26,016 research outputs found
Influence of Reciprocal links in Social Networks
In this Letter, we empirically study the influence of reciprocal links, in
order to understand its role in affecting the structure and function of
directed social networks. Experimental results on two representative datesets,
Sina Weibo and Douban, demonstrate that the reciprocal links indeed play a more
important role than non-reciprocal ones in both spreading information and
maintaining the network robustness. In particular, the information spreading
process can be significantly enhanced by considering the reciprocal effect. In
addition, reciprocal links are largely responsible for the connectivity and
efficiency of directed networks. This work may shed some light on the in-depth
understanding and application of the reciprocal effect in directed online
social networks
The energy distribution of relativistic electrons in the kilo-parsec scale jet of M87 with Chandra
The X-ray emission from the jets in Active Galactic Nuclei (AGN) carries
important information on the distributions of relativistic electrons and
magnetic fields on large scales. We reanalyze archival Chandra observations on
the jet of M87 from 2000 to 2016 with a total exposure of 1460 kiloseconds to
explore the X-ray emission characteristics along the jet. We investigate the
variability behaviours of the nucleus and the inner jet component HST-1, and
confirm indications for day-scale X-ray variability in the nucleus
contemporaneous to the 2010 high TeV gamma-ray state. HST-1 shows a general
decline in X-ray flux over the last few years consistent with its synchrotron
interpretation. We extract the X-ray spectra for the nucleus and all knots in
the jet, showing that they are compatible with a single power-law within the
X-ray band. There are indications of the resultant X-ray photon index to
exhibit a trend, with slight but significant index variations ranging from
(e.g. in knot D) to (in the outer knots F, A, and
B). When viewed in a multi-wavelength context, a more complex situation is
arising. Fitting the radio to X-ray spectral energy distributions (SEDs)
assuming a synchrotron origin, we show that a broken power-law electron
spectrum with break energy around TeV allows a
satisfactorily description of the multi-band SEDs for most of the knots.
However, in the case of knots B, C and D we find indications that an additional
high energy component is needed to adequately reproduce the broadband SEDs. We
discuss the implications and suggest that a stratified jet model may account
for the differences.Comment: accepted for publication in A&
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