A Black Hole in XTE J1118+480
ATel #64; J. McClintock, M. Garcia, P. Zhao, N. Caldwell, and E. Falco; Harvard-Smithsonian Center for Astrophysic
on 13 Dec 2000; 17:44 UT
Credential Certification: Michael R. Garcia (garcia@cfa.harvard.edu)
Subjects: X-ray, Black Hole, Transient
Referred to by ATel #: 383, 386
Spectroscopic observations of this X-ray nova with the new 6.5-m MMT on Dec. 1 & 4
show that it contains a black hole primary of at least 6 solar masses.
Our prior photometric observations using the FLWO 1.2-m telescope
showed that the X-ray nova was near its pre-outburst brightness (IAUC
7390 ) at V = 18.8 on Oct. 26. The quiescent state of the system was
confirmed on the nights of Nov. 30 & Dec. 1 by P. Garnavich who
observed a double-humped, ellipsoidal light curve using the VATT 1.8-m
(priv. comm.). Two MMT spectra were obtained on Dec. 1 and six
additional spectra were obtained on Dec. 4. As expected, the spectra
contain both broad Balmer emission lines and the numerous absorption
features characteristic of a late-type dwarf. Robust velocity
measurements were obtained by cross-correlating the individual spectra
(range 490-650 nm) against the spectra of several bright dwarfs
(K5-M2). The eight velocities provide good phase coverage and yield a
velocity amplitude of K = 698 +/- 11 km/s and an orbital period of P =
0.1701 +/- 0.0003 days (IAUC 7412 , 7418 ). The large value of the mass
function, f(M) = 6.0 +/- 0.3 solar masses, is rivaled only by that of
V404 Cyg. A time of maximum velocity occurred on 2000 Dec. 1.4776 +/-
0.0005 UT."
