Review of radiation belt relativistic electron losses

A high energy (35 MeV) gamma ray telescope employing a thirty-two level magnetic core spark chamber system was flown on SAS 2. The high energy galactic gamma radiation is observed to dominate over the general diffuse radiation along the entire galactic plane, and when examined in detail, the longitudinal and latitudinal distribution seem generally correlated with galactic structural features, particularly with arm segments. The general high energy gamma radiation from the galactic plane, explained on the basis of its angular distribution and magnitude, probably results primarily from cosmic ray interactions with interstellar matter.

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High energy gamma ray results from the second small astronomy satellite

We use Swift/BAT Earth occultation data at different geomagnetic latitudes to derive a sensitive measurement of the Cosmic X-ray background (CXB) and of the Earth albedo emission in the 15–200keV band. We compare our CXB spectrum with recent (INTEGRAL, BeppoSAX) and past results (HEAO-1) and find good agreement. Using an independent measurement of the CXB spectrum we are able to confirm our results. This study shows that the BAT CXB spectrum has a normalization � 8 ± 3% larger than the HEAO-1 measurement. The BAT accurate Earth albedo spectrum can be used to predict the level of photon background for satellites in low Earth and mid inclination orbits.

http://iopscience.iop.org/article/10.1086/592595/pdf

Cosmic X-Ray Background and Earth Albedo Spectra with Swift BAT

Suzaku Hard X-ray Detector (HXD) achieved the lowest background level than any other previously or currently operational missions sensitive in the energy range of 10–600 keV, by utilizing PIN photodiodes and GSO scintillators mounted in BGO active shields to reject particle background and Compton-scattered events as much as possible. Because it does not have an imaging capability nor rocking mode for the background monitor, the sensitivity is limited by the reproducibility of the non X-ray background (NXB) model. We modeled the HXD NXB, which varies with time as well as other satellites with a low-Earth orbit, by utilizing several parameters, including particle monitor counts and satellite orbital/attitude information. The model background is supplied as an event file in which the background events are generated by random numbers, and can be analyzed in the same way as the real data. The reproducibility of the NXB model depends on the event selection criteria (such as cut-off rigidity and energy band) and the integration time, and the 1 systematic error is estimated to be less than 3% (PIN 15–40 keV) and 1% (GSO 50–100 keV) for more than 10 ks exposure.

/pdf/modeling-and-reproducibility-of-suzaku-hxd-pin-gso-44fz9x2kjr.pdf

Modeling and Reproducibility of Suzaku HXD PIN/GSO Background

Suzaku Hard X-ray Detector (HXD) achieved the lowest background level than any other previously or currently operational missions sensitive in the energy range of 10--600 keV, by utilizing PIN photodiodes and GSO scintillators mounted in the BGO active shields to reject particle background and Compton-scattered events as much as possible. Because it does not have imaging capability nor rocking mode for the background monitor, the sensitivity is limited by the reproducibility of the non X-ray background (NXB) model. We modeled the HXD NXB, which varies with time as well as other satellites with a low-earth orbit, by utilizing several parameters, including particle monitor counts and satellite orbital/attitude information. The model background is supplied as an event file in which the background events are generated by random numbers, and can be analyzed in the same way as the real data. The reproducibility of the NXB model depends on the event selection criteria (such as cut-off rigidity and energy band) and the integration time, and the 1sigma systematic error is estimated to be less than 3% (PIN 15--40 keV) and 1% (GSO 50--100 keV) for more than 10 ksec exposure.

This is a preliminary report of the first satellite observations that have been made of the intensities and energy spectra of the bremsstrahlung >50 keV produced in the atmosphere by intense widespread precipitations of energetic electrons from the outer radiation belt. The measurements afford the opportunity to investigate nearly simultaneously the energetic electron behavior on a worldwide scale during magnetic disturbances. With such a technique, one may study different features of the precipitation processes than those covered by satellite-borne particle detectors, which can provide more detailed particle information in a local region but without simultaneous measurements from many satellites can provide worldwide particle precipitation information only from long-term statistical studies. The observations are made with a 50-cm³ Ge(Li) gamma ray spectrometer that was launched aboard the spin-stabilized satellite 1972–076B into a nearly circular polar orbit at 750-km altitude on October 2, 1972. Correlative measurements of precipitating electrons are also made with an energetic electron spectrometer on board the same satellite. The longitude and hence local time extents of the precipitations are derived by least square fitting techniques from the gamma ray spectrometer responses at various spin angle orientations and satellite locations. The observations indicate the occurrence of nearly simultaneous precipitations over a wide range of local times. Significant variations occur in the intensity versus local time, but in the limited number of cases studied to date the intensities near noon are generally greater than those in the early morning hours.

Satellite observations of Bremsstrahlung from widespread energetic electron precipitation events

Data are presented on the gamma rays emitted from the atmosphere to satellite altitudes in the absence of bremsstrahlung X rays associated with electron precipitation from the radiation belts. The measurements (40 keV to 2.7 MeV) were performed with a high-resolution germanium spectrometer on board the polar-orbiting satellite 1972-076B. With the collimated spectrometer on the spinning vehicle (5-s period) it was possible to separate sensor and vehicle backgrounds from the atmospheric and diffuse cosmic contributions. The atmospheric component was obtained by unfolding published values for the diffuse cosmic spectrum. Owing to variances in the measured values of the diffuse cosmic spectrum the uncertainties in the atmospheric gamma ray spectrum are greater near the equator and at lower energies than over the polar caps and/or at higher energies, where the atmospheric gamma rays dominate, and the errors in the atmospheric spectrum associated with the diffuse component are small. The variations of the atmospheric gamma rays with invariant latitude are presented. Over the polar caps the energy spectra are similar to those observed near the magnetic equator, and the intensities are higher by about a factor of 4. The spectral indices for least squares power law fits to the continuum are −1.34 ± 0.03 and −1.39 ± 0.08 for the polar cap and equatorial regions, respectively. A search was made for gamma ray lines emitted from the atmosphere in addition to the 511-keV annihilation line. Several peaks were observed in the background spectrum, but no other lines were seen to be emitted from the atmosphere with a significant intensity.

High‐Resolution Measurements of Atmospheric Gamma Rays from a Satellite

The locations and time histories of five gamma-ray bursts that occurred between 1979 March 7 and March 31 were studied. The error box for GB 790325 has a typical dimension of about 1.5 arcmin. The other localizations, while not precise enough for thorough optical examination, contribute to distribution studies and allow radio and X-ray observations, catalog searches, and other archival work. A search through selected catalogs did reveal one object, the star FY Aql (cataloged as a Mira-type variable but probably a dwarf nova) inside one of the gamma-ray burst boxes. Given the parameters of this particular search, the probability of at least one chance association is 0.03. Both recent and archival optical examinations of some of the error boxes were carried out, and no indications of any actual physical associations were seen. One event, GB 790331, had an interesting spectral behavior, in that the leading edges of the two main peaks within the burst had harder spectra than the remainder of the event.

Locations and time histories of five 1979 gamma-ray bursts

Simultaneous mappings of bremsstrahlung X ray events from the atmosphere resulting from electron precipitation have been performed from a satellite with an array of collimated cadmium telluride spectrometers. The X ray intensities and energy spectra (> or approx. =21 keV) where measured over contiguous view directions. The satellite, P78-1, was launched into a sun-synchronous noon-midnight orbital at approx.600-km altitude on February 24, 1979, and through its spinning motion with a approx.5.5-s period provides continual scans of the X ray sources below. Data are presented from three sporadic events in which the X ray intensities varied strongly with time. Within each of these events, bursts of approx.(30--100) second duration were observed. Some of the bursts were recorded in three or four sensors, thus setting a lower limit to their spatial extent of several hundred kilometers. Other bursts appeared in only one sensor, thereby restricting the area over which they could have been generated. These bursts of X rays emanated primarily from the dusk sector, a local time region where few balloon X ray measurements have been reported. The X ray fluxes were asymmetric about local dusk, the intensities at earlier times being quite low. During one of the X ray burstsmore » in which the precipitation was confined to a relatively small spatial region it is estimated that the total number of electrons (>21 keV) precipitating into the atmosphere was approx.10/sup 23/ per second.« less

G. H. Nakano

Papers

Satellite observations of Bremsstrahlung from widespread energetic electron precipitation events

High‐Resolution Measurements of Atmospheric Gamma Rays from a Satellite

Locations and time histories of five 1979 gamma-ray bursts

Satellite X ray mappings of sporadic auroral zone electron precipitation events in the local dusk sector

Spectra Measurements of a Cosmic Gamma-Ray Burst with Fast Time Resolution