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The high energy Universe at ultra-high resolution: the power and promise of X-ray interferometry
We propose the development of X-ray interferometry (XRI), to reveal the Universe at high energies with ultra-high spatial resolution. With baselines which can be accommodated on a single spacecraft, XRI can reach 100 μ as resolution at 10 Å (1.2 keV) and 20 μ as at 2 Å (6 keV), enabling imaging and imaging-spectroscopy of (for example) X-ray coronae of nearby accreting supermassive black holes (SMBH) and the SMBH ‘shadow’; SMBH accretion flows and outflows; X-ray binary winds and orbits; stellar coronae within ∼100 pc and many exoplanets which transit across them. For sufficiently luminous sources XRI will resolve sub-pc scales across the entire observable Universe, revealing accreting binary SMBHs and enabling trigonometric measurements of the Hubble constant with X-ray light echoes from quasars or explosive transients. A multi-spacecraft ‘constellation’ interferometer would resolve well below 1 μ as, enabling SMBH event horizons to be resolved in many active galaxies and the detailed study of the effects of strong field gravity on the dynamics and emission from accreting gas close to the black hole
GRB Radiative Efficiencies Derived from the Swift Data: GRBs vs. XRFs, Long vs. Short
We systematically analyze the prompt emission and the early afterglow data of
a sample of 31 GRBs detected by {\em Swift} before September 2005, and estimate
the GRB radiative efficiency. BAT's narrow band inhibits a precise
determination of the GRB spectral parameters, and we have developed a method to
estimate these parameters with the hardness ratio information. The shallow
decay component commonly existing in early X-ray afterglows, if interpreted as
continuous energy injection in the external shock, suggests that the GRB
efficiency previously derived from the late-time X-ray data were not reliable.
We calculate two radiative efficiencies using the afterglow kinetic energy E_K
derived at the putative deceleration time t_{dec}) and at the break time (t_b)
when the energy injection phase ends, respectively. At t_b XRFs appear to be
less efficient than normal GRBs. However, when we analyze the data at t_{dec}
XRFs are found to be as efficient as GRBs. Short GRBs have similar radiative
efficiencies to long GRBs despite of their different progenitors. Twenty-two
bursts in the sample are identified to have the afterglow cooling frequency
below the X-ray band. Assuming \epsilon_e = 0.1, we find \eta_\gamma(t_b)
usually 90%.
Nine GRBs in the sample have the afterglow cooling frequency above the X-ray
band for a very long time. This suggests a very small \epsilon_B and/or a very
low ambient density n.Comment: 43 pages, 10 figures, ApJ, in pres
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