ALBERT

Description: This study examined the association between local insulin-like growth factor I (IGF-I) overexpression and atrophy in skeletal muscle. We hypothesized that endogenous skeletal muscle IGF-I mRNA expression would decrease with hindlimb unloading (HU) in mice, and that transgenic mice overexpressing human IGF-I (hIGF-I) specifically in skeletal muscle would exhibit less atrophy after HU. Male transgenic mice and nontransgenic mice from the parent strain (FVB) were divided into four groups (n = 10/group): 1) transgenic, weight-bearing (IGF-I/WB); 2) transgenic, hindlimb unloaded (IGF-I/HU); 3) nontransgenic, weight-bearing (FVB/WB); and 4) nontransgenic, hindlimb unloaded (FVB/HU). HU groups were hindlimb unloaded for 14 days. Body mass was reduced (P 〈 0.05) after HU in both IGF-I (-9%) and FVB mice (-13%). Contrary to our hypothesis, we found that the relative abundance of mRNA for the endogenous rodent IGF-I (rIGF-I) was unaltered by HU in the gastrocnemius (GAST) muscle of wild-type FVB mice. High-level expression of hIGF-I peptide and mRNA was confirmed in the GAST and tibialis anterior (TA) muscles of the transgenic mice. Nevertheless, masses of the GAST and TA muscles were reduced (P 〈 0.05) in both FVB/HU and IGF-I/HU groups compared with FVB/WB and IGF-I/WB groups, respectively, and the percent atrophy in mass of these muscles did not differ between FVB and IGF-I mice. Therefore, skeletal muscle atrophy may not be associated with a reduction of endogenous rIGF-I mRNA level in 14-day HU mice. We conclude that high local expression of hIGF-I mRNA and peptide in skeletal muscle alone cannot attenuate unloading-induced atrophy of fast-twitch muscle in mice.

Description: The Hard X-Ray Burst Spectrometer (HXRBS) group at GSFC has developed and is maintaining a quick-look analysis system for solar flare hard x-ray data from the Burst and Transient Source Experiment (BATSE) on the recently launched Compton Gamma-Ray Observatory (GRO). The instrument consists, in part, of 8 large planar detectors, each 2025 sq cm, placed on the corners of the GRO spacecraft with the orientation of the faces being those of a regular octahedron. Although optimized for the detection of gamma-ray bursts, these detectors are far more sensitive than any previous spacecraft-borne hard x-ray flare instrumentation both for the detection of small microflares and the resolution of fine temporal structures. The data in this BATSE solar data base are from the discriminator large area (DISCLA) rates. From each of eight detectors there are hard x-ray data in four energy channels, 25-50, 50-100, 100-300, and greater than 300 keV with a time resolution of 1.024 seconds. These data are suitable for temporal correlation with data at other wavelengths, and they provide a first look into the BATSE and other GRO instrument flare data sets. The BATSE and other GRO principle investigator groups should be contacted for the availability of data sets at higher time or spectral resolution or at higher energies.

Description: Active Region 5395 produced an exceptional series of hard x ray bursts notable for their frequency, intensity, and impulsivity. Over the two weeks from March 6 to 19, 447 hard x ray flares were observed by the Hard X Ray Burst Spectrometer on Solar Maximum Mission (HXRBS/SMM), a rate of approx. 35 per day which exceeded the previous high by more than 50 percent. During one 5 day stretch, more than 250 flares were detected, also a new high. The three largest GOES X-flares were observed by HXRBS and had hard x ray rates over 100,000 s(exp -1) compared with only ten flares above 100,000(exp -1) during the previous nine years of the mission. An ongoing effort for the HXRBS group has been the correlated analysis of hard x ray data with flare data at other wavelengths with the most recent emphasis on those measurements with spatial information. During a series of bursts from AR 5395 at 1644 to 1648 UT on 12 March 1989, simultaneous observations were made by HXRBS and UVSP (Ultra Violet Spectrometer Polarimeter) on SMM, the two-element Owens Valley Radio Observatory (OVRO) interferometric array, and R. Canfield's H-alpha Echelle spectrograph at the National Solar Observatory at Sacramento Peak. The data show strong correlations in the hard x ray, microwave, and UV lightcurves. This event will be the subject of a combined analysis.

Description: This event list is a comprehensive reference for all Hard X ray bursts detected with the Hard X Ray Burst Spectrometer on the Solar Maximum Mission from the time of launch on Feb. 14, 1980 to the end of the mission in Dec. 1989. Some 12,776 events were detected in the energy range 30 to 600 keV with the vast majority being solar flares. This list includes the start time, peak time, duration, and peak rate of each event.

Description: Solar flare data from June 27, 1980 balloon-based observations were studied in terms of the hard X ray component. A temporal delay of 3 sec was observed for the X ray emissions above 235 keV. The delay occurred relative to the low-energy electrons and indicated a second acceleration stage. An estimation of the acceleration rate of the first-order Fermi process operating in a closed flare loop was found to be in agreement with the resulting data, including the acceleration of both protons and relativistic electrons. Additional support for the first-order Fermi process is noted in the fact that flares generally occur in magnetic loops, a condition which allows energetic particles to continually interact with the upward moving shock fronts. A correlation has also been observed between the delay times and the H-alpha areas, encouraging the interpretation that the delay times are the shock transit times.

Description: High-resolution (approximately 1 keV FWHM) spectral measurements from 13 to 300 keV of a solar flare hard X-ray burst observed on 1980 June 27 by a balloon-borne array of cooled germanium planar detectors are presented. At energies below about 35 keV, a new component of solar flare hard X-rays is identified. This component is characterized by an extremely steep spectrum which fits closely to that from a Maxwellian electron distribution with a maximum temperature of about 34 x 10 to the 6th K and an emission measure of 2.9 x 10 to the 48th per cu cm. This hot isothermal component appears at the peak of the normal power-law-like impulsive X-ray burst component, and it remains isothermal and dominates the X-ray emission below about 30 keV through the decay of the flare event.

Description: This report describes work performed under contract NAS5-32584 for Phase 3 of the Compton Gamma Ray Observatory (CGRO) from 1 November 1993 through 1 November 1994. We have made spectral observations of the hard x-ray and gamma-ray bremsstrahlung emissions from solar flares using the Burst and Transit Source Experiment (BASTE) on CGRO. These measurements of their spectrum and time profile provided valuable information on the fundamental flare processes of energy release, particle acceleration, and energy transport. Our scientific objective was to study both the thermal and non-thermal sources of solar flare hard x-ray and gamma-ray emission.

Description: Using balloon-borne instrumentation of very high sensitivity, approximately 25 hard X-ray bursts with peak fluxes of above 7 x 10 to the -3rd/(sq cm s keV) at 20 keV have been detected, in 141 minutes of observation of the sun on June 27, 1980. These hard X-ray microflares last from a few seconds to several tens of seconds and have power-law energy spectra. They are generally accompanied by small soft X-ray bursts, but H-alpha flares and solar radio bursts are reported for only a few of these hard X-ray bursts. The integral number of events varies approximately as the inverse of the peak flux, down to the limits of the measurements. These observations suggest that even very small transient releases of energy by the sun may be primarily nonthermal in character. It is speculated that the energy released in accelerated electrons for these microflares, averaged over time, may contribute significantly to the heating of the active corona.

Description: We compare the microwave, H-alpha, and hard X-ray observations for a west limb C7.3 flare that occurred at 17:10 UT, 1992 June 26. H-alpha movies were obtained at Big Bear Solar Observatory. Before the onset of the flare, overexposed H-alpha images show the complicated flux loop structure above the limb. Material was observed to descend along the loops toward the site where the flare occurred hours later. Using the five-antenna solar array at Owens Valley Radio Observatory, we obtain two-dimensional maps of flare emission from 1.4 to 14 GHz. In all three temporal peaks of the microwave bursts, the maps show the same characteristics. The peak low-frequency emission comes from the top of one bundle of the H-alpha loops and gradually shifts to the foot-point of the loops (the location of H-alpha flare) as the frequency increases. The location of the emission peak shifts 88 sec between 1 and 14 GHz. Seventy percent of the shift occurs between 1 and 5 GHz. The locus of the shift of the emission peak follows the shape of an H-alpha surge that occurred after the flare. For each point along the locus, we create the microwave brightness temperature spectrum and compare the radio-derived electron distribution with that derived from the high-resolution hard X-ray spectra measured with Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO). We find that the peak frequency changes from approximately 3 GHz at the loop top to approximately 7 GHz at the footprint, presumably due to the increase of the magnetic field from approximately 160 GHz at the loop top to approximately 300 G at the footpoint. The high-frequency slope of the microwave power-law spectrum decreases from approximately 10 at the loop top to approximately 5 at the footprint due to a change in the energy distribution of the dominant electrons. The microwave brightness temperature spectral index predicted by the BATSE power-law hard X-ray spectra agrees with the measured value only at the footpoint. At the loop top, the emission may be thermal gyrosynchrotron with a temperature of 3.5 x 10(exp 7) K, which is likely to correspond to the superhot component seen in the hard X-ray emission.

Description: We compare X-ray, microwave and H-alpha observations for the 1992 January 13 limb flare. The soft and hard X-ray images of the flare have been studied thoroughly by Masuda et al. (1994) with Yohkoh SXT and HXT images. We find that during the hard X-ray emission peak there is no H-alpha brightening on the disk nor at the limb, so the main ribbons of this flare must be beyond the limb. The microwave source maintains a fixed distance about 10 arcsecs from the optical limb in the frequency range 2.8-14.0 GHz. We interpret this limit in source position as due to the presence of a microwave limb that extends higher than the white-light limb -- to a height of 7300 +/- 1500 km. We believe that the high-frequency microwave emissions are occulted by this extended limb, while the soft and hard X-ray emissions are able to pass through largely unaffected. We also believe, however, that the hard X-ray footpoints are also partially occulted by the photospheric limb, despite the appearance of 'footpoint sources' in HXT data shown by Masuda et al. The smooth X-ray and microwave time profiles, microwave-rich emission relative to hard X-rays, and progressive hard X-ray spectral hardening through the flare peak are all characteristics that we interpret as being a direct result of the occultation of footpoint emission.