Kurt Mitman

Beaming, Baryon Loading, and the Synchrotron Self-Compton Component in Gamma-Ray Bursts

We present detailed calculations of nonthermal synchrotron and synchrotron self-Compton (SSC) spectra radiated by blast waves that are energized by interactions with a uniform surrounding medium. Radio, optical, X-ray and gamma-ray light curves and spectral indices are calculated for a standard parameter set that yields hard GRB spectra during the prompt emission phase. Because no lateral spreading of the blast-wave is assumed, the calculated temporal breaks represent the sharpest breaks possible from collimated outflows in a uniform surrounding medium. Absence of SSC hardenings in observed GRB X-ray afterglows indicates magnetic field generation toward equipartition as the blast wave evolves. EGRET detections of 100 MeV-GeV photons observed promptly and 90 minutes after GRB 940217 are attributed to nonthermal synchrotron radiation and SSC emission from a decelerating blast wave, respectively. The SSC process will produce prompt TeV emission that could be observed from GRBs with redshifts

Unemployment Benefits and Unemployment in the Great Recession: The Role of Macro Effects

z \lesssim 0.1

Short-Timescale Variability in the External Shock Model of Gamma-Ray Bursts

, provided

Pro-Cyclical Unemployment Benefits? Optimal Policy in an Equilibrium Business Cycle Model

\gamma

Defining time in a minimal hippocampal CA3 model by matching time-span of associative synaptic modification and input pattern duration

-

The Housing Boom and Bust: Model Meets Evidence

\gamma

Housing, mortgage bailout guarantees and the macro economy

opacity in the source is small. Measurements of the time dependence of the 100 MeV-GeV spectral indices with the planned {\it GLAST} mission will chart the evolution of the SSC component and test the external shock scenario. Transient optical and X-ray emissions from misaligned GRBs are generally much weaker than on-axis emissions produced by dirty and clean fireballs that would themselves not trigger a GRB detector; thus detection of long wavelength transients not associated with GRBs will not unambiguously demonstrate GRB beaming.We present detailed calculations of nonthermal synchrotron and synchrotron self-Compton (SSC) spectra radiated by blast waves that are energized by interactions with a uniform surrounding medium. Radio, optical, X-ray, and gamma-ray light curves and spectral indices are calculated for a standard parameter set that yields hard GRB spectra during the prompt emission phase. No lateral spreading of the blast wave is assumed. Absence of SSC hardenings in observed GRB X-ray afterglows indicates magnetic field generation toward equipartition as the blast wave evolves. EGRET detections of 100 MeV-GeV photons observed promptly and 90 minutes after GRB 940217 are attributed to nonthermal synchrotron radiation and SSC emission from a decelerating blast wave, respectively. The SSC process will produce prompt TeV emission that could be observed from GRBs with redshifts z 0.1, provided γ-γ opacity in the source is small. Measurements of the time dependence of the 100 MeV-GeV spectral indices with the planned Gamma-ray Large Area Space Telescope mission will chart the evolution of the SSC component and test the external shock scenario. Transient optical and X-ray emissions from misaligned GRBs are generally much weaker than on-axis emissions produced by dirty and clean fireballs that would themselves not trigger a GRB detector; thus, detection of long-wavelength transients not associated with GRBs will not unambiguously demonstrate GRB beaming.

Macroeconomic Effects of Bankruptcy and Foreclosure Policies

Equilibrium labor market theory suggests that unemployment benefit extensions affect unemployment by impacting both job search decisions by the unemployed and job creation decisions by employers. The existing empirical literature focused on the former effect only. We develop a new methodology necessary to incorporate the measurement of the latter effect. Implementing this methodology in the data, we find that benefit extensions raise equilibrium wages and lead to a sharp contraction in vacancy creation, employment, and a rise in unemployment.

Non-Durable Consumption and Housing Net Worth in the Great Recession: Evidence from Easily Accessible Data

We have developed a computer model to calculate gamma-ray burst (GRB) light curves and efficiencies from the interaction of a single, thin blast wave with clouds in the external medium. Large-amplitude, short-timescale variability occurs when the clouds have radii rR/Γ, where R is the mean distance of a cloud from the GRB source and Γ is the blast-wave Lorentz factor. Efficiencies 10% require a large number of small clouds, each with sufficiently large column densities to extract most of the available blast-wave energy in the region of interaction. The number and duration of pulses in the simulated GRB light curves are compared with the respective properties found in GRB light curves. If GRB sources are surrounded by clouds with such properties, then short-timescale variability of GRBs can be obtained in the external shock model.

Macroeconomics and Household Heterogeneity

We study the optimal provision of unemployment insurance (UI) over the business cycle. We consider an equilibrium Mortensen-Pissarides search and matching model with risk-averse workers and aggregate shocks to labor productivity. Both the vacancy creation decisions of firms and the search effort decisions of workers respond endogenously to aggregate shocks as well as to changes in UI policy. We characterize the optimal history-dependent UI policy. We find that, all else equal, the optimal benefit is decreasing in current productivity and decreasing in current unemployment. Optimal benefits are therefore lowest when current productivity is high and current unemployment is high. The optimal path of benefits reacts non-monotonically to a productivity shock. Following a drop in productivity, benefits initially rise in order to provide short-run relief to the unemployed and stabilize wages, but then fall significantly below their pre-recession level, in order to speed up the subsequent recovery. Under the optimal policy, the path of benefits is pro-cyclical overall. As compared to the existing US UI system, the optimal history-dependent benefits smooth cyclical fluctuations in unemployment and deliver non-negligible welfare gains.