Optical studies of the X-ray transient XTE J2123-058: Phase resolved spectroscopy (original) (raw)
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Optical studies of the X-ray transient XTE J2123-058 - II. Phase-resolved spectroscopy
Monthly Notices of the Royal Astronomical Society, 2001
We present time-resolved spectroscopy of the soft X-ray transient XTE J2123-058 in outburst. Spectral coverage of 3700-6700Å was achieved spanning two orbits of the binary. The strongest emission lines are He ii 4686Å and C iii /N iii 4640Å (Bowen blend). Other weak emission lines of He ii and C iv are present and Balmer lines show a complex structure, possibly contaminated by He ii. He ii 4686Å and C iii/N iii 4640Å show different orbital light curves indicating an origin in different regions. He ii 4686Å profiles show a complex multiple S-wave structure. Doppler tomography reveals this emission is not associated with the companion star, and occurs at velocities too low for Keplerian disk material. It can possibly be associated with overflowing or splashing stream material. The optical spectrum approximates a steep blue power-law, consistent with emission on the Rayleigh-Jeans tail of a black body spectrum. Orbital modulations show no wavelength dependence; this is as expected if both disk and companion star are hot enough for the peak of their spectral energy distributions to be in the UV. The hot continuum and presence of high-excitation emission lines indicate strong X-ray heating.
The Optical Counterpart to the Peculiar X‐Ray Transient XTE J1739−302
The Astrophysical Journal, 2006
The weak X-ray transient XTE J1739−302, characterized by extremely short outbursts, has recently been identified with a reddened star. Here we present spectroscopy and photometry of the counterpart, identifying it as a O8 Iab(f) supergiant at a distance of ∼ 2.3 kpc. XTE J1739−302 becomes thus characterized as the prototype of the new class of Supergiant Fast X-ray Transients. The optical and infrared spectra of the counterpart to XTE J1739−302 do not reveal any obvious characteristics setting it apart from other X-ray binaries with supergiant companions, which display a very different type of X-ray lightcurve.
Optical Spectral Monitoring of XTE J1118+480 in Outburst: Evidence for a Precessing Accretion Disk?
The Astrophysical Journal, 2002
We present spectroscopic observations of the X-ray transient XTE J1118+480 acquired during different epochs following the 2000 March outburst. We find that the emission line profiles show variations in their double-peak structure on time scales longer than the 4.1 hr orbital period. We suggest that these changes are due to a tidally driven precessing disk. Doppler imaging of the more intense Balmer lines and the Heii λ4686 line shows evidence of a persistent region of enhanced intensity superposed on the disk which is probably associated with the gas stream, the hotspot or both. We discuss the possible origins of the optical flux in the system and conclude that it may be due to a viscously heated disk.
XTE J1739−302 as a Supergiant Fast X‐Ray Transient
The Astrophysical Journal, 2006
XTE J1739-302 is a transient X-ray source with unusually short outbursts, lasting on the order of hours. Here we give a summary of X-ray observations we have made of this object in outburst with the Rossi X-ray Timing Explorer (RXTE) and at a low level of activity with the Chandra X-ray Observatory, as well as observations made by other groups. Visible and infrared spectroscopy of the mass donor of XTE J1739-302 are presented in a companion paper. The Xray spectrum is hard both at low levels and in outburst, but somewhat variable, and there is strong variability in the absorption column from one outburst to another. Although no pulsation has been observed, the outburst data from multiple observatories show a characteristic timescale for variability on the order of 1500-2000 s. The Chandra localization (right ascension 17 h 39 m 11.58 s , declination −30 • 20 ′ 37.6 ′′ , J2000) shows that despite being located less than 2 • from the Galactic Center and highly absorbed, XTE J1739-302 is actually a foreground object with a bright optical counterpart. The combination of a very short outburst timescale and a supergiant companion is shared with several other recently-discovered systems, forming a class we designate as Supergiant Fast X-ray Transients (SFXTs). Three persistently bright X-ray binaries with similar supergiant companions have also produced extremely short, bright outbursts: Cyg X-1, Vela X-1, and 1E 1145.1-6141.
Bowen Fluorescence from the Companion Star in X1822−371
The Astrophysical Journal, 2003
We present a clear evidence for the motion of the companion star in the Low Mass X-Ray Binary (LMXB) X1822-371. We detect NIII λ4640 emission moving in antiphase with the radial velocity curve of the neutron star and produced on the X-ray heated hemisphere of the donor star. From the motion of this feature we derive a lower limit to the radial velocity semi-amplitude of the companion star K 2 ≥ 300 ± 8 km s −1 , which, combined with a previous determination of the inclination angle and the pulsar's radial velocity curve, yield M 2 ≥ 0.36(2)M ⊙ and M 1 ≥ 1.14(6)M ⊙. The HeI λ4471 absorption line moves at lower velocities (≃ 225 km s −1) and with a-0.05 phase shift, suggests a likely origin on the gas stream near the L 1 point. In addition, we detect an S-wave emission of OVI λ3811 produced by illumination of the hot-spot bulge by the central source. The Balmer lines are dominated by broad absorptions probably due to obscuration of the accretion disc by vertically extended cool material from the splash region and overflowing stream. We also derive a more accurate, and significantly different (compared to earlier work) systemic velocity of γ = −44 ± 5 km s −1 based on the motion of the HeII λ4686 wings and Doppler tomography. This work confirms the power of imaging the companion stars in LMXBs and outbursting transients using the Bowen fluorescence transitions.
The Astrophysical Journal, 2003
We present optical photometry of XTE J2123-058 during its quiescent state taken in 1999 and 2000. The dominant feature of our R-band light curve is the ellipsoidal modulation of the secondary star, however, in order to fit this satisfactorily we require additional components which comprise an X-ray heated Roche-lobe filling secondary star, and an accretion disk bulge, i.e. where the gas stream impacts the accretion disk. The observed dip near phase 0.8 is interpreted as the eclipse of inner parts of the accretion disk by the bulge. This scenario is highly plausible given the high binary inclination. Our fits allow us to constrain the size of the quiescent accretion disk to lie in the range 0.26-0.56 R L1 (68 percent confidence). Using the distance of 9.6 kpc and the X-ray flux inferred from the heated hemisphere of the companion, we obtain an unabsorbed Xray luminosity of 1.2×10 33 erg s −1 for XTE J2123-058 in quiescence. From the observed quiescent optical/IR colors we find that the power-law index (-1.4) for the spectral distribution of the accretion disk compares well with other quiescent X-ray transients. We also re-analyse the optical light curves of the soft X-ray transient XTE J2123-058 taken during its outburst and decay in 1998. We use a robust method to fit the data using a refined X-ray binary model. The model computes the light arising from a Roche-lobe filling star and flared accretion disk irradiated by X-rays, and calculates the effects of shadowing and mutual star/disk eclipses. We obtain relatively accurate values for the binary inclination and mass ratio, which when combined with spectroscopic results obtained in paper II gives a neutron star mass in the range 1.04-1.56 M ⊙ (68% confidence).
The nature of the X-ray transient MAXI J0556−332
Monthly Notices of the Royal Astronomical Society, 2012
Phase-resolved spectroscopy of the newly discovered X-ray transient MAXI J0556−332 has revealed the presence of narrow emission lines in the Bowen region that most likely arise on the surface of the mass donor star in this low mass X-ray binary. A period search of the radial velocities of these lines provides two candidate orbital periods (16.43±0.12 and 9.754±0.048 hrs), which differ from any potential X-ray periods reported. Assuming that MAXI J0556−332 is a relatively high inclination system that harbors a precessing accretion disk in order to explain its X-ray properties, it is only possible to obtain a consistent set of system parameters for the longer period. These assumptions imply a mass ratio of q≃0.45, a radial velocity semi-amplitude of the secondary of K 2 ≃190 km s −1 and a compact object mass of the order of the canonical neutron star mass, making a black hole nature for MAXI J0556−332 unlikely. We also report the presence of strong N III emission lines in the spectrum, thereby inferring a high N/O abundance. Finally we note that the strength of all emission lines shows a continuing decay over the ≃1 month of our observations.
AstroSat and NuSTAR observations of XTE J1739−285 during the 2019-2020 outburst
Monthly Notices of the Royal Astronomical Society, 2023
We report results from a study of XTE J1739 −285, a transient neutron star low mass X-ray binary observed with AstroSat and NuSTAR during its 2019-2020 outburst. We detected accretion-powered X-ray pulsations at 386 Hz during very short intervals (0.5-1 s) of X-ray flares. These flares were observed during the 2019 observation of XTE J1739 −285. During this observation, we also observed a correlation between intensity and hardness ratios, suggesting an increase in hardness with the increase in intensity. Moreo v er, a thermonuclear X-ray burst detected in our AstroSat observation during the 2020 outburst revealed the presence of coherent burst oscillations at 383 Hz during its decay phase. The frequency drift of 3 Hz during X-ray burst can be explained with r modes. Thus, making XTE J1739 −285 belong to a subset of NS-LMXBs which exhibit both nuclear-and accretion-po wered pulsations. The po wer density spectrum created using the AstroSat-LAXPC observations in 2020 showed the presence of a quasi-periodic oscillation at ∼0.83 Hz. Our X-ray spectroscopy revealed significant changes in the spectra during the 2019 and 2020 outburst. We found a broad iron line emission feature in the X-ray spectrum during the 2020 observation, while this feature was relatively narrow and has a lower equivalent width in 2019, when the source was accreting at higher rates than 2020. Hard X-ray tail was observed during the 2019 observations, indicating the presence of non-thermal component in the X-ray spectra.
2002
From the observed quiescent optical/IR colors we find that the power-law index (-1.4) for the spectral distribution of the accretion disk compares well with other quiescent X-ray transients. We also re-analyse the optical light curves of the soft X-ray transient XTE J2123-058 taken during its outburst and decay in 1998. We use a robust method to fit the data using a refined X-ray binary model. The model computes the light arising from a Roche-lobe filling star and flared accretion disk irradiated by X-rays, and calculates the effects of shadowing and mutual star/disk eclipses. We obtain relatively accurate values for the binary inclination and mass ratio, which when combined with spectroscopic results obtained in paper II gives a neutron star mass in the range 1.04-1.56Mo (68% confidence).