The Flare that Time Forgot

From RHESSI Wiki

Introduction

RHESSI, over its lifetime in space thus far, has detected many, many flares. Often a single event inspires a single paper, and then a flood of literature even if it's not very typical The Masuda flare [1] would be a case in point, and we've had Nuggets on this topic before: "An alternative view...", "Acceleration without heating", "Acceleration-region densities", etc. In spite of this it is generally held that this particular event was of quite a rare type. Thus we were amazed when a retrospective view of the RHESSI flares disclosed that the very first M-class flare observed by RHESSI looks very much like a Masuda flare! Somehow nobody picked up on this one, in spite of its newsworthiness. See Browser for a concise overview.

How do we know nobody studied this one?

The RHESSI book [2] has an extensive index, which makes use of the now-standard IAU target designation scheme. A flare, in this scheme, has an identifier such as SOL2002-02-20T10:04 (with the option of an extension for location). This makes it easy to search any database, and (for example) a Google search just brought up an entire page of SOL2002-07-23 - but none of the "Flare that Time Forgot". The RHESSI index has one entry, for a study of the albedo patch, but nothing concerning the interesting coronal developments. By contrast everybody's favorite SOL2002-07-23 has no fewer than 79 entries, and featured in Bob Lin's final chapter of the book specifically because of its Masuda-like properties. The "flare that time forgot" of course had not made the top-10 list of RHESSI flares.

The flare

A couple of images show some of the attributes of this flare. Figure 1 shows soft, medium, and hard X-ray images via two imaging algorithms. They show the familiar cusp to be present at 25-50 keV, and above it a significant 50-keV source. In other words, it is possibly a much-sought-for Masuda event, and there it was on RHESSI's plate 11 years ago.

Fig. 1: RHESSI images from the flare using two inversion techniques: CLEAN at the top, and MEM at the bottom. From left to right, increasing energies (6-12, 25-50, and 50-100 keV). the simple structure seen in soft X-rays becomes more complicated with time, revealing a Masuda-type "above the loop top" source at high energies. Note that this appearance is in the early phase of the flare, as it was for Masuda's original event SOL1992-01-13 ([http://sprg.ssl.berkeley.edu/~tohban/browser/?show=qlpcr+qli02+qli03+qli04+qli05+ grwa&date=20020220&time=095921&bar=1 Browser).