Low-radio-frequency eclipses of the redback pulsar J2215+5135 observed in the image plane with LOFAR.

The eclipses of certain types of binary millisecond pulsars (i.e. 'black widows' and 'redbacks') are often studied using high-time-resolution, 'beamformed' radio observations. However, they may also be detected in images generated from interferometric data. As part of a larger imaging project to characterize the variable and transient sky at radio frequencies <200 MHz, we have blindly detected the redback system PSR J2215+5135 as a variable source of interest with the Low-Frequency Array (LOFAR). Using observations with cadences of two weeks - six months, we find preliminary evidence that the eclipse duration is frequency dependent (∝ν-0.4), such that the pulsar is eclipsed for longer at lower frequencies, in broad agreement with beamformed studies of other similar sources. Furthermore, the detection of the eclipses in imaging data suggests an eclipsing medium that absorbs the pulsed emission, rather than scattering it. Our study is also a demonstration of the prospects of finding pulsars in wide-field imaging surveys with the current generation of low-frequency radio telescopes.

The heating of gas in a galaxy cluster by X-ray cavities and large-scale shock fronts.

Most of the baryons in galaxy clusters reside between the galaxies in a hot, tenuous gas. The densest gas in their centres should cool and accrete onto giant central galaxies at rates of 10-1,000 solar masses per year. No viable repository for this gas, such as clouds or new stars, has been found. New X-ray observations, however, have revealed far less cooling below X-ray temperatures than expected, altering the previously accepted picture of cooling flows. As a result, most of the gas must be heated to and maintained at temperatures above approximately 2 keV (ref. 3). The most promising heating mechanism is powerful radio jets emanating from supermassive black holes in the central galaxies of clusters. Here we report the discovery of giant cavities and shock fronts in a distant (z = 0.22) cluster caused by an interaction between a radio source and the hot gas surrounding it. The energy involved is approximately 6 x 10(61) erg, the most powerful radio outburst known. This is enough energy to quench a cooling flow for several Gyr, and to provide approximately 1/3 keV per particle of heat to the surrounding cluster.

The effect of radiation therapy on the fixation strength of an experimental porous-coated implant in dogs.

Radiation therapy prevents heterotopic ossification after cemented total hip arthroplasty, but its effect on the fixation of porous-coated devices is not known. The purpose of this study was to determine the effect of irradiation on the pullout strength of a porous implant in the canine model. A custom-designed titanium fiber metal-coated cylinder was implanted into the distal femurs of 12 dogs. One femur of each dog was irradiated with 10 Gy, given in four 2.5-Gy daily fractions beginning one day after surgery. Serial bone scans were performed at one, two, four, and six weeks postoperatively. At six weeks, the femurs were harvested, and eight were randomly selected for mechanical testing. Scintigraphic evaluation showed a significant reduction in uptake at one and two weeks in the irradiated limb, but this had returned to normal at four and six weeks. The failure to pullout was significantly less in the irradiated limb compared with the control limb six weeks postoperatively. In this canine model, the pullout strength of the titanium fiber implant was significantly reduced by a dose of radiation commonly used in the prevention of heterotopic ossification. If irradiation is chosen for prophylaxis, either the porous implant should be adequately shielded or a cemented implant should be utilized.