HOP list   Monthly Events

HINODE Operation Plan (HOP)

accepted on


 HOP No.

 HOP title

HOP 0281

Coordinated quiet-Sun nanoflare investigations with NuSTAR

plan term


@ @


 name : Glesener, Smith @  e-mail : glesener[at]ssl.berkeley.edu

contact person in HINODE team

 name : Reeves @  e-mail : kreeves[at]cfa.harvard.edu

 abstract of observational proposal
The proposed Hinode observations are in support of NuSTAR investigations of nanoflares and coronal heating. Coronal heating is one of the major unsolved problems in solar physics. Low-level energy releases at high occurrence rates (so-called nanoflares) are one of the proposed mechanisms to heat the corona, since these events could transfer energy from coronal magnetic fields into heating. Not only are larger flares in active regions already known to be infrequent enough to supply the large energy needed to heat the corona, this energy input is required even at solar minimum, during times when no active regions are observed. Small gnanoflaresh in the quiet Sun are therefore necessary for flare heating to be a viable coronal heating mechanism.

NuSTAR searches for a nonthermal signature of nanoflares in the quiet Sun. Identification of such a signature would indicate that transient brightenings in the quiet Sun are indeed small flares, while the absence of nonthermal electrons would indicate that these brightenings do not accelerate electrons in the same way as regular flares do, and are therefore not flares as we currently understand them. Nanoflares could also be associated with jets that occur in coronal holes (notably the polar regions) via interchange reconnection. We ask for supporting observations from EIS and XRT to observe the thermal emissions associated with quiet-Sun nanoflares and jets. Furthermore, we ask for SOT observations to provide magnetic context observations, in order to determine if any observed hard X-ray events are indeed associated with strong magnetic fields.

 request to SOT
-- Context magnetograms (within part of the NuSTAR field of view). These are desired but lower priority than XRT.

 request to XRT
-- Default observation: High time cadence (Al-poly at 20 second cadence) in order to look for fast events. 384x384 FOV, 4s fixed exposure. Reduce frequency of FLD images to maintain the high cadence.

-- Alternative observation: If specified by the NuSTAR team, instead of a high time cadence observation, do an observation optimized for DEMs: Multiple filters, e.g. Alpoly, Ti-Poly, Al-poly/Ti-poly, thin-Be, med-Be, med-Al. 384hx384h FOV, fixed long exposure times for the thicker filters. Low cadence is OK.

-- If possible, include a full-disk synoptic in 1-2 filters, outside of the NuSTAR observation window within 2 hours of the observation start or stop. This is useful for characterizing hot plasma outside NuSTARfs field of view.

 request to EIS
-- Study to run: FOXSI_QS

-- EIS observations are lower-priority than XRT.

 other participating instruments
The Nuclear Spectroscopic Array (NuSTAR) is a soft/hard X-ray instrument producing direct focused images and spectra of faint astrophysical targets from 2 to 80 keV. While not a heliophysics mission, NuSTAR occasionally observes the Sun as a target of opportunity.

NuSTAR quiet-Sun solar pointings are called as ToOfs on a 3-4 day time scale. Solar observations are 1-4 orbits (~1 to 6 hours).

Because it was not designed/optimized for bright solar sources, NuSTAR has a limited count rate of 800 counts per second over the entire energy range. Therefore, the best opportunities to take advantage of NuSTARfs high sensitivity and straightforward imaging come during times of low solar activity. NuSTAR has a field of view of ~12x12 arcmin. NuSTAR quiet-Sun targets are chosen to be as far away as possible from active regions to reduce background caused by single-bounce photons (gghost raysh) from these active regions. This single-bounce background tends to be bright. The quietest part of the solar disk, often the polar regions, is thus the optimal target. This is also convenient for looking for hard X-rays from polar jets.

HOP list   Monthly Events