamics and particle propagation, quark and gluon confinement, elementariness of particles... Standard particle physics or string-like patterns may have a composite origin able to manifest itself through specific cosmic-ray signatures. Ultra-high energy cosmic rays, but also cosmic rays at lower energies, are probes of both "conventional" and new Physics. Status, prospects, new ideas, and open questions in the field are discussed. The Post Scriptum shows that several basic features of modern cosmology naturally appear in a SU(2) spinorial description of space-time without any need for matter, relativity or standard gravitation. New possible effects related to the spinorial space-time structure can also be foreseen. Similarly, the existence of spin-1/2 particles can be naturally related to physics beyond Planck scale and to a possible pre-Big Bang era.

Detectability of ultrahigh energy cosmic-ray signatures in gamma-rays

The injection of ultra-high energy cosmic rays in the intergalactic medium leads to the production of a GeV-TeV gamma-ray halo centered on the source location, through the production of a high electromagnetic component in the interactions of the primary particles with the radiation backgrounds. This paper examines the prospects for the detectability of such gamma ray halos. We explore a broad range of astrophysical parameters, including the inhomogeneous distribution of magnetic fields in the large scale structure as well as various possible chemical compositions and injection spectra; and we consider the case of a source located outside clusters of galaxies. With respect to the gamma-ray flux associated to synchrotron radiation of ultra-high energy secondary pairs, we demonstrate that it does not depend strongly on these parameters and conclude that its magnitude ultimately depends on the energy injected in the primary cosmic rays. Bounding the cosmic ray luminosity with the contribution to the measured cosmic ray spectrum, we then find that the gamma-ray halo produced by equal luminosity sources is well below current or planned instrument sensitivities. Only rare and powerful steady sources, located at distances larger than several hundreds of Mpc and contributing to a fraction > 10% of the flux at 10^19 eV might be detectable. We also discuss the gamma-ray halos that are produced by inverse Compton/pair production cascades seeded by ultra-high energy cosmic rays. This latter signal strongly depends on the configuration of the extragalactic magnetic fields; it is dominated by the synchrotron signal on a degree scale if the filling factor of magnetic fields with B > 10^(-14) G is smaller than a few percents. Finally, we discuss briefly the case of nearby potential sources such as Centaurus A.

Intense gamma-ray lines from hidden vector dark matter decay

Scenarios with hidden, spontaneously broken, non-abelian gauge groups contain a natural dark matter candidate, the hidden vector, whose longevity is due to an accidental custodial symmetry in the renormalizableLagrangian. Nevertheless, non-renormalizable dimension six operatorsbreak the custodial symmetry and induce the decayof the dark matter particle at cosmological times. We discuss in this paper the cosmicray signatures of this scenario and we showthat the decay of hidden vector dark matter particles genericallyproduce an intense gamma ray line which could be observedby the Fermi-LAT experiment, if the scale of custodial symmetry breaking is closeto the Grand Unification scale. This gamma line proceeds directly from a tree leveldark matter 2-body decay in association with a Higgs boson.Within this model we also perform a determination of the relic densityconstraints taking into account the dark matterannihilation processes with one dark matter particle in the final state. The corresponding direct detection rates can be easily of order the current experimental sensitivities.

Possible cosmic ray signatures in clouds?

The role of cosmic rays in cloud formation, by cloud condensation nuclei, is still not fully understood. Although it has been claimed by a number of authors that cosmic ray effects should be small—or even non-existent—it is still argued by others that cosmic ray effects do occur. The present work draws attention to the fact that cosmic rays do not constitute a continuous stream of particles but are characterized by occasional near-simultaneous showers of particles. Under certain circumstances, such showers should leave a signature in clouds—near vertical ‘cigar-shaped clouds’—and this work describes their properties. Our own observations have revealed no such structure, but it would be valuable to have a more careful search made.

Probing gravitino dark matter with PAMELA and Fermi

We analyse the cosmic-ray signatures of decaying gravitino dark matter in a model-independent way based on an operator analysis. Thermal leptogenesis and universal boundary conditions at the GUT scale restrict the gravitino mass to be below 600 GeV. Electron and positron fluxes from gravitino decays, together with the standard GALPROP background, cannot explain both the PAMELA positron fraction and the electron + positron flux recently measured by Fermi LAT. For gravitino dark matter, the observed fluxes require astrophysical sources. The measured antiproton flux allows for a sizable contribution of decaying gravitinos to the gamma-ray spectrum, in particular a line at an energy below 300 GeV. Future measurements of the gamma-ray flux will provide important constraints on possible signatures of decaying gravitino dark matter at the LHC.

Superparticle mass window from leptogenesis and decaying gravitino dark matter

Gravitino dark matter, together with thermal leptogenesis, implies an upper bound on the masses of superparticles. In the case of broken R-parity the constraints from primordial nucleosynthesis are naturally satisfied and decaying gravitinos lead to characteristic signatures in high energy cosmic rays. We analyse the implications for supergravity models with universal boundary conditions at the grand unification scale. Together with low-energy observables one obtains a window of superparticle masses, which will soon be probed at the LHC, and a range of allowed reheating temperatures.

Feedback heating by cosmic rays in clusters of galaxies

Recent observations show that the cooling flows in the central regions of galaxy clusters are highly suppressed. Observed active galactic nuclei (AGN)-induced cavities/bubbles are a leading candidate for suppressing cooling, usually via some form of mechanical heating. At the same time, observed X-ray cavities and synchrotron emission point towards a significant nonthermal particle population. Previous studies have focused on the dynamical effects of cosmic ray pressure support, but none has built successful models in which cosmic ray heating is significant. Here, we investigate a new model of AGN heating, in which the intracluster medium is efficiently heated by cosmic rays, which are injected into the intra-cluster medium (ICM) through diffusion or the shredding of the bubbles by Rayleigh‐Taylor or Kelvin‐Helmholtz instabilities. We include thermal conduction as well. Using numerical simulations, we show that the cooling catastrophe is efficiently suppressed. The cluster quickly relaxes to a quasiequilibrium state with a highly reduced accretion rate and temperature and density profiles which match observations. Unlike the conduction-only case, no fine-tuning of the Spitzer conduction suppression factor f is needed. The cosmic ray pressure, Pc/Pg � 0.1 and ∇Pc � 0.1ρg, is well within observational bounds. Cosmic ray heating is a very attractive alternative to mechanical heating, and may become particularly compelling if Gamma-ray Large Array Space Telescope (GLAST) detects the γ -ray signature of cosmic rays in clusters.

Automatic removal of cosmic ray signatures in Deep Impact images

The results of recognition of cosmic ray (CR) signatures on single images made during the Deep Impact mission were analyzed for several codes written by several authors. For automatic removal of CR signatures on many images, we suggest using the code imgclean ( http://pdssbn.astro.umd.edu/volume/didoc_0001/document/calibration_software/dical_v5/) written by E. Deutsch as other codes considered do not work properly automatically with a large number of images and do not run to completion for some images; however, other codes can be better for analysis of certain specific images. Sometimes imgclean detects false CR signatures near the edge of a comet nucleus, and it often does not recognize all pixels of long CR signatures. Our code rmcr is the only code among those considered that allows one to work with raw images. For most visual images made during low solar activity at exposure time t > 4 s, the number of clusters of bright pixels on an image per second per sq. cm of CCD was about 2–4, both for dark and normal sky images. At high solar activity, it sometimes exceeded 10. The ratio of the number of CR signatures consisting of n pixels obtained at high solar activity to that at low solar activity was greater for greater n. The number of clusters detected as CR signatures on a single infrared image is by at least a factor of several greater than the actual number of CR signatures; the number of clusters based on analysis of two successive dark infrared frames is in agreement with an expected number of CR signatures. Some glitches of false CR signatures include bright pixels repeatedly present on different infrared images. Our interactive code imr allows a user to choose the regions on a considered image where glitches detected by imgclean as CR signatures are ignored. In other regions chosen by the user, the brightness of some pixels is replaced by the local median brightness if the brightness of these pixels is greater by some factor than the median brightness. The interactive code allows one to delete long CR signatures and prevents removal of false CR signatures near the edge of the nucleus of the comet. The interactive code can be applied to editing any digital images. Results obtained can be used for other missions to comets.

Diffuse gamma rays from the Galactic Plane: Probing the “GeV excess” and identifying the “TeV excess”

Pion decay gamma rays have long been recognized as a unique signature of hadronic cosmic rays and their interactions with the interstellar medium. We present a model-independent way of constraining this signal with observations of the Galactic Plane in diffuse gamma rays. We combine detections by the EGRET instrument at GeV energies and the Milagro Čerenkov detector at TeV energies with upper limits from KASCADE and CASA-MIA ground arrays at PeV energies. Such a long “lever arm”, spanning at least six orders of magnitude in energy, reveals a “TeV excess” in the diffuse Galactic Plane gamma-ray spectrum. While the origin of this excess is unknown, it likely implies also enhanced TeV neutrino fluxes, significantly improving the prospects for their detection. We show that unresolved point sources are a possible source of the TeV excess. In fact, the spectra of the unidentified EGRET sources in the Milagro region must break between ∼10 GeV and ∼1 TeV to avoid strongly overshooting the Milagro measurement; this may have important implications for cosmic-ray acceleration. Finally, we use our approach to examine the recent suggestion that dark-matter annihilation may account for the observed excess in diffuse Galactic gamma-rays detected by EGRET at energies above 1 GeV. Within our model-independent approach, current data cannot rule this possibility in or out; however we point out how a long “lever arm” can be used to constrain the pionic gamma-ray component and in turn limit the “GeV excess” and its possible sources. Experiments such as HESS and MAGIC, and the upcoming VERITAS and GLAST, should be able to finally disentangle the main sources of the Galactic gamma rays.

THE GIANT FLARE FROM SGR 1806–20 AND ITS RADIO AFTERGLOW

The multi-wavelength observations of the 2004 December 27 Giant Flare (GF) from SGR 1806–20 and its long-lived radio afterglow are briefly reviewed. The GF appears to have been produced by a dramatic reconfiguration of the magnetic field near the surface of the neutron star, possibly accompanied by fractures in the crust. The explosive release of over 1046 erg (isotropic equivalent) powered a one-sided mildly relativistic outflow. The outflow produced a new expanding radio nebula that is still visible over a year after the GF. Also considered are the constraints on the total energy in the GF, the energy and mass in the outflow, and on the external density, as well as possible implications for short γ-ray bursts and potential signatures in high energy neutrinos, photons, or cosmic rays. Some possible future observations of this and other GFs are briefly discussed.