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 PART II: low- ṁ bursts Or how we finally found them, in a slowly rotating neutron star.  Sensitive to neutron star spin? 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

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

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

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

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

PART I: high- ṁ bursts PART II: low- ṁ bursts Or how we finally found them, in a slowly rotating neutron star.  Sensitive to neutron star spin? 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

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.

FoV: all unocculted (75%) sky. X-ray response: down to 8 keV.  Optimal instrument to detect rare & bright X-ray bursts. 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. Systematic X-ray burst search and processing at NSSTC & MIT. So far (March 2010–June 2012): 1490 XRB candidates (~1.8/day).

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

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

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

PART I: high- ṁ bursts PART II: low- 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? Burst recurrence time in 4U = 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? Summary & Conclusions

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 (Linares et al. 2012, ApJ, to be submitted) Refs. Thanks!