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1.
We have studied the 1999 soft X-ray transient outburst of XTE J1859+226 at radio and X-ray wavelengths. The event was characterized by strong variability in the disc, corona and jet – in particular, a number of radio flares (ejections) took place and seemed well-correlated with hard X-ray events. Apparently unusual for the canonical 'soft' X-ray transient, there was an initial period of low/hard state behaviour during the rise from quiescence but prior to the peak of the main outburst – we show that not only could this initial low/hard state be a ubiquitous feature of soft X-ray transient outbursts, but also it could be extremely important in our study of outburst mechanisms.  相似文献   

2.
We present Swift observations of the black hole X-ray transient, GRO J1655−40, during the recent outburst. With its multiwavelength capabilities and flexible scheduling, Swift is extremely well suited for monitoring the spectral evolution of such an event. GRO J1655−40 was observed on 20 occasions and data were obtained by all instruments for the majority of epochs. X-ray spectroscopy revealed spectral shapes consistent with the 'canonical' low/hard, high/soft and very high states at various epochs. The soft X-ray source (0.3–10 keV) rose from quiescence and entered the low/hard state, when an iron emission line was detected. The soft X-ray source then softened and decayed, before beginning a slow rebrightening and then spending ∼3 weeks in the very high state. The hard X-rays (14–150 keV) behaved similarly but their peaks preceded those of the soft X-rays by up to a few days; in addition, the average hard X-ray flux remained approximately constant during the slow soft X-ray rebrightening, increasing suddenly as the source entered the very high state. These observations indicate (and confirm previous suggestions) that the low/hard state is key to improving our understanding of the outburst trigger and mechanism. The optical/ultraviolet light curve behaved very differently from that of the X-rays; this might suggest that the soft X-ray light curve is actually a composite of the two known spectral components, one gradually increasing with the optical/ultraviolet emission (accretion disc) and the other following the behaviour of the hard X-rays (jet and/or corona).  相似文献   

3.
XTE J1748−288 is a black hole X-ray transient which went into outburst in 1998 June. The X-ray light curves showed canonical morphologies, with minor variations on the 'fast rise exponential decay' profile. The radio source, however, reached an unusually high flux density of over 600 mJy. This high radio flux was accompanied by an exceptional  (>20  per cent)  fractional linear polarization, the variability of which was anticorrelated with the flux density. We use this variability to discuss possible depolarization mechanisms and to predict the underlying behaviour of the (unresolved) core/jet components.  相似文献   

4.
We present optical spectroscopy and optical and infrared photometry of the neutron star soft X-ray transient Aql X–1 during its X-ray outburst of 1997 August. By modelling the X-ray, optical and IR light curves, we find a 3-d delay between the IR and X-ray rise times, analogous to the UV–optical delay seen in dwarf novae outbursts and black hole X-ray transients. We interpret this delay as the signature of an 'outside-in' outburst, in which a thermal instability in the outer disc propagates inward. This outburst is the first of this type definitively identified in a neutron star X-ray transient.  相似文献   

5.
The transient black-hole binary XTE J1118+480 exhibited dramatic rapid variability at all wavelengths which were suitably observed during its 2000 April–July outburst. We examine time-resolved X-ray, ultraviolet, optical and infrared data spanning the plateau phase of the outburst. We find that both X-ray and infrared bands show large amplitude variability. The ultraviolet and optical variability is more subdued, but clearly correlated with that seen in the X-rays. The ultraviolet, at least, appears to be dominated by the continuum, although the lines are also variable. Using the X-ray variations as a reference point, we find that the ultraviolet (UV) variability at long wavelengths occurs later than that at short wavelengths. Uncertainty in the Hubble Space Telescope timing prohibits a determination of the absolute lag with respect to the X-rays, however. The transfer function is clearly not a delta-function, exhibiting significant repeatable structure. For the main signal we can rule out an origin in reprocessing on the companion star – the lack of variation in the lags is not consistent with this, given a relatively high orbital inclination. Weak reprocessing from the disc and/or companion star may be present, but is not required, and another component must dominate the variability. This could be variable synchrotron emission correlated with X-ray variability, consistent with our earlier interpretation of the infrared (IR) flux as due to synchrotron emission rather than thermal disc emission. In fact, the broad-band energy distribution of the variability from IR to X-rays is consistent with expectations of optically thin synchrotron emission. We also follow the evolution of the low-frequency quasi-periodic oscillation in X-rays, UV, and optical. Its properties at all wavelengths are similar, indicating a common origin.  相似文献   

6.
We observed the neutron star X-ray transient 2S 1803−245 in quiescence with the X-ray satellite XMM–Newton , but did not detect it. An analysis of the X-ray bursts observed during the 1998 outburst of 2S 1803−245 gives an upper limit to the distance of ≤7.3 kpc, leading to an upper limit on the quiescent 0.5–10 keV X-ray luminosity of  ≤2.8 × 1032 erg s−1  (3σ). Since the expected orbital period of 2S 1803−245 is several hours, this limit is not much higher than those observed for the quiescent black hole transients with similar orbital periods.  相似文献   

7.
We present the results of a study with the Swift Burst Alert Telescope in the 14–195 keV range of the long-term variability of five low-mass X-ray binaries with reported or suspected superorbital periods – 4U 1636−536, 4U 1820−303, 4U 1916−053, Cyg X-2 and Sco X-1. No significant persistent periodic modulation was detected around the previously reported periods in the 4U 1916−053, Cyg X-2 or Sco X-1 light curves. The ∼170-d period of 4U 1820−303 was detected up to 24 keV, consistent with variable accretion due to the previously proposed triple system model. The ∼46-d period in 4U 1636−536 was detected up to 100 keV, with the modulation in the low- and high-energy bands found to be phase shifted by ∼180° with respect to each other. This phase shift, when taken together with the near-coincident onset of the ∼46-d modulation and the low/hard X-ray state, leads us to speculate that the modulation could herald transient jet formation.  相似文献   

8.
We present observations of the X-ray transient XTE J1118+480 during its low/hard X-ray state outburst in 2000, at radio and submillimetre wavelengths with the VLA, Ryle Telescope, MERLIN and JCMT. The high-resolution MERLIN observations reveal all the radio emission (at 5 GHz) to come from a compact core with physical dimensions smaller than 65 d (kpc) au. The combined radio data reveal a persistent and inverted radio spectrum, with spectral index ∼ +0.5. The source is also detected at 350 GHz, on an extrapolation of the radio spectrum. Flat or inverted radio spectra are now known to be typical of the low/hard X-ray state, and are believed to arise in synchrotron emission from a partially self-absorbed jet. Comparison of the radio and submillimetre data with reported near-infrared observations suggest that the synchrotron emission from the jet extends to the near-infrared, or possibly even optical regimes. In this case the ratio of jet power to total X-ray luminosity is likely to be P J L X≫0.01, depending on the radiative efficiency and relativistic Doppler factor of the jet. Based on these arguments we conclude that during the period of our observations XTE J1118+480 was producing a powerful outflow which extracted a large fraction of the total accretion power.  相似文献   

9.
The 2006 outburst of GK Persei differed significantly at optical and ultraviolet (UV) wavelengths from typical outbursts of this object. We present multiwavelength (X-ray, UV and optical) Swift and AAVSO data, giving unprecedented broad-band coverage of the outburst, allowing us to follow the evolution of the longer-than-normal 2006 outburst across these wavelengths. In the optical and UV we see a triple-peaked morphology with maximum brightness ∼1.5 mag lower than in previous years. In contrast, the peak hard X-ray flux is the same as in previous outbursts. We resolve this dichotomy by demonstrating that the hard X-ray flux only accounts for a small fraction of the total energy liberated during accretion, and interpret the optical/UV outburst profile as arising from a series of heating and cooling waves traversing the disc, caused by its variable density profile.  相似文献   

10.
The second known outburst of the WZ Sge type dwarf nova GW Lib was observed in 2007 April. We have obtained unique multiwavelength data of this outburst which lasted ∼26 days. The American Association of Variable Star Observers ( AAVSO ) recorded the outburst in the optical, which was also monitored by Wide Angle Search for Planets , with a peak V magnitude of ∼8. The outburst was followed in the ultraviolet and X-ray wavelengths by the Swift ultraviolet/optical and X-ray telescopes. The X-ray flux at optical maximum was found to be three orders of magnitude above the pre-outburst quiescent level, whereas X-rays are normally suppressed during dwarf nova outbursts. A distinct supersoft X-ray component was also detected at optical maximum, which probably arises from an optically thick boundary layer. Follow-up Swift observations taken 1 and 2 years after the outburst show that the post-outburst quiescent X-ray flux remains an order of magnitude higher than the pre-outburst flux. The long interoutburst time-scale of GW Lib with no observed normal outbursts support the idea that the inner disc in GW Lib is evacuated or the disc viscosity is very low.  相似文献   

11.
We show that the light curves of soft X-ray transients (SXTs) follow naturally from the disc instability picture, adapted to take account of irradiation by the central X-ray source during the outburst. Irradiation prevents the disc from returning to the cool state until central accretion is greatly reduced. This happens only after most of the disc mass has been accreted by the central object, on a viscous time-scale, accounting naturally for the exponential decay of the outburst on a far longer time-scale (τ20–40 d) than seen in dwarf novae, without any need to manipulate the viscosity parameter α. The accretion of most of the disc mass in outburst explains the much longer recurrence time of SXTs compared with dwarf novae. This picture also suggests an explanation of the secondary maximum seen in SXT light curves about 50–75 d after the start of each outburst, since central irradiation triggers the thermal instability of the outer disc, adding to the central accretion rate one viscous time later. The X-ray outburst decay constant τ should on average increase with orbital period, but saturate at a roughly constant value ∼40 d for orbital periods longer than about a day. The bolometric light curve should show a linear rather than an exponential decay at late times (a few times τ). Outbursts of long-period systems should be entirely in the linear decay regime, as is observed in GRO J1744−28. UV and optical light curves should resemble the X-rays but have decay time-scales up to 2–4 times longer.  相似文献   

12.
We present the results of the analysis of Rossi X-ray Timing Explorer ( RXTE ) observations of the new X-ray transient, SWIFT J1753.5−0127, during its outburst in 2005 July. The source was caught at the peak of the burst with a flux of 7.19e-09 erg s−1cm−2 in the 3–25 keV energy range and observed until it decreased by about a factor of 10. The photon index of the power-law component, which is dominant during the entire outburst, decreases from ∼1.76 to 1.6. However, towards the end of the observations the photon index is found to increase, indicating a softening of the spectra. The presence of an ultrasoft thermal component, during the bright phases of the burst, is clear from the fits to the data. The temperature associated with this thermal component is 0.4 keV. We believe that this thermal component could be due to the presence of an accretion disc. Assuming a distance of 8.5 kpc,   L X/ L Edd≃ 0.05  at the peak of the burst, for a black hole of mass  10 M⊙  . The source is found to be locked in the low/hard state during the entire outburst and likely falls in the category of the X-ray transients that are observed in the low/hard state throughout the outburst. We discuss the physical scenario of the low/hard state outburst for this source.  相似文献   

13.
We revisit the discovery outburst of the X-ray transient XTE J1550−564 during which relativistic jets were observed in 1998 September, and review the radio images obtained with the Australian Long Baseline Array, and light curves obtained with the Molonglo Observatory Synthesis Telescope and the Australia Telescope Compact Array. Based on H i spectra, we constrain the source distance to between 3.3 and 4.9 kpc. The radio images, taken some 2 d apart, show the evolution of an ejection event. The apparent separation velocity of the two outermost ejecta is at least  1.3 c   and may be as large as  1.9 c   ; when relativistic effects are taken into account, the inferred true velocity is  ≥ 0.8 c   . The flux densities appear to peak simultaneously during the outburst, with a rather flat (although still optically thin) spectral index of −0.2.  相似文献   

14.
We present results from modelling of quasi-simultaneous broad-band (radio through X-ray) observations of the Galactic stellar black hole (BH) transient X-ray binary (XRB) systems XTE J1118+480 and GX 339−4 using an irradiated disc + compact jet model. In addition to quantifying the physical properties of the jet, we have developed a new irradiated disc model which also constrains the geometry and temperature of the outer accretion disc by assuming a disc heated by viscous energy release and X-ray irradiation from the inner regions. For the source XTE J1118+480, which has better spectral coverage of the two in optical and near-infrared (OIR) wavelengths, we show that the entire broad-band continuum can be well described by an outflow-dominated model + an irradiated disc. The best-fitting radius of the outer edge of the disc is consistent with the Roche lobe geometry of the system, and the temperature of the outer edge of the accretion disc is similar to those found for other XRBs. Irradiation of the disc by the jet is found to be negligible for this source. For GX 339−4, the entire continuum is well described by the jet-dominated model only, with no disc component required. For the two XRBs, which have very different physical and orbital parameters and were in different accretion states during the observations, the sizes of the jet base are similar and both seem to prefer a high fraction of non-thermal electrons in the acceleration/shock region and a magnetically dominated plasma in the jet. These results, along with recent similar results from modelling other galactic XRBs and AGNs, may suggest an inherent unity in diversity in the geometric and radiative properties of compact jets from accreting black holes.  相似文献   

15.
We report the first extensive set of optical photometric observations of the counterpart to SAX J1808.4−3658 (V4580 Sagittarii) in quiescence. The source was detected at V ∼21 , 5 mag fainter than at the peak of its 1998 outburst. However, a comparable ∼6 per cent semi-amplitude 2-h modulation of its flux is revealed. This has the same phasing and approximately sinusoidal modulation as seen during outburst, and with photometric minimum when the pulsar is behind the companion. The lack of a double-humped morphology rules out an ellipsoidal origin, implying that the bulk of the optical flux does not arise from the companion. Moreover, applying crude modelling to the disc and X-ray irradiated face of the donor shows that the internal energy release of a remnant disc (with mass transfer driven by gravitational radiation) is sufficient to explain most of the optical emission, and with the modulation because of the varying contribution of the heated face of the star. We note that this model is also consistent with the much lower X-ray to optical flux ratio in quiescence versus outburst, and with the phasing of the optical modulation.  相似文献   

16.
We present the most complete multiwavelength coverage of any dwarf nova outburst: simultaneous optical, Extreme Ultraviolet Explorer and Rossi X-ray Timing Explorer observations of SS Cygni throughout a narrow asymmetric outburst. Our data show that the high-energy outburst begins in the X-ray waveband 0.9–1.4 d after the beginning of the optical rise and 0.6 d before the extreme-ultraviolet rise. The X-ray flux drops suddenly, immediately before the extreme-ultraviolet flux rise, supporting the view that both components arise in the boundary layer between the accretion disc and white dwarf surface. The early rise of the X-ray flux shows that the propagation time of the outburst heating wave may have been previously overestimated.
The transitions between X-ray and extreme-ultraviolet dominated emission are accompanied by intense variability in the X-ray flux, with time-scales of minutes. As detailed by Mauche & Robinson, dwarf nova oscillations are detected throughout the extreme-ultraviolet outburst, but we find they are absent from the X-ray light curve.
X-ray and extreme-ultraviolet luminosities imply accretion rates of  3 × 1015 g s−1  in quiescence,  1 × 1016 g s−1  when the boundary layer becomes optically thick, and  ∼1018 g s−1  at the peak of the outburst. The quiescent accretion rate is two and a half orders of magnitude higher than predicted by the standard disc instability model, and we suggest this may be because the inner accretion disc in SS Cyg is in a permanent outburst state.  相似文献   

17.
We present a detailed study of the X-ray energy and power spectral properties of the neutron star transient IGR J17191−2821. We discovered four instances of pairs of simultaneous kilohertz quasi-periodic oscillations (kHz QPOs). The frequency difference between these kHz QPOs is between 315 and 362 Hz. We also report on the detection of five thermonuclear type I X-ray bursts and the discovery of burst oscillations at ∼294 Hz during three of them. Finally, we report on a faint and short outburst precursor, which occurred about two months before the main outburst. Our results on the broad-band spectral and variability properties allow us to firmly establish the atoll source nature of IGR J17191−2821.  相似文献   

18.
Observations of V404 Cyg performed using the Westerbork Synthesis Radio Telescope at four frequencies, over the interval 1.4–8.4 GHz, have provided us with the first broad-band radio spectrum of a 'quiescent' stellar mass black hole. The measured mean flux density is of 0.35 mJy, with a spectral index  α=+0.09 ± 0.19  (such that   S ν∝να  ). Synchrotron emission from an inhomogeneous partially self-absorbed outflow of plasma accounts for the flat/inverted radio spectrum, in analogy with hard-state black hole X-ray binaries, indicating that a steady jet is being produced between a few 10−6 and a few per cent of the Eddington X-ray luminosity.  相似文献   

19.
We present time-resolved spectroscopy of the soft X-ray transient XTE J2123–058 in outburst. A useful spectral coverage of 3700–6700 Å was achieved spanning two orbits of the binary, with single-epoch coverage extending to ∼9000 Å. The optical spectrum approximates a steep blue power law, consistent with emission on the Rayleigh–Jeans tail of a hot blackbody spectrum. The strongest spectral lines are He  ii 4686 Å and C  iii /N  iii 4640 Å (Bowen blend) in emission. Their relative strengths suggest that XTE J2123–058 was formed in the Galactic plane, not in the halo. Other weak emission lines of He  ii and C  iv are present, and Balmer lines show a complex structure, blended with He  ii . He  ii 4686-Å profiles show a complex multiple S-wave structure, with the strongest component appearing at low velocities in the lower-left quadrant of a Doppler tomogram. H α shows transient absorption between phases 0.35 and 0.55. Both of these effects appear to be analogous to similar behaviour in SW Sex type cataclysmic variables. We therefore consider whether the spectral line behaviour of XTE J2123–058 can be explained by the same models invoked for those systems.  相似文献   

20.
We report on a comprehensive and consistent investigation into the X-ray emission from GX 339−4. All public observations in the 11 year RXTE archive were analysed. Three different types of model – single power law, broken power law and a disc + power law – were fitted to investigate the evolution of the disc, along with a fixed Gaussian component at 6.4 keV to investigate any iron line in the spectrum. We show that the relative variation in flux and X-ray colour between the two best sampled outbursts are very similar. The decay of the disc temperature during the outburst is clearly seen in the soft state. The expected decay is   S Disc∝ T 4  ; we measure   T 4.75±0.23  . This implies that the inner disc radius is approximately constant in the soft state. We also show a significant anticorrelation between the iron line equivalent width (EW) and the X-ray flux in the soft state while in the hard state the EW is independent of the flux. This results in hysteresis in the relation between X-ray flux and both line flux and EW. To compare the X-ray binary outburst to the behaviour seen in active galactic nuclei (AGN), we construct a disc fraction luminosity diagram for GX 339−4, the first for an X-ray binary. The shape qualitatively matches that produced for AGN. Linking this with the radio emission from GX 339−4 the change in radio spectrum between the disc and power-law-dominated states is clearly visible.  相似文献   

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