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Exploring Timing Features of XTE J1807-294 Outburst in 2003 March: Evidence for Accreting Blobs

This paper discusses the timing features observed in XTE J1807-294 during the 2003 March outburst, highlighting correlations among count rate, pulse amplitude, and QPO frequencies. The study identifies four distinct flares and discusses possible origins of these events, providing constraints on QPO models and shedding light on the nature of the observed spectral variations. The paper also raises open questions regarding the behavior of QPOs in different source types and suggests potential links between twin kHz QPOs and neutron star spin. This research contributes to our understanding of accretion processes in compact binary systems and the variability of X-ray pulsars.

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Exploring Timing Features of XTE J1807-294 Outburst in 2003 March: Evidence for Accreting Blobs

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  1. Timing Features of XTE J1807-294 in 2003 March outburst --Possible Evidence for Accreting Blobs Fan Zhang et al. (astro-ph/0602529)

  2. Content 1. Introduction • LMXBs : correlations of spectral state and timing variability • MXPs : basic observational results 2. Timing features of J1807-294 • Four flares distinguished in 2003 March RXTE observation • Correlations among count rate, basic fractional pulse amplitude and QPO frequencies 3. Discussion of our results • Constraints on QPO models • Possible origin of the relatively soft broad ‘puny’ flares

  3. Introduction of LMXBs Van der Klis 2004, astro-ph/0410551

  4. Source state

  5. Power density spectrum

  6. Common frequency correlation ? L_Hz ~150Hz ? L_h2 (harmonic) ? L_LFN

  7. Open questions • Is hecto-hertz QPO specific for atoll ? • Is L_h harmonic specific for Z ? • Does LFN really vary in different Z ? • Are twin kHz QPOs correlated with NS spin ? ----- MXP,e.g. SAX J1808.4-3658 ----- burst oscillation-spin

  8. Introduction of MXPs

  9. Introduction of MXPs Accretion powerd millisecond X-ray pulsar • Ultra-compact group (Porb<40 min) XTE J1807-294 (2003) XTE J1751-305 (2002) XTE J0929-314 (2002) • Relatively wide group (Porb=2.~4.28 hour) SAX J1808.4-3658 (1998) XTE J1814-338 (2003) IGR J00291+5934 (2005) ---------type I thermal nuclear outburst ---------kHz QPOs

  10. Frequency correlation in MXPs

  11. Lightcurve of MXPs -----Wijnands (astro-ph/0501264)

  12. Why choose XTE J1807-294? • Twin kHz QPOs – inner disk evolution • Binary parameters – pulse profiles – NS surface emission • Compton dominated spectrum • No type I thermonuclear bursts so we can focus on studying the effect of disk evolutions on the NS surface emission

  13. XTE J1807-294: 4 flares 1. Hours-to-days low-amplitude intensity fluctuation; 2. Stronger soft emission enhancement 3. Apparent basic pulse amplitude variability

  14. Power Spectra

  15. Frequency correlation 1,Common frequency correlations between Lu,Ll,LhHz,Lh,Lb 2, Additional components of L_h2, L_LFN 3,shift factor of 1.5 for Lu, Ll, L_LFN

  16. Correlations between net count rate,kHz QPOs and the fractional basic pulse profile Are parallel tracks related to the flares? Inner disk movement is correlated with NS surface emissions

  17. Discussion: constraints on QPO models • Both L_Hz and L_h harmonic are observed in one source XTE J1807-294, so they are not specific components for atoll or Z sources. • L_b and L_LFN appear simultaneously in the spectrum of XTE J1807-294, so they are two components with different origins. L_LFN of GX17+2 is a different component from L_LFN observed in other Z sources, so its distribution can not be explained by the same QPO model for L_b of atoll or L_LFN of other Z sources. • Shift factor of about 1.5 exists also in XTE J1807-294. • The kHz QPO frequency separation varies around 191Hz. Abramowicz et al. 2003, A&A, 404, L21

  18. Discussion: origin of the flares Inner disk radius variability (Accretion rate? Accretion pattern?) • groups 1-3, groups 4-6 QPO frequency variability NS emission variability • Variable relationship between a0/c0 and c0 Possible Origin: 1.Accreting inhomogeneous disk flow 2.Nuclear burning, e.g. ‘fires’ on the NS surface (Bildsten 1993) Poutanen, J. & Gierlinski, M. 2003, MNRAS, 343, 1301 Bildsten, L. 1993, Apj, 418, L21 Strohmyer, T. E. Astro-ph/0301544

  19. Thanks !

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