Low-state Spectra Research Articles

X-ray spectral components of the blazar and binary black hole candidate OJ 287 (2005–2020)

ABSTRACT We present a comprehensive analysis of all XMM–Newton spectra of OJ 287 spanning 15 yr of X-ray spectroscopy of this bright blazar. We also report the latest results from our dedicated Swift UVOT and XRT monitoring of OJ 287, which started in 2015, along with all earlier public Swift data since 2005. During this time interval, OJ 287 was caught in extreme minima and outburst states. Its X-ray spectrum is highly variable and encompasses all states seen in blazars from very flat to exceptionally steep. The spectrum can be decomposed into three spectral components: Inverse Compton (IC) emission dominant at low-state, supersoft synchrotron emission that becomes increasingly dominant as OJ 287 brightens, and an intermediately-soft (Γx = 2.2) additional component seen at outburst. This last component extends beyond 10 keV and plausibly represents either a second synchrotron/IC component and/or a temporary disc corona of the primary supermassive black hole (SMBH). Our 2018 XMM–Newton observation, quasi-simultaneous with the Event Horizon Telescope observation of OJ 287, is well described by a two-component model with a hard IC component of Γx = 1.5 and a soft synchrotron component. Low-state spectra limit any long-lived accretion disc/corona contribution in X-rays to a very low value of Lx/LEdd < 5.6 × 10−4 (for MBH, primary = 1.8 × 1010 M⊙). Some implications for the binary SMBH model of OJ 287 are discussed.

Neglected X-ray discovered polars

We report on the X-ray observations of the eclipsing polar HY Eri (RX J0501–0359), along with its photometric, spectrophotometric, and spectropolarimetric optical variations, collected over 30 years. With an orbital period of 2.855 h, HY Eri falls near the upper edge of the 2–3 h period gap. After 2011, the system went into a prolonged low state, continuing to accrete at a low level. We present an accurate alias-free long-term orbital ephemeris and report a highly significant period change by 10 ms that took place over the time interval from 2011 to 2018. We acquired a high-quality eclipse spectrum that shows the secondary star as a dM5–6 dwarf at a distance d = 1050 ± 110 pc. Based on phase-resolved cyclotron and Zeeman spectroscopy, we identify the white dwarf (WD) in HY Eri as a two-pole accretor with nearly opposite accretion spots of 28 and 30 MG. The Zeeman analysis of the low state spectrum reveals a complex magnetic field structure, which we fit by a multipole model. We detected narrow emission lines from the irradiated face of the secondary star, of which Mg Iλ5170 with a radial velocity amplitude of K′2 = 139 ± 10 km s−1 (90% confidence) tracks the secondary more reliably than the narrow Hα line. Based on the combined dynamical analysis and spectroscopic measurement of the angular radius of the WD, we obtain a primary mass of M1 = 0.42 ± 0.05 M⊙ (90% confidence errors), identifying it as a probable He WD or hybrid HeCO WD. The secondary is a main sequence star of M2 = 0.24 ± 0.04 M⊙ that seems to be slightly inflated. The large distance of HY Eri and the lack of similar systems suggest a very low space density of polars with low-mass primary. According to current theory, these systems are destroyed by induced runaway mass transfer, suggesting that HY Eri may be doomed to destruction. Over the last 30 years, HY Eri experienced high and low states with mass transfer rates that differed by three orders of magnitude, varying between Ṁ ≃ 10−9 M⊙ yr−1 and 10−12 M⊙ yr−1. At a galactic latitude of −26.1°, it is located about 500 pc below the galactic plane.

An Optical Study of Two VY Sculptoris-type Cataclysmic Binary Stars: V704 And and RX J2338+431

Abstract We report observations of the known cataclysmic variable star (CV) V704 And, and also confirm that the optical counterpart of the ROSAT Galactic Plane Survey source RX J2338+431 is a heretofore-neglected CV. Photometric and spectroscopic observations from MDM Observatory show both systems to be nova-like variables that exhibit dips of 4–5 mag from their mean brightnesses, establishing them as members of the VY Scl subclass. From high-state emission-line radial velocities, we determine orbital periods of 0.151424(3) days (3.63 hr) for V704 And and 0.130400 (1) days (3.13 hr) for RX J2338+431. In V704 And, we find that the Hα emission-line measures cluster into distinct regions on a plot of equivalent width versus full width at half-maximum, which evidently correspond to high, intermediate, and low photometric states. This allows us to assign spectra to photometric states when contemporaneous photometry is not available, an apparently novel method that may be useful in studies of other novalikes. Our low-state spectra of RX J2338+431 show features of an M-type secondary star, from which we estimate a distance of 890 ± 200 pc, in good agreement with the Gaia DR2 parallax.

Absorption at the dust sublimation radius and the dichotomy between X-ray and optical classification in the Seyfert galaxy H0557-385★

In this work, the analysis of multi-epoch (1995-2010) X-ray observations of the Seyfert 1 galaxy H0557-385 is presented. The wealth of data presented in this analysis show that the source exhibits dramatic spectral variability, from a typical unabsorbed Seyfert 1 type spectrum to a Compton-thin absorbed state, on time scales of ~5 years. This extreme change in spectral shape can be attributed to variations in the column density and covering fraction of a neutral absorbing medium attenuating the emission from the central continuum source. Evidence for Compton reflection of the intrinsic nuclear emission is present in each of the spectra, though this feature is most prominent in the low-state spectra, where the associated Fe emission line complex is clearly visible. In addition to the variable absorbing medium, a warm absorber component has been detected in each spectral state. Optical spectroscopy concurrent with the 2010 XMM-Newton observation campaign have detected the presence of broad optical emission lines during an X-ray absorption event.From the analysis of both X-ray and optical spectroscopic data, it has been inferred that the X-ray spectral variability is a result of obscuration of the central emission region by a clumpy absorber covering >80 per cent of the source with an average column density of NH ~7x10^{23} cm^{-2}, and which is located outside the broad line region at a distance from the central source consistent with the dust sublimation radius of the AGN.

A REMARKABLE LONG-TERM LIGHT CURVE AND DEEP, LOW-STATE SPECTROSCOPY: SWIFT AND XMM-NEWTON MONITORING OF THE NLS1 GALAXY Mkn 335

The narrow-line Seyfert 1 galaxy (NLS1) Mkn 335 is remarkable because it has repeatedly shown deep, long X-ray low states that show pronounced spectral structure. It has become one of the prototype active galactic nuclei (AGNs) in deep minimum X-ray states. Here we report on the continuation of our ongoing monitoring campaign with Swift and the examination of the low-state X-ray spectra based on a 200 ks triggered observation with XMM-Newton in 2009 June. Swift has continuously monitored Mkn 335 since 2007 May typically on a monthly basis. This is one of the longest simultaneous UV/X-ray light curves so far obtained for an AGN. Mkn 335 has shown strong X-ray variability even on timescales of hours. In the UV, it turns out to be one of the most variable among NLS1s. Long-term Swift monitoring allows us to examine correlations between the UV, X-rays, and X-ray hardness ratios. We find no significant correlation or lag between the UV and X-ray variability; however, we do find distinct trends in the behavior of the hardness ratio variability. The hardness ratio and count rate are correlated in the low-flux state, but no correlation is seen in the high state. The X-ray low-state spectra of the 2007 and 2009 XMM-Newton observations display significant spectral variability. We fit the X-ray spectra with a suite of phenomenological models in order to characterize the data. The broadband CCD spectrum can be fitted equally well with partial absorption and blurred reflection models. These more complicated models are explored in further detail in upcoming work.

A characterization of the NGC 4051 soft X-ray spectrum as observed byXMM-Newton

<i>Context. <i/>Soft X-ray high resolution spectroscopy of obscured AGNs shows a complex soft X-ray spectrum dominated by emission lines of He and H-like transitions of elements from carbon to neon, as well as L-shell transitions due to iron ions.<i>Aims. <i/>In this paper we characterize the <i>XMM<i/>-Newton RGS spectrum of the Seyfert 1 galaxy NGC 4051 observed during a low flux state and infer the physical properties of the emitting and absorbing gas in the soft X-ray regime.<i>Methods. <i/>X-ray high-resolution spectroscopy offers a powerful diagnostic tool because the observed spectral features strongly depend on the physical properties of matter (ionization parameter <i>U<i/>, electron density <i>n<i/><sub>e<sub/>, hydrogen column density <i>N<i/><sub>H<sub/>), which in turn are tightly related to the location and size of the X-ray emitting clouds. We carried out a phenomenological study to identify the atomic transitions detected in the spectra. This study suggests that the spectrum is dominated by emission from a photoionized plasma. Then we used the photoionization code Cloudy to produce synthetic models for the emission line component and the warm absorber observed during phases of high intrinsic luminosity.<i>Results. <i/>The low state spectrum cannot be described by a single photoionization component. A multi-ionization phase gas with an ionization parameter in the range of log <i>U<i/> ~ 0.63–1.90 and a column density log <i>N<i/><sub>H<sub/> = 22.10–22.72 cm<sup>-2<sup/> is required, while the electron density <i>n<i/><sub>e<sub/> remains unconstrained. A warm absorber medium is required by the fit with the parameters log <i>U<i/> ~ 0.85, log <i>N<i/><sub>H<sub/> = 23.40 and log <i>n<i/><sub>e<sub/> 5. The model is consistent with an X-ray emitting region at a distance 5 × 10<sup>-2<sup/> pc from the central engine.

MASS OUTFLOW IN THE SEYFERT 1 GALAXY NGC 5548

We present a study of the intrinsic UV absorption and emission lines in an historically low-state spectrum of the Seyfert 1 galaxy NGC 5548, which we obtained in 2004 February at high spatial and spectral resolution with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. We isolate a component of emission with a width of 680 km/s (FWHM) that arises from an "intermediate line region" (ILR), similar to the one we discovered in NGC 4151, at a distance of ~1 pc from the central continuum source. From a detailed analysis of the five intrinsic absorption components in NGC 5548 and their behavior over a span of 8 years, we present evidence that most of the UV absorbers only partially cover the ILR and do not cover an extended region of UV continuum emission, most likely from hot stars in the circumnuclear region. We also find that four of the UV absorbers are at much greater distances (>70 pc) than the ILR, and none have sufficient N V or C IV column densities to be the ILR in absorption. At least a portion of the UV absorption component 3, at a radial velocity of -530 km/s, is likely responsible for most of the X-ray absorption, at a distance < 7 pc from the central source. The fact that we see the ILR in absorption in NGC 4151 and not in NGC 5548 suggests that the ILR is located at a relatively large polar angle (~45 degrees) with respect to the narrow-line region outflow axis.

New Complexities in the Low‐State Line Profiles of AM Herculis

When accretion temporarily ceases in the polar AM Her, the emission-line profiles are known to develop several distinct components, whose origin remains poorly understood. The new low-state spectra reported here have a more favorable combination of spectral resolution (R ~4500), time resolution (~3 minute exposures), and S/N than earlier work, revealing additional details of the orbital dependence of the line profiles. The central strong feature of Hα is found to be composed of two components of similar strength, one having K ~ 100 km s^−1 and phased with the motion of the secondary star, the other having little or no detectable radial velocity variations. We attribute the central line component to gas near the coupling region, perhaps with a contribution from irradiation of the secondary star. The two satellite components have radial velocity offsets of ~±250 km s^−1 on either side of the central strong Hα peak. These satellites most likely arise in large loops of magnetically confined gas near the secondary star due to magnetic activity on the donor star and/or interactions of the magnetic fields of the two stars. Doppler maps show that these two satellite features have concentrations at velocities that match the velocity locations of L4 and L5 in the system.

Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. IV. The Variable UV Absorption Lines

We report the detection of variable UV absorption lines in NGC 4395, based on UV observations with the HST STIS carried out in April and July, 2004, as part of a reverberation-mapping campaign. Low-ionization lines of O I, N I, Si II, C II, and Fe II, are present in the low-state spectra (April 2004) at a velocity v_shift=-250 km/s (system A_l), and additional high-ionization lines of C IV and N V appear in the high-state spectra (July 2004) at v_shift=-250 km/s (system A_h) and at v_shift=-840 km/s (system B). The absence of absorption from the low metastable levels of Si II implies a density <~10^3 cm^(-3) for system A_l, indicating a location outside the narrow line region (NLR). System A_h is peculiar as only N V absorption is clearly detected. A high N V/C IV absorption ratio is expected for a high metallicity absorber, but this is excluded here as the metallicity of the host galaxy and of the nuclear gas is significantly subsolar. A simple acceptable model for systems A_h and B is an absorber located between the broad line region (BLR) and the NLR, which absorbs only the continuum and the BLR. At the low-state the strong narrow emission lines of C IV and N V dominate the spectrum, making the absorption invisible. At the high-state the absorbed continuum and BLR emission dominate the spectrum. Thus, the change in the observed absorption does not reflect a change in the absorber, but rather a change in the continuum and BLR emission from behind the absorber, relative to the emission from the NLR in front of the absorber. Studies of the absorption line variability in highly variable objects can thus break the degeneracy in the absorber distance determination inherent to single epoch studies.

Ultra-luminous sources in nearby galaxies

This paper presents an update of what we have learned in the last year about the ULX phenomenon. New results are presented on radio emission from Holmberg II and a review is given on the recent X-ray data on timing and spectra. The new X-ray spectroscopic and optical imaging survey of nearby ULX with XMM allows us, for the first time, to place the average properties of these objects on a statistical basis. Direct examination of the sites of ULXs in nearby galaxies shows that ∼1/3 of them are not in or near star forming regions, indicating that a substantial fraction of ULX are not directly associated with young star formation. There are two ULX which have been identified with B stars as the optical counterparts on the basis of optical spectroscopy. Radio imaging of the Holmberg II ULX shows that it lies in a luminous extended radio source and that the radio emission is not beamed. A statistical study of ULX spectra in nearby galaxies shows that the ratio of ‘high state’ to ‘low state’ ULXs is ∼1:1 and that the high state objects, in general, are best fit with low temperature black bodies with a steep power law index. The objects with high state spectra are systematically more luminous than the objects with low state spectra consistent with the hypothesis that both are drawn from a population which shows state changes similar to those of black holes in the Milky Way. If this is true then the masses implied for the objects with the low state spectra are greater than 50 M ⊙.

TheBeppoSAXview of the galactic high-mass X-ray binary 4U 0114+65

A pointed observation of the galactic high-mass X-ray binary 4U 0114+65 was carried out with BeppoSAX to compare the X-ray spectral and timing characteristics observed by this satellite over the broadest range of energies thus far (1.5-100 keV) with the information previously obtained with other spacecraft. The light curve of 4U 0114+65 shows a large flare at the beginning of the BeppoSAX pointing and no significant hardness evolution either during the flare or in the low state occurring after the flare itself. The modulation at �2.7 hours, attributed to the accreting neutron star (NS) spin periodicity, is not significantly detected in our data, although fluctuations with timescales of �3 hours can be seen in the 2-10 keV light curve. Shorter modulations down to timescales of minutes are also found and interpreted as due to accretion of matter onto the NS. The flaring and the low state spectra of 4U 0114+65 can be equally well fitted either with a power law modulated by a high-energy exponential cutoff or with a Comptonization model. During the low state the presence, although tentative, of a thermal component (with kT � 0.3 keV) at low energies, possibly produced by an ionized plasma cloud around the NS, cannot be excluded. Contrary to previous claims, a cyclotron resonant feature in absorption at �22 keV was not detected in the BeppoSAX spectroscopic data, whereas evidence for a Fe emission line around 6.4 keV is found only during the low state emission. Using all of the above information, a scenario for the system in which the NS is embedded in, and accreting from, a low angular momentum gas cloud is envisaged.

INTEGRAL observations of six AGN in the Galactic Plane

We present results on approximately one year of INTEGRAL observations of six AGN detected during the regular scans of the Galactic Plane. The sample is composed by five Seyfert 2 objects (MCG -05-23-16, NGC 4945, the Circinus galaxy, NGC 6300, ESO 103-G35) and the radio galaxy Centaurus A. The continuum emission of each of these sources is well represented by a highly absorbed (N H > 10 22 cm -2 ) power law, with average spectral index Γ = 1.9 ± 0.3. A high energy exponential cut-off at E c ∼ 50 keV is required to fit the spectrum of the Circinus galaxy, whereas a lower limit of 130 keV has been found for NGC 4945 and no cut-off has been detected for NGC 6300 in the energy range covered by these INTEGRAL data. The flux of Centaurus A was found to vary by a factor of ∼2 in 10 months, showing a spectral change between the high and low state, which can be modelled equally well by a change in the absorption (N H from 17 to 33 x 10 22 cm -2 ) or by the presence of a cut-off at ≥120 keV in the low state spectrum. A comparison with recently reprocessed BeppoSAX/PDS data shows a general agreement with INTEGRAL results. The high energy cut-off in the hard X-ray spectra appears to be a common but not universal characteristic of Seyfert 2 and to span a wide range of energies.

Photoionized Lines in X‐Ray Spectra of SMC X‐1

We present a detailed spectral analysis of Chandra ACIS-S continuous clocking (CC) mode observations of the massive X-ray binary system SMC X-1. The system was observed during both the high and low X-ray states of the roughly 60 day superorbital period. The continuum spectra during both states are well represented by a power law with photon index α = 0.9 and a blackbody of kT = 0.15 keV. The high-state spectra are dominated by the continuum and independent of orbital phase, whereas the low-state spectra show a strong orbital dependence as well as line emission from O, Ne, Mg, Fe, and Si. This is consistent with the states attributed to disk precession: during the high state, X-ray emission is dominated by the compact source, which is abruptly eclipsed; during the low state, the compact object is hidden by the disk, and a larger, less luminous scattering region is responsible for the X-ray emission. A prominent Ne IX feature places a stringent limit (log ξ = 2.0-2.5) on the ionization parameter, which constrains the wind dynamics of the system. The Fe line fluxes are related linearly to the blackbody fluxes, indicating that both originate in the same region or are excited by the same mechanism. There is evidence for structure in the Fe line that cannot be fully resolved by the current observations. The pulse period measured during our observations, 0.7057147 ± 0.00000027 s, shows that the uninterrupted spin-up trend of SMC X-1 continues. We discuss the implications of our results for models of SMC X-1.

Gamma‐Ray Spectral State Transitions of GRO J1719−24

We report the results of an in-depth study of the long-term soft gamma-ray (30 keV to 1.7 MeV) flux and spectral variability of the transient source GRO J1719-24 that was first discovered by BATSE and SIGMA in the fall of 1993. Our results were obtained from the JPL BATSE-EBOP database covering a 1000 day period between 1993 January 13 and 1995 October 10. During this period, the source underwent a major outburst in the fall of 1993 when the 35-100 keV flux rose from a quiescent state of less than 16 mcrab before 1993 September 17 to a level of 1.5 crab on October 3. The source remained in this high-intensity state over the next ~70 days, during which the 35-100 keV flux decreased monotonically by ~33% to ~1 crab on December 12, then decreased sharply to the pre-transition quiescent level of ~44 mcrab on December 21, where it remained until 1994 September 5. During a 400 day period between 1994 September 5 and 1995 October 10, the source again underwent a series of five transitions when the 35-100 keV flux increased to low-intensity levels of ~200-400 mcrab, a factor of 4-7 times lower than what was observed in 1993. The low- and high-intensity states were characterized by two different spectral shapes. The low-state spectra are described by a power law with a spectral index of ~2. The high-state spectra, on the other hand, have two components: a thermal Comptonized shape below ~200 keV with electron temperature kTe of ~37 keV and optical depth τ ~ 2.8, and a soft power-law tail with photon index of ~3.4 above 200 keV that extends to ~500 keV. The softer high-intensity spectrum and the harder low-intensity spectrum intersect at ~400 keV. The nonthermal power-law gamma-ray component in both the high- and low-intensity spectra suggests that the persistent nonthermal emission source is coupled to the hot and variable thermal emission source in the system. Furthermore, the correlation of the spectral characteristics with the high- and low-intensity states resembles that seen in two other gamma-ray-emitting black hole candidates, GRO J0422+32 and Cygnus X-1, suggesting that perhaps similar system configurations and processes are occurring in these systems. Possible scenarios for interpreting these behaviors are discussed.

Evidence of an Intermediate-Mass Black Hole: Chandra and XMM-Newton Observations of the Ultraluminous Supersoft X-Ray Source in M101 during Its 2004 Outburst

We report the results of Chandra and XMM-Newton observations of a new outburst of an ultraluminous supersoft X-ray source in M101. CXOU J140332.3+542103 was observed in a low-luminosity state (LX ~ 1037 ergs s-1) between 2004 January and May. The low-state X-ray spectra were relatively hard; the combined low-state spectrum can be fitted with a combination of a power law with photon index of 1.4 and a blackbody of 63 eV. During 2004 July, the source underwent a strong outburst and the peak 0.3-7 keV luminosity reached 3 × 1040 ergs s-1, with a bolometric luminosity of about 1041 ergs s-1. The outburst spectra were very soft and can be generally fitted with a blackbody model with temperatures of 50-100 eV. In two of the observations, absorption edges at 0.33, 0.56, 0.66, and 0.88 keV were found. An XMM-Newton observation was also performed during the decay of the outburst, and a power-law tail was seen in addition to the supersoft spectrum. We consider different accretion models; one involving an intermediate-mass black hole can explain the observations.

Time-resolved Ultraviolet Spectroscopy of the SW Sex Star DW UMa: Confirmation of a Hidden White Dwarf and the Ultraviolet Counterpart to Phase 0.5 Absorption Events

We present time-resolved ultraviolet (UV) spectroscopy of the SW Sex star DW UMa in the high state. We confirm that shortward of 1500 A, the high-state UV continuum level is lower than the white dwarf (WD) dominated low-state level. We also do not see the WD contact phases in the high-state eclipse light curves. These results confirm our earlier finding that the WD in this system is hidden from view in the high state. On the basis of this, we caution that eclipse mapping of high-inclination SW Sex stars in the high state may yield incorrect or misleading results. In the context of DW UMa, we demonstrate explicitly that distance estimates obtained by recent eclipse-mapping studies cannot be reconciled with the WD-dominated low-state spectrum. We also show that the fluxes of the UV emission lines in the high state drop near orbital phase 0.5. This is the first detection of a UV counterpart to the class-defining phase 0.5 absorption seen in the optical emission lines of SW Sex stars.

AnXMM‐NewtonObservation of the Seyfert 1 Galaxy 1H 0419−577 in an Extreme Low State

Previous observations of the luminous Seyfert 1 galaxy 1H 0419-577 have found its X-ray spectrum to range from that of a typical Seyfert 1 with 2-10 keV power law index Gamma ~ 1.9 to a much flatter power law of Gamma ~ 1.5 or less. We report here a new XMM-Newton observation which allows the low state spectrum to be studied in much greater detail than hitherto. We find a very hard spectrum (Gamma ~ 1.0), which exhibits broad features that can be modelled with the addition of an extreme relativistic Fe K emission line or with partial covering of the underlying continuum by a substantial column density of near-neutral gas. Both the EPIC and RGS data show evidence for strong line emission of OVII and OVIII requiring an extended region of low density photoionised gas in 1H 0419-577. Comparison with an earlier XMM-Newton observation when 1H 0419-577 was 'X-ray bright' indicates the dominant spectral variability occurs via a steep power law component.

Catching NGC 4051 in the Low State withChandra

We report the results from a Chandra TOO observation of the low-luminosity Narrow Line Seyfert 1 galaxy NGC 4051, obtained during a 6-week duration low-flux state in 2001 February. During the Chandra observation, the 2-10 keV source flux was 7e-12 erg/cm^2/s, corresponding to a 2-10 keV luminosity of 8e40 erg/s. We confirm the absence of strong extended soft X-ray emission in NGC 4051, and that the low state spectrum is dominated by the central point source. The X-ray spectrum has an unusual, hybrid shape, very soft below ~3 keV (and which we model with a black body of temperature 0.14 keV) and very hard at higher energies (power-law slope of Gamma~1). The lightcurves in both soft and hard bands are significantly variable and correlated, implying a connection between hard and soft components and proving that the hard component is dominated by primary continuum emission and is not due to pure reflection from distant cold material. However, a comparison with RXTE data obtained during the same 2001 low state suggests the presence of unusually prominent disk reflection features, which may help to explain the apparent upwards curvature and extreme hardness of the Chandra spectrum above a few keV. The shape of the 2001 low state spectrum is consistent with that observed in a brief (<3 d) low flux excursion during the source's normal state in April 2000, suggesting that emission processes during the low state are not significantly different to those in the normal state. The unusual spectral shape observed in the low state may be a continuation to low fluxes of the normal, flux-dependent spectral variability of the source.

1RXS J232953.9+062814: A Dwarf Nova with a 64 Minute Orbital Period and a Conspicuous Secondary Star

We present spectroscopy and time-series photometry of the newly discovered dwarf nova 1RXS J232953.9+062814. Photometry in superoutburst reveals a superhump with a period of 66.06(6) minutes. The low state spectrum shows Balmer and HeI emission on a blue continuum, and in addition shows a rich absorption spectrum of type K4 +- 2. The absorption velocity is modulated sinusoidally at P_orb = 64.176(5) min, with semi-amplitude K = 348(4) km/s. The low-state light curve is double-humped at this period, and phased as expected for ellipsoidal variations. The absorption strength does not vary appreciably around the orbit. The orbital period is shorter than any other cataclysmic variable save for a handful of helium-star systems and V485 Centauri (59 minutes). The secondary is much hotter than main sequence stars of similar mass, but is well-matched by helium-enriched models, indicating that the secondary evolved from a more massive progenitor. A preliminary calculation in which a 1.2 solar-mass star begins mass transfer near the end of H burning matches this system's characteristics remarkably well.

Simultaneous [ITAL]Chandra[/ITAL] and [ITAL]Hubble Space Telescope[/ITAL] Observations of SMC X-1

We present first results from simultaneous ultraviolet (Hubble Space Telescope/STIS) and X-ray (Chandra/ACIS) observations of the SMC X-1/SK 160 eclipsing binary system. Observations covering four orbital phases during each of the X-ray high and X-ray low states were taken in 2000 October-November and 2001 April. The ultraviolet P Cygni lines show strong broad absorption near X-ray eclipse and narrow absorption when the X-ray source is in the line of sight. The effect is visible during both the X-ray high and X-ray low states; the UV continuum flux remains roughly constant in spite of more than an order-of-magnitude reduction in X-ray flux, as expected if the X-ray flux reduction is due to occultation of the X-ray source by a precessing disk rather than an intrinsic change in X-ray luminosity. The X-ray spectra are dominated by continuum emission in the X-ray high state. Occultation of the neutron star by the disk during the low state also implies that X-ray emission from the disk surface should be present, and the low-state spectra do show strong emission lines. During eclipse and during the X-ray low state, the continuum emission largely disappears, and we see line emission from O, Ne, Mg, and Fe and possibly from Si and S. The emission lines are consistent with recombination lines from mostly hydrogenic and helium-like species, which could be produced by photoionization in an extended stellar wind.