Search Publications
Measuring Black Hole Spin Using X-Ray Reflection Spectroscopy
Reynolds, Christopher S.
I review the current status of X-ray reflection (a.k.a. broad iron line) based black hole spin measurements. This is a powerful technique that allows us to measure robust black hole spins across the mass range, from the stellar-mass black holes in X-ray binaries to the supermassive black holes in active galactic nuclei. After describing the basic …
Circulation of Heavy Ions and Their Dynamical Effects in the Magnetosphere: Recent Observations and Models
Dandouras, Iannis; Malova, Helmi V.; Grigorenko, Elena E. +13 more
Knowledge of the ion composition in the near-Earth's magnetosphere and plasma sheet is essential for the understanding of magnetospheric processes and instabilities. The presence of heavy ions of ionospheric origin in the magnetosphere, in particular oxygen (O+), influences the plasma sheet bulk properties, current sheet (CS) thickness …
Magnetic Helicity, Tilt, and Twist
Pevtsov, Alexei A.; van Driel-Gesztelyi, Lidia; Norton, Aimee A. +2 more
Since its introduction to astro- and solar physics, the concept of helicity has proven to be useful in providing critical insights into physics of various processes from astrophysical dynamos, to magnetic reconnection and eruptive phenomena. Signature of helicity was also detected in many solar features, including orientation of solar active regio…
Kelvin Helmholtz Instability in Planetary Magnetospheres
Wing, Simon; Delamere, Peter A.; Johnson, Jay R.
Kelvin-Helmholtz instability plays a particularly important role in plasma transport at magnetospheric boundaries because it can control the development of a turbulent boundary layer, which governs the transport of mass, momentum, and energy across the boundary. Waves generated at the interface can also couple into body modes in the plasma sheet a…
Review of Solar Wind Entry into and Transport Within the Plasma Sheet
Escoubet, C. P.; Wing, S.; Lavraud, B. +8 more
The plasma sheet is populated in part by the solar wind plasma. Four solar entry mechanisms are examined: (1) double cusp or double lobe reconnection, (2) Kelvin-Helmholtz Instability (KHI), (3) Kinetic Alfvén waves (KAW), and (4) Impulsive Penetration. These mechanisms can efficiently fill the plasma sheet with cold dense ions during northward in…
Solar Cycle Variation in Solar Irradiance
Solanki, S. K.; Yeo, K. L.; Krivova, N. A.
The correlation between solar irradiance and the 11-year solar activity cycle is evident in the body of measurements made from space, which extend over the past four decades. Models relating variation in solar irradiance to photospheric magnetism have made significant progress in explaining most of the apparent trends in these observations. There …
The Extended Cycle of Solar Activity and the Sun's 22-Year Magnetic Cycle
Cliver, E. W.
The Sun has two characteristic migrations of surface features—the equatorward movement of sunspots and the poleward movement of high-latitude prominences. The first of these migrations is a defining aspect of the 11-yr Schwabe cycle and the second is a tracer of the process that culminates in solar polarity reversal, signaling the onset of the 22-…
Solar Polar Fields and the 22-Year Activity Cycle: Observations and Models
Petrie, G. J. D.; Petrovay, K.; Schatten, K.
We explore observations and models of the interacting, cyclical behavior of the active regions and the polar magnetic fields of the Sun. We focus on observational evidence of these fields interacting across the corridor between active and polar latitudes. We present observations of diverse magnetic signatures on, above and beneath the solar surfac…
The Sun's Interior Structure and Dynamics, and the Solar Cycle
Thompson, M. J.; Howe, R.; Broomhall, A. -M. +2 more
The Sun's internal structure and dynamics can be studied with helioseismology, which uses the Sun's natural acoustic oscillations to build up a profile of the solar interior. We discuss how solar acoustic oscillations are affected by the Sun's magnetic field. Careful observations of these effects can be inverted to determine the variations in the …
X-Ray Observations of Powerful AGN Outflows. Implications for Feedback
Pounds, Ken
Highly ionised winds with velocities ∼0.1-0.2 c were first detected in X-ray spectra of non-BAL AGN a decade ago. Subsequent observations and archival searches have shown such winds to be a common feature of luminous AGN, increasing the belief that powerful ionised winds have a wider importance in galaxy feedback models. Paradoxically, for the bes…