P. Castangia [1], C. M. V. Impellizzeri [2], J. P. McKean [3], C. Henkel [4], A. Brunthaler [4], A. L. Roy [4], O. Wucknitz [5], J. Ott [6], and E. Momjian [6]
Methods: We monitored the maser line in the lensed quasar MG J0414+0534 at z = 2.64 with the 300-m Arecibo telescope for ∼15 months to detect possible additional maser components and to measure a potential velocity drift of the lines. In addition, we follow the maser and continuum emissions to reveal significant variations in their flux density and to determine correlation or time-lag, if any, between them.
Results: Themain maser line profile is complex and can be resolved into a number of broad features with line widths of 30–160 kms−1.
A new maser component was tentatively detected in October 2008 that is redshifted by 470 kms−1 w.r.t the systemic velocity
of the quasar. The line width of the main maser feature increased by a factor of two between the Effelsberg and EVLA observations
reported by Impellizzeri et al. (2008) and the first epoch of the Arecibo monitoring campaign. After correcting for
the lens magnification, we find that the total H2O isotropic luminosity of the maser in MG J0414+0534 is now ∼30,000 L⊙,
making this source the most luminous ever discovered. Both the main line peak and continuum flux densities are surprisingly stable
throughout the period of the observations. The integrated flux density shows instead significant variations on monthly time scales, possibly
due to changes in the individual velocity components. The velocity of the peak of the line emission drifts by <∼
2 kms−1 yr−1.
Conclusions. The large line width of the main maser line and the absence of a clear triple-peak pattern in the maser spectrum of
MG J0414+0534 favors the jet-maser scenario. However, the stability of the line and continuum emission, and the presence of the
tentative new maser component, potentially identified as a high-velocity feature of a rotating disk, seems partly going against this
interpretation. Sensitive monitoring on a longer time-scale and VLBI observations are mandatory to draw a definite conclusion.