FIRST IMAGES FROM THE
                    <i>FOCUSING OPTICS X-RAY SOLAR IMAGER</i>

Krucker, S.; Christe, Steven; Glesener, Lindsay; Ishikawa, Shin; Ramsey, Brian D.; Takahashi, Tadayuki; Watanabe, Shin; Saito, Shinya; Gubarev, Mikhail V.; Kilaru, Kiranmayee; Tajima, H.; Tanaka, Takaaki; Turin, P.; McBride, Steve; Glaser, David L.; Fermin, Jose; White, S. M.; Lin, R. P.

doi:10.1088/2041-8205/793/2/l32

Cited by 78 publications

(49 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These observations would greatly benefit from new, more sensitive, solar X-ray telescopes such as the FOXSI (Krucker et al 2014) and MaGIXS (Kobayashi et al 2011) sounding rockets, as well as the MinXSS CubeSats (Mason et al 2016). New data combined with NuSTAR observations during quieter periods of solar activity should provide detection of the hightemperature and possible non-thermal emission in even smaller microflares, which should, in turn, provide a robust measure of their contribution to heating coronal loops in ARs.…”

Section: Discussionmentioning

confidence: 99%

Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA

Wright

Hannah

Grefenstette

et al. 2017

ApJ

Self Cite

View full text Add to dashboard Cite

NuSTAR is a highly sensitive focusing hard X-ray (HXR) telescope and has observed several small microflares in its initial solar pointings. In this paper, we present the first joint observation of a microflare with NuSTAR and Hinode/ XRT on 2015 April 29 at ∼11:29 UT. This microflare shows the heating of material to several million Kelvin, observed in soft X-rays with Hinode/XRT, and was faintly visible in the extreme ultraviolet with SDO/AIA. For three of the four NuSTAR observations of this region (pre-flare, decay, and post-flare phases), the spectrum is well fitted by a single thermal model of 3.2-3.5 MK, but the spectrum during the impulsive phase shows additional emission up to 10 MK, emission equivalent to the A0.1 GOES class. We recover the differential emission measure (DEM) using SDO/AIA, Hinode/XRT, and NuSTAR, giving unprecedented coverage in temperature. We find that the pre-flare DEM peaks at ∼3 MK and falls off sharply by 5 MK; but during the microflare's impulsive phase, the emission above 3 MK is brighter and extends to 10 MK, giving a heating rate of about2.5 10 25 erg s −1. As the NuSTAR spectrum is purely thermal, we determined upper limits on the possible non-thermal bremsstrahlung emission. We find that for the accelerated electrons to be the source of heating, a power-law spectrum of  d 7 with a low-energy cutoff  E 7 c keV is required. In summary, this first NuSTAR microflare strongly resembles much more powerful flares.

show abstract

Section: Discussionmentioning

confidence: 99%

Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA

Wright

Hannah

Grefenstette

et al. 2017

ApJ

Self Cite

View full text Add to dashboard Cite

show abstract

“…We therefore assume that the intensity distribution is correlated with the energy flux carried by the electron beam on each thread, thus composing a powerlaw of beam fluxes. Although the correlation between TR lines and HXR emission is well established at the large scale, both spatially and temporally, future HXR instrumentation (e.g., FOXSI, Krucker et al 2014) should verify that this remains true at smaller scales.…”

Section: Monte Carlo Modelmentioning

confidence: 98%

Transition Region and Chromospheric Signatures of Impulsive Heating Events. Ii. Modeling

Reep

Warren

Crump

et al. 2016

ApJ

View full text Add to dashboard Cite

Results from the Solar Maximum Mission showed a close connection between the hard X-ray (HXR) and transition region (TR) emission in solar flares. Analogously, the modern combination of RHESSI and IRIS data can inform the details of heating processes in ways that were never before possible. We study a small event that was observed with RHESSI, IRIS, SDO, and Hinode, allowing us to strongly constrain the heating and hydrodynamical properties of the flare, with detailed observations presented in a previous paper. Long duration redshifts of TR lines observed in this event, as well as many other events, are fundamentally incompatible with chromospheric condensation on a single loop. We combine RHESSI and IRIS data to measure the energy partition among the many magnetic strands that comprise the flare. Using that observationally determined energy partition, we show that a proper multithreaded model can reproduce these redshifts in magnitude, duration, and line intensity, while simultaneously being well constrained by the observed density, temperature, and emission measure. We comment on the implications for both RHESSI and IRIS observations of flares in general, namely that: (1) a single loop model is inconsistent with long duration redshifts, among other observables; (2) the average time between energization of strands is less than 10 s, which implies that for a HXR burst lasting 10 minutes, there were at least 60 strands within a single IRIS pixel located on the flare ribbon; (3) the majority of these strands were explosively heated with an energy distribution well described by a power law of slope »-1.6; (4) the multi-stranded model reproduces the observed line profiles, peak temperatures, differential emission measure distributions, and densities.

show abstract

“…In recent years, new instruments have begun to demonstrate the dramatically increased sensitivity available via direct HXR focusing as opposed to RHESSI's indirect imaging method , with the first two flights of the Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket (Krucker et al 2014;Glesener et al 2016) and occasional solar pointings by the Nuclear Spectroscopic Telescope Array (NuSTAR) astrophysics spacecraft (Harrison et al 2013;Grefenstette et al 2016). Focusing HXR instruments, with their larger effective areas and drastically reduced detector backgrounds, can measure flares of smaller temperatures, brightnesses, and total energies than those available to indirect imagers.…”

Section: Introductionmentioning

confidence: 99%

NuSTAR Hard X-Ray Observation of a Sub-A Class Solar Flare

Glesener

Krucker

Hannah

et al. 2017

ApJ

Self Cite

View full text Add to dashboard Cite

We report a Nuclear Spectroscopic Telescope Array (NuSTAR) observation of a solar microflare, SOL2015-09-01T04. Although it was too faint to be observed by the GOES X-ray Sensor, we estimate the event to be an A0.1 class flare in brightness. This microflare, with only ∼5 counts s −1 detector −1 observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), is fainter than any hard X-ray (HXR) flare in the existing literature. The microflare occurred during a solar pointing by the highly sensitive NuSTAR astrophysical observatory, which used its direct focusing optics to produce detailed HXR microflare spectra and images. The microflare exhibits HXR properties commonly observed in larger flares, including a fast rise and more gradual decay, earlier peak time with higher energy, spatial dimensions similar to the RHESSI microflares, and a high-energy excess beyond an isothermal spectral component during the impulsive phase. The microflare is small in emission measure, temperature, and energy, though not in physical size; observations are consistent with an origin via the interaction of at least two magnetic loops. We estimate the increase in thermal energy at the time of the microflare to be 2.4×10 27 erg. The observation suggests that flares do indeed scale down to extremely small energies and retain what we customarily think of as "flare-like" properties.

show abstract

FIRST IMAGES FROM THE FOCUSING OPTICS X-RAY SOLAR IMAGER

Cited by 78 publications

References 21 publications

Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA

Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA

Transition Region and Chromospheric Signatures of Impulsive Heating Events. Ii. Modeling

NuSTAR Hard X-Ray Observation of a Sub-A Class Solar Flare

Contact Info

Product

Resources

About