Discovery of mHz X-ray Oscillations in a Transient Ultraluminous X-ray Source in M82

TL;DR

This paper reports the discovery of 3-4 mHz X-ray quasi-periodic oscillations in a transient ultraluminous X-ray source in M82, suggesting a black hole of 12,000-43,000 solar masses and providing insights into high-mass black hole accretion.

Contribution

The study identifies and characterizes low-frequency QPOs in a ULX, inferring the presence of an intermediate-mass black hole, which is a novel finding in this context.

Findings

Detection of 3-4 mHz QPOs in M82 ULX

Black hole mass estimated at 12,000-43,000 solar masses

Cool disk emission observed supporting high-mass black hole presence

Abstract

We report the discovery of X-ray quasi-periodic oscillations (QPOs) at frequencies of 3-4 mHz from a transient ultraluminous X-ray source (ULX) X42.3+59 in M82. The QPOs are strong and broad and appear with weak or absent red noise, and are detected only in Chandra observations when the source is brighter than 10^40 ergs/s. The QPO behavior is similar to the type A-I QPOs found in XTE J1550-564, which is a subclass of low frequency QPOs with properties in between type A and B. Therefore, we identify the QPOs in X42.3+59 as of type A or B, and rule out the possibility of type C. With this identification, the mass of the black hole in X42.3+59 can be inferred as in the range of 12,000-43,000 solar masses by scaling the QPO frequency to that of the type A/B QPOs in stellar mass black holes. Cool disk emission is detected in one Chandra observation, and the disk inner radius suggests a similar black hole mass range. Black holes of such a high mass are able to produce an energy output in a manner similar to X42.3+59 by accreting from the interstellar medium directly.