During the past week, NuSTAR performed a 5-day long observation of the nearby active galaxy MCG-06-30-15 in coordination with JAXA/NASA/ESA’s XRISM observatory and NASA’s IXPE observatory. For nearly three decades, this source has been a premier X-ray target for studying the extreme environment around a supermassive black hole. One long-standing puzzle is the dramatic variability of direct X-ray emission from the hot corona—the compact cloud of energetic particles near the central engine—while reflected X-rays off the accretion disk vary much less. One possible explanation is relativistic light-bending by the supermassive black hole: changes in the geometry of the corona, particularly its height above the black hole, will strongly affect X-ray photon paths. MCG-06-30-15 naturally cycles through bright and faint states on timescales of only a few hours, so a 5-day observation should track this evolution in real time. NuSTAR’s unique sensitivity to high-energy X-rays allows it to track both the primary coronal emission and reflected X-rays across flux states, while XRISM's unprecedented spectral resolution simultaneously measures changes in iron emission line from the accretion disk. Together, these observations will provide one of the most direct tests yet of whether relativistic light bending drives the observed X-ray variability, while revealing how the geometry of the corona evolves as the source changes brightness. Simultaneous X-ray polarization measurements from NASA’s IXPE observatory will also provide an independent probe of the coronal geometry, offering a powerful complementary test of this picture.

Author: Indrani Pal (Postdoctoral Fellow, Clemson University)