Browsing by Author "Chang, C. -s."

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    Joint ALMA/X-ray monitoring of the radio-quiet type 1 active galactic nucleus IC 4329A
    (2024) Shablovinskaya, E.; Ricci, C.; Chang, C. -s.; Tortosa, A.; del Palacio, S.; Kawamuro, T.; Aalto, S.; Arzoumanian, Z.; Balokovic, M.; Bauer, F. E.; Gendreau, K. C.; Ho, L. C.; Kakkad, D.; Kara, E.; Koss, M. J.; Liu, T.; Loewenstein, M.; Mushotzky, R.; Paltani, S.; Privon, G. C.; Smith, K.; Tombesi, F.; Trakhtenbrot, B.
    The origin of a compact millimeter (mm, 100-250 GHz) emission in radio-quiet active galactic nuclei (RQ AGN) remains debated. Recent studies propose a connection with self-absorbed synchrotron emission from the accretion disk X-ray corona. We present the first joint ALMA (similar to 100 GHz) and X-ray (NICER/XMM-Newton/Swift; 2-10 keV) observations of the unobscured RQ AGN, IC 4329A (z = 0.016). The time-averaged mm-to-X-ray flux ratio aligns with recently established trends for larger samples, but with a tighter scatter (similar to 0.1 dex) compared to previous studies. However, there is no significant correlation on timescales of less than 20 days. The compact mm emission exhibits a spectral index of -0.23 +/- 0.18, remains unresolved with a 13 pc upper limit, and shows no jet signatures. Notably, the mm flux density varies significantly (by factor of 3) within four days, exceeding the contemporaneous X-ray variability and showing the largest mm variations ever detected in RQ AGN over daily timescales. The high amplitude variability rules out scenarios of heated dust and thermal free-free emission, pointing toward a synchrotron origin for the mm radiation in a source of similar to 1 light day (similar to 120 gravitational radii) size. While the exact source is not yet certain, an X-ray corona scenario emerges as the most plausible compared to a scaled-down jet or outflow-driven shocks.