Turnover Frequency

Category:Observational
Date:Apr 2019
Citations:

Probing the Jet Turnover Frequency Dependence on Black Hole Mass and Mass Accretion Rate

Hammerstein, Erica; Gültekin, Kayhan; King, Ashley

The Astrophysical Journal, Volume 875, Issue 2, article id. 82, 8 pp. (2019).

Figure showing log of flux density in Jy as a function of log of frequency in MHz. The y-axis ranges from -4 to 1. The x-axis ranges from 3.0 to 4.75. The data from x = 3.0 to 3.505 are flat at about y = 0. The data from x = 3.505 to 4.6 are going down. The legend indicates that the source is IC 1459, that the low-frequency spectral index is -0.08 +/- 0.08, the high-frequency spectral index is 0.73 +/- 0.01, and the log of the turnover frequency is 3.55 +/- 0.022. — IC 1459 SED
This figure shows a spectral energy distribution (SED) of IC 1459. The red line indicates the fit to the SED data points, the values of which are noted in the legend as α_1 or α_2, where α_1 and α_2 are the spectral indices before and after the turnover frequency, respectively. The turnover frequency is indicated by a blue box, with error bars.

Figure showing log of turnover frequency in units of MHz as a function of log of X-ray luminosity divided by Eddington luminosity. The y-axis ranges from 2.5 to 7, and the x-axis ranges from -9 to -5.5. There is a title that says "Constant Mass", and 8 data points with error bars and limits, each with a unique identifying number across the plot with no apparent correlation. — Turnover frequency as a function of L_x / L_Edd
The turnover frequency as a function of fractional X-ray luminosity, which we use as a proxy for mass accretion rate. The sources in this figure all have approximately constant mass. Each source is given a unique number annotated on the figure that corresponds to the ID column in Table in the paper. Correlation testing by assigning arbitrary extreme values for limits reveals a weak positive correlation. With a very high p-value, however, this result is not statistically significant.

Figure showing log of turnover frequency in units of MHz as a function of log of mass in units of solar masses. The y-axis ranges from about 3.0 to 6.0, and the x-axis ranges from about 7.5 to 10.0. There is a title that says "Constant L_x / L_Edd", and 8 data points with error bars and limits, each with a unique identifying number across the plot with no apparent correlation. — Turnover frequency as a function of mass
The turnover frequency as a function of mass of the central supermassive black hole. The sources in this figure all have approximately constant L_X / L_Edd. Each source is given a unique number annotated on the figure that corresponds to the ID column in the Table of the paper. First inspection of this figure reveals a possible slight positive correlation and correlation testing confirms this. This result is not statistically significant, as testing also yields a very high p-value.

A paper written by former UM undergraduate Erica Hammerstein (now a PhD student at the University of Maryland, College Park). AGN that are very sub-Eddington should be jet dominated. Where the jet is optically thick, the jet’s spectrum should look flat in F_nu vs nu space; and have a negative slope at higher frequencies where the jet is optically thin. The frequency at which this transition happens is called the turnover frequency. If jets are simple, we would expect the turnover frequency to show strong correlations with black hole mass and mass accretion rate. We used VLA to observe two samples of low-luminosity AGN that either had a very similar black hole mass or a very similar mass accretion rate. We measured the turnover frequency (or put limits on it) for all of the sources. Then we tested how the turnover frequency scales with black hole mass and mass accretion rate, and found that there was no strong correlation, indicating that jets are not so simple.

Project info

Probing the Jet Turnover Frequency Dependence on Black Hole Mass and Mass Accretion Rate

Hammerstein, Erica; Gültekin, Kayhan; King, Ashley

The Astrophysical Journal, Volume 875, Issue 2, article id. 82, 8 pp. (2019).