VLBI IMAGES OF 49 RADIO SUPERNOVAE IN ARP 220

摘要: We have used a very long baseline interferometry (VLBI) array at 18 cm wavelength to image the nucleus of luminous IR galaxy Arp 220 ∼1 pc linear resolution, with high sensitivity. The resulting map has an rms 5.5 μJy beam -1, and careful analysis results in 49 confirmed point sources ranging flux density from 1.2 mJy down ∼60 μJy. Comparison high-sensitivity data 12 months earlier reveals least four new sources. favored interpretation these is that they are radio supernovae, if all supernovae detectable this sensitivity, estimate supernova rate system 4 ± 2 per year. implied star formation sufficient power entire observed far-infrared luminosity galaxy. two nuclei exhibit striking similarities their properties, although western more compact, appears be ∼3 times than eastern nucleus. There also some puzzling differences, differential free-free absorption, synchrotron aging, expansion losses may playing role. nearby starburst M82 supports hypothesis activity essentially scaled-up version M82.