Cosmic-ray Density Research Articles

Global Analysis of the Extended Decreases in Cosmic Rays Observed with Worldwide Networks of Neutron Monitors and Muon Detectors: Temporal Variation of the Rigidity Spectrum and Its Implication

This paper presents the global analysis of two extended decreases in the galactic cosmic-ray intensity observed by worldwide networks of ground-based detectors in 2012. This analysis is capable of separately deriving the cosmic-ray density (or omnidirectional intensity) and anisotropy, each as a function of time and rigidity. A simple diffusion model along the spiral field line between Earth and a cosmic-ray barrier indicates the long duration of these events, resulting from about 190° eastern extent of a barrier such as an interplanetary shock followed by the sheath region and/or the corotating interaction region (CIR). It is suggested that the coronal mass ejection merging with and compressing the preexisting CIR at its flank can produce such an extended barrier. The derived rigidity spectra of the density and anisotropy both vary in time during each event period. In particular we find that the temporal feature of the “phantom Forbush decrease (FD)” reported in an analyzed period is dependent on rigidity, and looks quite different at different rigidities. From these rigidity spectra of the density and anisotropy, we derive the rigidity spectrum of the average parallel mean free path of pitch angle scattering along the spiral field line and infer the power spectrum of the magnetic fluctuation and its temporal variation. The possible physical cause of the strong rigidity dependence of the phantom FD is also discussed. These results demonstrate the high-energy cosmic rays observed at Earth responding to remote space weather.

Revisit of GeV Gamma-Ray Emission from Orion B with the Fermi Large Area Telescope

We revisit the γ-ray emission above 300 MeV towards the massive star-forming region of Orion B by adopting 14 yr observations with the Fermi Large Area Telescope and utilizing the updated software tools. The extended γ-ray emission region around Orion B is resolved into two components (region I and region II). The γ-ray spectrum of region I agrees with the predicted γ-ray spectrum assuming the cosmic ray (CR) density is the same as that of Alpha Magnetic Spectrometer (AMS-02) measured locally. The γ-ray emissivity of region II appears to be deficit at low energy band (E < 3 GeV). Through modeling we find that CR densities exhibit a significant deficit below 20 GeV, which may be caused by a slow diffusion inside the dense region. This is probably caused by an increased magnetic field whose strength increases with the gas density.

Suppressed Cosmic-Ray Energy Densities in Molecular Clouds from Streaming Instability-regulated Transport

Cosmic rays (CRs) are the primary driver of ionization in star-forming molecular clouds (MCs). Despite their potential impacts on gas dynamics and chemistry, no simulations of star cluster formation following the creation of individual stars have included explicit cosmic-ray transport (CRT) to date. We conduct the first numerical simulations following the collapse of a 2000M ⊙ MC and the subsequent star formation including CRT using the STAR FORmation in Gaseous Environments framework implemented in the GIZMO code. We show that when CRT is streaming-dominated, the CR energy in the cloud is strongly attenuated due to energy losses from the streaming instability. Consequently, in a Milky Way–like environment the median CR ionization rate in the cloud is low (ζ ≲ 2 × 10−19 s−1) during the main star-forming epoch of the calculation and the impact of CRs on the star formation in the cloud is limited. However, in high-CR environments, the CR distribution in the cloud is elevated (ζ ≲ 6 × 10−18), and the relatively higher CR pressure outside the cloud causes slightly earlier cloud collapse and increases the star formation efficiency by 50% to ∼13%. The initial mass function is similar in all cases except with possible variations in a high-CR environment. Further studies are needed to explain the range of ionization rates observed in MCs and explore star formation in extreme CR environments.

Non-thermal emission from microquasar jets: The case of GRS 1915+105

Microquasars (μQs) represent a prominent population of Galactic sources, from which broadband non-thermal emission was detected. At present, the potential of μQs as sources of gamma-ray emission is poorly understood and constrained. In most cases, even the power of μQ jets remains largely uncertain, and this hinders the study of gamma-ray generation in these sources. Using observational data obtained in the radio band, we derive an estimate of the jet power in one of the most famous Galactic μQ, in GRS 1915+105. Compared to other studies of this subject, we additionally consider constraints related to the energy dissipated at internal shocks in the jet, the conditions at which are obtained using properties of the radio blobs detected in the jets. We show that even if one subtracts the rest-energy of matter in the jet, the jet power in this source should be very high, 1039ergs−1, or even higher. The properties of the detected radio emission favor jets with a Gauss-strength magnetic field at parsec distances from the black hole. Such a strong magnetic field should suppress inverse Compton (IC) emission from relativistic electrons, at least from parsec-scale jet. On the other hand, this strong magnetic field makes μQ jets perfect proton accelerators. If present, protons should easily be accelerated in the ultra-high-energy regime. However, due to a diluted target, protons should not lose a notable fraction of their energy in the jet, injected into the interstellar medium at the jet termination. This should significantly enhance the density of cosmic rays in the vicinity of GRS 1915+105. This may manifest itself as an extended gamma-ray source or as several compact sources if the target gas has a highly inhomogeneous distribution. This analysis has direct implication for studying Galactic μQ with such gamma-ray observatories as LHAASO, CTA, and SWGA in the next decades.

Examining a hadronic γ-ray scenario for the radiative shell and molecular clouds of the old GeV supernova remnant G298.6−0.0

Abstract Based on the 13.7 yr Fermi-LAT data, Yeung, Bamba, and Sano (2023, PASJ, 75, 384) claimed detection of two γ-ray sources (namely Src-NE and Src-NW) associated with the supernova remnant (SNR) G298.6−0.0, and interpreted it as an old GeV SNR interacting with molecular clouds (MCs). In this follow-up study, we refine the flux measurements below 2 GeV with Fermi-LAT event types of better angular reconstruction. Then, we report our γ-ray spectral fittings and cosmic-ray phenomenology in a hadronic scenario, considering both the shell and MC regions of SNR G298.6−0.0. We confirm that the γ-ray spectra of both Src-NE and Src-NW exhibit spectral breaks, at $1.50_{-0.50}^{+0.60}$ and $0.68_{-0.11}^{+0.32}\:$GeV, respectively. Src-NW has a harder broad-band photon index than Src-NE, suggesting an appreciable difference between the physical separations of their respective emission sites from SNR G298.6−0.0. The cosmic-ray spectrum responsible for Src-NE starts with a minimum energy $E_\mathrm{CR,min}=1.38_{-0.16}^{+0.47}\:$GeV, and has a proton index $\Gamma _\mathrm{CR}=2.57_{-0.21}^{+0.18}$ below the exponential cutoff energy $E_\mathrm{CR,max}=240_{-150}^{+240}\:$GeV. Accordingly, we argue that Src-NE is dominated by the SNR shell, while only a minor portion of lower-energy emission is contributed by the MCs interacting with the SNR. The cosmic-ray population for Src-NW starts at a higher energy such that the ECR, min ratio of Src-NW to Src-NE is ≳2. The high ECR, min, as well as the high cosmic-ray energy density required (∼26 eV cm−3), supports the interpretation that Src-NW is predominantly the γ-ray emission from the farther MCs being bombarded by protons that had earlier escaped from SNR G298.6−0.0. By comparing the high-energy features of G298.6−0.0 with those of analogical SNRs, especially SNR W 28 and SNR W 44, we further constrain the age of SNR G298.6−0.0 to be 10–30 kyr, under the assumption of a purely hadronic scenario.

Main time characteristics of cosmic ray variations and related parameters in magnetic clouds

The behavior of the main parameters of the interplanetary medium, cosmic rays, and geomagnetic activity during the passage of magnetic clouds past the Earth (465 events over the period from 1967 to 2021) has been studied. Time distributions of these parameters inside magnetic clouds are considered. It is shown that the maximum values of the solar wind velocity, interplanetary magnetic field strength, and geomagnetic activity indices are more often recorded at the beginning of the magnetic cloud, while the minimum values of the temperature index, cosmic ray density and equatorial component of anisotropy can be observed in any part of the structure under study.

Origin of 60Fe nuclei in cosmic rays: the contribution of local OB associations

ABSTRACT The presence of live 60Fe nuclei (lifetime of 3.8 Myr) in cosmic rays detected by the Advanced Composition Explorer/Cosmic Ray Isotope Spectrometer instrument suggests a nearby nucleosynthesis source. 60Fe is primarily produced in core-collapse supernovae, and we aim to clarify whether the detected 60Fe nuclei can be associated with a particular local supernova. We consider 25 OB associations and subgroups located within 1 kpc of the Solar system based on recent Gaia census. A model is developed that combines stellar population synthesis within these OB associations, cosmic ray acceleration within associated superbubbles, and cosmic ray transport to the Solar system. The most critical model parameter impacting 60Fe cosmic ray production is the explodability criterion, which determines if a massive star ends its life as a supernova. Our study points to the Scorpius–Centaurus (Sco–Cen) OB association as the most probable origin of the observed 60Fe nuclei, particularly suggesting they were accelerated in the Sco–Cen superbubble by a young supernova aged ≤500 kyr with a progenitor mass of approximately 13–20 M⊙. A less likely source is the supernova at the origin of the Geminga pulsar 342 kyr ago, if the progenitor originated in the Orion OB1 association. The contribution of local OB associations to the cosmic ray density of stable 56Fe is estimated to be around 20 per cent, with some sensitivity to cosmic ray acceleration efficiency and diffusion coefficient. These findings shed light on the origins of cosmic ray nuclei, connecting them to nucleosynthesis events within our local cosmic neighbourhood.

Evolution of Chemistry in the envelope of HOt corinoS (ECHOS)

Context. Within the project Evolution of Chemistry in the envelope of HOt corinoS (ECHOS), we present a study of sulphur chemistry in the envelope of the Class 0 source B 335 through observations in the spectral range λ = 7, 3, and 2 mm. Aims. Our goal is to characterise the sulphur chemistry in this isolated protostellar source and compare it with other Class 0 objects to determine the environmental and evolutionary effects on the sulphur chemistry in these young sources. Methods. We have modelled observations and computed column densities assuming local thermodynamic equilibrium and large velocity gradient approximation. We have also used the code Nautilus to study the time evolution of sulphur species, as well as of several sulphur molecular ratios. Results. We have detected 20 sulphur species in B 335 with a total gas-phase S abundance similar to that found in the envelopes of other Class 0 objects, but with significant differences in the abundances between sulphur carbon chains and sulphur molecules containing oxygen and nitrogen. Our results highlight the nature of B 335 as a source especially rich in sulphur carbon chains unlike other Class 0 sources. The low presence or absence of some molecules, such as SO and SO+, suggests a chemistry not particularly influenced by shocks. We, however, detect a large presence of HCS+ that, together with the low rotational temperatures obtained for all the S species (&lt;15 K), reveals the moderate or low density of the envelope of B 335. Model results also show the large influence of the cosmic ray ionisation rate and density variations on the abundances of some S species (e.g. SO, SO2, CCS, and CCCS) with differences of up to ~4 orders of magnitude. We also find that observations are better reproduced by models with a sulphur depletion factor of 10 with respect to the sulphur cosmic elemental abundance. Conclusions. The comparison between our model and observational results for B 335 reveals an age of 104 &lt; t &lt; 105 yr, which high-lights the particularly early evolutionary stage of this source. B 335 presents a different chemistry compared to other young protostars that have formed in dense molecular clouds, which could be the result of accretion of surrounding material from the diffuse cloud onto the protostellar envelope of B 335. In addition, the theoretical analysis and comparison with observations of the SO2/C2S, SO/CS, and HCS+/CS ratios within a sample of prestellar cores and Class 0 objects show that they could be used as good chemical evolutionary indicators of the prestellar to protostellar transition.

Forbush Decreases Associated with Coronal Holes, Coronal Ejections from Active Regions, and Filament Ejections: Comparison in Solar Cycles 23 and 24

In this paper, we study the similarities and differences of Forbush decreases in solar cycles 23 and24. Groups of events associated with various types of solar sources were analyzed: coronal mass ejections fromactive regions accompanied by solar flares (CME1 group), filament ejections outside active regions (CME2group), and high-velocity streams from coronal holes (CH group). The distributions and relations of variousparameters were studied: the amplitude of Forbush decreases, the maximum values of the hourly decrease inthe cosmic ray density, the equatorial cosmic ray anisotropy, the solar wind velocity, and the magnetic fieldstrength, as well as the values of the solar wind velocity and the magnetic field strength 1 hour before the onsetof the Forbush decrease during the event. The results showed that the number of events, parameter values,and their relations depend on the phase and cycle of solar activity. In the 24th cycle, the number of events inthe CME1 group decreased, did not change in CME2, and increased in CH. The values of the parametersand the difference between them in various groups of events are higher in cycle 23, which is characterized bygreater asymmetry and long “tails” of distributions. The magnitude of the Forbush decreases in the CME1group in cycle 23 depends more strongly on the solar wind velocity while, in cycle 24, on the magnetic fieldstrength, as in the CME2 group in both solar cycles. Multiple linear regression describes the dependences ofthe parameters of Forbush reductions in the CME1 and CME2 groups in the 23rd cycle and in the CME1group in the 24th cycle well.

Steady states of the Parker instability: the effects of rotation

ABSTRACT We model the Parker instability in vertically stratified isothermal gas using non-ideal MHD three-dimensional simulations. Rotation, especially differential, more strongly and diversely affects the nonlinear state than the linear stage (where we confirm the most important conclusions of analytical models), and stronger than any linear analyses predict. Steady-state magnetic fields are stronger and cosmic ray energy density is higher than in comparable non-rotating systems. Transient gas outflows induced by the nonlinear instability persist longer, of order 2 Gyr, with rotation. Stratification combined with (differential) rotation drives helical flows, leading to mean-field dynamo. Consequently, the nonlinear state becomes oscillatory (while both the linear instability and the dynamo are non-oscillatory). The horizontal magnetic field near the mid-plane reverses its direction propagating to higher altitudes as the reversed field spreads buoyantly. The spatial pattern of the large-scale magnetic field may explain the alternating magnetic field directions in the halo of the edge-on galaxy NGC 4631. Our model is unique in producing a large-scale magnetic structure similar to such observation. Furthermore, our simulations show that the mean kinetic helicity of the magnetically driven flows has the sign opposite to that in the conventional non-magnetic flows. This has profound consequences for the nature of the dynamo action and large-scale magnetic field structure in the coronae of spiral galaxies that remain to be systematically explored and understood. We show that the energy density of cosmic rays and magnetic field strength are not correlated at scales of order 1 kiloparsec.

Efficiency of mechanisms for the formation of sporadic Forbush decreases

From the measurements of the neutron monitors world network in the period 1996–2018, 31 strong Forbush decreases (5%) were identified that satisfy the accepted event selection criterion. The superposed epoch analyses is used to determine the consistent spatial distributions of the solar wind parameters and the decrease in cosmic ray density. It has been established that the contributions of the formation mechanisms of the Forbush decrease differ greatly in two groups of events. The difference may be since the formation of the Forbush depression in one group occurs in the frontal part, and in the other group in the peripheral part of the disturbance.

Peculiarities of medium parameter dynamics and cosmic ray density in strong Forbush decreases associated with magnetic clouds

Diffusion and electromagnetic mechanisms determine the formation of sporadic Forbush decreases. The diffusion mechanism affects the Forbush decrease amplitude in the turbulent layer, and the part of the coronal mass ejection preceding the magnetic cloud, and its efficiency depends on the level of magnetic field turbulence. The electromagnetic mechanism works in a magnetic cloud, and its efficiency depends on the intensity of regular magnetic and electric fields. We analyze solar wind parameters and cosmic ray density, using the superposed epoch analysis. In 1996–2006, 23 strong Forbush decreases (amplitude &gt;5 %) were detected. The average amplitude of 7 % is equally formed by both mechanisms. The events can be divided into 2 groups depending on the contribution of the mechanisms to Forbush decrease amplitude. Group 1 includes the strongest Forbush decreases (amplitude=8.5 %), formed by both diffusion and electromagnetic mechanisms. The diffusion mechanism forms 0.26 amplitude, and the electromagnetic mechanism is responsible for 0.74 one. In group 2, the averege amplitude Forbush decrease =5.7 %, the diffusion mechanism forms 0.79 of amplitude; and the electromagnetic one, 0.21. The spatial distributions of the mean values of the medium parameters in the region of disturbances in the groups differ. This difference can be explained by the fact that Forbush decrease amplitude in groups 1 and 2 are formed in the central and peripheral parts of coronal mass ejection respectively.

Особенности динамики параметров среды и плотности космических лучей в сильных форбуш-понижениях, связанных с магнитными облаками

Diffusion and electromagnetic mechanisms determine the formation of sporadic Forbush decreases. The diffusion mechanism affects the Forbush decrease amplitude in the turbulent layer, and the part of the coronal mass ejection preceding the magnetic cloud, and its efficiency depends on the level of magnetic field turbulence. The electromagnetic mechanism works in a magnetic cloud, and its efficiency depends on the intensity of regular magnetic and electric fields. We analyze solar wind parameters and cosmic ray density, using the superposed epoch analysis. In 1996–2006, 23 strong Forbush decreases (amplitude &gt;5 %) were detected. The average amplitude of 7 % is equally formed by both mechanisms. The events can be divided into 2 groups depending on the contribution of the mechanisms to Forbush decrease amplitude. Group 1 includes the strongest Forbush decreases (amplitude=8.5 %), formed by both diffusion and electromagnetic mechanisms. The diffusion mechanism forms 0.26 amplitude, and the electromagnetic mechanism is responsible for 0.74 one. In group 2, the averege amplitude Forbush decrease =5.7 %, the diffusion mechanism forms 0.79 of amplitude; and the electromagnetic one, 0.21. The spatial distributions of the mean values of the medium parameters in the region of disturbances in the groups differ. This difference can be explained by the fact that Forbush decrease amplitude in groups 1 and 2 are formed in the central and peripheral parts of coronal mass ejection respectively.

Statistical comparison of time profiles of Forbush decreases associated with coronal mass ejections and streams from coronal holes in solar cycles 23–24

ABSTRACT In this paper, Forbush decrease (FD) profiles are compared for events associated with (i) coronal mass ejections from active regions accompanied by solar flares (AR CMEs), (ii) filament eruptions away from active regions (non-AR CMEs), and (iii) high-speed streams (HSSs) from coronal holes (CHs). FD profiles are described by time parameters that are delayed from an FD onset to the registration of maximum values of cosmic ray (CR) density variations, CR density hourly decrease, CR equatorial anisotropy, solar wind (SW) speed, interplanetary magnetic field (IMF) strength and minimum Dst index. Distributions of these parameters from 1997 to 2020 and within maxima and minima of the last solar cycles (SCs) were compared by statistical methods. The results obtained reveal that statistical properties of the time parameters depend both on the FD source and on the solar activity period. FDs associated with AR CMEs develop even at close values of SW parameters faster than those associated with non-AR CMEs and HSS from CHs. Differences between typical FD profiles for events associated with AR and non-AR CMEs are more significant when the interplanetary disturbance contains a magnetic cloud. The difference between FD profiles for events associated with AR and non-AR CMEs is less distinguishable within maximum SC 24 than within maximum SC 23. For FDs associated with HSS from CHs, the main phase durations and the time delays of maximal SW speed are longer within SC 23–24 minimum, while the time delays of maximal IMF strength differ insignificantly between 23–24 and 24–25 minima.

Effective shielding of ≲10 GeV cosmic rays from dense molecular clumps

The density of cosmic rays inside molecular clouds determines the ionization rate in the dense cores where stars form. It is also one of the drivers of astrochemistry leading to the creation of complex molecules. Through Fermi Large Area Telescope observations of nearby giant molecular clouds, we observed deficits (holes) in the gamma-ray residual map when modelling with the expected gamma-ray diffuse emission from uniform cosmic rays interacting with the molecular content. We propose that the deficit is due to the lack of penetration of the low-energy (sub-GeV to GeV) cosmic rays into denser regions or clumps. This differs from the prevailing view of fast cosmic ray transport in giant molecular clouds where the magnetic turbulence is suppressed by neutral-ion damping, as our results require a slow diffusion inside dense molecular clumps. Through modelling we find that while the shielding is negligible on the cloud scale, it becomes important in the denser, parsec-sized regions where the gravitational collapse is already at play, changing the initial condition of star formation and astrochemistry.

Development of Forbush Decreases Associated with Coronal Ejections from Active Regions and non-Active Regions

In this paper, we study the development of Forbush decreases associated with coronal mass ejectionsfrom active regions accompanied by solar flares and filament eruptions from non-active regions usingthe database of Forbush effects and interplanetary disturbances created at IZMIRAN. We compared thedevelopment of two types of Forbush decreases during solar cycles 23–24, the maxima of these cycles, andthe minimum between them. Using statistical methods, we studied the distributions of time intervals from thebeginning of the Forbush decrease to registration: the minimum cosmic ray density, the maximum hourlydecrease in density, the maximum cosmic ray anisotropy, the maximum solar wind velocity, the maximumstrength of the interplanetary magnetic field, and the minimum of the Dst index. The difference in the developmentof two types of Forbush decreases was compared when the interplanetary disturbance contains ordoes not contain a magnetic cloud near the Earth. The results showed that flare-associated events developfaster than filament-associated events, even at close values of the solar wind parameters. The difference in thedevelopment of two types of Forbush decreases is more noticeable in the case of the presence of a magneticcloud near the Earth’s orbit. The largest difference between the time parameters in the two types of events isobserved for the time of registration of the maximum intensity of the interplanetary magnetic field. The mainphase of the two types of Forbush decreases is the same at the solar cycle 23 maximum and longer for filament-associated events at the cycle 24 maximum and 23–24 minimum. Considering all time parameters, thedifference in the development of the two types of Forbush decreases is more noticeable at the maximum ofcycle 23 and at the minimum of cycle 23–24 than at the maximum of cycle 24

The amplitude and phase distributions of cosmic ray variation at different conditions of Forbush decrease

The Forbush effect is one of the striking examples of irregular variations in the cosmic ray (CR) flux. It is a heliospheric phenomenon that includes a decrease and a recovery of the CR intensity and small changes in the CR density and anisotropy before the start of the main decrease. They were first noted as the effects of decreasing the intensity of cosmic rays, coinciding with geomagnetic storms. The increased interest is observed in recent years and it is primarily because their variables are strongly related to processes in solar-terrestrial physics. Forbush effects convey significant information regarding interplanetary disturbances. In the present work, fifty-three Forbush decrease (FD) events were categorized into four types according to their profile shape. From 1990 to 2020, cosmic ray intensity data from five neutron monitor stations (two subpolar and three mid-latitude) were used. The superposed epoch technique has been used to calculate the vectorial average of the observed diurnal vectors for every day of the four types of FD. It can be found that the subpolar stations (McMurdo and Thule) showed different behavior than the other stations. The solar-diurnal variation at the Thule and McMurdo subpolar stations is comparable on some days to the variation at mid-latitude stations, indicating that CR anisotropy on these days is not the only (and sometimes not the main) source of the solar-diurnal variation. The contribution of the solar-diurnal anisotropy to the diurnal variation at subpolar stations is small, much less than at other neutron monitors.

Large-amplitude Bidirectional Anisotropy of Cosmic-Ray Intensity Observed with Worldwide Networks of Ground-based Neutron Monitors and Muon Detectors in 2021 November

We analyze the cosmic-ray variations during a significant Forbush decrease observed with worldwide networks of ground-based neutron monitors and muon detectors during 2021 November 3–5. Utilizing the difference between primary cosmic-ray rigidities monitored by neutron monitors and muon detectors, we deduce the rigidity spectra of the cosmic-ray density (or omnidirectional intensity) and the first- and second-order anisotropies separately for each hour of data. A clear two-step decrease is seen in the cosmic-ray density with the first ∼2% decrease after the interplanetary shock arrival followed by the second ∼5% decrease inside the magnetic flux rope (MFR) at 15 GV. Most strikingly, a large bidirectional streaming along the magnetic field is observed in the MFR with a peak amplitude of ∼5% at 15 GV, which is comparable to the total density decrease inside the MFR. The bidirectional streaming could be explained by adiabatic deceleration and/or focusing in the expanding MFR, which have stronger effects for pitch angles near 90°, or by selective entry of GCRs along a leg of the MFR. The peak anisotropy and density depression in the flux rope both decrease with increasing rigidity. The spectra vary dynamically, indicating that the temporal variations of density and anisotropy appear different in neutron monitor and muon detector data.

Cosmic-Ray Ionization Rate in Protoplanetary Disks with Sheared Magnetic Fields

We investigate the effects of magnetic-field configurations on the ionization rate by cosmic rays in protoplanetary disks. First, we consider cosmic-ray propagation from the interstellar medium (ISM) to the protoplanetary disks and showed that the cosmic-ray density around the disk should be 2 times lower than the ISM value. Then, we compute the attenuation of cosmic rays in protoplanetary disks. The magnetic fields in the disk are stretched to the azimuthal directions, and cosmic rays need to detour while propagating to the midplane. Our results show that the detouring effectively enhances the column density by about two orders of magnitude. We employ a typical ionization rate by cosmic rays in diffuse ISM, which is considered too high to be consistent with observations of protoplanetary disks, and find that the cosmic rays are significantly shielded at the midplane. In the case of the disk around IM Lup, the midplane ionization rate is very low for r ≲ 100 au, while the value is as large as a diffuse ISM in the outer radii. Our results are consistent with the recent Atacama Large Millimeter/submillimeter Array observation that indicates the radial gradient in the cosmic-ray ionization rate. The high ionization rate in the outer radii of disks may activate the magnetorotational instability that was thought to be suppressed due to ambipolar diffusion. These results will have a strong influence on the dynamical and chemical evolutions of protoplanetary disks.

Hot spots in the neutrino flux created by cosmic rays from Cygnus and Vela

An analysis of 7.5 years of data in the high-energy starting event sample has been recently published by the IceCube collaboration. The hottest spot in a search for neutrino sources was found far above the Galactic plane and is thus, at first sight, difficult to reconcile with a Galactic origin. In this work, we calculate the cosmic ray (CR) density around nearby, young supernova remnants assuming anisotropic diffusion. Combining the obtained CR densities with the matter distribution deduced from extinction maps, we find two prominent hot spots: The one close to the most significant point in the IceCube search for point sources is created by CRs from the Cygnus loop and has an intensity corresponding to two to four neutrino events. Another, more extended one may be caused by CRs from Vela if CR trajectories are sufficiently disturbed by the magnetic field in the shell around the superbubble Loop I.