Global e-VLBI observations of the gamma-ray narrow line Seyfert 1 PMN J0948+0022

There is growing evidence of relativistic jets in radio-loud narrow-line Seyfert 1 (RL-NLS1) galaxies. We constrain the observational properties of the radio emission in the first RL-NLS1 galaxy ever detected in gamma-rays, PMN J0948+0022, i.e., its flux density and structure in total intensity and in polarization, its compactness, and variability. We performed three real-time e-VLBI observations of PMN J0948+0022 at 22 GHz, using a global array including telescopes in Europe, East Asia, and Australia. These are the first e-VLBI science observations ever carried out with a global array, reaching a maximum baseline length of 12458 km. The observations were part of a large multiwavelength campaign in 2009. The source is detected at all three epochs. The structure is dominated by a bright component, more compact than 55 microarcsec, with a fainter component at a position angle theta~ 35deg. Relativistic beaming is required by the observed brightness temperature of 3.4x10^11 K. Polarization is detected at a level of about 1%. The parameters derived by the VLBI observations, in addition to the broad-band properties, confirm that PMN J0948+0022 is similar to flat spectrum radio quasars. Global e-VLBI is a reliable and promising technique for future studies.