4. Preliminary IR results: Phase-concentrated spectral evolution

1. Piercing the Dust – Infrared and X-ray observations of Circinus X-1 Will Clarkson1, Simon Clark2, Phil Charles3,4, Malcolm Coe4, Natalie Onyett5 1The Open University, Milton Keynes. w.i.clarkson@open.ac.uk 2 Astrophysics Group, University College London 3 South African Astronomical Observatory 4School of Physics and Astronomy, Southampton University 5 Sussex Astronomy Centre, University of Sussex Circinus X-1 is a puzzling neutron star X-ray Binary that mixes properties of both high-mass and low-mass XRB types, with evidence for both a highly eccentric orbit (typical of HMXBs) and a weak neutron star magnetic field (typical of LMXBs). Recent radio detection of the most highly relativistic outflow ever discovered from a stellar-mass object makes this a key system for accretion/outflow studies, yet high, uncertain reddening (AV ~7-14) makes optical observations highly difficult. We present preliminary results of an IR/X-ray campaign to better constrain this mysterious system. (1): X-ray analysis of archival observations suggest the system must be highly eccentric, but no spatially-resolved X-ray counterpart to the radio nebula is apparent, ruling out immediate post-SN evolution. (2): An initial set of service spectra with IRIS2 on the AAT show clear evidence for line profile evolution, but the dependence of this transition on orbital phase is unclear. (3): Followup observations were obtained nightly through a full half-orbit, to connect the dots from apastron to periastron, with simultaneous XTE/PCA observations to simultaneously probe the accretion disk. (4): Preliminary reduction suggests the emission-line profile evolution is highly concentrated in orbital phase. (5): It is currently unclear if this represents a single evolving emission region undergoing brief interaction or the introduction of a second emission site, possibly outflow-related. 0. An eccentric-orbit, non-pulsating Neutron-Star XRB 2. AAT / IRIS2 service observations suggest line profile evolution • Established Properties • K-band only, three visits • Compare with quasar & known Be/XRB • Mid-B supergiant ? • No CO bandheads  < F-type? • Significant contamination from disk/outflow (c.f. 1915+105) • See Clark, Charles, Clarkson & Coe 2003 A&A 400, 655 K Compact Object Neutron Star Donor Object Unknown Orbital Period 16.6d, possibly decreasing Distance 6.4-8.0 kpc Location Galactic Equator (b=0.04) Inclination Unknown X-Ray LuminosityUp to a few LEdd Magnetic Field Unknown, probably < 109 G X-Ray Pulsations None Observed Age Unknown Orbital Eccentricity Unknown, probably high (>0.7) QPO Behaviour Z-Source Reddening Av ~ 7-14 Radio Observations Radio flares seen in the 1970’s establish quadratic ephemeris, Ultrarelativistic outflow ( >10 ); Fender et al (2004) • Post-periastron, July 2002 XTE/ASM • Apastron, September 2003 XTE/ASM K Hs • Multiwavelength Variability Left: 6.3cm radio lightcurve. From Fender (1998) Right: Radio image of a ~7’x7’ region surrounding Cir X-1. From Stewart et al (1993) Radio mJy IR • Br evolves from single- to double- peaked from periastron to apastron. • Visits widely separated in time, thus this variation might be random rather than orbital • Possible wavelength calibration artifacts? • 2.275m line – CI Cam-like? K mag K-band lightcurve. From Glass (1994) X-ray 3. The first simultaneous X-ray / IR study through a full half-orbit ASM c/s 1-12keV X-ray Lightcurve from RXTE/ASM. From Clarkson et al (2004) • Periastron, July 2004 0 1 2 3 phase XTE/ASM • Eight Contiguous nights’ ground-based coverage - 28th June –5th July 2004 • Beginning orbital phase ~0.6 • Four Hours per night JHK spectra with AAT/IRIS2: R ~ 2400 • 3-4ks / night simultaneous XTE/PCA coverage (analysis in prep) • Further K-band service spectrum just after ~0.5 in subsequent orbit 1. X-ray attempts to constrain the donor . • Use X-ray dips as a surrogate for accretion rate M • Semianalytic model for eccentric-orbit M from Brown & Boyle (1984 A&A 141, 369): fit to observed dip-rate . . . Ndips . M1 4. Preliminary IR results: Phase-concentrated spectral evolution • Initial reductions from the ORAC-DR reduction pipeline – only A0V standard used • Full reduction will include both G2V and A0V observed standards Orbital Phase Predicted M() (BB84) • Fit orbit to observed dipping rate • Profile depends on M2,e,T2 • For realistic T2,  e > 0.6 • But model used perhaps excessively simplistic • Awaits more modern simulation… • See Clarkson, Charles & Onyett 2004 M2 0.0 0.2 e 0.6 0.8 1.0 • Search for spatially-resolved X-ray SNR • Archival Chandra observations covering dipping July 14 Outside Dipping • Br , He-I clearly show evolution of component separation • Continuum changes by factor ~5 in ~2 days • No obvious CO, Na, Mg absorption Above: XTE/PCA lightcurve of a typical X-ray dip. • Service spectrum on subsequent orbit (July 14) suggests profile evolution may be a feature of the orbit. • Single-peak profile may represent the addition of a separate, outflow-related component over an otherwise steady double-peaked source. The accretion disk should show dramatic velocity evolution over the orbit, yet the velocity separation of this steady component is ~constant throughout half an orbit • Might the double-peaked component thus be donor emission? During Dipping • Nebula, halo and background spatial regions vary in step with point-source, consistent with ISM scattering (c.f. GX13+1; Smith, Edgar & Shafer 2002) Above: Spatially resolved X-ray spectra with Chandra.ACIS-S XTE/PCA and detailed JHK reductions in progress – watch this space… 6. Upcoming Observations 5. Comparison with Soft X-ray Transients in Outburst • Gemini South/GNIRS: Semester 2005A, 2 nights in Queue mode, expect R~5900, ~ 5 min per spectrum set. High time-resolution spectral evolution • Simultaneous VLT1-ISAAC/XMM-EPIC, September 4-7 2005. High time- and Spectral-resolution simultaneous X-ray/near-IR spectral evolution. • Further proposals submitted to increase orbital phase coverage. • Emission profile shape in optical spectra of SXT’s is dependent on the irradiating X-ray flux; e.g. GRO J1655-40 (Soria et al 2000): • High soft X-ray flux in outburst  temperature inversion on accretion disk  double-peaked, highly variable emission features. • High X-ray flux > 20keV  thick outflow of disk material, producing a strong, single-peaked emission feature, while the double-peaked profile disappears (c.f. Murray & Chiang 1997; Soria et al 2000). • Cir X-1 has never been strongly detected > 20keV (e.g. Bird et al 2004); however an equivalent, single-peak-emitting disk outflow may still be driven by massively SuperEddington, quasi-spherical accretion during periastron passage. • Model 1: Evolution from single-to-double peaked near-IR emission profile may represent settling of accretion configuration into a disk and/or thinning of an optically thick outflow surrounding the disk as for the SXT’s. • Model 2:The timescale for the outflow to thin out may be too long for the accretion disk ever to become visible. Instead, the double-peaked emission represents a constant contribution from the hitherto unknown mass donor. 7. References • Bird et al 2004 ApJ Lett 607, 33 • Clark, Charles, Clarkson & Coe 2003 A&A 400, 655 • Clarkson, Charles & Onyett 2004 MNRAS 348, 458 • Clarkson, Charles et al 2005 in prep • Fender et al. 2004 Nature 427, 222 • Fender, 1998 IAUC 164, astro-ph/9707045 • Glass 1994 MNRAS 628, 742 • Murray & Chiang 1997 ApJ 474, 91 • Smith, Edgar & Shafer 2002 ApJ 581, 562 • Soria, Wu & Hunstead 2000 ApJ 539, 445 • Stewart, Caswell, Haynes & Nelson 1993 MNRAS 261, 593 Above: GRO J1655-40 H profile during an interval of high X-ray flux > 20keV. Adapted from Soria et al (2000) Left: GRO J1655-40 H orbital evolution during soft X-ray outburst (adapted from Soria et al 2000) •  Rapid variability of double-peaked lines on a sub-day timescale. •  Little or no variation of double-peaked lines on a sub-day timescale. High time-resolution near-IR spectra are required to distinguish these possibilities. With thanks to Stuart Ryder, AAO