Delving into the depths of NGC 3783 with XRISM
Liyi Gu, Keigo Fukumura, Jelle Kaastra, Megan Eckart, Ralf Ballhausen, Ehud Behar, Camille Diez, Matteo Guainazzi, Timothy Kallman, Erin Kara, Chen Li, Missagh Mehdipour, Misaki Mizumoto, Shoji Ogawa, Christos Panagiotou, Matilde Signorini, Atsushi Tanimoto, Keqin Zhao, Hirofumi Noda, Jon Miller, Satoshi Yamada
Abstract
The 2024 X-ray/UV observation campaign of NGC 3783, led by XRISM, revealed the launch of an ultrafast outflow (UFO) with a radial velocity of 0.19 c (57 000 km s −1 ). This event is synchronized with the sharp decay, within less than half a day, of a prominent soft X-ray/UV flare. Accounting for the look-elsewhere effect, the XRISM Resolve data alone indicate a low probability of 2 × 10 −5 that this UFO detection is due to random chance. The UFO features narrow H-like and He-like Fe lines with a velocity dispersion of ∼1000 km s −1 , suggesting that it originates from a dense clump. Beyond this primary detection, there are hints of weaker outflow signatures throughout the rise and fall phases of the soft flare. Their velocities increase from 0.05 c to 0.3 c over approximately three days, and they may be associated with a larger stream in which the clump is embedded. The radiation pressure is insufficient to drive the acceleration of this rapidly evolving outflow. The observed evolution of the outflow kinematics instead closely resembles that of solar coronal mass ejections, implying magnetic driving and, conceivably, reconnection near the accretion disk as the likely mechanisms behind both the UFO launch and the associated soft flare.