What is the Mass of the NGC 300 X-1 Black Hole?

Revised buffer time according to COS Handbook 5.4.5, calculated using 2/3 COS ETC buffer time - 2/25/20. For review by Alison Vick to determine appropriate spacing between visits. removed ToO response time, added FGS3 use. Using phases/orbital period. removed remaing after bys, opened phase windows to 0.10 added FGS3 to both obsets put the phase requirement on the science exposures only. put phase on target acq, used extended gs acq -1094360522 ----- Attempting Submission 1 (Wed Sep 04 19:04:11 GMT 2019) ----- ----- Attempting Submission 2 (Wed Sep 04 19:20:22 GMT 2019) ----- ----- Attempting Submission 3 (Wed Sep 04 20:24:37 GMT 2019) ----- ----- Attempting Submission 4 (Wed Sep 04 20:38:10 GMT 2019) ----- HST Phase II Proposal 15999 (15999.apt) successfully submitted. Receipt: # 15999-4 ----- Attempting Submission 5 (Wed Sep 04 20:42:27 GMT 2019) ----- ----- Attempting Submission 6 (Thu Sep 05 15:51:31 GMT 2019) ----- ----- Attempting Submission 7 (Mon Sep 09 17:05:24 GMT 2019) ----- ----- Attempting Submission 8 (Tue Feb 25 19:15:12 GMT 2020) ----- What is the Mass of the NGC 300 X-1 Black Hole? NGC 300 X-1 is a high mass Wolf-Rayet + black hole X-ray binary located ~2 Mpc away in the spiral galaxy NGC 300. Radial velocity measurements of the He II 4686 line were used to derive a black hole mass M_BH~20 M_sun, making X-1 one of the heaviest known X-ray-bright solar-mass BHs. However, follow-up Chandra observations revealed a phase shift between the X-ray emission and the He II 4686 radial velocity, indicating that this emission line did not trace the motion of the WR donor; recent XMM-Newton observations have confirmed this discrepancy, thereby invalidating prior estimates of M_BH. With combined Chandra X-ray imaging/timing and HST/COS FUV spectroscopy that samples the binary orbital period, we will be able to reliably separate the spectral features of the WR donor and provide correct measurements of the system's component masses. We will collect COS spectra for the Wolf-Rayet + black hole binary NGC 300 X-1 at four different orbital phases (with 2 orbits per visit). The instrument settings for all four visits is identical: NGC 300 X-1 (4 x 2 orbits): COS/FUV G140L. The best measurement of the binary orbital period is 32.7932 +/- 0.0029 hr, with a zero-point time corresponding to phase=0 (e.g., the deepest part of the X-ray dip) on MJD 57741.3642. The Hubble visits should roughly sample the entire binary orbital period, although they need not be taken during a single orbital cycle. However, to keep the orbital phase uncertainty to a minimum, all HST visits and the Chandra X-ray observations should be completed within roughly one month of one another. PI Binder is an expert on the NGC 300 X-1 system (Binder et al. 2011), and presented the first study that invalidated the He II emission line as a tracer of the Wolf-Rayet star (Binder et al. 2015). She has extensive experience with Chandra X-ray data reduction and analysis and has experience with modeling UV/optical spectral features. Co-I Williams is an experienced HST user and provided key insights to interpreting prior observations of NGC 300 X-1. He has led or supervised graduate students on X-ray binary population studies (a secondary science goal of this program). Co-I Eracleous is an experiences HST/COS user and will provide support for reducing and analyzing COS spectra. He also has experience in interpreting COS spectroscopy in accreting black hole systems. Co-I Plucinsky has expertise in Chandra data reduction and analysis, and has extensively collaborated with the PI on the interpretation of X-ray binary evolution and population studies. 6 false false false false false false false SUPPORTED STAR WIND WOLF RAYET WOLF RAYET - WN NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 1582740066992 The scheduling data was generated by CASM 28.0. 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