Solar Maximum Mission Satellite Research Articles

Axion-sourced fireballs from supernovae

New feebly interacting particles would emerge from a supernova core with 100-MeV-range energies and produce $\gamma$-rays by subsequent decays. These would contribute to the diffuse cosmic $\gamma$-ray background or would have shown up in the Solar Maximum Mission (SMM) satellite from SN~1987A. However, we show for the example of axion-like particles (ALPs) that, even at distances beyond the progenitor star, the decay photons may not escape, and can instead form a fireball, a plasma shell with $T\lesssim 1$ MeV. Thus, existing arguments do not exclude ALPs with few 10 MeV masses and a two-photon coupling of a few $10^{-10}~{\rm GeV}^{-1}$. However, the energy would have showed up in sub-MeV photons, which were not seen from SN 1987A in the Pioneer Venus Orbiter (PVO), closing again this new window. A careful re-assessment is required for other particles that were constrained in similar ways.

Spectropolarimetry of the Solar Mg II h and k Lines

We report on spectropolarimetric observations across the Mg II h and k-lines at 2800 angstrom made by the Ultraviolet Spectrometer and Polarimeter onboard the Solar Maximum Mission satellite. Our analysis confirms the strong linear polarization in the wings of both lines observed near the limb, as previously reported, but also demonstrates the presence of a negatively (i.e., radially oriented) polarized signal between the two lines. We find evidence for fluctuations of the polarization pattern over a broad spectral range, resulting in some depolarization with respect to the pure scattering case when observed at very low spatial and temporal resolutions. This is consistent with recent theoretical modeling that predicts this to be the result of redistribution effects, quantum interference between the atomic levels of the upper term, and magneto-optical effects. A first attempt at a quantitative exploitation of these signals for the diagnosis of magnetic fields in the chromosphere is attempted. In active regions, we present observations of circular polarization dominated by the Zeeman effect. We are able to constrain the magnetic field strength in the upper active chromosphere using an analysis based on the magnetograph formula, as justified by theoretical modeling. We inferred a significantly strong magnetic field (~500 G) at the 2.5 sigma level on an exceptionally active, flaring region.

NEON INSIGHTS FROM OLD SOLAR X-RAYS: A PLASMA TEMPERATURE DEPENDENCE OF THE CORONAL NEON CONTENT

An analysis using modern atomic data of fluxes culled from the literature for O VIII and Ne IX lines observed in solar active regions by the P78 and Solar Maximum Mission satellites confirms that the coronal Ne/O abundance ratio varies by a factor of two or more, and finds an increase in Ne/O with increasing active region plasma temperature. The latter is reminiscent of evidence for increasing Ne/O with stellar activity in low-activity coronae that reaches a "neon saturation" in moderately active stars at approximately twice the historically accepted solar value of about 0.15 by number. We argue that neon saturation represents the underlying stellar photospheric compositions, and that low activity coronae, including that of the Sun, are generally depleted in neon. The implication would be that the solar Ne/O abundance ratio should be revised upward by a factor of about two to n(Ne)/n(O)~0.3. Diverse observations of neon in the local cosmos provide some support for such a revision. Neon would still be of some relevance for reconciling helioseismology with solar models computed using recently advocated chemical mixtures with lower metal content.

Spatial and temporal variability of the gamma radiation from Earth's atmosphere during a solar cycle

The Solar Maximum Mission satellite's Gamma Ray Spectrometer spent much of its 1980–1989 mission pointed at Earth, accumulating spectra of atmospheric albedo γ‐rays. Its 28° orbit ensured that a range of geomagnetic latitudes was sampled. We measured the variation with time and cutoff rigidity of some key γ‐ray lines which are diagnostic of the intensity of the Galactic cosmic radiation penetrating the geomagnetic cutoff and of the secondary neutrons produced in the atmosphere. We found that the intensities of nuclear lines at 1.6 MeV, 2.3 MeV and 4.4 MeV varied inversely with solar activity in cycles 21–22 as expected from the theory of solar modulation of cosmic rays. They were found to be strongly anticorrelated with cutoff rigidity, as expected from the theory of the cutoff, falling by a factor ∼3.6 between the lowest (<7 GV) and highest (>13 GV) rigidities sampled. The solar cycle modulation was particularly marked at the lowest rigidities, reaching an amplitude of 16%. The ratios of the intensities of the lines produced by nuclear de‐excitation (1.6 MeV, 2.3 MeV) and those from nuclear spallation (4.4 MeV) did not vary with either solar activity or cutoff rigidity, indicating that the shape of the secondary neutron spectrum in the atmosphere above 5 MeV was approximately constant over the times and regions sampled. If it is approximated by a power law in energy, we derive constraints on the absolute value of the power law index ∼−1.15–−1.45 and better constraints on its variability, ≤5% over a solar cycle, and ≤6% over SMM's range of sampled cutoff rigidities. We also measured the intensity of the electron‐positron annihilation line at 0.511 MeV. This line also varies with the solar cycle, but its variation with cutoff rigidity is weaker than that of the nuclear lines, falling by a factor 2 (rather than 3.6) over SMM's range of sampled cutoff rigidities. This can be understood in terms of the energy dependences of the cross sections for positron production and for the hadronic interactions which produce secondary neutrons.

HIGH-SPECTRAL-RESOLUTION SOLAR IRRADIANCE IN THE 184.5 TO 232.5 nm RANGE FROM THE SOLSPEC AND UVSP SPECTROMETERS

The study of the minor constituents of the planetary atmospheres from the analysis of the scattered light properties requires the knowledge of the absolute incident solar irradiance at high resolution. The data were obtained from the UVSP experiment on board the Solar Maximum Mission satellite in the 184.5–232.5 nm spectral range. We have reconstituted the solar spectrum measured in three different regions of the solar disk with a spectral resolution of 0.01 nm and a spatial resolution of 3 arc sec. The wavelength scale was determined with a standard deviation of 0.0025 nm. The comparison of the relative intensities in three locations of the solar disk with those obtained by other authors allowed us to determine these positions accurately and to derive the integrated spectrum of the whole disk. Finally, the resulting spectrum has been expressed in absolute units using the spectral irradiance by the SOLSPEC and SUSIM spectrometers, respectively operated with the ATLAS 1 mission and from the Upper Atmosphere Research Satellite. We obtained the absolute solar irradiance with an accuracy of 10% in the 184.5–232.5 nm spectral range with a spectral resolution of 0.01 nm for the first time using data from space observations.

TheSolar Maximum MissionAtlas of Gamma‐Ray Flares

We present a compilation of data for all 258 gamma-ray —ares detected above 300 keV by the Gamma Ray Spectrometer (GRS) aboard the Solar Maximum Mission satellite. This gamma-ray —are sample was collected during the period from 1980 February to 1989 November; covering the latter half of the 21st solar sunspot cycle and the onset of the 22d solar sunspot cycle. We describe the SMM/GRS instrument, its in-orbit operation, and the principal data reduction methods used to derive the gamma-ray —are properties. Utilizing measurements for 185 —ares that were sufficiently intense to allow the derivation of gamma-ray spectra, we present an atlas of time pro—les and gamma-ray spectra. The —are parameters derived from the gamma-ray spectra include bremsstrahlung —uence and best-—t power-law parameters, narrow nuclear line —uence, positron annihilation line —uence, neutron capture line —uence, and an indi- cation of whether or not emissions greater than 10 MeV were present. Since a uniform methodology was adopted for deriving the parameters, this atlas should be very useful for future statistical and correlative studies of solar —ares. Subject headings: catalogsgamma rays: burstsSun: —ares

FexviiSoft X‐Ray Lines: Theory and Data Comparisons

Fe XVII soft X-ray spectral emission lines are examined using data from the Flat Crystal Spectrometer (FCS) on the Solar Maximum Mission satellite. Results are compared with theoretical calculations and with other recent observational results. Disparate findings from different studies on the inferred opacity of the bright resonance line at 15.01 A and on its center-to-limb behavior are reviewed. Present limitations on the use of resonance scattering to infer coronal plasma densities and absolute elemental abundances are discussed. An analysis is made of the temperature-insensitive ratio of the 15.01 A line of Fe XVII to the optically thin 16.78 A line. This analysis shows that approximately half of the photons expected in the 15.01 A line are missing from the bright emission cores of quiescent active regions on the solar disk; the missing fraction increases at most by 50% near the solar limb. If the missing flux has been resonantly scattered out of the line of sight, then the equivalent optical depth at line center of the 15.01 A line is τ0~2 on the disk, based on a simple escape probability treatment for a slab geometry. This suggests that the effects of resonance scattering for other FCS lines, with the possible exception of the O VIII doublet at 18.97 A, should be negligible for quiescent active region conditions. This is consistent with the lack of systematic center-to-limb dependence found previously for FCS lines other than Fe XVII at 15.01 A. Yohkoh Soft X-ray Telescope measurements of the expected lines of sight for active regions as a function of location on the solar disk, and resonance scattering results from other soft X-ray active region data sets all support a trend of increased opacity at the limb compared to disk center.

Detailed Evidence for Flare‐to‐Flare Variations of the Coronal Calcium Abundance

The analysis of X-ray solar flare spectra obtained by the Bent Crystal Spectrometer on board the Solar Maximum Mission satellite is presented. The ratio of the Ca XIX resonance line intensity to the nearby continuum is used to measure the calcium abundance relative to hydrogen (ACa). A description of the spectroscopic method of determining the absolute calcium abundance is given. Possible instrumental and solar effects that might influence the abundance estimates are evaluated. Over 5000 spectra from more than 100 flares are analyzed. We find a flare-to-flare variation for ACa that is not correlated with flare size, Hα importance, or with several other flare characteristics. For flares observed from two active regions, the observed value of ACa increases as a function of time. The average for all flares is ACa = (5.77 ± 1.41) × 10-6. A discussion of investigated correlations of derived ACa values with several flare characteristics is presented.

On the association of eruptive prominences, coronal holes and current sheets with the coronal mass ejections

In this paper, a study of the coronal mass ejections (CMEs) observed by Solar Maximum Mission satellite (SMM) during the period March – September, 1980, is presented. An attempt to identify various possible associations of the solar phenomena, for example, the location of coronal holes, the role of eruptive filaments or prominences, and current-sheets with the CMEs is carried out. It is shown that the combined associations of these three play an important role in the occurrence of geoeffective CMEs and also act as a tool to predict the associated geomagnetic activity.

Fe XVIII EMISSION LINES IN SOLAR X-RAY SPECTRA

Abstract : We have calculated intensity ratios for emission lines of Fe XVIII in the 19-94A wavelength range at electron temperatures characteristic of the solar corona, Te = 2-10 x 10 to the 6th power K. Our model ion includes data for transitions among the 2s22p5, 2s2p6, 2s22p43l, and 2s2p53l (l = s, p, and d) states. Test calculations that omit the 2s2p53l levels show that cascades from these are important. We compare our results with observed ratios determined from four solar X-ray instruments, a rocket-borne spectrograph, and spectrometers on the P78-1, OV1-17 and Solar Maximum Mission (SMM) satellites. In addition, we have generated synthetic spectra which we compare directly with flare observations from SMM. Agreement between theory and observation is generally quite good, with differences that are mostly less than 30%, providing limited support for the accuracy of the atomic physics data used in our calculations. However, large discrepancies are found for ratios involving the 2s22p5 2P3/2-2s2p6 2S line at 93.84A, which currently remain unexplained. Our analysis indicates that the Fe XVIII feature at 15.83A is the 2s22p5 2P3/2-2s22p4(3P)3s4 P3/2 transition, rather than 2s22p5 2P3/2-2s22p4(3P)3s 2P3/2, as suggested by some authors.

Gamma Rays from SN 1987A due to Pseudoscalar Conversion.

A light pseudoscalar coupled to two photons would be copiously emitted by the core of a supernova. Part of this flux would be converted to $\ensuremath{\gamma}$ rays by the galactic magnetic field. Measurements on the SN 1987A $\ensuremath{\gamma}$-ray flux by the Gamma-Ray Spectrometer on the Solar Maximum Mission satellite already imply a bound on the coupling $gl3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}{\mathrm{GeV}}^{\ensuremath{-}1}$. The improved generation of satellite-borne detectors, like EGRET or the project GLAST, could be able to detect a pseudoscalar-to-photon signal from a nearby supernova, for allowed values of $g$.

Microscopic and chemical analyses of major impact sites on timeband capture cell experiment of the eureca spacecraft

Extensive studies of over 100 impact sites on aluminium foils and mesh supports of the Timeband Capture Cell Experiment (TiCCE) on the European Retrievable Carrier (EuReCa) spacecraft were conducted with scanning electron microscope and energy dispersive X-ray spectrum analyser. Chemical elements of residues in and around the perforations and craters were examined to identify the origin of impactors. 73% of the impacts were classified: the minimum of 15% was due to natural particle impacts and the rest indicated high silicon presence. Possible origins of these silicon profiles were discussed. For micrometeoroid craters, the depths to diameter ratios were compared with those of meteoroid and orbital debris impacts on the Solar Maximum Mission satellite.

White-light flares observed by the solar maximum mission satellite

White-light flares observed by the solar maximum mission satellite

Search for gamma-ray emission lines from SS 433: 2: 1980-1989

We have searched through the Solar Maximum Mission satellite gamma-ray spectrometer database for evidence of red and blue Doppler-shifted 1.37 MeV (24)Mg* nuclear lines. The data were obtained between 1980 and 1989 and span a total of 720 days when SS 433 was in the field of view. No evidence of Doppler-shifted line emission was found in any of our spectra. The range of 3 sigma upper limits for individual 9 day integration periods was (0.8-2.4) x 10(exp -3) photons/sq cm/s for the blue beam, encompassing the approximately 1.5 MeV feature reported by Lamb et al., and (0.2-2.1) x 10(exp -3) photons/sq cm/s for the red beam, encompassing the reported approximately 1.2 MeV feature. The average 3 sigma upper limit in each beam for shifted 1.37 MeV was 1.5 x 10(exp -3) photons/sq cm/s for single 9 day integration. The 3 sigma upper limits over 56 9 day integration intervals (504 days) for the red beam and 69 intervals (621 days) for the blue beam are 1.2 x 10(exp -4) photons/sq cm/s. The new limits can be reconciled with the HEAO 3 results only if SS 433 emits gamma rays at or above the SMM sensitivity limit on rare occasions due to variable physical conditions in the system.

Supernova bounds on neutrino radiative decays

The Solar Maximum Mission satellite did not record any γ-ray counts in excess of the background for a time interval of 223 s after the arrival of the first ν e's from the supernova 1987A. On the basis of the original data we derive a new 3σ upper limit on the γ fluence for this period and derive improved bounds on the ν i → ν j γ and ν T → ν ee −e + γ radiative decay channels for neutrino masses up to the experimentally allowed value of around 30 MeV.

The association of Coronal Mass Ejections during solar maximum times with the heliomagnetic current sheet

The distance distribution of Coronal Mass Ejections (CMEs) with respect to the Heliomagnetic Current Sheet is studied. The analysis is carried out for all CMEs observed by the Solar Maximum Mission Satellite, years 1980 and 1984–86. We foud that during solar minimum times the CMEs are better associated with the heliomagnetic equator than at solar maximum.

Frequency distributions and correlations of solar X-ray flare parameters

We have determined frequency distributions of flare parameters from over 12000 solar flares recorded with the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission (SMM) satellite. These parameters include the flare duration, the peak counting rate, the peak hard X-ray flux, the total energy in electrons, and the peak energy flux in electrons (the latter two computed assuming a thick-target flare model). The energies were computed above a threshold energy between 25 and 50 keV. All of the distributions can be represented by power laws above the HXRBS sensitivity threshold. Correlations among these parameters are determined from linear regression fits as well as from the slopes of the frequency distributions. Variations of the frequency distributions were investigated with respect to the solar activity cycle. Theoretical models for the frequency distribution of flare parameters depend on the probability of flaring and the temporal evolution of the flare energy build-up. Our results are consistent with stochastic flaring and exponential energy build-up, with an average build-up time constant that is 0.5 times the mean time between flares. The measured distributions of flares are also consistent with predicted distributions of flares from computer simulations of avalanche models that are governed by the principle of self-organized criticality.

A statistical analysis of hard X-Ray solar flares

In this study we perform a statistical study on, 8319 X-Ray solar flares observed with the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission satellite (SMM). The events are examined in terms of the durations, maximum intensities, and intensity profiles. It is concluded that there is no evidence for a correlation between flare intensity, flare duration, and flare asymmetry. However, we do find evidence for a rapid fall-of in the number of short-duration events.

X-ray emission-line ratios in MG XI as electron temperature diagnostics for solar flares and active regions

Electron impact excitation rates for transitions in helium-like Mg XI, calculated with the R-matrix code, are used to derive the electron temperature-sensitive emission-line ratios G = [I(1s2 1S-1s2s 3S) + I(1s2 1S-1s2p 3P1,2)]/I(1s2 1S-1s2p 1P) = [I(9.314 angstrom) + I(9.232 angstrom)]/I(9.169 angstrom), R1 = I(1s2 1S-1s3p 1P)/I(1s2 1S-1s2p 1P) = I(7.850 angstrom)/I(9.169 angstrom), and R2 = I(1s2 1S-1s4p 1P)/I(1s2 1S-1s2p 1P) = I(7.472 angstrom)/I(9.169 angstrom). These are found to be significantly different from the earlier diagnostic calculations of Keenan, Tayal, & Kingston, and Keenan, Kingston, & McKenzie, and will lead to electron temperature estimates up to a factor of approximately 1.6 larger. Values of T(e) deduced from R1 and R2 ratios measured from solar flare and active region spectra obtained with the Flat Crystal Spectrometer (FCS) on board the Solar Maximum Mission (SMM) satellite are consistent, and furthermore are in good agreement with temperatures estimated from the observed G ratios for these solar features. This provides support both for the validity of the theoretical R1 and R2 diagnostics, and for the FCS calibration curve in the wavelength region covering the Mg XI transitions, 7.472-9.314 angstrom.

Accelerator measurement of NaI response to medium energy neutrons and application to a Satellite-Borne Spectrometer

We report on the response of a prototype detector to medium energy neutrons. The neutrons were produced by n-p scattering of a neutron beam on a hydrogen target. The measurements provide unique data on the efficiency and response of large NaI scintillators to neutrons in the energy range 36–709 MeV. We apply the results to the high-energy mode of the Gamma-Ray Spectrometer (GRS) on the Solar Maximum Mission satellite by estimating its efficiency for neutron detection. This estimate is compared to earlier Monte Carlo calculations of the GRS efficiency.