Cosmic rays and terrestrial life: A brief review

“The investigation into the possible effects of cosmic rays on living organisms will also offer great interest.” – Victor F. Hess, Nobel Lecture, December 12, 1936High-energy radiation bursts are commonplace in our Universe. From nearby solar flares to distant gamma ray bursts, a variety of physical processes accelerate charged particles to a wide range of energies, which subsequently reach the Earth. Such particles contribute to a number of physical processes occurring in the Earth system. A large fraction of the energy of charged particles gets deposited in the atmosphere, ionizing it, causing changes in its chemistry and affecting the global electric circuit. Remaining secondary particles contribute to the background dose of cosmic rays on the surface and parts of the subsurface region. Life has evolved over the past ∼3 billion years in presence of this background radiation, which itself has varied considerably during the period [1], [2], [3]. As demonstrated by the Miller–Urey experiment, lightning plays a very important role in the formation of complex organic molecules, which are the building blocks of more complex structures forming life. There is growing evidence of increase in the lightning rate with increasing flux of charged particles. Is there a connection between enhanced rate of cosmic rays and the origin of life? Cosmic ray secondaries are also known to damage DNA and cause mutations, leading to cancer and other diseases. It is now possible to compute radiation doses from secondary particles, in particular muons and neutrons. Have the variations in cosmic ray flux affected the evolution of life on earth? We describe the mechanisms of cosmic rays affecting terrestrial life and review the potential implications of the variation of high-energy astrophysical radiation on the history of life on earth.     

双漏模式中的弥散宇宙γ射线

弥散宇宙γ射线产生于初级宇宙线的传播过程,本文利用宇宙线传播的“双漏模式”得出与实验观测谱接近的银河系弥散宇宙γ射线谱。     

A study of secondary cosmic ray flux variation during the annular eclipse of 15 January 2010 at Rameswaram, India

The gamma ray flux was measured during the annular solar eclipse on January 15, 2010 at Rameswaram, India using NaI (Tl) scintillator detectors and the variation in charged particles and gamma rays was monitored using Geiger Mu¨ller (GM) counters. The gamma ray flux variation was studied in energy range of 0.1–3.5 MeV. Weather parameters (temperature and humidity) were continuously recorded throughout the duration of the eclipse at the site and correlation between gamma ray flux and weather parameters was examined. Analysis of the secondary cosmic ray flux using Fast Fourier Transform (FFT) was carried out to study the impact of the eclipse on the flux modulation. An overall decrease in flux was observed by both GM counters and scintillator detectors. A relative enhancement observed for short time during the eclipse which could be associated with the presence of counter electrojet observed at Rameswaram. This is suggestive of an increase in secondary cosmic ray flux at the geomagnetic equator during every counter electrojet due to decrease in geomagnetic rigidity.     

Power spectra of cosmic ray intensity variations at the ground and atmospheric pressure oscillations

Power spectrum estimates are computed for cosmic ray and pressure variations in the frequency range of 1.6 × 10⁻⁶ to 4.15 × 10⁻³ c/sec for three data sets each of 27 days length (2 min interval) recorded at Chacaltaya (Bolivia) during 1965–1966. The general trend of these spectra showy ƒ⁻ fit having exponent values from −1.5 to −1.9 for L.F. side. From the semi-diurnal peaks both in cosmic rays and pressure, the average value of pressure coefficient is found to be 0.3 per cent/mm of Hg. For the same three sets of data, a detailed analysis of cross-spectrum, coherence and phase relationship between cosmic rays and pressure is carried out in the frequency range of 1–12 c/day. Besides semi-diurnal peak, variations of 3, 4, 7 and 8 c/day are found to be common both in cosmic rays and pressure. The value of pressure coefficient and residual amplitude of cosmic rays for these particular frequencies are calculated.     

高海拔宇宙线观测站LHAASO概况

宇宙线发现百年以来,宇宙线起源仍然是一个谜.研究宇宙线起源主要在甚高能(VHE)伽马射线天文学和宇宙线物理学两个领域交叉展开.新一代高海拔宇宙线观测站(LHAASO)拥有高海拔、全天候和大规模优势,利用多种探测手段对宇宙线开展联合观测,大幅提升对伽马射线和宇宙线的鉴别能力.LHAASO将开展全天区伽马源扫描搜索以大量发现新伽马源,将获得30TeV以上伽马射线探测的最高灵敏度,将在宽达5个数量级的能量范围内精确测量宇宙线分成份能谱,为揭开宇宙线起源谜团给出重要判据.系统介绍了LHAASO的探测器结构、性能优势和科学目标.     

Relationship between high-energy physical phenomena on the sun and in astrophysics

High energy phenomena on the surface of the Sun are manifestations of part of the solar dynamo cycle. Convection and magnetic field give rise to unstable, twisted flux loops that become solar flares when the resistive tearing mode proceeds to the nonlinear limit. If such twisted flux loops did not dissipate rapidly due to an enhanced resistivity, then the dynamo would not work. The act of dissipation leads to intense heating and acceleration leading to X-rays and accelerated particles. The particles in turn give rise to hard X-rays, gamma rays, neutrons, and solar cosmic rays. In high-energy astrophysics such phenomena occur in accretion disks around compact objects like black holes in quasars and SS433. The resulting acceleration may explain the observed extremely high-energy cosmic rays of up to 10²⁰ eV and the high-energy gamma rays of 10¹² to 10¹⁵ eV. These high energies are more readily explained by acceleration E parallel to B as opposed to stochastic shock acceleration. The anisotropy and localization of gamma rays from solar flares potentially may indicate which mechanism is prevalent.     

OSO-III: Preliminary scientific results

OSO-III was placed into orbit on March 8, 1967; observations were made of the solar extreme ultraviolet, soft and hard solar X-rays, cosmic X-rays and -rays, cosmic ray particles, and the near-earth optical wavelength radiation environment.     

Measuring the chemical composition of cosmic rays at ∼ 1013–1015 eV by utilizing the solar and geomagnetic fields

According to a proposal of Lloyd-Evans (1985), the average charge of particles in the cosmic radiation near 10¹⁴eV can be determined by observing the effect of the solar magnetic field on the Sun's shadow in the angular distribution of energetic primary cosmic ray particles. This suggestion is shown to be realizable with a new type of EAS-array proposed for the purpose of high energy -ray astronomy. The same measurement provides information on the integrated strength of the solar magnetic field. As the array will be sensitive and provide good angular resolution down to a few times 10¹²eV, more detailed results on the primary composition near 10¹³eV can be obtained by investigating the shape of the shadow of the Moon as affected by the geomagnetic field.     

On the generation of high-energy particles in solar flares

This paper discusses the relationship between some characteristics of microwave type IV radio bursts and solar cosmic ray protons of MeV energy. It is shown that the peak flux intensity of those bursts is almost linearly correlated with the MeV proton peak flux observed by satellites near the Earth and that protons and electrons would be accelerated simultaneously by a similar mechanism during the explosive phase of solar flares.Brief discussion is given on the propagation of solar cosmic rays in the solar envelope after ejection from the flare regions.     

Broad-band non-thermal emission from molecular clouds illuminated by cosmic rays from nearby supernova remnants

Molecular clouds are expected to emit non-thermal radiation due to cosmic ray interactions in the dense magnetized gas. Such emission is amplified if a cloud is located close to an accelerator of cosmic rays and if energetic particles can leave the accelerator site and diffusively reach the cloud. We consider here a situation in which a molecular cloud is located in the proximity of a supernova remnant which is efficiently accelerating cosmic rays and gradually releasing them in the interstellar medium. We calculate the multiwavelength spectrum from radio to gamma rays which is emerging from the cloud as the result of cosmic ray interactions. The total energy output is dominated by the gamma-ray emission, which can exceed the emission in other bands by an order of magnitude or more. This suggests that some of the unidentified TeV sources detected so far, with no obvious or very weak counterparts in other wavelengths, might be in fact associated with clouds illuminated by cosmic rays coming from a nearby source. Moreover, under certain conditions, the gamma-ray spectrum exhibits a concave shape, being steep at low energies and hard at high energies. This fact might have important implications for the studies of the spectral compatibility of GeV and TeV gamma-ray sources.     

Energetic particles from the sun

This paper discusses solar cosmic ray phenomena and related topics from the solar physical point of view. Basic physics of the solar atmosphere and solar flare phenomena are, therefore, considered in some detail. Since solar cosmic rays are usually produced by solar flares, we must first understand the processes and mechanism of solar flares, especially the so-called proton flares, in order to understand the acceleration mechanism of solar cosmic rays and their behaviour in both the solar atmosphere and interplanetary space. For this reason, detailed discussion is given on various phenomena associated with solar flares, proton flare characteristics, and the mechanism of solar flares.Since the discovery of solar cosmic rays by Forbush, the interplanetary space has been thought of as medium in which solar cosmic rays propagate. In this paper, the propagation of solar cosmic rays in this space is, therefore, discussed briefly by referring to the observed magnetic properties of this space. Finally, some problems related to the physics of galactic cosmic rays are discussed.Astrophysics and Space Science Review Paper.     

Evolution and observational signature of diffused antiworld

The existence of macroscopic regions with antibaryon excess in the baryon asymmetric Universe with general baryon excess is the possible consequence of practically all models of baryosynthesis. Diffusion of matter and antimatter to the border of antimatter domains defines the minimal scale of the antimatter domains surviving to the present time. A model of diffused antiworld is considered, in which the density within the surviving antimatter domains is too low to form gravitationally bound objects. The possibility to test this model by measurements of cosmic gamma ray fluxes is discussed. The expected gamma ray flux is found to be acceptable for modern cosmic gamma ray detectors and for those planned for the near future.     

Cosmic ray and hydrogen distributions and cosmic gamma — rays

We calculate the spectrum of the diffuse cosmic gamma ray in the single and double leaky box models for several galactic distribution laws of cosmic rays and hdydrogen. The results show that LI Ti-pei's distribution law for the cosmic rays is the best and that the number of interstellar hydrogen molecules should be less than Gordon's value divided by 1.7. The observed spectrum of gamma rays can be reproduced by a suitable choice of the galactic distributions within certain ranges.     

Spatial distribution of high energy cosmic ray electrons perpendicular to the galactic plane

With the help of empirical data concerning the latitudinal distribution of galactic gamma rays the contribution of inverse Compton scattered gamma rays is calculated using various models concerning the distribution of high energy cosmic ray electrons perpendicular to the galactic plane. It is shown that gamma ray astronomy from regions with vanishing stellar and interstellar matter densities at energies greater than 100 MeV provides instructive information on the cosmic ray electron density. We find evidence for the existence of a broad galactic electron disk with a total thickness of at least 6.4 kpc. The uncertainties of the cosmic ray electron spectrum measurements above 100 GeV imply an additional uncertainty in the inverse Compton source function of at least a factor 6.     

Cosmic flux of low energy gamma rays

Measurements have been made on the cosmic gamma rays of energy between 0.25 and 4.2 MeV from a balloon experiment made near the geomagnetic equator using a collimated 7.6 cm×7.6 cm NaI(T1) crystal assembly. The depth-intensity curves obtained were used to estimate the contribution due to the diffuse cosmic gamma rays in the above energy interval; an unfolding of the counting rates was then performed to obtain the energy spectrum. It is found that a power law fitted to the present data points has a spectral index of –1.8±0.2. A critical examination is then made of all the observational data between 1 keV and 100 MeV to deduce information on the spectral shape in this energy region. Upper limits on low energy gamma ray fluxes from Sco X-1 and the Galactic centre region are also reported.     

Calibration of particle detectors for secondary cosmic rays using gamma-ray beams from thunderclouds

After observation of hundreds of Thunderstorm Ground Enhancements (TGEs) we measure energy spectra of particles originated in clouds and directed towards Earth. We use these “beams” for calibration of cosmic ray detectors located beneath the clouds at an altitude of 3200 m at Mount Aragats in Armenia. The calibrations of particle detectors with fluxes of TGE gamma rays are in good agreement with simulation results and allow estimation of the energy thresholds and efficiencies of numerous particle detectors used for studying galactic and solar cosmic rays.     

Stellar and solar flares

Some ideas are developed concerning solar flares which have been presented earlier by the author (Schatzman, 1966a). Emphasis is laid on the problem of energy transport; from the energy supply to the region of the optical flare, on the storage of low energy cosmic ray particles in a magnetic bottle before the beginning of the optical flare, and the mechanism which triggers both the optical flare, and the production of high-energy cosmic rays. The relation between solar and stellar flares is considered.Lecture given at Goddard Space Flight Center, November 4, 1966.     

The cosmic γ-ray spectrum from secondary particle production in cosmic-ray interactions

The cosmic -ray spectrum below 1 GeV arising from cosmic ray p-p interactions is calculated. Its characteristics are determined by the properties of secondary neutral pion production occurring at accelerator energies. A model is chosen for numerical calculations in which the two dominant modes of neutral pion production at accelerator energies are the production of the (1.238) isobar and one fireball. The effect of -p and p- interactions on the cosmic -ray spectrum is also calculated. The final results are given in terms of both differential and integral -ray energy spectra.     

The solar particle events of May 23 and May 28, 1967

McMath plage region 8818 passed over the visible solar disk on May 17–31, 1967. It was very active from its first appearance on the Eastern limb, several times producing bright optical flares and hard X-ray emission, accompanied by intense type II, type IV and centimeter radio bursts. Nevertheless, no solar particles could be detected near the earth until the evening of May 23, when three bright flares were observed in close succession at 25°–28° E. During the following build-up of the solar particle flux over 36 hours, the galactic cosmic ray flux > 1 GeV decreased gradually by about 5%. The flux of solar particles decreased in two steps on May 25, both accompanied by decreases in the equatorial geomagnetic field. These field depressions are attributed to storm plasma ejected from the parent flare of the May 23 particle event. The propagation of solar particles from May 23 on thus appears to be strongly affected by storm plasma from the parent flare of the May 23 event, without any indications of solar particles being trapped in that plasma.A later particle event early on May 28 was also associated with a bright flare in McMath region 8818, at 33° W. This event displayed a rapid build-up, with electrons arriving first, and an exponential decay. A smooth proton peak, 20 min wide, was detected on May 30 closely associated with an SSC attributed to plasma ejection from the parent flare of the May 28 event.Between the geomagnetic storms beginning on May 25 and May 30 an anomalous daily variation was observed in the cosmic ray flux >1 GeV, the time of maximum falling 7–10 hours earlier than normal. Storm time increases in the flux of galactic cosmic rays were seen on May 26 when the equatorial geomagnetic field was depressed by more than 400 . Low latitude auroras were also observed during that time.On leave from the University of Uppsala, Sweden.     

Cosmic rays and cosmic strings

It has been suggested that the highest-energy cosmic rays might be protons resulting from collapsing cosmic strings in the Universe. We point out that this mechanism, although attractive, has important shortcomings, notably the fact that gamma rays produced along with the protons and those produced by the protons in their interactions with the cosmic background radiation generate cascades in the Universe and result in unacceptably high fluxes of cosmic gamma rays in the region of hundreds of MeV.