Raj K. Jain

A black hole in the superluminal source sax j1819.3-2525 (v4641 sgr)

Spectroscopic observations of the fast X-ray transient and superluminal jet source SAX J1819.3-2525 (V4641 Sgr) reveal a best-fitting period of Pspect = 2.81678 ± 0.00056 days and a semiamplitude of K2 = 211.0 ± 3.1 km s-1. The optical mass function is f(M) = 2.74 ± 0.12 M☉. We find a photometric period of Pphoto = 2.81730 ± 0.00001 days using a light curve measured from photographic plates. The folded light curve resembles an ellipsoidal light curve with two maxima of roughly equal height and two minima of unequal depth per orbital cycle. The secondary star is a late B-type star that has evolved off the main sequence. Using a moderate resolution spectrum (R = 7000) we measure Teff = 10500 ± 200 K, log g = 3.5 ± 0.1, and Vrot sin i = 123 ± 4 km s-1 (1 σ errors). Assuming synchronous rotation, our measured value of the projected rotational velocity implies a mass ratio of Q ≡ M1/M2 = 1.50 ± 0.08 (1 σ). The lack of X-ray eclipses implies an upper limit to the inclination of i ≤ 707. On the other hand, the large amplitude of the folded light curve (≈0.5 mag) implies a large inclination (i 60°). Using the above mass function, mass ratio, and inclination range, the mass of the compact object is in the range 8.73 ≤ M1 ≤ 11.70 M☉ and the mass of the secondary star is in the range 5.49 ≤ M2 ≤ 8.14 M☉ (90% confidence). The mass of the compact object is well above the maximum mass of a stable neutron star, and we conclude that V4641 Sgr contains a black hole. The B-star secondary is by far the most massive, the hottest, and the most luminous secondary of the dynamically confirmed black hole X-ray transients. We find that the α-process elements nitrogen, oxygen, calcium, magnesium, and titanium may be overabundant in the secondary star by factors of 2-10 times with respect to the Sun. Finally, assuming E(B-V) = 0.32 ± 0.10, we find a distance 7.40 ≤ d ≤ 12.31 kpc (90% confidence). This large distance and the high proper motions observed for the radio counterpart make V4641 Sgr possibly the most superluminal galactic source known, with an apparent expansion velocity of 9.5c and a bulk Lorentz factor of Γ 9.5, assuming that the jets were ejected during one of the bright X-ray flares observed with the Rossi X-ray Timing Explorer.

The Mass Distribution of Stellar Black Holes

We examine the distribution of masses of black holes in transient low-mass X-ray binary systems. A Bayesian analysis suggests that it is probable that six of the seven systems with measured mass functions have black hole masses clustered near seven solar masses. There appears to be a significant gap between the masses of these systems and those of the observed neutron stars. The remaining source, V404 Cyg, has a mass significantly larger than the others, and our analysis suggests that it is probably drawn from a different distribution. Selection effects do not appear to play a role in producing the observed mass distribution, which may be explained by currently unknown details of the supernova explosions and of binary evolution prior to the supernova.

X-Ray States and Radio Emission in the Black Hole Candidate XTE J1550–564

We report on radio and X-ray observations of the black hole candidate (BHC) XTE J1550-564 performed during its 2000 X-ray outburst. Observations were conducted with the Australia Telescope Compact Array and allowed us to sample the radio behavior of XTE J1550-564 in the X-ray low hard and intermediate/very high states. We observed optically thin radio emission from XTE J1550-564 5 days after a transition to an intermediate/very high state, but we observed no radio emission 6 days later, while XTE J1550-564 was still in the intermediate/very high state. In the low hard state, XTE J1550-564 is detected with an inverted radio spectrum. The radio emission in the low hard state most likely originates from a compact jet; optical observations suggest that the synchrotron emission from this jet may extend up to the optical range. The total power of the compact jet might therefore be a significant fraction of the total luminosity of the system. We suggest that the optically thin radio emission detected 5 days after the transition to the intermediate/very high state is due to a discrete ejection of relativistic plasma during the state transition. Subsequent to the decay of the optically thin radio emission associated with the state transition, it seems that in the intermediate/very high state the radio emission is quenched by a factor greater than 50, implying a suppression of the outflow. We discuss the properties of radio emission in the X-ray states of BHCs.

Orbital Parameters for the Soft X-Ray Transient 4U 1543?47: Evidence for a Black Hole

Spectroscopic observations of the soft X-ray transient 4U 1543-47 reveal a radial velocity curve with a period of P = 1.123 ± 0.008 days and a semiamplitude of K2 = 124 ± 4 km s-1. The resulting mass function is f(M) = 0.22 ± 0.02 M☉. We classify the secondary star as A2 V, in agreement with previous work, and measure Teff = 9000 ± 500 K and E(B-V) = 0.50 ± 0.05 from fits to synthetic spectra. We derive a distance of d = 9.1 ± 1.1 kpc if the secondary is on the main sequence. We see no emission lines from the accretion disk, and the measured fractions of disk light in the B- and V-bands are 10% and 21%, respectively. The V and I light curves exhibit two waves per orbital cycle with amplitudes ≈ 0.08 mag. We model the light curves as ellipsoidal variations in the secondary star and derive extreme inclination limits of 20° ≤ i ≤ 40°. The formal 3 σ limits on the inclination from a simultaneous fit to the V and I light curves are 24° ≤ i ≤ 36° for a mass ratio Q ≡ M1/M2 ≥ 1. However, there are systematic effects in the data that the model does not account for, so the above constraints should be treated with caution. We argue that the secondary star is still on the main sequence with the mass transfer being driven by expansion due to normal main sequence evolution. If the secondary star has a mass near the main sequence values for early A stars (2.3 ≤ M2 ≤ 2.6 M☉), then the best fits for the 3 σ inclination range (24° ≤ i ≤ 36°) and the 3 σ mass function range (0.16 ≤ f(M) ≤ 0.28 M☉) imply a primary mass in the range 2.7 ≤ M1 ≤ 7.5 M☉. The mass of the compact object in 4U 1543-47 is likely to be in excess of ≈ 3 M☉, which is widely regarded as the maximum mass of a stable neutron star. Thus we conclude that 4U 1543-47 most likely contains a black hole.

Multiwavelength Observations of the Black Hole Candidate XTE J1550–564 during the 2000 Outburst

We report optical, infrared, and X-ray light curves for the outburst, in 2000, of the black hole candidate XTE J1550-564. We find that the start of the outburst in the H and V bands precedes that seen in the RXTE All Sky Monitor by 11.5 +/- 0.9 and 8.8 +/- 0.6 days, respectively; a similar delay has been observed in two other systems. About 50 days after the primary maxima in the VIH light curves, we find secondary maxima, most prominently in H. This secondary peak is absent in the X-ray light curve, but coincides with a transition to the low/hard state. We suggest that this secondary peak may be due to non-thermal emission associated with the formation of a jet.

X-ray Nova XTE J1550-564: optical observations

We report the identification of the optical counterpart of the X-ray transient XTE J1550-564 described in two companion papers by Sobczak et al. and Remillard et al. We find that the optical source brightened by ≈4 mag over the quiescent counterpart seen at B≈22 on a SERC survey plate and then decayed by ≈1.5 mag over the 7 week-long observation period. There was an optical response to the large X-ray flare described by Sobczak et al., but it was much smaller and delayed by ≈1 day.

Nova Velorum 1999=V382 Vel: Astrometry and Photometry

We present the absolute proper motion of Nova Velorum 1999=V382 Vel based on photographic plate material from the Yale/San Juan Southern Proper Motion program. The absolute motion, on the system of the International Celestial Reference System, is μαcos δ = -11.5 ± 2.3 and μδ = -1.7 ± 1.9 mas yr−1. This proper‐motion measure adds to the growing number of such measures for novae and will eventually allow the secular parallax for this class of objects to be determined.We also report the preoutburst B and V photometry of V382 Vel. In its quiescent state, the nova has mean values of V = 16.56 and B−V = 0.14. A brightening by 0.5 mag is noted in 1970 (JD 2,440,705.542).

Parameters for the soft X-ray transient 4U 1543-47: Evidence for a black hole

Spectroscopic observations of the soft X-ray transient 4U 1543-47 reveal a sinusoidal radial velocity curve with a period of P=1.123±0.008 days and an amplitude of K=124±4 km sec−1. The resulting mass function is f(M)=0.22±0.02 M⊙. The V and I light curves exhibit two waves per orbital cycle with amplitudes about 0.08 mag. We modeled the light curves as ellipsoidal variations in the secondary star and found that the formal 3σ limits on the inclination from a simultaneous fit to the V and I light curves are 24°⩽i⩽36° for Q=M1/M2⩾1. However, there are systematic effects in the data that the model does not account for, so the above constraints should be treated with caution. We argue that the secondary star is still on the main sequence with a mass in the range 2.3⩽M2⩽2.6 M⊙. This mass range, the 3σ inclination range (24°⩽i⩽36°), and the 3σ mass function range (0.16⩽f(M)⩽0.28 M⊙) imply a primary mass in the range 2.7⩽M1⩽7.5 M⊙. Thus the mass of the compact object in 4U 1543-47 is likely to be in excess of ≈3...