Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDetection of superhumps in XTE J1118+480 approaching quiescence
75
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present the results of our monitoring of the halo black-hole soft X-ray transient (SXT) XTE J1118+480 during its decline to quiescence. The system has decayed 0.5 mags from December 2000 to its present near quiescent level at R=18.65 (June 2001). The ellipsoidal lightcurve is distorted by an additional modulation that we interpret as a superhump of P_sh=0.17049(1) d i.e. 0.3% longer than the orbital period. This implies a disc precession period P_prec= 52 d. After correcting the average phase-folded light curve for veiling, the amplitude difference between the minima suggests that the binary inclination angle lies in the range i=71-82 deg. However, we urge caution in the interpretation of these values because of residual systematic contamination of the ellipsoidal lightcurve by the complex form of the superhump modulation. The orbital--mean H-alpha profiles exhibit clear velocity variations with ~500 km/s amplitude. We interpret this as the first spectroscopic evidence of an eccentric precessing disc.
rate research
Read More
We present Doppler and modulation tomography of the X-ray nova XTE J1118+480 with data obtained during quiescence using the 10-m Keck II telescope. The hot spot where the gas stream hits the accretion disc is seen in H-Alpha, H-Beta, He I Lambda-5876, and Ca II Lambda-8662, thus verifying the presence of continued mass transfer within the system. The disc is clearly seen in H-Alpha and Ca II Lambda-8662. We image the mass-donor star in narrow absorption lines of Na I Lambda-Lambda-5890, 5896, 8183, 8195 and Ca II Lambda-8662, implying an origin from the secondary itself rather than the interstellar medium. We also detect deviations in the centroid of the double peak of H-Alpha akin to those found by Zurita et al. 2002 suggesting disc eccentricity.
We report on the analysis of new and previously published MMT optical spectra of the black hole binary XTE J1118+480 during the decline from the 2000 outburst to true quiescence. From cross-correlation with template stars, we measure the radial velocity of the secondary to derive a new spectroscopic ephemeris. The observations acquired during approach to quiescence confirm the earlier reported modulation in the centroid of the double-peaked Halpha emission line. Additionally, our data combined with the results presented by Zurita et al. (2002) provide support for a modulation with a periodicity in agreement with the expected precession period of the accretion disk of ~52 day. Doppler images during the decline phase of the Halpha emission line show evidence for a hotspot and emission from the gas stream: the hotspot is observed to vary its position, which may be due to the precession of the disk. The data available during quiescence show that the centroid of the Halpha emission line is offset by about -100 km/s from the systemic velocity which suggests that the disk continues to precess. A Halpha tomogram reveals emission from near the donor star after subtraction of the ring-like contribution from the accretion disk which we attribute to chromospheric emission. No hotspot is present suggesting that accretion from the secondary has stopped (or decreased significantly) during quiescence. Finally, a comparison is made with the black hole XRN GRO J0422+32: we show that the Halpha profile of this system also exhibits a behaviour consistent with a precessing disk.
We present contemporaneous, broadband, near-infrared spectroscopy (0.9-2.45 micron) and H-band photometry of the black hole X-ray binary, XTE J1118+480. We determined the fractional dilution of the NIR ellipsoidal light curves of the donor star from other emission sources in the system by comparing the absorption features in the spectrum with field stars of known spectral type. We constrained the donor star spectral type to K7 V - M1 V and determined that the donor star contributed 54+/-27% of the H-band flux at the epoch of our observations. This result underscores the conclusion that the donor star cannot be assumed to be the only NIR emission source in quiescent X-ray binaries. The H-band light curve shows a double-humped asymmetric modulation with extra flux at orbital phase 0.75. The light curve was fit with a donor star model light curve, taking into account a constant second flux component based on the dilution analysis. We also fit models that included emission from the donor star, a constant component from the accretion disk, and a phase-variable component from the bright spot where the mass accretion stream impacts the disk. These simple models with reasonable estimates for the component physical parameters can fully account for the observed light curve, including the extra emission at phase 0.75. From our fits, we constrained the binary inclination to 68 <= i <= 79 deg. This leads to a black hole mass of 6.9 <= M_BH <= 8.2 solar masses. Long-term variations in the NIR light curve shape in XTE J1118+480 are similar to those seen in other X-ray binaries and demonstrate the presence of continued activity and variability in these systems even when in full quiescence.
Optical spectra were obtained of the optical counterpart of the high latitude soft X-ray transient XTE J1118+480 near its quiescent state with the new 6.5 m MMT and the 4.2 m WHT. The spectrum exhibits broad, double-peaked, emission lines of hydrogen from an accretion disk superposed with absorption lines of a K7V-M0V secondary star. Cross-correlation of the 27 individual spectra with late-type stellar template spectra reveals a sinusoidal variation in radial velocity with amplitude K = 701 +/- 10 km/s and orbital period P = 0.169930 +/- 0.000004 d. The mass function, 6.1 +/- 0.3 solar masses, is a firm lower limit on the mass of the compact object and strongly implies that it is a black hole. Photometric observations (R-band) with the IAC 0.8 m telescope reveal ellipsoidal light variations of full amplitude 0.2 mag. Modeling gives a large mass ratio (M1/M2 ~ 20) and a high orbital inclination (i = 81 +/- 2 deg). Our combined fits yield a mass of the black hole in the range M1 = 6.0-7.7 solar masses (90% confidence) for plausible secondary star masses of M2 = 0.09-0.5 solar masses. The photometric period measured during the outburst is 0.5% longer than our orbital period and probably reflects superhump modulations as observed in some other soft X-ray transients. The estimated distance is d = 1.9 +/- 0.4 kpc corresponding to a height of 1.7 +/- 0.4 kpc above the Galactic plane. The spectroscopic, photometric, and dynamical results indicate that XTE J1118+480 is the first firmly identified black hole X-ray system in the Galactic halo.
We present simultaneous multicolor infrared and optical photometry of the black hole X-ray transient XTE J1118+480 during its short 2005 January outburst, supported by simultaneous X-ray observations. The variability is dominated by short timescales, ~10s, although a weak superhump also appears to be present in the optical. The optical rapid variations, at least, are well correlated with those in X-rays. Infrared JHKs photometry, as in the previous outburst, exhibits especially large amplitude variability. The spectral energy distribution (SED) of the variable infrared component can be fitted with a power-law of slope alpha=-0.78 where Fnu is proportional to nu^alpha. There is no compelling evidence for evolution in the slope over five nights, during which time the source brightness decayed along almost the same track as seen in variations within the nights. We conclude that both short-term variability, and longer timescale fading, are dominated by a single component of constant spectral shape. We cannot fit the SED of the IR variability with a credible thermal component, either optically thick or thin. This IR SED is, however, approximately consistent with optically thin synchrotron emission from a jet. These observations therefore provide indirect evidence to support jet-dominated models for XTE J1118+480 and also provide a direct measurement of the slope of the optically thin emission which is impossible based on the average spectral energy distribution alone.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
