High-sensitivity search for transient solar X-ray emission with NuSTAR
Abstract
We present the first results of a search for transient X-ray emission in quiet solar regions with the NuSTAR astrophysics satellite. Transient brightenings of 1024-1027 ergs, or "nanoflares," have been observed as thermal emission in EUV and soft X-rays, but never in hard X-rays (HXRs) due to lack of sensitivity. Frequent nanoflares could account for a significant fraction of the energy release needed to heat the corona to >1 MK. NuSTAR directly images X-rays from ~2-80 keV, with much higher sensitivity than dedicated solar HXR instruments. More importantly it can point at the Sun without suffering damage, a rare capability for an astrophysics instrument. We have developed an algorithm to search the NuSTAR data in space and time for transient events, while taking into account instrumental and systematic effects. Preliminary analysis yields a sensitivity to events ~0.001 times as bright as an “typical” RHESSI microflare (Hannah et al. 2008), for linear scaling and event duration of 10 seconds. Future observations at full-Sun flux levels below GOES ~B5 will increase our sensitivity by an order of magnitude or more.
- Publication:
-
AAS/AGU Triennial Earth-Sun Summit
- Pub Date:
- April 2015
- Bibcode:
- 2015TESS....121302M