J. D. Romney

Very Long Baseline Array Observations of the Zeeman Effect in H2O Masers in W3 IRS 5

We present Very Long Baseline Array (VLBA) observations of the Zeeman effect in H2O masers in W3 IRS 5. These observations have yielded the first ultrahigh spatial resolution maps of the magnetic field in a star-forming region measured via the Zeeman effect—masers for which we can independently measure the magnetic field are separated by ≤25 mas (60 AU). This is the first VLBA detection of the Zeeman effect in H2O masers in a star-forming region. These observations also remove the confusion in observed magnetic fields from closely spaced masers. We shall explicitly demonstrate that observations at lower resolution can yield lower magnetic fields than with the VLBA, even though there are no field reversals within the larger beam.

RADIOASTRON OBSERVATIONS OF THE QUASAR 3C273: A CHALLENGE TO THE BRIGHTNESS TEMPERATURE LIMIT

Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of

Sensitive Very Long Baseline Interferometry Studies of the OH Megamaser Emission from IRAS 17208–0014

10^{11.5}

Global VLBI Observations of the High-Velocity H I Absorption toward NGC 1275

K. Relativistic boosting can increase its observed value, but apparent brightness temperatures much in excess of

VLBA Observations of the Zeeman Effect in H2O Masers in OH 43.8-0.1

10^{13}

Probing the Accretion Region of NGC 1275 with VLBI

K are inaccessible using ground-based very long baseline interferometry (VLBI) at any wavelength. We present observations of the quasar 3C273, made with the space VLBI mission RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as small as 26

VLBA studies of the accretion region in NGC 1275

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Simultaneous Multi-Frequency Imaging of the Nucleus of NGC 1275

as (2.7 light months) and brightness temperature in excess of

The Very Long Baseline Array

10^{13}

VLBA Absorption Imaging of Ionized Gas Associated with the Accretion Disk in NGC 1275

K. These measurements challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive black holes and require a much higher Doppler factor than what is determined from jet apparent kinematics.