Dynamical Evidence for a Black Hole in the Microquasar XTE J1550−564

Abstract

Optical spectroscopic observations of the companion star (type G8IV to K4III) in the microquasar system XTE J1550-564 reveal a radial velocity curve with a best fitting spectroscopic period of P sp = 1.552 ± 0.010 days and a semiamplitude of K 2 = 349 ± 12 km s −1 . The optical mass function is f (M) = 6.86 ± 0.71 M ⊙ (1σ). We tentatively measure the rotational velocity of the companion star to be V rot sin i = 90 ± 10 km s −1 , which when taken at face value implies a mass ratio of Q ≡ M 1 /M 2 = 6.6 +2.5 −1.6 (1σ), using the above value of K 2 . We derive constraints on the binary parameters from simultaneous modelling of the ellipsoidal light and radial velocity curves. We find 1σ ranges for the photometric period (1.5430 d ≤ P ph ≤ 1.5440 d), K−velocity (350.2 ≤ K 2 ≤ 368.6 km s −1 ), inclination (67.0 • ≤ i ≤ 77.4 • ), mass ratio (Q ≥ 12.0), and orbital separation (11.55 R ⊙ ≤ a ≤ 12.50 R ⊙ ). Given these geometrical constraints we find the most likely value of the mass of the compact object is 9.41 M ⊙ with a 1σ range of 8.36 M ⊙ ≤ M 1 ≤ 10.76 M ⊙ . If we apply our tentative value of V rot sin i = 90 ± 10 km s −1 as an additional constraint in the ellipsoidal modelling, we find 1σ ranges of 1.5432 d ≤ P ph ≤ 1.5441 d for the photometric period, 352.2 ≤ K 2 ≤ 370.1 km s −1 for the K−velocity, 70.8 • ≤ i ≤ 75.4 • for the inclination, 6.7 ≤ Q ≤ 11.0 for the mass ratio, and 12.35 R ⊙ ≤ a ≤ 13.22 R ⊙ for the orbital separation. These geometrical constraints imply the most likely value of the mass of the compact object of 10.56 M ⊙ with a 1σ range of 9.68 M ⊙ ≤ M 1 ≤ 11.58 M ⊙ . In either case the mass of the compact object is well above the maximum mass of a stable neutron star, and we therefore conclude XTE J1550-564 contains a black hole.

Limits on pair production and multizone Comptonization: the broad-band X/γ-ray spectrum of XTE J1550–564 revisited

“…Cyg X-1 (Gierliński et al 1997), it is certainly not so in the more luminous sources and/or states. Our modelling gives a source luminosity of ∼3.7 × 10 38 erg s −1 (for M = 10 M and D = 5.3 kpc; Orosz et al 2002). In the very high state, we expect a fairly large overlapping region of the hot flow and the disc.…”

“…These parameters were frozen to their best-fitting values, except for the normalization, in the two-component model fits, and the variability spectrum thus makes up the additional Comptonized component in the two-component models. The unabsorbed bolometric luminosity is L tot = 3.7 × 10 38 erg s −1 cm −2 for M = 10 M and D = 5.3 kpc Orosz et al (2002 The spectrum contains a strong disc component. The bestfitting inner disc temperature of the unscattered disc component is 0.56 keV, in agreement with or slightly higher than in DG03, KD04 and AHD13.…”

“…A few days into the outburst a radio jet was observed (Hannikainen et al 2001). The companion is a main-sequence star of type G-K, and the mass of the compact object has been estimated to 8.4-11.2 M (Orosz, Groot & van der Klis 2002), and it is thus considered to be a black hole. The source displays all the canonical spectral states typically associated with black hole binaries.…”

“…The main parameters are the relative amplitude of the reflected component, Ref l, the inclination and the ionization parameter of the reprocessing matter, ξ . For the inclination, we use i = 70 • (Orosz et al 2002). We allow for relativistic smearing of the reflection features using KDBLUR.…”

Evidence for Harmonic Relationships in the High‐Frequency Quasi‐periodic Oscillations of XTE J1550−564 and GRO J1655−40

“…Optical spectroscopy and photometry during accretion quiescence have recently established that the system is a dynamical black hole binary with a black hole mass of 10:0 AE 1:5 M (Orosz et al 2002). The companion star is a late-type subgiant (G8 IV-K4 III), and the binary inclination angle is constrained to the range 72 AE 5 (Orosz et al 2002).…”