EVE/ESP and the Neupert Effect

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Nugget
Number: 151
1st Author: H. Hudson
2nd Author:
Published: 9 May 2011
Next Nugget: TBD
Previous Nugget: Decimetric Pulsations
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Contents

Introduction

This Nugget follows a [previous Nugget] introducing [EVE] spectroscopy and its applications. Here we will look at the [ESP] component of EVE; this is a broad-band photometric observation of solar soft X-rays; it is thus similar to the standard [GOES] photometry, but better in some ways. In illustrating these data we refer to the flare SOL2011-02-24, a limb event with white-light continuum emission (as in SOL2010-06-12, the subject of our previous Nugget]. Because EVE (and its component ESP) observe in the [extreme ultraviolet], where opacities are large, a limb event will systematically differ from a disk event in its morphology - not only because of [limb darkening], but also because of absorption by structures intervening on the line of sight.

ESP data

Figure 1: Three of the four ESP irradiance passbands, plus the zeroth-order (soft X-ray channel, lower right) for the SOL2011-02-24 limb event. A similar plot for a disk event (SOL2010-06-12, another white-light flare) is in a [previous Nugget]. The broad-band ESP channels have different profiles because they integrate different sets of emission lines, basically. Note that this event is not typical because of it proximity to the limb (and because it is a gamma-ray flare).
Figure 2: Does the Neupert Effect really apply here? This is a comparison of the differentiated soft X-ray signal in the ESP zeroth-order record (red) with the RHESSI >100 keV counting rate (blue). We can see similar features, and both leads and lags, but also striking discrepancies. On the other hand, both time series start and stop in the impulsive phase of the flare, so on the longer time scales the Neupert Effect works well. In detail, the discrepancies are probably very interesting when studied using AIA images.
Figure 3: Left: Comparison of the [ESP] zeroth-order signal ("QD"), in red, and the GOES low-energy channel (blue). Two features are striking: first, the EVE signal peaks later, and second, it has a substantial preflare excess. These both point to longer effective wavelengths. Right: A blow-up of the preflare variation, showing how much better the ESP photometry (1/4 sec binning, much lower noise) than GOES is (3 sec binning, much greater noise).
Figure 4: RHESSI images, from the quicklook images, for SOL2011-02-24. This compares the low-resolution file images for 6-12 keV (left) and 50-100 keV (right), showing the looptops at a higher altitude than the footpoints. In fact this white-light (and gamma-ray) flare was on the visible disk, rather than being occulted.



How does GOES compare?

The Neupert Effect

Conclusions

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