The Axial Double Probe (ADP) instrument measures the DC to ∼100 kHz electric field along the spin axis of the Magnetospheric Multiscale (MMS) spacecraft (Burch et al., Space Sci. Rev., 2014, this issue ), completing the vector electric field when combined with the spin plane double probes (SDP) (Torbert et al., Space Sci. Rev., 2014, this issue , Lindqvist et al., Space Sci. Rev., 2014, this issue ). Two cylindrical sensors are separated by over 30 m tip-to-tip, the longest baseline on an axial DC electric field ever attempted in space. The ADP on each of the spacecraft consists of two identical, 12.67 m graphite coilable booms with second, smaller 2.25 m booms mounted on their ends. A significant effort was carried out to assure that the potential field of the MMS spacecraft acts equally on the two sensors and that photo- and secondary electron currents do not vary over the spacecraft spin. The ADP on MMS is expected to measure DC electric field with a precision of ∼1 mV/m, a resolution of ∼25 μV/m, and a range of ∼±1 V/m in most of the plasma environments MMS will encounter. The Digital Signal Processing (DSP) units on the MMS spacecraft are designed to perform analog conditioning, analog-to-digital (A/D) conversion, and digital processing on the ADP, SDP, and search coil magnetometer (SCM) (Le Contel et al., Space Sci. Rev., 2014, this issue ) signals. The DSP units include digital filters, spectral processing, a high-speed burst memory, a solitary structure detector, and data compression. The DSP uses precision analog processing with, in most cases, >100 dB in dynamic range, better that −80 dB common mode rejection in electric field ( E ) signal processing, and better that −80 dB cross talk between the E and SCM ( B ) signals. The A/D conversion is at 16 bits with ∼1/4 LSB accuracy and ∼1 LSB noise. The digital signal processing is powerful and highly flexible allowing for maximum scientific return under a limited telemetry volume. The ADP and DSP are described in this article.

The Student Dust Counter (SDC) experiment of the New Horizons Mission is an impact dust detector to map the spatial and size distribution of dust along the trajectory of the spacecraft across the solar system. The sensors are thin, permanently polarized polyvinylidene fluoride (PVDF) plastic films that generate an electrical signal when dust particles penetrate their surface. SDC is capable of detecting particles with masses m>10−12 g, and it has a total sensitive surface area of about 0.1 m2, pointing most of the time close to the ram direction of the spacecraft. SDC is part of the Education and Public Outreach (EPO) effort of this mission. The instrument was designed, built, tested, integrated, and now is operated by students.

The possibility is investigated that a significant fraction of the X-ray background in the energy range 0.2–0.28 keV originates in the geocorona through bremsstrahlung. It is concluded that the geocoronal flux must be substantial at some times and the possibility exists that an observable geocoronal background exists at all times. The existing data on the soft X-ray background is found to be compatible with the hypothesis of a geocoronal component.

view Abstract Citations References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Effect of the GUM Nebula on Soft X-Rays from Galactic Sources Mack, John E. Abstract The effect of He ionization in the Gum Nebula on the observed soft X-ray flux from galactic sources is investigated. A strong enhancement is predicted if a substantial fraction of He in the nebula is doubly ionized. Because of the high recombination rate of He iii, this effect can be used to distinguish between "instantaneous" ionization models of the nebula, and models where the ionization mechanism persists for 10 years. A preliminary calculation, based on published results of a single observation, supports a nebula model in which the fraction of He iii is low. Subject headings: excitation and ionization - nebulae - supernovae remnants - X-rays Publication: The Astrophysical Journal Pub Date: October 1973 DOI: 10.1086/152418 Bibcode: 1973ApJ...185..323M full text sources ADS |

view Abstract Citations (3) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observational Evidence against Supernovae Being the Source of the Universal X-Ray Background Mack, John E. ; Robbins, Donald E. Abstract An analysis has been made of the theory that the universal X-ray background originates in supernovae. Observational evidence relating to such theories has been critically examined. it is concluded that evidence presently exists which can be interpreted to exclude such theories of the origin of the background radiation, regardless of the timescale of the X-ray emission from a supernova. Publication: The Astrophysical Journal Pub Date: August 1972 DOI: 10.1086/151612 Bibcode: 1972ApJ...176...99M full text sources ADS |

WICKRAMASINGHE1 has put forward a hypothesis about the alignment mechanism by which interstellar grains may be lined up in accordance with the requirements of the measurements of interstellar polarization. His hypothesis involves the effect of galactic X-rays on grains. The energy range of photons which would be effective through this mechanism is 0.2–0.4 keV. The flux required in this range is 300 keV cm−2 s−1, which must be in the plane of the galaxy and be in excess of any flux from directions far from parallel to the galactic plane. In this letter I will estimate the X-ray intensities which, according to the data available at present, actually occur in this energy range in the galaxy.

Cooke, Griffiths and Pounds1 have recently reported an excess in the diffuse X-ray background intensity observed at low galactic latitudes, compatible with a line source of radiation in the galactic plane. Wickramasinghe2 has put forward an explanation based on small angle scattering of the universal isotropic flux of X-rays by grains in the galaxy. The purpose of this article is seriously to question this hypothesis. Briefly, Wickramasinghe first argues that the albedo of the galaxy is near unity in the X-ray band, that is, the scattering cross-section of galactic material is quite high in certain directions, while the absorption cross-section is quite low. The second point in the argument is a derivation of a first order solution to the scattered component of the diffuse X-ray background. The answer obtained is where θ is the angle of the detector axis with the galactic plane, I1 is the intensity of once-scattered X-rays observed in the direction θ, and I is the intensity of extra-galactic diffuse X-rays. Hence the observed intensity in a direction close to the plane would be about double that observed at large θ.

The cosmic X-ray background has been found to be anisotropic. It is interpreted as being made up of two components: an isotropic background, possibly of extragalactic origin, and an anomalous emission, perhaps located within the Galaxy.