THE ACCRETING BLACK HOLE SWIFT J1753.5-0127 FROM RADIO TO HARD X-RAY

We report on multiwavelength measurements of the accreting black hole Swift J1753.5-0127 in the hard state at low luminosity (L similar to 2.7 x 10(36) erg s(-1) assuming a distance of d = 3 kpc) in 2014 April. The radio emission is optically thick synchrotron, presumably from a compact jet. We take advantage of the low extinction (E (B - V) = 0.45 from earlier work) and model the near-IR to UV emission with a multitemperature disk model. Assuming a black hole mass of M-BH = 5M(circle dot) and a system inclination of i = 40 degrees, the fits imply an inner radius for the disk of R-in/R-g > 212 d(3)(M-BH/5M(circle dot))(-1), where R-g is the gravitational radius of the black hole. and d(3) is the distance to the source in units of 3 kpc. The outer radius is R-out/R-g = 90,000 d(3)(M-BH/5M(circle dot))(-1), which corresponds to 6.6 x 10(10) d(3) cm, consistent with the expected size of the disk given previous measurements of the size of the companion's Roche lobe. The 0.5-240 keV energy spectrum measured by Swift/X-ray Telescope (XRT), Suzaku (XIS, PIN, and GSO), and Nuclear Spectroscopic Telescope Array is relatively well characterized by an absorbed power. law with a photon index of Gamma = 1.722 +/- 0.003 (90% confidence error), but a significant improvement is seen when a second continuum component is added. Reflection is a possibility, but no iron line is detected, implying a low iron abundance. We are able to fit the entire (radio to 240 keV) spectral energy distribution (SED) with a multitemperature disk component, a Comptonization component, and a broken power. law, representing the emission from the compact jet. The broken power. law cannot significantly contribute to the soft X-ray emission, and this may be related to why Swift J1753.5-0127 is an outlier in the radio/X-ray correlation. The broken power. law (i.e., the jet) might dominate above 20 keV, which would constrain the break frequency to be between 2.4 x 10(10) and 3.6 x 10(12) Hz. Although the fits to the full SED do not include significant thermal emission in the X-ray band, previous observations have consistently seen such a component, and we find that there is evidence at the 3.1s level for a disk-blackbody component with a temperature of kT(in) = 150(-20)(+30) eV and an inner radius of 5R(g)-14R(g). If this component is real, it might imply the presence of an inner optically thick accretion disk in addition to the strongly truncated (R-in > 212R(g)) disk. We also perform X-ray timing analysis, and the power spectrum is dominated by a Lorentzian component with.max = 0.110 (C) 0.003 Hz and sigma(max) = 0.16 +/- 0.04 Hz as measured by XIS and XRT, respectively.