Simultaneous Millimeter-wave and X-ray monitoring of the Seyfert Galaxy NGC 7469

TL;DR

This study presents simultaneous millimeter-wave and X-ray monitoring of the Seyfert galaxy NGC 7469, revealing correlated variability suggesting a common origin in the AGN's corona, and highlights the need for higher cadence observations.

Contribution

First simultaneous multi-band monitoring of NGC 7469 in mm, X-ray, and UV/optical bands, providing new insights into AGN variability and coronal activity.

Findings

Millimeter and X-ray fluxes vary in tandem, indicating a shared origin.

UV/optical variability is much less pronounced, originating from a different component.

A tentative 14-day lag suggests a physical connection between the corona and mm emission.

Abstract

We report on daily monitoring of the Seyfert galaxy NGC 7469, around 95 GHz and 143 GHz, with the IRAM 30 m radio telescope, and with the Swift X-Ray and UV/Optical telescopes, over an overlapping period of 45 days. The source was observed on 36 days with IRAM, and the flux density in both mm bands was on average $\sim 10$ mJy, but varied by $\pm50\%$, and by up to a factor of 2 between days. The present IRAM variability parameters are consistent with earlier CARMA monitoring, which had only 18 data points. The X-ray light curve of NGC 7469 over the same period spans a factor of 5 in flux with small uncertainties. Similar variability in the mm-band and in the X-rays lends support to the notion of both sources originating in the same physical component of the AGN, likely the accretion disk corona. Simultaneous monitoring in eight UV/optical bands shows much less variability than the mm and X-rays, implying this light originates from a different AGN component, likely the accretion disk itself. We use a tentative 14 day lag of the X-ray light curve with respect to the 95 GHz light curve to speculate on coronal implications. More precise mm-band measurements of a sample of X-ray-variable AGN are needed, preferably also on time scales of less than a day where X-rays vary dramatically, in order to properly test the physical connection between the two bands.