Optical Observations of the Radio Source 3C 273.

The radio source 3C 273 has recently been identified with a star-like object of magnitude 12.6 and an adjacent thin wisp or jet. The two components of the radio source coincide, within 1", with the star-like object itself and the end of the jet. Photographic spectra show several broad emission lines. Photoelectric spectrum scanner observations in the infrared indicate a strong, broad emission line at ~7590. The observed emission lines at ~7590, ~5632, X5032, ~4753, and X4595 are identified with the Balmer lines H~ to HE. The line X7590 is displaced to the violet by several angstroms due to the absorption of the atmospheric A band. The redshift is found to be A~/N0=0.158, corresponding to an apparent velocity of 47 400 km/sec. Other emission lines X5792 and X3239 are identified respectively as X5007 of EO iii~ and ~2798 of Mg ii. The absolute energy distribution in the continuous spectrum, from X3300 to N8400, can be represented accurately by the relation Fp ~+O.25, where Fe is the flux per unit frequency interval and p is the frequency. Beyond X8400 the flux may increase significantly. The observed energy distribution is very different from that of a blackbody or a normal star; at least part of the optical radiation must be synchrotron radiation. The absolute flux at X5600 is 3.5X10-28 W m-2 cps-3. The corresponding radio flux at 960 Mc is 5.0X10-25 W m-2 cps-1. The large observed redshift and the stellar appearance of the object suggest two possibilities. (1) The star is a neutron star with a radius of 10 km. The appearance of both forbidden and permitted lines with the same redshift and the breadth of the lines (1 to 2% of the wavelength) make this explanation very unlikely. (2) The object is the luminous nucleus of a galaxy at a distance of 500 Mpc. The diameter of the nucleus region would be less than 1 kpc. The optical jet and component A of the radio source would be at a distance of at least 50 kpc, implying a time scale in excess of 10~ yr.