The Wolf-Rayet + Black Hole Binary NGC 300 X-1: What is the Mass of the Black Hole?

Breanna A. Binder, Janelle M. Sy, Michael Eracleous, Dimitris M. Christodoulou, Sayantan Bhattacharya, Rigel Cappallo, Silas Laycock, Paul P. Plucinsky, Benjamin F. Williams

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


We present new X-ray and UV observations of the Wolf-Rayet + black hole (BH) binary system NGC 300 X-1 with the Chandra X-ray Observatory and the Hubble Space Telescope Cosmic Origins Spectrograph. When combined with archival X-ray observations, our X-ray and UV observations sample the entire binary orbit, providing clues to the system geometry and interaction between the BH accretion disk and the donor star wind. We measure a binary orbital period of 32.7921 0.0003 hr, in agreement with previous studies, and perform phase-resolved spectroscopy using the X-ray data. The X-ray light curve reveals a deep eclipse, consistent with inclination angles of i = 60-75, and a pre-eclipse excess consistent with an accretion stream impacting the disk edge. We further measure radial velocity variations for several prominent far-UV spectral lines, most notably H ii λ1640 and C iv λ1550. We find that the He ii emission lines systematically lag the expected Wolf-Rayet star orbital motion by a phase difference of Δφ ∼ 0.3, while C iv λ1550 matches the phase of the anticipated radial velocity curve of the Wolf-Rayet donor. We assume the C iv λ1550 emission line follows a sinusoidal radial velocity curve (semi-amplitude = 250 km s-1) and infer a BH mass of 17 4 M o˙. Our observations are consistent with the presence of a wind-Roche lobe overflow accretion disk, where an accretion stream forms from gravitationally focused wind material and impacts the edge of the BH accretion disk.

Original languageEnglish (US)
Article number74
JournalAstrophysical Journal
Issue number1
StatePublished - Mar 20 2021

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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