MAX MILLENNIUM COORDINATED OBSERVING PLAN # 015

VLA-RHESSI-TRACE Observations of Flare Buildup and Impulsive Energy Release in Active Regions

We have obtained observing time at the VLA on March 28 (1700-2200 UT), March 29 (1730-2230 UT) and March 30 (1530-2030 UT) to study the centimeter wavelength signatures of hard X-ray and EUV bursts detected by RHESSI amd TRACE. These observations continue a program that was begun in July and August, 2002 under the auspices of Max Millennium Campaign #15. The goal of these observations is to combine the microwave, hard X-ray and EUV data to provide information about the buildup and impulsive release of energy during solar flares. The high angular resolution of these instruments together with their unique spectral capabilities will be used to investigate the temporal evolution of the flare emission that, together with models for the propagation and containment of the particles, can constrain the plasma parameters of the magnetic structures where energy release takes place.

Scientific goals:

This Max Millennium Campaign involves VLA observations of the Sun in collaboration with RHESSI and TRACE. The VLA will image the microwave radiation of energetic electrons with spatial and temporal resolution that are comparable to RHESSI and TRACE and the combined results will be used to understand the radiation mechanisms of flares as well as their relationship to the evolving magnetic environment in which impulsive energy release occurs.

Past observations of solar flares have demonstrated a close similarity in the time profiles of the impulsive flare continuum radiation at the centimeter and hard X-ray wavelengths that will be respectively observed with the VLA and RHESSI. This similarity, on timescales as short as a second, suggests that the energetic, nonthermal electrons that produce the radio emission originate in the same population as those that produce the hard X-rays, and that these electrons have a common spatial origin. Since the radiation in the two spectral domains is emitted by different processes, their comparison will provide complementary perspectives of the same energetic electrons. The VLA, RHESSI and TRACE will together specify the location and physical environment of the flare electrons as they propagate away from the site of particle acceleration. Preliminary analysis of VLA, RHESSI and TRACE data taken on August 22, 2002, in fact, show intriguing relationships among the sources detected at microwave, hard X-ray and EUV wavelengths

The VLA (D configuration) will provide angular resolution snapshot maps on time intervals of 3 seconds at 3.5 and 6.2 cm. We also hope to obtain observations with the Owens Valley Solar Array (OVSA), which provides spectral coverage at 45 frequencies between 1 and 18 GHz. Synthesis maps of total intensity, I, and circular polarization, V, will specify the evolving structure of long lasting (hours) magnetic loops in the transition region and low corona where impulsive hard X-ray bursts take place. RHESSI will establish the energy distribution of the emitting particles that give clues to the nature of the emission process (i.e., thermal or nonthermal) while high-cadence TRACE images at different wavelengths will provide additional information about source variability at different temperatures.

The Target Selection will be done by the Max Millennium Chief Observer and announced each day using the Mmmotd mailing list.