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Engineering-Physics Space Plasma Seminar



4:00pm - 5:00pm ET

Wilder 202/Online

Meeting ID: 927 5142 0885
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"On the Sun's faintest coronal hard X-rays observed with the FOXSI rocket"

Solar nanoflares are small eruptive events releasing magnetic energy in the quiet corona. If nanoflares follow the same physics as their larger counterparts, they should emit hard X-rays (HXRs) but with a rather faint intensity. A copious and continuous presence of nanoflares would result in a sustained and persistent emission in HXRs, which in turn would deliver enormous amounts of energy into the solar corona, possibly accounting for its high temperatures. To date, there has not been any direct observation of such sustained and persistent HXRs from the quiescent Sun. However, Hannah et al. in 2010 constrained the quiet Sun HXR emission using almost 12 days of quiescent solar-off-pointing observations by RHESSI. These observations set 2 sigma upper limits at 3.4x10^(-2) photons / s / cm^2 / keV and 9.5x10^(-4) photons / s / cm^2 / keV for the 3-6 keV and 6-12 keV energy ranges, respectively. Observing feeble HXRs is challenging because it demands high sensitivity and dynamic range instruments in the HXR energy band. The Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket experiment excels in these two attributes when compared with RHESSI. Particularly, FOXSI completed its third successful flight (FOXSI-3) on September 7th, 2018. During FOXSI-3’s flight, the Sun exhibited a fairly quiet configuration, displaying only one aged non-flaring active region. Using the entire ~6.5 minutes of FOXSI-3 data, we constrained the quiet Sun emission in HXRs. We found 2 sigma upper limits in the order of 10^(-3) photons / s / cm^2 / keV for the 5-10 keV energy range. FOXSI-3's upper limit is consistent with what was reported by Hannah et al., 2010, but FOXSI-3 achieved this result using ~1/2640 of the time that RHESSI did. A possible future spacecraft using FOXSI's concept would allow enough observation time to constrain the current HXR quiet Sun limits further or perhaps even make direct detections.

Hosted by Jeffersson A Agudelo Rueda

About the Speaker(s)

Milo Buitrago-Casas
SSL Berkeley


For more information, contact Tressena Manning at or +1 (603) 646-2854.