X-ray Observations of the Black Hole Transient 4u 1630–47 during Two Years of X-ray Activity

The black hole candidate (BHC) X-ray transient 4U 1630–47 continuously produced strong X-ray emission for over 2 years during its 2002–2004 outburst, which is one of the brightest and longest outbursts ever seen from this source. We use over 300 observations made with the Rossi X-ray Timing Explorer (RXTE) to study the source throughout the outburst along with hard X-ray images from the INTErnational Gamma-Ray Astrophysics Laboratory, which are critical for interpreting the RXTE data in this crowded field. The source exhibits extreme behaviors, which can be interpreted as an indication that the system luminosity approaches the Eddington limit. For 15 observations, fitting the spectral continuum with a disk-blackbody plus power-law model results in measured inner disk temperatures between 2.7 and 3.8 keV, and such temperatures are only rivaled by the brightest BHC systems such as GRS 1915+105 and XTE J1550–564. If the high temperatures are caused by the dominance of electron scattering opacity in the inner regions of the accretion disk, it is theoretically required that the source luminosity is considerably higher than 20% of the Eddington limit. We detect a variety of highamplitude variability, including hard 10–100 s flares, which peak at levels as much as 2–3 times higher than non-flare levels. This flaring occurs at the highest disk luminosities in a regime where the source deviates from the Ldisk ∝ T 4 in relationship that is seen at lower luminosities, possibly suggesting that we are seeing transitions between a Shakura & Sunyaev disk and a “slim” disk, which is predicted to occur at very high mass accretion rates. The X-ray properties in 2002–2004 are significantly different from those seen during the 1998 outburst, which is the only outburst with detected radio jet emission. Our results support the “jet-line” concept recently advanced by Fender and co-workers. Our study allows for a test of the quantitative McClintock & Remillard spectral state definitions, and we find that these definitions alone do not provide a complete description of the outburst. Finally, for several of the observations, the high energy emission is dominated by the nearby sources IGR J16320–4751 and IGR J16358–4726, and we provide information on when these sources were bright and on the nature of their energy spectra. Subject headings: accretion, accretion disks — black hole physics: general — stars: individual (4U 1630–47, IGR J16320–4751, IGR J16358–4726) — stars: black holes — X-rays: stars