Chandra and XMM-Newton observations of the exceptional pulsar PSR B0628-28

PSR B0628-28 is a radio pulsar which was first detected in the X-ray band by ROSAT and then later observed with Chandra and XMM-Newton. The Chandra observation yielded an X-ray luminosity two orders of magnitude higher than what is expected for spin-powered pulsars, also there were no pulsations detected. The XMM-Newton observation, however, reveals pulsations at the expected radio period, P=1.244 s. The simultaneously analyzed spectra also gives a luminosity (in cgs) Log Lx=30.34, which is ~350 times greater than what would be expected from the correlation between Lx-Edot.Comment: 13 pages, 4 figures, to be published in ApJ

Discovery of extended emission around the pulsar B0355+54

PSR B0355+54 is one of the handful of pulsars that have been observed with both Chandra and XMM-Newton. The analysis of the archival data has revealed the pulsar and a similar to 30" compact nebula surrounding it. XMM-Newton also has detected a trail that extends similar to 6' and, similar to the compact nebula, is also counteraligned with the proper motion of the pulsar. The spectra of both the pulsar and the extended emission are well described by an absorbed power-law model. The measured flux corresponds to an efficiency of converting the spin-down luminosity into X-rays in the 2-10 keV band of similar to 0.01% and similar to 1% for the pulsar and the extended emission, respectively. From the XMM-Newton data we have detected pulsations at the expected radio period. The energetics and the extent of the extended emission can be explained by a bow shock formed by the motion of the pulsar through the interstellar medium

Frequency-Shift Zero-Forcing Time-Varying Equalization for Doubly Selective SIMO Channels

<p/> <p>This paper deals with the problem of designing linear time-varying (LTV) finite-impulse response zero-forcing (ZF) equalizers for time- and frequency-selective (so-called doubly selective) single-input multiple-output (SIMO) channels. Specifically, relying on a basis expansion model (BEM) of the rapidly time-varying channel impulse response, we derive the canonical frequency-domain representation of the minimal norm LTV-ZF equalizer, which allows one to implement it as a parallel bank of linear time-invariant filters having, as input signals, different frequency-shift (FRESH) versions of the received data. Moreover, on the basis of this FRESH representation, we propose a simple and effective low-complexity version of the minimal norm LTV-ZF equalizer and we discuss the relationships between the devised FRESH equalizers and a LTV-ZF equalizer recently proposed in the literature. The performance analysis, carried out by means of computer simulations, shows that the proposed FRESH-LTV-ZF equalizers significantly outperform their competitive alternative.</p