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Thermonuclear bursts from slowly and rapidly accreting neutron stars

Thermonuclear bursts from slowly and rapidly accreting neutron stars. Manu Linares D. Chakrabarty, D. Altamirano, A. Cumming, L. Keek. V. Connaughton, P. Jenke, A. Camero-Arranz, A. van der Horst, et al. 50 years of Sco X-1, Boston, July 2012. PART I: high-ṁ bursts.

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Thermonuclear bursts from slowly and rapidly accreting neutron stars

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  1. Thermonuclear bursts from slowly and rapidly accreting neutron stars Manu Linares D. Chakrabarty, D. Altamirano, A. Cumming, L. Keek. V. Connaughton, P. Jenke, A. Camero-Arranz, A. van der Horst, et al. 50 years of Sco X-1, Boston, July 2012

  2. PART I: high-ṁ bursts Or how we finally found them, in a slowly rotating neutron star.  Sensitive to neutron star spin? PART II: low-ṁ bursts Or how we hunt them in a systematic search and find the first overlap between normal and long/intermediate bursts. (Sensitive to neutron star crust temperature) ṁ = mass accretion rate per unit area

  3. Burning regimes (a shell flash in a nutshell) ṁ=accreted mass/time/area (Eddington-normalized: ṁ/ṁEdd) • Unstable H burning: ṁ/ṁEdd<0.01 Thermally unstable H burning. • Pure He ignition: 0.01<ṁ/ṁEdd<0.04 He ignites in the absence of H. • Mixed H/He ignition: 0.04<ṁ/ṁEdd<1 He ignites in a mix of H&He. • Stable H&He burning: ṁ/ṁEdd>1 Both H and He burn stably. No bursts. Increasing ṁ Pic: Horowitz; Refs: Woosley & Taam (1976); Fujimoto ea (1981); Taam (1981); Bildsten (1998); Cumming & Bildsten (2000); Woosley ea (2004)

  4. Burning regimes (a shell flash in a nutshell) • Unstable H burning: ṁ/ṁEdd<0.01 Thermally unstable H burning. • Pure He ignition: 0.01<ṁ/ṁEdd<0.04 He ignites in the absence of H. • Mixed H/He ignition: 0.04<ṁ/ṁEdd<1 He ignites in a mix of H&He. • Stable H&He burning: ṁ/ṁEdd>1 Both H and He burn stably. No bursts. Increasing ṁ BURST RATE INCREASES!

  5. Bursting regimes (observational status until 2010) Linares et al. (2011) Where are the bursts at ṁ > 0.1 ṁEdd?? Cornelisse ea (03); in ‘t Zand ea (07); Galloway ea (08)

  6. T5X2: smooth burst evolution ~50% Edd ~10% Edd RXTE PCA 11 Hz X-ray pulsar. Unprecedented smooth evolution: bursts-mHz QPO-bursts! Did we underestimate influence of fast spin on burning regimes? Linares ea (2010,2011,2012); Strohmayer ea (2010); Papitto ea (2010); Motta ea (2011); Chakraborty & Bhattacharyya (2011)

  7. PART I: high-ṁ bursts Or how we finally found them, in a slowly rotating neutron star.  Sensitive to neutron star spin? PART II: low-ṁ bursts Or how we hunt them in a systematic search and find the first overlap between normal and long/intermediate bursts. (Sensitive to neutron star crust temperature) ṁ = mass accretion rate per unit area

  8. Low-ṁ bursts (how frequent are they?) Low-ṁ bursts recur on ~week-months timescales, but such recurrence times are ill-constrained using pointed observations.

  9. The Fermi-GBM X-ray burst monitor • World English Dictionary: • monitor  — n 1. a person or piece of equipment that warns, checks, controls, or keeps a continuous record of something. • FoV: all unocculted (75%) sky. • X-ray response: down to 8 keV. Optimal instrument to detect rare & bright X-ray bursts. Systematic X-ray burst search and processing at NSSTC & MIT. So far (March 2010–June 2012): 1490 XRB candidates (~1.8/day).

  10. GBM & thermonuclear bursts: 4U0614+09 15 GBM bursts from 4U 0614+09 in the 1st year! (33 bursts detected in the previous >30 years; Kuulkers et al. 2010)

  11. GBM & thermonuclear bursts: 4U0614+09 Linares et al. (2012) Burst recurrence time in 4U 0614+09 (2010-2011): 12 +/- 3 d Shortest burst pair ever seen from the source: 2.8 days apart.

  12. GBM & thermonuclear bursts: 4U0614+09 Chenevez et al. (2008) Does the long burst population reflect a distinct ignition regime or a selection effect? Burst energies in 4U 0614+09 overlap with normal and long burst populations.

  13. Summary & Conclusions PART I: high-ṁ bursts • Unprecedented burst behavior in the 11 Hz pulsar T5X2, in agreement with theoretical burning regimes. • Three bursting regimes when mdot increased 10-50% Edd; marginally stable burning, mHz QPOs.  Are burning regimes sensitive to neutron star spin? PART II: low-ṁ bursts • Burst recurrence time in 4U 0614+09 = 12 +/- 3 d; two bursts only 2.8 d apart. • Burst energies between those of normal and long bursts.  Are normal and long bursts two distinct populations?

  14. Thanks! Refs. Millihertz Quasi-periodic Oscillations and Thermonuclear Bursts from Terzan 5: A Showcase of Burning Regimes (Linares et al. 2012, ApJ, 748, 82) The Fermi-GBM X-ray burst monitor: thermonuclear bursts from 4U 0614+09 (Linares et al. 2012, ApJ, to be submitted)

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