Details

Autor(en) / Beteiligte

• Wright, Paul J.
• Hannah, Iain G.
• Grefenstette, Brian W.
• Glesener, Lindsay
• Krucker, Säm
• Hudson, Hugh S.
• Smith, David M.
• Marsh, Andrew J.
• White, Stephen M.
• Kuhar, Matej

Titel

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

Ist Teil von

• The Astrophysical journal, 2017-08, Vol.844 (2), p.132

Ort / Verlag

Philadelphia: The American Astronomical Society

Erscheinungsjahr

2017

Quelle

Free E-Journal (出版社公開部分のみ）

Beschreibungen/Notizen

• 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 about 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 with a low-energy cutoff keV is required. In summary, this first NuSTAR microflare strongly resembles much more powerful flares.