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NASA NTRS2018

Explaining the Asymmetric Line Profile in Cepheus X-4 with Spectral Variation Across Pulse Phase

The high mass X-ray binary Cepheus X-4, during its 2014 outburst, showed evidence for an asymmetric cyclotron line in its hard X-ray spectrum. The 2014 spectrum provides one of the clearest cases of an asymmetric line profile among all studied sources with Cyclotron Resonance Scattering Features (CRSF). We present a phase-resolved analysis of NuSTAR and Suzaku data taken at the peak and during the decline phases of this outburst. We find that the pulse-phased resolved spectra are well-fit by a single, symmetric cyclotron feature. The fit parameters vary strongly with pulse phase: most notably the central energy and depth of the cyclotron feature, the slope of the power-law component, and the absorbing column density. We synthesise a ‘phase averaged’ spectrum using the best-fitting parameters for these individual pulse phases, and find that this combined model spectrum has a similar asymmetry in the cyclotron features as discovered in phase-averaged data. We conclude that the pulse phase resolved analysis with simple symmetric line profiles when combined can explain the asymmetry detected in the phase-averaged data.

Bhargave, Yash↗

NASA NTRS1985

Simulations of heavy ion heating by electromagnetic ion cyclotron waves driven by proton temperature anisotropies

Heating of heavy ions by the electromagnetic ion cyclotron (EMIC) waves, which are driven by proton temperature anisotropies, is studied by means of hybrid particle simulations. Initially, relaxation of the temperature anisotropies in the proton distribution and isotropic heating of the heavy ions are observed (phase I), followed by substantial perpendicular heating of the heavy ions (phase II). The heavy ions are distinctly gyrophase modulated by the EMIC waves. The isotropic heating in phase I is due to magnetic trapping by the excited proton cyclotron waves. The perpendicular heating in phase II is attributed to cyclotron resonance with the EMIC waves, which becomes possible by means of the preceding heating in phase I. Saturation of the EMIC instability is instead attributed to magnetic trapping of the majority ions: protons. When the proton anisotropy is very large, frequency shift (decrease) of the proton cyclotron waves to less than 1/2 Ohm(p) is observed. The present mechanism is not only relevant to He(+) heating in the dayside equator of the magnetosphere, but it also predicts hot He2(+) ions behind the earth's bow shock.

Tanaka, M.↗

NASA NTRS1981

Jikiken /EXOS-B/ observation of Siple transmissions

Preliminary results of observations by the Japanese magnetospheric satellite Jikiken (EXOS-B) of Siple transmissions and VLF emissions triggered by the Siple signals are reviewed. The experiments discussed were carried out in July, August, and September of 1979 and in December 1979 and January 1980. Only four events concentrated within the period from August 14 to 18 were found in which triggered emissions were associated with Siple transmissions. The electron distributions observed on the equatorial crossing passes, when Siple triggered emissions were detected, suggest that the cyclotron resonance condition is satisfied for Siple signals and electrons of energy around 1 keV or less, provided the interaction region is inside the plasmapause. It is noted that if these emissions were generated outside the plasmapause, electron energies much higher than 10 keV would be necessary for the cyclotron interaction, which were above the range of the measurements. For the high latitude passes of August 14 and 17, the electron fluxes were found to be very small.

Kimura, I.↗

NASA NTRS1981

A model for X-ray pulsar spectra

The transfer of X-rays through a hot, magnetized, scattering atmosphere is studied using a Monte Carlo technique. The process considered is Compton scattering, including cyclotron resonance scattering. Unlike previous work on the subject, the effects of frequency shifts, relativistic corrections, recoil, and polarization mode changes have been included. It is found that the emergent X-ray spectra harden toward the magnetic equator, are cut off at a frequency less than the fundamental cyclotron frequency, and depend on the magnetic field strength. The relevance of the results to observed pulsar spectra is indicated.

Pravdo, S. H.↗

NASA NTRS1992

Synchrotron emission from a cosmological jet as a model of gamma-ray bursts

The nonthermal rapidly varying spectra of gamma-ray bursts require relativistic beaming if the source is at a cosmological distance. Limits on the Lorentz factors and magnetic fields of extragalactic jet models of gamma-ray bursts are derived from the synchrotron source function, the position of the fundamental cyclotron resonance, the Thomson optical depth of radiating electrons, and the Thomson optical depth of electron-positron pairs created in photon-photon collisions of Compton upscattered radiation. The last of these constraints is the strongest, and it is satisfied by the observations if the jet's Lorentz factor is greater than 100. The limit from the position of the cyclotron fundamental requires a magnetic field strength below approximately 10 exp 10 G. Jet models producing observable cyclotron lines are allowed. The acceleration region in the burst must be separate from the emission region. The similarity of gamma-ray burst jet models to models of quasars and BL Lac objects suggest that if gamma-ray bursts are cosmological sources, they are a type of active galaxy.

Brainerd, J. J.↗

NASA NTRS1990

Energetics and dynamics of resonant and nonresonant scattering in strong magnetic fields

The energetics and the dynamics resulting from electron-photon resonant and nonresonant scattering in a plasma with magnetic field about 10 to the 12th G are studied in detail. Precise analytic results are obtained in the optically thin limit, and numerical results are presented for the optically thick case. For the latter, it is found that when the equilibrium temperature T(C) is determined by the cooling/heating balance due solely to cyclotron resonant scattering, the ratio of T(C) to the superstrong field B remains fairly constant for N(e) up to about 6 x 10 to the 21st electrons/sq cm. This line-dominated region comes to an end when the extra heating from the hard continuum photons becomes competitive with the line processes and drives T(C) well above the pure line value. For parameters characteristic of GB 880205, the thickness of the line-dominated region is determined to be between 10 to the 21st and 10 to the 22nd electrons/sq cm.

Lamb, Don Q.↗

NASA NTRS2012

Lunar Precursor Effects in the Solar Wind and Terrestrial Magnetosphere

The two ARTEMIS probes observe significant precursor activity upstream from the Moon, when magnetically connected to the dayside lunar surface. The most common signature consists of high levels of whistler wave activity near half of the electron cyclotron frequency. This precursor activity extends to distances of many thousands of km, in both the solar wind and terrestrial magnetosphere. In the magnetosphere, electrons reflect from a combination of magnetic and electrostatic fields above the lunar surface, forming loss cone distributions. In the solar wind they generally form conics, as a result of reflection from an obstacle moving with respect to the plasma frame (just as at a shock). The anisotropy associated with these reflected electrons provides the free energy source for the whistlers, with cyclotron resonance conditions met between the reflected source population and Moonward-propagating waves. These waves can in turn affect incoming plasma, and we observe significant perpendicular electron heating and plasma density depletions in some cases. In the magnetosphere, we also observe broadband electrostatic modes driven by beams of secondary electrons and/or photoelectrons accelerated outward from the surface. We also occasionally see waves near the ion cyclotron frequency in the magnetosphere. These lower frequency waves, which may result from the presence of ions of lunar origin, modulate the whistlers described above, as well as the electrons. Taken together, our observations suggest that the presence of the Moon leads to the formation of an upstream region analogous in many ways to the terrestrial electron foreshock.

Magnetosphere↗

NASA NTRS1988

Mapping of auroral kilometric radiation sources to the aurora

Auroral kilometric radiation (AKR) and optical auroral emissions are observed simultaneously using plasma wave instrumentation and auroral imaging photometers carried on the DE 1 spacecraft. The DE 1 plasma wave instrument measures the relative phase of signals from orthogonal electric dipole antennas, and from these measurements, apparent source directions can be determined with a high degree of precision. Wave data are analyzed for several strong AKR events, and source directions are determined for several emission frequencies. By assuming that the AKR originates at cyclotron resonant altitudes, a candidate source field line is identified. When the selected source field line is traced down to auroral altitudes on the concurrent DE 1 auroral image, a striking correspondece between the AKR source field line and localized auroral features is produced. The magnetic mapping study provides strong evidence that AKR sources occur on field lines associated with discrete auroral arcs, and it provides confirmation that AKR is generated near the electron cyclotron frequency.

Huff, R. L.↗

NASA NTRS2012

A Suzaku View of Cyclotron Line Sources and Candidates

Seventeen accreting neutron star pulsars, mostly high mass X-ray binaries with half of them Be-type transients, are known to exhibit Cyclotron Resonance Scattering Features (CRSFs) in their X-ray spectra, with characteristic line energies from 10 to 60 keY. To date about two thirds of them, plus a few similar systems without known CRSFs, have been observed with Suzaku. We present an overview of results from these observations, including the discovery of a CRSF in the transient IA1118-61 and pulse phase resolved spectroscopy of OX 301-2. These observations allow for the determination of cyclotron line parameters to an unprecedented degree of accuracy within a moderate amount of observing time. This is important since these parameters vary - e.g., with orbital phase, pulse phase, or luminosity - depending on the geometry of the magnetic field of the pulsar and the properties of the accretion column at the magnetic poles. We briefly introduce a spectral model for CRSFs that is currently being developed and that for the first time is based on these physical properties. In addition to cyclotron line measurements, selected highlights from the Suzaku analyses include dip and flare studies, e.g., of 4U 1907+09 and Vela X-I, which show clumpy wind effects (like partial absorption and/or a decrease in the mass accretion rate supplied by the wind) and may also display magnetospheric gating effects.

Pottschmidt, K.↗

NASA NTRS1979

Diffuse Jovian aurora influenced by plasma injection from Io

The paper demonstrates that the broad band of whistler-mode waves observed within the high density torus surrounding Io is consistent with electron cyclotron generation. Cyclotron resonant instability of Jovian energetic electrons is enhanced due to the lower resonant electron energy within the equatorial high density plasma torus surrounding the orbit of Io. The higher energy resonant electron scattering and the corresponding energetic electron lifetimes indicate that an efficient local acceleration process is required to replenish the precipitating relativistic electrons. Calculated energy deposition into the Jovian atmosphere should provide a dominant source of middle atmospheric ionization and excite a continuous band of diffuse auroral emission. It is suggested that the diffuse Jovian aurora should be influenced by the variable volcanic activity on Io which is thought to be an important source of plasma, since the cyclotron scattering process is strongly influenced by the ambient equatorial thermal plasma density.

Thorne, R. M.↗

NASA NTRS2016

Maven Observations of Electron-Induced Whistler Mode Waves in the Martian Magnetosphere

We report on narrowband electromagnetic waves at frequencies between the local electron cyclotron and lower hybrid frequencies observed by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft in the Martian induced magnetosphere. The peaked electric field wave spectra below the electron cyclotron frequency were first observed by Phobos-2 in the Martian magnetosphere, but the lack of magnetic field wave data prevented definitive identification of the wave mode and their generation mechanisms remain unclear. Analysis of electric and magnetic field wave spectra obtained by MAVEN demonstrates that the observed narrowband waves have properties consistent with the whistler mode. Linear growth rates computed from the measured electron velocity distributions suggest that these whistler mode waves can be generated by cyclotron resonance with anisotropic electrons. Large electron anisotropy in the Martian magnetosphere is caused by absorption of parallel electrons by the collisional atmosphere. The narrowband whistler mode waves and anisotropic electrons are observed on both open and closed field lines and have similar spatial distributions in MSO and planetary coordinates. Some of the waves on closed field lines exhibit complex frequency-time structures such as discrete elements of rising tones and two bands above and below half the electron cyclotron frequency. These MAVEN observations indicate that whistler mode waves driven by anisotropic electrons, which are commonly observed in intrinsic magnetospheres and at unmagnetized airless bodies, are also present at Mars. The wave-induced electron precipitation into the Martian atmosphere should be evaluated in future studies.

martian↗

NASA NTRS1987

Electromagnetic ion beam instabilities - Growth at cyclotron harmonic wave numbers

The linear theory of electromagnetic ion beam instabilities for arbitrary angles of propagation is studied, with an emphasis on the conditions necessary to generate unstable modes at low harmonics of the ion cyclotron resonance condition. The present results extend the analysis of Smith et al. (1985). That paper considered only the plasma parameters at a time during which harmonic wave modes were observed in the earth's foreshock. The parameters of that paper are used as the basis of parametric variations here to establish the range of beam properties which may give rise to observable harmonic spectra. It is shown that the growth rates of both left-hand and right-hand cyclotron harmonic instabilities are enhanced by an increase in the beam temperature anisotropy and/or the beam speed. Decreases in the beam density and/or the core-ion beta reduce the overall growth of the cyclotron harmonic instabilities but favor the growth of these modes over the growth of the nonresonant instability and thereby enhance the observability of the harmonics.

Smith, Charles W.↗

NASA NTRS1992

Sulfur and nitrogen reactions for cometary comae ion chemistry

The low pressure reactions of sulfur dioxide, carbon disulfide, and hydrazine with H2O+ and H3O+ were studied by the ion cyclotron resonance technique. These reactions are potentially important for sulphur chemistry in cometary comae. Rate coefficients and branching ratios of product channels are presented.

NASA Center JPL↗

NASA NTRS2020

NuSTAR Observation of GROJ1744−28 at Low Mass Accretion Rate

Context.Neutron stars in low-mass X-ray binaries (LMXBs) are important systems to study the physics of accretion onto compact ob-jects. The system GRO J1744−28 is particularly interesting, as it usually shows clear pulsations as well as X-ray bursts. Additionally,there are claims for a magnetic field of 5×1011G through the detection of a Cyclotron Resonant Scattering Feature (CRSF).Aims.We present the spectral analysis of GRO J1744−28 using∼29 ks of NuSTAR data taken in 2017 February at a low luminosityof 3.2×1036erg s−1(3–50 keV). Our goal is to study the variability of the source spectrum with pulse phase and to search for the claimed CRSF. Methods.The continuum spectrum is modeled with an absorbed power-law with exponential cut-off, and an additional iron line component. We find no obvious indications for a CRSF and therefore perform a detailed cyclotron line search using statistical methods.We perform this search on pulse phase-averaged as well as phase-resolved spectra. Results.GRO J1744−28 was observed at one of the lowest luminosities studied so far. The previously detected Type II X-ray bursts re absent. Clear pulsations at a period of 2.141124(9) Hz are detected. The pulse profile shows an indication of a secondary peak,which was not seen at higher flux. The 4σupper limit for the strength of a CRSF in the 3–20 keV band is 0.07 keV, lower than the strength of the line found at higher luminosity. Conclusions.The detection of pulsations shows that the source did not enter the “propeller” regime, even though the source flux of4.15×10−10erg cm−2s−1was almost one order of magnitude below the threshold for the propeller regime claimed in previous studies on this source. The transition into the propeller regime in GRO J1744−28 must therefore be below a luminosity of 3.2×1036erg s−1(3–50 keV), which implies a surface magnetic field.2.9×1011G and mass accretion rate.1.7×1016g s−1. A change of the CRSF depth as function of luminosity is not unexpected and has been observed in other sources. This result possibly implies a change in emission geometry as function of mass accretion rate to reduce the depth of the line below our detection limit.

Ole König↗

NASA NTRS2014

NuSTAR Discovery of a Cyclotron Line in KS 1947+300

We present a spectral analysis of three simultaneous Nuclear Spectroscopy Telescope Array and Swift/XRT observations of the transient Be-neutron star binary KS 1947+300 taken during its outburst in 2013/2014. These broadband observations were supported by Swift/XRTmonitoring snapshots every three days, which we use to study the evolution of the spectrum over the outburst.We find strong changes of the power-law photon index, which shows a weak trend of softening with increasing X-ray flux. The neutron star shows very strong pulsations with a period of P ≈ [almost equal to] 18.8 s. The 0.8-79 keV broadband spectrum can be described by a power law with an exponential cutoff and a blackbody component at low energies. During the second observation we detect a cyclotron resonant scattering feature at 12.5 keV, which is absent in the phase-averaged spectra of observations 1 and 3. Pulse phase-resolved spectroscopy reveals that the strength of the feature changes strongly with pulse phase and is most prominent during the broad minimum of the pulse profile. At the same phases the line also becomes visible in the first and third observation at the same energy. This discovery implies that KS 1947+300 has a magnetic field strength of B ≈ [almost equal to] 1.1 × 1012(1 + z) G, which is at the lower end of known cyclotron line sources.

radiation: dynamics↗

NASA NTRS1994

Semiannual Status Report

During the last six months, we have continued our study of the excitation of electromagnetic waves in the whistler frequency range and the role that these waves will play in the acceleration of electrons and ions in the auroral region. A paper entitled 'Electron Beam Excitation of Upstream Waves in the Whistler Mode Frequency Range' was listed in the Journal of Geophysical Research. In this paper, we have shown that an anisotropic electron beam (or gyrating electron beam) is capable of generating both left-hand and right-hand polarized electromagnetic waves in the whistler frequency range. Since right-hand polarized electromagnetic waves can interact with background electrons and left-hand polarized waves can interact with background ions through cyclotron resonance, it is possible that these beam generated left-hand and right-hand polarized electromagnetic waves can accelerate either ions or electrons (or both), depending on the physical parameters under consideration. We are currently carrying out a comprehensive study of the electromagnetic whistler and lower hybrid like waves observed in the auroral zone using both wave and particle data. Our first task is to identify these wave modes and compare it with particle observations. Using both the DE-1 particle and wave measurements, we can positively identify those electromagnetics lower hybrid like waves as fast magnetosonic waves and the upper cutoff of these waves is the local lower hybrid frequency. From the upper cutoff of the frequency spectrum, one can infer the particle density and the result is in very good agreement with the particle data. Since these electromagnetic lower hybrid like waves can have frequencies extended down to the local ion cyclotron frequency, it practically confirms that they are not whistler waves.

Source record↗

NASA NTRS2021

Continuum, cyclotron line, and absorption variability in the high-mass X-ray binary Vela X-1

Because of its complex clumpy wind, prominent cyclotron resonant scattering features, intrinsic variability, and convenient physical parameters (close distance, high inclination, and small orbital separation), which facilitate the observation and analysis of the system, Vela X-1 is one of the key systems for understanding accretion processes in high-mass X-ray binaries on all scales. We revisit Vela X-1 with two new observations taken with NuSTAR at orbital phases ∼0.68–0.78 and ∼0.36–0.52, which show a plethora of variability and allow us to study the accretion geometry and stellar wind properties of the system. We follow the evolution of spectral parameters down to the pulse period timescale using a partially covered power law continuum with a Fermi-Dirac cutoff to model the continuum and local absorption. We are able to confirm anti-correlations between the photon index and the luminosity and, for low fluxes, between the folding energy and the luminosity, implying a change of properties in the Comptonising plasma. We were not able to confirm a previously seen correlation between the cyclotron line energy and the luminosity of the source in the overall observation, but we observed a drop in the cyclotron line energy following a strong flare. We see strong variability in absorption between the two observations and within one observation (for the ∼0.36–0.52 orbital phases) that can be explained by the presence of a large-scale structure, such as accretion and photoionisation wakes in the system, and our variable line of sight through this structure.

C. M. Diez↗

NASA NTRS1968

Physics

Ion cyclotron resonance study of energy dependence of ion-molecule reaction in gaseous hydrogen, and fluorine 19 isotopic NMR chemical shifts due to chlorine 35 and chlorine 37 isotopes

Source record↗