X-ray spectral scaling of black hole mass in quasi-periodic eruptive source RX J1301.9+2747

We present a spectral and timing analysis of X-ray emission from the actively accreting supermassive black hole (SMBH) in RX J1301.9+2747 with prominent quasi-periodic eruptions (QPEs) using ASCA, ROSAT, XMM-Newton, and NICER observations. NICER detected renewed QPE activity from this source in 2024. We examined in detail the X-ray spectrum formation in this source during QPE outbursts applying the first-principal model, Bulk Motion Comptonization. We find an increase of the photon index Γ with a mass accretion rate M, the index saturation at Γ sat=2.7 plus or minus 0.1 at high M value during outburst peaks. Based on the derived Γ- M correlation, we apply the scaling technique for the first time to measure the black hole mass in RX J1301.9+2747. The SMBH mass in this source was estimated to be between 4 times 10 5 M and 7 times 10 6 M for the inclination range from 0 to 70, which is adopted as a plausible range based on the AGN unified model assumption, applying HLX--1 ESO 243--49, OJ 287, and 1H 0707--495 as reference scaling sources. We also estimate a BH mass in RX J1301.9+2747 applying a timing analysis, in which the Compton cloud size to be about 10 11 cm, estimated from the quasi-periodic oscillation frequency, ν about 10-4 Hz, indicates SMBH mass in RX J1301.9+2747 is of order of 10 6 M. Overall, the BH mass obtained by the scaling method in this source is consistent with previous measurements using other methods.