Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Microflare Heating of a Solar Active Region Observed with NuSTAR,
  Hinode/XRT, and SDO/AIA   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 heating of
material to several million Kelvin, observed in Soft X-rays (SXRs) with
Hinode/XRT, and was faintly visible in Extreme Ultraviolet (EUV) with SDO/AIA.
For three of the four NuSTAR observations of this region (pre-, decay, and post
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 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 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 $2.5 \times 10^{25}$ 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 the
heating requires a power-law spectrum of $\delta \ge 7$ with a low energy
cut-off $E_{c} \lesssim 7$ keV. In summary, this first NuSTAR microflare
strongly resembles much more powerful flares.

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The categories of this paper are: q-bio
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The categories of this paper are: supr-con
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The categories of this paper are: math
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The categories of this paper are: stat
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The categories of this paper are: physics
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The categories of this paper are: q-fin
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The categories of this paper are: comp-gas
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The categories of this paper are: dg-ga
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-th
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The categories of this paper are: adap-org
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The categories of this paper are: nlin
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The categories of this paper are: solv-int
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The categories of this paper are: q-alg
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The categories of this paper are: econ
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The categories of this paper are: atom-ph