The Fermi Bubbles: Gamma-ray, Microwave, and Polarization Signatures of Leptonic AGN Jets

The origin of the Fermi bubbles and the microwave haze is yet to be determined. To disentangle different models requires detailed comparisons between theoretical predictions and multi-wavelength observations. Our previous simulations have demonstrated that the primary features of the Fermi bubbles could be successfully reproduced by recent jet activity from the central active galactic nucleus (AGN). In this work, we generate gamma-ray and microwave maps and spectra based on the simulated properties of cosmic rays (CRs) and magnetic fields in order to examine whether the observed bubble and haze emission could be explained by leptons contained in the AGN jets. We also investigate the model predictions of the polarization properties of the Fermi bubbles. We find that: (1) The same population of leptons can simultaneously explain the bubble and haze emission given that the magnetic fields within the bubbles are very close to the exponentially distributed ambient field, which can be explained by mixing in of the ambient field followed by turbulent field amplification; (2) The centrally peaked microwave profile suggests CR replenishment, which is consistent with the presence of a more recent second jet event; (3) The bubble interior exhibits a high degree of polarization because of ordered radial magnetic field lines stretched by elongated vortices behind the shocks; highly-polarized signals could also be observed inside the draping layer; (4) Enhancement of rotation measures could exist within the shock-compressed layer because of increased gas density and more amplified and ordered magnetic fields. We discuss the possibility that the deficient haze emission at b<-35 degrees is due to the suppression of magnetic fields, which is consistent with the existence of lower-energy CRs causing the polarized emission at 2.3 GHz. Possible AGN jet composition in the leptonic scenario is also discussed.Comment: 15 pages, 9 figures, matched with MNRAS published versio

Shock-Driven Periodic Variability in a Low-Mass-Ratio Supermassive Black Hole Binary

We investigate the time-varying electromagnetic emission of a low-mass-ratio supermassive black hole binary (SMBHB) embedded in a circumprimary disk, with a particular interest in variability of shocks driven by the binary. We perform a 2D, locally isothermal hydrodynamics simulation of a SMBHB with mass ratio $q=0.01$ and separation $a=100\;R_g$, using a physically self-consistent steady disk model. We estimate the electromagnetic variability from the system by monitoring accretion onto the secondary and using an artificial viscosity scheme to capture shocks and monitor the energy dissipated. The SMBHB produces a wide, eccentric gap in the disk, previously only observed for larger mass ratios, which we attribute to our disk model being much thinner ($H/R\approx0.01$ near the secondary) than is typical of previous works. The eccentric gap drives periodic accretion onto the secondary SMBH on a timescale matching the orbital period of the binary, $t_{\rm{bin}}\approx0.1\;\rm{yr}$, implying that the variable accretion regime of the SMBHB parameter space extends to lower mass ratios than previously established. Shocks driven by the binary are periodic, with a period matching the orbital period, and the shocks are correlated with the accretion rate, with peaks in the shock luminosity lagging peaks in the accretion rate by $0.43\;t_{\rm{bin}}$. We propose that the correlation of these quantities represents a useful identifier of SMBHB candidates, via observations of correlated variability in X-ray and UV monitoring of AGN, rather than single-waveband periodicity alone.Comment: 12 pages, 8 figures, accepted by MNRA

ATD-2 Integrated Arrival/Departure/Surface (IADS) System Software Version 3.1.x Releases and Notes

This document summarizes the change reports for the ATD-2 V3.1.x series of software releases to Charlotte-Douglas International Airport (CLT). These list all the changes since the previous release. The Release Notes for Distribution are meant to be more readable by stakeholders. [Includes updates to changes for RTC (Ramp Traffic Console), Scheduler, STBO (Surface Trajectory-Based Operations), and Surface Metering Display (graphical-user interface, GUI) clients.

Quasi-hydrostatic intracluster gas under radiative cooling

Quasi-hydrostatic cooling of the intracluster gas is studied. In the quasi-hydrostatic model, work done by gravity on the inflow gas with dP \neq 0, where P is the gas pressure, is taken into account in the thermal balance. The gas flows in from the outer part so as to compensate the pressure loss of the gas undergoing radiative cooling, but the mass flow is so moderate and smooth that the gas is considered to be quasi-hydrostatic. The temperature of the cooling gas decreases toward the cluster center, but, unlike cooling flows with dP = 0, approaches a constant temperature of \sim 1/3 the temperature of the non-cooling ambient gas. This does not mean that gravitational work cancels out radiative cooling, but means that the temperature of the cooling gas appears to approach a constant value toward the cluster center if the gas maintains the quasi-hydrostatic balance. We discuss the mass flow in quasi-hydrostatic cooling, and compare it with the standard isobaric cooling flow model. We also discuss the implication of \dot{M} for the standard cooling flow model.Comment: 5 pages, 1 figure, accepted for publication in A&

Interferometric Detection of Linear Polarization from Sagittarius A* at 230 GHz

We measured the linear polarization of Sagittarius A* to be 7.2 +/- 0.6 % at 230 GHzusing the BIMA array with a resolution of 3.6 x 0.9 arcsec. This confirms the previously reported detection with the JCMT 14-m antenna. Our high resolution observations demonstrate that the polarization does not arise from dust but from a synchrotron source associated with Sgr A*. We see no change in the polarization position angle and only a small change in the polarization fraction in four observations distributed over 60 days. We find a position angle 139 +/- 4 degrees that differs substantially from what was found in earlier JCMT observations at the same frequency. Polarized dust emission cannot account for this discrepancy leaving variability and observational error as the only explanations. The BIMA observations alone place an upper limit on the magnitude of the rotation measure of 2 x 10^6 rad m^-2. These new observations when combined with the JCMT observations at 150, 375 and 400 GHz suggest RM =-4.3 +/- 0.1 x 10^5 rad m^-2. This RM may be caused by an external Faraday screen. Barring a special geometry or a high number of field reversals, this RM rules out accretion rates greater than ~ 10^-7 M_sun y^-1. This measurement is inconsistent with high accretion rates necessary in standard advection dominated accretion flow and Bondi-Hoyle models for Sgr A*. It argues for low accretion rates as a major factor in the overall faintness of Sgr A*.Comment: accepted for publication in ApJ, 18 pages, 4 figure

2-D Magnetohydrodynamic Simulations of Induced Plasma Dynamics in the Near-Core Region of a Galaxy Cluster

We present results from numerical simulations of the cooling-core cluster A2199 produced by the two-dimensional (2-D) resistive magnetohydrodynamics (MHD) code MACH2. In our simulations we explore the effect of anisotropic thermal conduction on the energy balance of the system. The results from idealized cases in 2-D axisymmetric geometry underscore the importance of the initial plasma density in ICM simulations, especially the near-core values since the radiation cooling rate is proportional to ${n_e}^2$. Heat conduction is found to be non-effective in preventing catastrophic cooling in this cluster. In addition we performed 2-D planar MHD simulations starting from initial conditions deliberately violating both thermal balance and hydrostatic equilibrium in the ICM, to assess contributions of the convective terms in the energy balance of the system against anisotropic thermal conduction. We find that in this case work done by the pressure on the plasma can dominate the early evolution of the internal energy over anisotropic thermal conduction in the presence of subsonic flows, thereby reducing the impact of the magnetic field. Deviations from hydrostatic equilibrium near the cluster core may be associated with transient activity of a central active galactic nucleus and/or remnant dynamical activity in the ICM and warrant further study in three dimensions.Comment: 16 pages, 13 figures, accepted for publication in MNRA