We conducted very long baseline interferometry ( VLBI ) observations of five radio-loud narrow-line Seyfert 1 ( NLS1 ) galaxies in milliarcsecond resolutions at 1.7 GHz ( \lambda 18 cm ) using the Very Long Baseline Array ( VLBA ) .
Significant parsec-scale structures were revealed for three out of the five sources with high brightness temperature by direct imaging ; this is convincing evidence for nonthermal jets .
FBQSÂ J1644+2619 with an inverted spectrum showed a prominent one-sided linear structure , indicating Doppler beaming with an intrinsic jet speed of > 0.74 c .
FBQSÂ J1629+4007 , also with an inverted spectrum , showed rapid flux variability , indicating Doppler beaming with an intrinsic jet speed of > 0.88 c .
Thus , we found convincing evidence that these two NLS1s can generate at least mildly or highly relativistic jets , which may make them apparently radio loud even if they are intrinsically radio quiet .
On the other hand , the other three NLS1s had steep spectra and two of them showed significantly diffuse pc-scale structures , which were unlikely to be strongly beamed .
Thus , some NLS1s have the ability to generate jets strong enough to make them intrinsically radio loud without Doppler beaming .
NLS1s as a class show a number of extreme properties and radio-loud ones are very rare .
We build on these radio results to understand that the central engines of radio-loud NLS1s are essentially the same as that of other radio-loud AGNs in terms of the formation of nonthermal jets .