A decade of quasi-periodic heartbeats in M82
Thirty-nine NuSTAR observations spanning ten years reveal the long-term evolution of quasi-periodic oscillations in the ultraluminous X-ray sources of M82.
M82 is the galaxy that started everything for me. It is home to M82 X-2, the first ultraluminous pulsar, that I discovered in 2014. But its neighbour, M82 X-1, has long been intriguing in its own right: it is still considered among the best intermediate-mass black hole candidates in ULXs.
We analyzed 39 NuSTAR observations taken between 2014 and 2024 and tracked the two ULXs’ quasi-periodic oscillations (QPOs), variations of the flux whose origin is still uncertain, but might be related to important frequencies in the system. The oscillation frequency wanders across the 20–300 mHz range, and its behaviour closely mirrors the low-frequency QPOs seen from accreting black holes and neutron stars inside our own Galaxy.
The first author of the work is Hamza el Byad, a PhD student in Maths that I supervised at University of Cagliari. The work applies a number of data analysis techniques that we implemented and developed as part of the PhD.