Issue |
A&A
Volume 671, March 2023
|
|
---|---|---|
Article Number | A159 | |
Number of page(s) | 9 | |
Section | Astrophysical processes | |
DOI | https://doi.org/10.1051/0004-6361/202345923 | |
Published online | 20 March 2023 |
OJ 287: A new BH mass estimate of the secondary
1
Dipartimento di Fisica, University di Ferrara, Via Saragat 1, 44122 Ferrara, Italy
e-mail: titarchuk@fe.infn.it
2
Lomonosov Moscow State University/Sternberg Astronomical Institute, Universitetsky Prospect 13, Moscow 119992, Russia
e-mail: seif@sai.msu.ru
3
NASA Goddard Space Flight Center, NASA, Astrophysics Science Division, Code 661, Greenbelt, MD 20771, USA
e-mail: Chris.R.Shrader@nasa.gov
4
Universities Space Research Association, 10211 Wincopin Cir, Suite 500, Columbia, MD 21044, USA
Received:
17
January
2023
Accepted:
10
February
2023
We present a study of outburst activity in the BL Lacertae source OJ 287, which has been observed extensively with the X-ray telescope (XRT) on board the Neil Gehrels Swift Observatory. We demonstrate that the results of our analysis of X-ray flaring activity using the Swift/XRT data allow for the key characteristics of the OJ 287 secondary to be refined (its nature and mass). We discover that the energy spectra in all spectral states can be fitted using the XSPEC bulk motion Comptonization (BMC) model. As a result we find that the X-ray photon index of the BMC model, Γ, correlates with the mass accretion rate, Ṁ. We establish that Γ increases monotonically with Ṁ from the low-hard state, Γ ∼ 1.5, to the high-soft state, Γ ∼ 2.8, and finally saturates. The index behavior is similar to that in a number of black hole (BH) candidates in which we show that its saturation is observational evidence of the presence of a BH. Based on this correlation, we applied a scaling method and determine that a secondary BH mass in OJ 287 is about ∼1.25 × 108 solar masses, using the well-studied X-ray BH binaries XTE 1550–564, H 1743–322, 4U 1630–47, and GRS 1915+105 as well as extragalactic BHs ESO 243–49 and M101 ULX–1, as reference sources. Also, using the power spectrum analysis, we infer the size of the Compton cloud LCC ∼ 1013 cm where X-ray spectra were formed. Using this value of LCC, we confirm that a BH mass of the secondary in OJ 287 was on the order of 108 solar masses as we derived using the index, Γ–correlation (the scaling method) with respect of the mass accretion rate.
Key words: accretion / accretion disks / black hole physics / galaxies: active / BL Lacertae objects: individual: OJ 287 / X-rays: galaxies
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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