LOW FREQUENCY EXTENDED RADIO SOURCES——MAGNETIC FIELD STRENGTH AND CLASSIFICATION ATTEMPT

Using very recently published X-ray and low frequency radio data we have calculated thelower limit of the magnetic field and several other related quantities for 25 clusters of galaxies（which are classified into 'normal', distant and steep spectrum clusters） and 12 radiogalaxies. Our main results are as follows: （1）The magnetic field in the extended lobes of radio galaxies is larger than 10-6 G.Thus radio galaxies, whether they belong to clusters or not, emit few X-rays through theinverse Compton effect. （2）The low frequency radio emission from clusters can be divided into two components:one or several radio galaxies, and an extended halo where the magnetic field is about 10-8G, and where inverse Compton X-rays are most probably emitted. （3）Our sample of distant clusters is biased towards high radio luminosity and givesresults comparable to those obtained for radio galaxies. This can naturally be explained bythe fact that the radio galaxy component daminates the radio emission. （4）In steep spectrum clusters, the equipartition magnetic field is the same as that in'normal' clusters, but the lower limit of the magnetic field has a rather high value andseems to increase with the spectral indcx. We explain this as follows: a high frequencyturnover can occur hi the weak intraculuster magnetic field; the extrapolation of the power lawelectron spectrum is then incorrect, and the magnetic field; the extrapolation of the power lawvalue.

Expected Number Counts of Radio Galaxy Clusters

Clusters of galaxies may contain radio sources if they still experience successive mergers at present. This has been confirmed by radio observations that about 30% of nearby clusters possess radio halos. We present a theoretical pre- diction of radio cluster counts using a semi-analytic approach which incorporates the empirical correlation between radio power and dynamical mass of clusters, and the cluster mass function described by the Press-Schechter formalism. The total population of radio clusters over the whole sky and their redshift distribution are given.

Image reconstruction for the coded aperture system in nuclear safety and security using a Monte Carlo-based system matrix

Purpose Accurate localization of radioactive materials is critical to nuclear safety and nuclear security.A coded aperture imaging system provides a visualization solution.However,the correlation method has poor reconstruction performance for sources with low counts and for extended sources.Methods In this study,a Monte Carlo optimization-based MLEM algorithm(MC-MLEM)is proposed.The system matrix was obtained by accurate Monte Carlo simulation,so the physical effects such as mask penetration that affect the imaging process were taken into account in the MLEM algorithm.In the simulation process,the normalization of the system matrix was realized by controlling the source at different position of the source plane to have the same activity and emission angle.Results The experimental results showed that compared with the correlation method,the MC-MLEM algorithm could improve the signal-to-noise ratio and angular resolution and locate the source position quickly and accurately under low count conditions.Furthermore,the MC-MLEM algorithm could reconstruct the shape of the extended source and the expected activity ratio of cold-hot sources with large activity differences.Conclusion The MC-MLEM algorithm improved the imaging results and enhanced the reconstruction performance.