10,603 research outputs found
A statistical analysis and description of the Kendbrin swimming club of Riverside, Rhode Island indicating the present interests of the membership
Thesis (M.A.)--Boston Universit
Post-flare UV light curves explained with thermal instability of loop plasma
In the present work we study the C8 flare occurred on September 26, 2000 at
19:49 UT and observed by the SOHO/SUMER spectrometer from the beginning of the
impulsive phase to well beyond the disappearance in the X-rays. The emission
first decayed progressively through equilibrium states until the plasma reached
2-3 MK. Then, a series of cooler lines, i.e. Ca x, Ca vii, Ne vi, O iv and Si
iii (formed in the temperature range log T = 4.3 - 6.3 under equilibrium
conditions), are emitted at the same time and all evolve in a similar way. Here
we show that the simultaneous emission of lines with such a different formation
temperature is due to thermal instability occurring in the flaring plasma as
soon as it has cooled below ~ 2 MK. We can qualitatively reproduce the relative
start time of the light curves of each line in the correct order with a simple
(and standard) model of a single flaring loop. The agreement with the observed
light curves is greatly improved, and a slower evolution of the line emission
is predicted, if we assume that the model loop consists of an ensemble of
subloops or strands heated at slightly different times. Our analysis can be
useful for flare observations with SDO/EVE.Comment: 24 pages, 7 figures, accepted for publicatio
Multi-wavelength Signatures of Cosmic Rays in the Milky Way
Cosmic rays (CRs) propagate in the Milky Way and interact with the
interstellar medium and magnetic fields. These interactions produce emissions
that span the electromagnetic spectrum, and are an invaluable tool for
understanding the intensities and spectra of CRs in distant regions, far beyond
those probed by direct CR measurements. We present updates on the study of CR
properties by combining multi-frequency observations of the interstellar
emission and latest CR direct measurements with propagation models.Comment: 8 pages, 4 figures. Proceedings of the 35th International Cosmic Ray
Conference, ICRC201
Spatial distribution of X-ray emitting ejecta in Tycho's SNR: indications of shocked Titanium
Young supernova remnants show a characteristic ejecta-dominated X-ray
emission that allows us to probe the products of the explosive nucleosynthesis
processes and to ascertain important information about the physics of the
supernova explosions. Hard X-ray observations have recently revealed the
radioactive decay lines of 44Ti at ~67.9 keV and ~78.4 keV in the Tycho's SNR.
We here analyze the set of XMM-Newton archive observations of the Tycho's SNR.
We produce equivalent width maps of the Fe K and Ca XIX emission lines and find
indications for a stratification of the abundances of these elements and
significant anisotropies. We then perform a spatially resolved spectral
analysis by identifying five different regions characterized by high/low values
of the Fe K equivalent width. We find that the spatial distribution of the Fe K
emission is correlated with that of the Cr XXII. We also detect the Ti K-line
complex in the spectra extracted from the two regions with the highest values
of the Fe and Cr equivalent widths. The Ti line emissions remains undetected in
regions where the Fe and Cr equivalent widths are low. Our results indicate
that the post-shock Ti is spatially co-located with other iron-peak nuclei in
Tycho's SNR, in agreement with the predictions of multi-D models of Type Ia
supernovae.Comment: Accepted for publication in Ap
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