66 research outputs found
Multi-color optical monitoring of the quasar 3C 273 from 2005 to 2016
We have monitored the quasar 3C 273 in optical , and bands from
2005 to 2016. Intraday variability (IDV) is detected on seven nights. The
variability amplitudes for most of nights are less than 10\% and four nights
more than 20\%. When considering the nights with time spans hours, the
value of duty cycle (DC) is 14.17 per cent. Over the twelve years, the overall
magnitude and color index variabilities are ,
, , and
respectively. The largest clear IDV has an
amplitude of 42% over just 5.8 minutes and the weakest detected IDV is 5.4%
over 175 minutes. The BWB (bluer when brighter) chromatic trend is dominant for
3C 273 and appears at different flux levels on intraday timescales. The BWB
trend exists for short-term timescales and intermediate-term timescales but
different timescales have different correlations. There is no BWB trend for our
whole time-series data sets. A significant anti-correlation between BWB trend
and length of timescales is found. Combining with -band data from previous
works, we find a possible quasi-periodicity of days. The
possible explanations for the observed variability, BWB chromatic trend and
periodicity are discussed.Comment: 63 pages, 11 figures, 6 tables. Accepted for publication in ApJ
A Spread Willingness Computing-Based Information Dissemination Model
This paper constructs a kind of spread willingness computing based on information dissemination model for social network. The model takes into account the impact of node degree and dissemination mechanism, combined with the complex network theory and dynamics of infectious diseases, and further establishes the dynamical evolution equations. Equations characterize the evolutionary relationship between different types of nodes with time. The spread willingness computing contains three factors which have impact on user’s spread behavior: strength of the relationship between the nodes, views identity, and frequency of contact. Simulation results show that different degrees of nodes show the same trend in the network, and even if the degree of node is very small, there is likelihood of a large area of information dissemination. The weaker the relationship between nodes, the higher probability of views selection and the higher the frequency of contact with information so that information spreads rapidly and leads to a wide range of dissemination. As the dissemination probability and immune probability change, the speed of information dissemination is also changing accordingly. The studies meet social networking features and can help to master the behavior of users and understand and analyze characteristics of information dissemination in social network
PEARLS: Low Stellar Density Galaxies in the El Gordo Cluster Observed with JWST
A full understanding of how unusually large "Ultra Diffuse Galaxies" (UDGs)
fit into our conventional understanding of dwarf galaxies remains elusive,
despite the large number of objects identified locally. A natural extension of
UDG research is the study of similar galaxies at higher redshift to establish
how their properties may evolve over time. However, this has been a challenging
task given how severely systematic effects and cosmological surface brightness
dimming inhibit our ability to study low-surface brightness galaxies at
high-. Here, we present an identification of low stellar surface density
galaxies (LDGs), likely the progenitors of local UDGs, at moderate redshift
with deep near-IR observations of the El Gordo cluster at with JWST.
By stacking 8 NIRCAM filters, we are able to achieve an apparent surface
brightness sensitivity of mag arcsec, faint enough to be
complete to the bright end of the LDG population. Our analysis identifies
significant differences between this population and local UDGs, such as their
color and size distributions, which suggest that UDG progenitors are bluer and
more extended at high- than at . This suggests that multiple
mechanisms are responsible for UDG formation and that prolonged transformation
of cluster dwarfs is not a primary UDG formation mechanism at high-.
Furthermore, we find a slight overabundance of LDGs in El Gordo, and, in
contrast to findings in local clusters, our analysis does not show a deficit of
LDGs in the center of El Gordo, implying that tidal destruction of LDGs is
significant between and .Comment: Resubmitted to ApJ after minor revision
Punctuated bursts in human male demography inferred from 1,244 worldwide Y-chromosome sequences
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