2,003 research outputs found
A magnetohydrodynamic model for multi-wavelength flares from Sagittarius~A (I): model and the near-infrared and X-ray flares
Flares from the supermassive black hole in our Galaxy, Sagittarius~A
(Sgr A), are routinely observed over the last decade or so. Despite
numerous observational and theoretical efforts, the nature of such flares still
remains poorly understood, although a few phenomenological scenarios have been
proposed. In this work, we develop the Yuan et al. (2009) scenario into a
magnetohydrodynamic (MHD) model for Sgr A flares. This model is
analogous with the theory of solar flares and coronal mass ejection in solar
physics. In the model, magnetic field loops emerge from the accretion flow onto
Sgr A and are twisted to form flux ropes because of shear and
turbulence. The magnetic energy is also accumulated in this process until a
threshold is reached. This then results in a catastrophic evolution of a flux
rope with the help of magnetic reconnection in the current sheet. In this
catastrophic process, the magnetic energy is partially converted into the
energy of non-thermal electrons. We have quantitatively calculated the
dynamical evolution of the height, size, and velocity of the flux rope, as well
as the magnetic field in the flare regions, and the energy distribution of
relativistic electrons in this process. We further calculate the synchrotron
radiation from these electrons and compare the obtained light curves with the
observed ones. We find that the model can reasonably explain the main
observations of near-infrared (NIR) and X-ray flares including their light
curves and spectra. It can also potentially explain the frequency-dependent
time delay seen in radio flare light curves.Comment: 17 pages, 13 figures, accepted by MNRA
Suppression of maximal linear gluon polarization in angular asymmetries
We perform a phenomenological analysis of the azimuthal
asymmetry in virtual photon plus jet production induced by the linear
polarization of gluons in unpolarized collisions. Although the linearly
polarized gluon distribution becomes maximal at small , TMD evolutionleads
to a Sudakov suppression of the asymmetry with increasing invariant mass of the
-jet pair. Employing a small- model input distribution, the
asymmetry is found to be strongly suppressed under TMD evolution, but still
remains sufficiently large to be measurable in the typical kinematical region
accessible at RHIC or LHC at moderate photon virtuality, whereas it is expected
to be negligible in -jet pair production at LHC. We point out the optimal
kinematics for RHIC and LHC studies, in order to expedite the first
experimental studies of the linearly polarized gluon distribution through this
process. We further argue that this is a particularly clean process to test the
-resummation formalism in the small- regime.Comment: 11 pages, 6 figure
Experimental and Finite Element Analysis for a Multifunctional Beam with Frequency-dependent Viscoelastic Behavior
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106430/1/AIAA2013-1640.pd
Statistics of X-ray flares of Sagittarius A*: evidence for solar-like self-organized criticality phenomenon
X-ray flares have routinely been observed from the supermassive black hole,
Sagittarius A (Sgr A), at our Galactic center. The nature of
these flares remains largely unclear, despite of many theoretical models. In
this paper, we study the statistical properties of the Sgr A X-ray
flares, by fitting the count rate (CR) distribution and the structure function
(SF) of the light curve with a Markov Chain Monte Carlo (MCMC) method. With the
3 million second \textit{Chandra} observations accumulated in the Sgr A
X-ray Visionary Project, we construct the theoretical light curves through
Monte Carlo simulations. We find that the keV X-ray light curve can be
decomposed into a quiescent component with a constant count rate of
count s and a flare component with a power-law
fluence distribution with . The duration-fluence correlation can also be modelled as a
power-law with (
confidence). These statistical properties are consistent with the theoretical
prediction of the self-organized criticality (SOC) system with the spatial
dimension . We suggest that the X-ray flares represent plasmoid
ejections driven by magnetic reconnection (similar to solar flares) in the
accretion flow onto the black hole.Comment: to appear in Ap
- …