Does the 62-day X-ray periodicity come from ULX M82 X-1?

TL;DR

This study uses high-resolution Swift/XRT data to investigate the origin of the 62-day X-ray periodicity in M82, finding it likely arises from multiple sources near M82 X-1 rather than the source itself.

Contribution

The paper demonstrates that the previously attributed 62-day periodicity to M82 X-1 is likely due to multiple nearby sources, challenging earlier assumptions based on lower-resolution data.

Findings

The 62-day periodicity is not from M82 X-1 but from several sources nearby.

Swift/XRT data cannot resolve individual sources, limiting precise localization.

Higher spatial resolution observations are needed for definitive conclusions.

Abstract

M82 X-1 is the brightest ultraluminous X-ray source in starburst galaxy M82 and is one of the best intermediate mass black hole candidates. Previous studies based on the Rossi X-ray Timing Explorer/Proportional Counter Array (RXTE/PCA) reported a regular X-ray flux modulation of M82 with a period of 62 days, and attributed this periodic modulation to M82 X-1. However, this modulation is not necessarily from M82 X-1 because RXTE/PCA has a very poor spatial resolution of ~1 degree. In this work, we analyzed 1000 days of monitoring data of M82 X-1 from the Swift/X-ray telescope (XRT), which has a much better spatial resolution than RXTE/PCA. The periodicity distribution map of M82 reveals that the 62-day periodicity is most likely not from M82 X-1, but from the summed contributions of several periodic X-ray sources 4 arcsec southeast of M82 X-1. However, Swift/XRT is not able to resolve those periodic sources and locate the precise origin of the periodicity of M82. Thus, more long-term observations with higher spatial resolution are required.