OJ 287 Analysis Summary
Black hole mass estimate
The analysis yielded an estimate of approximately 200 million solar masses (2 × 108 M⊙), likely corresponding to the secondary black hole in the proposed OJ 287 binary system.
Core data-analysis problem
The Swift/XRT data set for OJ 287 consists of many short exposures, most of which contain too few counts for reliable spectral modelling on their own. The observations were therefore grouped by flux and averaged within each group, producing statistically robust spectra without losing their dependence on source flux.
Background
OJ 287 is a blazar and a long-standing candidate for hosting a binary system of supermassive black holes. Swift/XRT monitored the source extensively through many short and fragmented pointings, allowing its combined X-ray spectral evolution to be studied.
Motivation
The analysis was undertaken in response to a request from a theoretical astrophysics group studying accretion-flow models. The predicted behaviour was a rise of the X-ray photon index at lower accretion rates followed by saturation at higher values.
Method
All available Swift/XRT observations were uniformly reprocessed, sorted by source flux, and combined within defined flux intervals. The averaged spectra were analysed with the bulk-motion Comptonization (BMC) model.
The relation between photon index and BMC normalization was then compared with reference black-hole systems using the established scaling method.
Results
The reconstructed relation shows the required rise and subsequent saturation of the photon index. Applying the scaling relation yielded a black-hole mass estimate of approximately 2 × 108 M⊙ (about 200 million solar masses), most likely corresponding to the secondary component of the proposed binary system.
Later studies of OJ 287 by Valtonen et al. (2023) and Komossa et al. (2023) also arrived at black-hole mass scales of order 108 M⊙, using different physical models and observational approaches. Although the interpretations differ, the numerical estimates are broadly comparable.
References
Kuznetsov, S. 2024, MNRAS, 535, 3732 —
article
Valtonen, M. J., et al. 2023, MNRAS, 525, 1153 —
article
Komossa, S., et al. 2023, MNRAS Letters, 522, L84 —
article
Data sources
• Swift/XRT event files (UKSSDC)
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• XRT analysis documentation (UKSSDC)
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• HEASoft & NASA/HEASARC XRT tools
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