Iain Hannah Submitted: 27-Apr-2006 13:47
Description: We are using RHESSI's excellent sensitivity in 3-100 keV to
determine the X-ray spectrum of the non-flaring, spotless,
active-region-free Sun, i.e. the quiet Sun. RHESSI's normal imaging method
is not suited to measuring signals that are potentially widely distributed
across the Sun, so instead we have had to adopt a novel offpointing
technique. By making RHESSI point slightly away from the Sun the quiet Sun
signal is modulated against the background allowing it to be measured
directly. However the quiet Sun signal is still weak and we need to
accumulate a lot of data to determine whether we have an actual signal or
only noise upper limits. We have been able to put RHESSI into this
offpointing mode 4 times so far (up to April-2006) during periods of low
activity and have determined that the technique works and have preliminary
quiet Sun spectra. These spectra are not of the quietest possible times
however, and so this work is an ongoing investigation, with us planning
further offpointing periods as we pass through Solar minimum. See
http://sprg.ssl.berkeley.edu/~tohban/nuggets/?page=article&article_id=16
for more information.
Participants: Hannah, I.G., Hurford, G.J, Hudson H.S, Lin, R.P
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