Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Global sausage oscillation of solar flare loops detected by the
  Interface Region Imaging Spectrograph   An observation from the Interface Region Imaging Spectrograph reveals
coherent oscillations in the loops of an M1.6 flare on 2015 March 12. Both the
intensity and Doppler shift of Fe~{\sc{xxi}}~1354.08\AA{}~show clear
oscillations with a period of $\sim$25 seconds. Remarkably similar oscillations
were also detected in the soft X-ray flux recorded by the Geostationary
Operational Environmental Satellites (GOES). With an estimated phase speed of
$\sim$2420~km~s$^{-1}$ and a derived electron density of at least
5.4$\times$10$^{10}$ cm$^{-3}$, the observed short-period oscillation is most
likely the global fast sausage mode of a hot flare loop. We find a phase shift
of $\sim$$\pi$/2 (1/4 period) between the Doppler shift oscillation and the
intensity/GOES oscillations, which is consistent with a recent forward modeling
study of the sausage mode. The observed oscillation requires a density contrast
between the flare loop and coronal background of a factor $\geqslant$42. The
estimated phase speed of the global mode provides an lower limit of the
Alfv\'en speed outside the flare loop. We also find an increase of the
oscillation period, which might be caused by the separation of the loop
footpoints with time.

34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
18
The categories of this paper are: econ
37
The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
7
The categories of this paper are: hep-th
27
The categories of this paper are: comp-gas
4
The categories of this paper are: cond-mat
15
The categories of this paper are: nucl-ex
22
The categories of this paper are: chao-dyn
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga