Carla June Carroll and Professor Michael D. Joner, Department of Physics and Astronomy
Introduction
The environment surrounding supermassive black holes in active galaxies is very difficult to probe. The physical size of the region of interest can usually fit within our solar system, yet is hundreds of thousands of light years away. It can, however, be probed through the reverberation mapping technique. This technique requires the galactic nuclei to be simultaneously observed both spectroscopically with a large 2 meter-class telescope and photometrically (can be done with a smaller telescope). Since obtaining large telescope time for long observing campaigns is difcult, we present a new broadband photometric reverberation mapping technique that can be performed on meter-class telescopes.
Materials/Methods
Observations in the R and V band lters provide a measurement of time variable emission in Hα and Hβ respectively mixed with an observation of the continuum (see Figure 1). The I band lter provides a continuum-only measurement. See image one for a visual of the filters used with respect to spectroscopic data for the object of interest (Mrk 926). This is a key distinction from traditional reverberation mapping, which uses spectroscopy. Spectroscopy requires a small range of wavelength so information can be gathered on variations of the data as a function of wavelength. As previously mentioned, this method requires large telescopes. To acquire large telescope time, one must apply many months in advance to use only a few days on the telescope and hope that weather and technical difficulties will not interfere. A broadband technique that can be used on meter-class telescopes would allow for long periods of observations (yielding more useful and accurate conclusions) with less cost. Though this method still requires some spectroscopy, single epoch spectroscopy will be enough for the information needed.
Results
We obtained photometric observations in VRI on the 0.9-meter telescope at the West Mountain Observatory of the very broad-line Seyfert I galaxy Mrk 926 to test this technique. We found Mrk 926 relatively quiescent during the fall of 2012, though we originally selected Mrk 926 due to its strong emission lines and strong variability as described by Kollatschny & Zetzl (2010). This made estimation of Mrk 926’s supermassive black hole mass impossible.
Discussion
Despite the quiescent results of Mrk 926, we produced high precision light curves from all lters over the period of several months. Our data are sufcient that had our target AGN been variable, we would have been able to measure delay times between the BLR and the nucleus. These quiescent results would have occurred, even with a larger telescope using the traditional reverberation mapping technique. There is not recognizable periodicity in active galaxies and thus a quiescent result is unpredictable. Our results emphasize the need for a more accessible method to perform reverberation mapping to estimate the mass of supermassive black holes inside active galaxies.