The Chandra X-Ray Observatory was used to image the collisional ring galaxy Arp 147 for 42 ks. We detect nine X-ray sources with luminosities in the range of (1.4–7) × 1039 erg s−1 (assuming that the sources emit isotropically) in or near the blue knots of star formation associated with the ring. A source with an X-ray luminosity of 1.4 × 1040 erg s−1 is detected in the nuclear region of the in...

Starting from an abstract setting which extends the property \skip{free to the left" for transition matrices to a partition of the state space, we develop bounds for the mean hitting time to an arbitrary subset from an arbitrary initial law. We illustrate our theory with an asymptotic analysis of a non{reversible Markovian star network with loss.

Observations show that neutron stars can have space velocities much higher than those of their progenitors. On average pulsar birth velocities are in the range of 200-500 km/s and significant fraction might move with more than 1000 km/s (see [1] and references therein). The powerful and highly variable acceleration mechanism that leads to the measured velocities is still unclear. It is possible...

We have obtained complete redshift information for a sample of 442 radio-loud quasars with flux densities S 11 ≥ 0.25 Jy. These come from a completely-identified sample of 878 flat-spectrum radio sources, so there is no optical magnitude limit. With these quasars, therefore, we can map out the entire quasar epoch, unhindered by optical selection effects and any intervening dust. The rapid decli...