Bibcode
DOI
Gallimore, J. F.; Henkel, C.; Baum, S. A.; Glass, I. S.; Claussen, M. J.; Prieto, M. A.; Von Kap-herr, A.
Bibliographical reference
The Astrophysical Journal, Volume 556, Issue 2, pp. 694-715.
Advertised on:
8
2001
Journal
Citations
112
Refereed citations
100
Description
We report new (1995) Very Large Array (VLA) observations and (1984-1999)
Effelsberg 100 m monitoring observations of the 22 GHz H2O
maser spectrum of the Seyfert 2 galaxy NGC 1068. The sensitive VLA
observations provide a registration of the 22 GHz continuum emission and
the location of the maser spots with an accuracy of ~5 mas. Within the
monitoring data, we find evidence that the nuclear masers vary
coherently on timescales of months to years, much more rapidly than the
dynamical timescale. We argue that the nuclear masers are responding in
reverberation to a central power source, presumably the central engine.
Between 1997 October and November, we detected a simultaneous flare of
the blueshifted and redshifted satellite maser lines. Reverberation in a
rotating disk naturally explains the simultaneous flaring. There is also
evidence that near-IR emission from dust grains associated with the
maser disk also responds to the central engine. We present a model in
which an X-ray flare results in both the loss of maser signal in 1990
and the peak of the near-IR light curve in 1994. In support of rotating
disk geometry for the nuclear masers, we find no evidence for
centripetal accelerations of the redshifted nuclear masers; the limits
are +/-0.006 km s-1 yr-1, implying that the masers
are located within 2° of the kinematic line of nodes. We also
searched for high-velocity maser emission like that observed in NGC
4258. In both VLA and Effelsberg spectra, we detect no high-velocity
lines between approximately +/-350 and +/-850 km s-1 relative
to systemic, arguing that masers only lie outside a radius of ~0.6 pc
(1.9 lt-yr) from the central engine (assuming a distance of 14.4 Mpc).
We also consider possible models for the jet masers near radio continuum
component C. We favor a shock precursor model, in which the molecular
gas surrounding the jet is heated by X-ray emission from a shock front
between the jet and a molecular cloud.