ALBERT

Description: During its full-sky survey, the Energetic Gamma Ray Experiment Telescope (EGRET) high-energy instrument aboard the Compton Gamma-Ray Observatory detected gamma-ray emission in the energy range above 30 MeV from a source identified as the blazar PKS 0420-014. This object was observed during two separate viewing periods in 1992 February/March and May/June. An intensity decrease above 100 MeV of a factor of at least 1.5 from a maximum of (5.0 +/- 1.4) x 10(exp -7) photons 1 sq cm/s was observed during that time interval indicating extensive variability. The photon spectrum in the range between 30 and 10,000 MeV at the time of the maximum intensity is well represented by a power law with an exponent of -1.9 +/- 0.3. Some similarities with other EGRET detected blazars are briefly discussed.

Description: Multi-instrument data sets from the ground and satellites at both low and high altitude have provided new results concerning substorm onset and its source region in the magnetosphere. Twenty-six out of 37 substorm onset events showed evidence of azimuthally spaced auroral forms (AAFs) prior to the explosive poleward motion associated with optical substorm onset. AAFs can span 8 hours of local time prior to onset and generally propagate eastward in the morning sector. Onset itself is, however, more localized spanning only about 1 hour local time. AAF onset occur during time periods when the solar wind pressure is relatively high. AAFs brighten in conjunction with substorm onset leading to the conclusion that they are a growth phase activity casually related to substorm onset. Precursor activity associated with these AAFs is also seen near geosynchronous orbit altitude and examples show the relationship between the various instrumental definitions of substorm onset. The implied mode number (30 to 135) derived from this work is inconsistent with cavity mode resonances but is consistent with a modified flute/ballooning instability which requires azimuthal pressure gradients. The extended source region and the distance to the open-closed field line region constrain reconnection theory and local mechanisms for substorm onset. It is demonstrated that multiple onset substorms can exist for which localized dipolarizations and the Pi 2 occur simultaneously with tail stretching existing elsewhere. These pseudobreakups can be initiated by auroral streamers which originate at the most poleward set of arc systems and drift to the more equatorward main UV oval. Observations are presented of these AAFs in conjunction with low- and high-altitutde particle and magnetic field data. These place the activations at the interface between dipolar and taillike field lines probably near the peak in the cross-tail current. These onsets are put in the context of a new scenario for substorm morphology which employs individual modules which operate independently or couple together. This allows particular substorm events to be more accurately described and investigated.

Description: The dual jet aircraft Sprites94 campaign yielded the first color imagery and unambiguously triangulated physical dimensions and heights of upper atmospheric optical emissions associated with thunderstorm systems. Low light level television images, in both color and in black and white (B/W), obtained during the campaign show that there are at least two distinctively different types of optical emissions spanning part or all of the distance between the anvil tops and the ionosphere. The first of these emissions, dubbed 'sprites' after their elusive nature, are luminous structures of brief (less than 16 ms) duration with a red main body that typically spans the latitude range 50-90 km, and possessing lateral dimensions of 5-30 km. Faint bluish tendrils often extend downward from the main body of sprites, occasionally appearing to reach cloud tops near 20 km. In this paper the principal characteristics of red sprites as observed during the Sprites94 campaign are described. The second distinctive type of emissions, 'blue jets,' are described in a companion paper (Wescott et al., this issue).

Description: We present radio observations of the gravitational lens PKS 1830-211 at 8.4 and 15 GHz acquired using the Very Large Array. The observations were made over a 13 month period. Significant flux density changes over this period provide strong constraints on the time delay between the two lensed images and suffest a value of 44 +/- 9 days. This offers new direct evidence that this source is indeed a gravitational lens. The lens distance is dependent upon the model chosen, but reasonable limits on the mass of the lensing galaxy suggest that it is unlikely to be at a redshift less than a few tenths, and may well be significantly more distant.

Description: A nonlinear filtering method is introduced for the study of the solar wind -- magnetosphere coupling and related to earlier linear techniques. The filters are derived from the magnetospheric state, a representation of the magnetospheric conditions in terms of a few global variables, here the auroral electrojet indices. The filters also couple to the input, a representation of the solar wind variables, here the rectified electric field. Filter-based iterative prediction of the indices has been obtained for up to 20 hours. The prediction is stable with respect to perturbations in the initial magnetospheric state; these decrease exponentially at the rate of 30/min. The performance of the method is examined for a wide range of parameters and is superior to that of other linear and nonlinear techniques. In the magnetospheric state representation the coupling is modeled as a small number of nonlinear equations under a time-dependent input.

Description: Initial observations of a newly documented type of optical emission above thunderstorms are reported. 'Blue jets', or narrowly collimated beams of blue light that appear to propagate upwards from the tops of thunderstorms, were recorded on B/W and color video cameras for the first time during the Sprites94 aircraft campaign, June-July, 1994. The jets appear to propagate upward at speeds of about 100 km/s and reach terminal altitudes of 40-50 m. Fifty six examples were recorded during a 22 minute interval during a storm over Arkansas. We examine some possible mechanisms, but have no satisfactory theory of this phenomenon.

Description: The poleward arc system of a double oval distribution is shown to activate at the end of the optical expansion phase signifying the beginning of substorm recovery. The velocity dispersed ion signature (VDIS) can exist coincident with this discrete aurora developing on the most poleward oval. Although the VDIS is usually associated with ion beams in the plasma sheet boundary layer, it is demonstrated that the ionospheric signature is not beamlike but distributed in pitch angle. At the time when the double oval begins to form, the magnetic field in the magnetotail lobe becomes less flared and can show Pc 5 period oscillations. Similar pulsations also exist in the ionosphere associated with the most poleward oval and with stationary surge formation. Theoretical considerations link this phenomenon with a wave source tailward of x(sub GSE) = -30R(sub E) and fast mode evanescent waves propagating earthward in the tail lobe region. In this case the magnetotail appears to act like a waveguide and the plasma sheet boundary layer as a resonance region. This implies that the coupling of this fast mode waves is with the plasma sheet boundary layer and not with dipolar like field lines. The implications of this for the reconnection model of substorms are discussed.

Description: During the later stages of the auroral substorm the luminosity distribution frequently resembles a double oval, one oval lying poleward of the normal or main UV auroral oval. We interpret the double oval morphology as being due to the plasma sheet boundary layer becoming active in the later stages of the substorm process. If the disturbance engulfs the nightside low-latitude boundary layers, then the double oval configuration extends into the dayside ionospheric region. The main UV oval is associated with the inner portion of the central plasma sheet and can rapidly change its auroral character from being diffuse to discrete. This transition is associated with the substorm process and is fundamental to understanding the near-Earth character of substorm onset. On the other hand, the poleward arc system in the nightside ionosphere occurs adjacent to or near the open-closed field line boundary. This system activates at the end of the optical expansion phase and is a part of the recovery phase configuration in substorms where it occurs. These two source regions for nightside discrete auroral arcs are important in resolving the controversy concerning the mapping of arcs to the magnetosphere. The dayside extension of this double oval configuration is also investigated and shows particle signatures which differ considerably from those on the nightside giving clues to the magnetospheric source regions of the aurora in the two local time sectors. Near-Earth substorm onsets are shown to be coupled to processes occurring much further tailward and indicate the importance of understanding the temporal development of features within the double oval. Using 'variance images,' a new technqiue for the investigation of these dynamics is outlined.

Description: We investigate spectral evolution in 37 bright, long gamma-ray bursts observed with the Burst and Transient Source Experiment (BATSE) spectroscopy detectors. High-resolution spectra are chracterized by the energy of the peak of nu F(sub nu), and the evolution of this quantity is examined relative to the emission intensity. In most cases it is found that this peak energy either rises with or slightly precedes major intensity increases and softens for the remainder of the pulse. Interpulse emission is generally harder early in the burst. For bursts with multiple intensity pulses, later spikes tend to be softer than earlier ones, indicating that the energy of the peak of nu F(sub nu) is bounded by an envelope which decays with time. Evidence is found that bursts in which the bulk of the flux comes well after the event which triggers the instrument tend to show less peak energy variability and are not as hard as several bursts in which the emission occurs promptly after the trigger. Several recently proposed burst models are examined in light of these results and no qualitative conflicts with the observations presented here are found.

Description: We present a detailed study of the highest-frequency component of smooth radio emission observed during the Voyager 2 encounter with Neptune in August 1989. This emission occurs during three distinct periods on August 24 and 25, 1989, in the frequency range of 550 to 900 kHz. By assuming straight-line propagation from sources of both fundamental and second harmonic gyroemission, we perform a detailed analysis of the observed polarization of the emission. The data are most consistent with an L-O mode source in the north magnetic polar region, around 50 deg W, 50 deg N. A second possible source is in the north magnetic polar region, around 270 deg W, 50 deg N. This source must emit in the R-X mode.