Monte Carlo particle-trajectory models for neutral cometary gases. I - Models and equations. II - The spatial morphology of the Lyman-alpha coma
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view Abstract Citations (86) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Monte Carlo Particle Trajectory Models for Neutral Cometary Gases. I. Models and Equations Combi, M. R. ; Smyth, W. H. Abstract The Monte Carlo particle-trajectory models for the distributions of neutral gases in cometary atmospheres, developed in original form several years ago, have been greatly extended and generalized. In a Monte Carlo particle-trajectory model (MCPTM) the spatial distribution of a neutral cometary species is determined by calculating the explicit trajectories of many individual particles following the chain of parent vaporization, coma outflow, photodissociations, collisions, and decay through the appropriate number of generations. In this paper the mathematical derivations of the various methods employed in the MCPTM are presented in detail, and the application of the MCPTM to the calculation of the photochemical heating of the inner coma through the partial thermalization of cometary hydrogen atoms produced by the photodissociation of water is discussed. Publication: The Astrophysical Journal Pub Date: April 1988 DOI: 10.1086/166260 Bibcode: 1988ApJ...327.1026C Keywords: Comet Tails; Cosmic Gases; Mathematical Models; Monte Carlo Method; Particle Trajectories; Stellar Atmospheres; Computational Astrophysics; Particle Acceleration; Radiation Pressure; Solar Radiation; Time Dependence; COMETS; MONTE CARLO METHODS; PARTICLES; TRAJECTORIES; NEUTRAL PARTICLES; GASES; MODELS; CALCULATIONS; NUMERICAL METHODS; DISTRIBUTION; ENERGY; ATMOSPHERE; COMAE; PARAMETERS; RADIATION; PRESSURE; EJECTION; VELOCITY; TEMPERATURE; TIME DEPENDENCY; PHOTOCHEMISTRY; HEATING; GEOMETRY; ACCELERATION; DIAGRAMS; Astrophysics; Comets; COMETS; PARTICLE ACCELERATION full text sources ADS | Related Materials (1) Part 2: 1988ApJ...327.1044CKeywords:
Radiation Pressure
Particle (ecology)
Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries associated with OB supergiant companions and characterized by an X-ray flaring behaviour whose dynamical range reaches 5 orders of magnitude on time scales of a few hundred to thousands of seconds. Current investigations concentrate on finding possible mechanisms to inhibit accretion in SFXTs and to explain their unusually low average X-ray luminosity. We present the Swift observations of an exceptionally bright outburst displayed by the SFXT IGR J17544−2619 on 2014 October 10 when the source achieved a peak luminosity of 3 × 1038 erg s-1. This extends the total source dynamic range to ≳106, the largest (by a factor of 10) recorded so far from an SFXT. Tentative evidence for pulsations at a period of 11.6 s is also reported. We show that these observations challenge, for the first time, the maximum theoretical luminosity achievable by an SFXT and propose that this giant outburst was due to the formation of a transient accretion disc around the compact object.
X-ray transient
High mass
Transient (computer programming)
Accretion disc
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A shock-accelerated particle flux is proportional to p(-s), where p is the particle momentum, follows from simple theoretical considerations of cosmic-ray acceleration at nonrelativistic shocks followed by rigidity-dependent escape into the Galactic halo. A flux of shock-accelerated cosmic-ray protons with s≈2.8 provides an adequate fit to the Fermi Large Area Telescope γ-ray emission spectra of high-latitude and molecular cloud gas when uncertainties in nuclear production models are considered. A break in the spectrum of cosmic-ray protons claimed by Neronov, Semikoz, and Taylor [Phys. Rev. Lett. 108, 051105 (2012)] when fitting the γ-ray spectra of high-latitude molecular clouds is a consequence of using a cosmic-ray proton flux described by a power law in kinetic energy.
Cosmic ray spallation
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Geiger-M\"uller tube experiments have been performed to determine the nature of the cosmic rays present at depths of 30 and 300 meters water equivalent from the top of the atmosphere. At both of these depths, the observable cosmic rays are penetrating ionizing rays accompanied by soft showers. The ratio of the soft showers to the penetrating rays increases with depth.
Soft X-rays
Geiger counter
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Galactic plane
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Explaining the existence of $\gtrsim10^8\,\mathrm{M_\odot}$ SMBHs at $z>6$ is a persistent challenge to modern astrophysics. Multi-wavelength observations of $z\gtrsim6$ QSOs reveal that, on average, their accretion physics is similar to that of their counterparts at lower redshift. However, QSOs showing properties that deviate from the general behavior can provide useful insights into the physical processes responsible for the rapid growth of SMBHs in the early universe. We present X-ray (XMM-Newton, 100 ks) follow-up observations of a $z\approx6$ QSO, J1641+3755, which was found to be remarkably X-ray bright in a 2018 Chandra dataset. J1641+3755 is not detected in the 2021 XMM-Newton observation, implying that its X-ray flux decreased by a factor $\gtrsim7$ on a notably short timescale (i.e., $\approx115$ rest-frame days), making it the $z>4$ QSO with the largest variability amplitude. We also obtained rest-frame UV spectroscopic and photometric data with textit{LBT}, and compared them with archival datasets. Surprisingly, we found that J1641+3755 became brighter in the rest-frame UV band from 2003 to 2016, while no strong variation occurred from 2016 to 2021. Multiple narrow absorption features are detected in its rest-frame UV spectrum, and several of them can be associated with an intervening system at $z=5.67$. The variability properties of J1641+3755 can be due to intrinsic variations of the accretion rate, a small-scale obscuration event, gravitational lensing due to an intervening object, or an unrelated X-ray transient in a foreground galaxy in 2018. Accounting for all of the $z>6$ QSOs with multiple X-ray observations separated by $>10$ rest-frame days, we found an enhancement of strongly (i.e., by a factor $>3$) X-ray variable objects compared to QSOs at later cosmic times. This finding may be related to the physics of fast accretion in high-redshift QSOs.
QSOS
Rest frame
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In this paper we summarize our modelling efforts for cosmic rays near the heliopause, and discuss whether galactic cosmic ray modulation beyond the heliopause is possible and present an explanation for the anisotropic nature of the observed cosmic ray intensities in the very local interstellar medium. We show that (i) modulation beyond the heliopause is possible, but highly dependent on the assumed parameters (most notable, the perpendicular diffusion coefficient). Treating the heliopause as a tangential discontinuity, significantly damps this modulation effect and leads to modelled results that are similar to Voyager 1 observations. (ii) By choosing an appropriate functional form of the perpendicular diffusion coefficient on the pitch-angle level, we are able to account for the anisotropic behaviour observed for both galactic and anomalous cosmic rays in the local interstellar medium.
Heliosphere
Modulation (music)
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Explaining the existence of $\gtrsim10^8\,\mathrm{M_\odot}$ SMBHs at $z>6$ is a persistent challenge to modern astrophysics. Multi-wavelength observations of $z\gtrsim6$ QSOs reveal that, on average, their accretion physics is similar to that of their counterparts at lower redshift. However, QSOs showing properties that deviate from the general behavior can provide useful insights into the physical processes responsible for the rapid growth of SMBHs in the early universe. We present X-ray (XMM-Newton, 100 ks) follow-up observations of a $z\approx6$ QSO, J1641+3755, which was found to be remarkably X-ray bright in a 2018 Chandra dataset. J1641+3755 is not detected in the 2021 XMM-Newton observation, implying that its X-ray flux decreased by a factor $\gtrsim7$ on a notably short timescale (i.e., $\approx115$ rest-frame days), making it the $z>4$ QSO with the largest variability amplitude. We also obtained rest-frame UV spectroscopic and photometric data with textit{LBT}, and compared them with archival datasets. Surprisingly, we found that J1641+3755 became brighter in the rest-frame UV band from 2003 to 2016, while no strong variation occurred from 2016 to 2021. Multiple narrow absorption features are detected in its rest-frame UV spectrum, and several of them can be associated with an intervening system at $z=5.67$. The variability properties of J1641+3755 can be due to intrinsic variations of the accretion rate, a small-scale obscuration event, gravitational lensing due to an intervening object, or an unrelated X-ray transient in a foreground galaxy in 2018. Accounting for all of the $z>6$ QSOs with multiple X-ray observations separated by $>10$ rest-frame days, we found an enhancement of strongly (i.e., by a factor $>3$) X-ray variable objects compared to QSOs at later cosmic times. This finding may be related to the physics of fast accretion in high-redshift QSOs.
QSOS
Rest frame
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Chemical composition of ultrahigh-energy cosmic rays is estimated through the reliably determined (both experimentally and theoretically) distribution of the number of showers in the galactic latitude. Experimental data at energies of ∼1019 eV agree with the theoretical calculations, provided that cosmic rays involve predominantly heavy nuclei. An enhanced flux of cosmic rays from the galactic plane is detected at energies of ∼1019 eV.
Galactic plane
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Abstract Galactic cosmic rays (GCRs) originate from sources outside the solar system and reach the Earth’s environment from all directions. More than 100 years after the first detection of cosmic rays, the origin of high-energy cosmic rays is still a mystery. Although our knowledge of the origin and propagation of cosmic rays is relatively limited, we can study the radiation conditions in the near-Earth space environment in more detail. The origin, composition, and energy spectra of cosmic rays are briefly discussed in this paper. A brief review of the transport of galactic cosmic rays in the heliosphere is given. The geomagnetic effects on galactic cosmic rays and the atmospheric interactions of primary particles are also discussed in the paper.
PAMELA detector
Heliosphere
Cosmic ray spallation
Forbush decrease
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The transport and acceleration of galactic cosmic rays is discussed with emphasis on the highest energies. The mechanism of diffusive shock acceleration is shown to produce a near-universal spectrum which can account for most observed cosmic rays. A quasi-perpendicular shock in general accelerates particles faster and to higher energies than a comparable quasi-parallel shock. Application of these ideas to supernova blast waves suggests that they can produce galactic cosmic rays to the knee in the spectrum, some 3 ×10 15 eV. A similar blast wave, recently identified near the galactic center could accelerate particles to an energy of some 10 18 Z eV or higher (hereinafter Z is the charge in units of the elementary charge). It is possible that the highest-energy cosmic rays could come from the galactic center. If this is the case, there should be an enhancement of the flux of high-energy cosmic rays coming from the galactic center.
Blast wave
Energy spectrum
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