23 research outputs found
Multi-wavelength observations of the binary system PSR B1259â63/LS 2883 around the 2014 periastron passage
We report on the results of the extensive multi-wavelength campaign from optical to GeV Îł-rays of the 2014 periastron passage of PSR B1259â63, which is a unique high-mass Îł-ray emitting binary system with a young pulsar companion. Observations demonstrate the stable nature of the post-periastron GeV flare and prove the coincidence of the flare with the start of rapid decay of the Hα equivalent width, usually interpreted as a disruption of the Be stellar disc. Intensive X-ray observations reveal changes in the X-ray spectral behaviour happening at the moment of the GeV flare. We demonstrate that these changes can be naturally explained as a result of synchrotron cooling of monoenergetic relativistic electrons injected into the system during the GeV flare
Circumgalactic Gas and the Precipitation Limit
During the last decade, numerous and varied observations, along with
increasingly sophisticated numerical simulations, have awakened astronomers to
the central role the circumgalactic medium (CGM) plays in regulating galaxy
evolution. It contains the majority of the baryonic matter associated with a
galaxy, along with most of the metals, and must continually replenish the star
forming gas in galaxies that continue to sustain star formation. And while the
CGM is complex, containing gas ranging over orders of magnitude in temperature
and density, a simple emergent property may be governing its structure and
role. Observations increasingly suggest that the ambient CGM pressure cannot
exceed the limit at which cold clouds start to condense out and precipitate
toward the center of the potential well. If feedback fueled by those clouds
then heats the CGM and causes it to expand, the pressure will drop and the
"rain" will diminish. Such a feedback loop tends to suspend the CGM at the
threshold pressure for precipitation. The coming decade will offer many
opportunities to test this potentially fundamental principle of galaxy
evolution.Comment: Astro2020 White Paper, 8 pages, 2 figures (differences from Astro2020
version: some typos fixed, some references added
Hot atmospheres of galaxies, groups, and clusters of galaxies
Most of the ordinary matter in the local Universe has not been converted into
stars but resides in a largely unexplored diffuse, hot, X-ray emitting plasma.
It pervades the gravitational potentials of massive galaxies, groups and
clusters of galaxies, as well as the filaments of the cosmic web. The physics
of this hot medium, such as its dynamics, thermodynamics and chemical
composition can be studied using X-ray spectroscopy in great detail. Here, we
present an overview of the basic properties and discuss the self similarity of
the hot "atmospheres" permeating the gravitational halos from the scale of
galaxies, through groups, to massive clusters. Hot atmospheres are stabilised
by the activity of supermassive black holes and, in many ways, they are of key
importance for the evolution of their host galaxies. The hot plasma has been
significantly enriched in heavy elements by supernovae during the period of
maximum star formation activity, probably more than 10 billion years ago. High
resolution X-ray spectroscopy just started to be able to probe the dynamics of
atmospheric gas and future space observatories will determine the properties of
the currently unseen hot diffuse medium throughout the cosmic web.Comment: Accepted for publication in the book "Reviews in Frontiers of Modern
Astrophysics: From Space Debris to Cosmology" (eds Kabath, Jones and Skarka;
publisher Springer Nature) funded by the European Union Erasmus+ Strategic
Partnership grant "Per Aspera Ad Astra Simul" 2017-1-CZ01-KA203-03556