Thermonuclear bursts from slowly and rapidly accreting neutron stars

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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
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PART I high-? bursts
Or how we finally found them, in a slowly
rotating neutron star. ? Sensitive to neutron
star spin?
PART II low-? 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)
? mass accretion rate per unit area
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Burning regimes (a shell flash in a nutshell)

• Unstable H burning
• ?/?Eddlt0.01
• Thermally unstable H burning.
• Pure He ignition
• 0.01lt?/?Eddlt0.04
• He ignites in the absence of H.
• Mixed H/He ignition
• 0.04lt?/?Eddlt1
• He ignites in a mix of HHe.
• Stable HHe burning
• ?/?Eddgt1
• Both H and He burn stably. No bursts.

?accreted mass/time/area (Eddington-normalized
?/?Edd)
Increasing ?
Pic Horowitz Refs Woosley Taam (1976)
Fujimoto ea (1981) Taam (1981) Bildsten (1998)
Cumming Bildsten (2000) Woosley ea (2004)
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Burning regimes (a shell flash in a nutshell)

• Unstable H burning
• ?/?Eddlt0.01
• Thermally unstable H burning.
• Pure He ignition
• 0.01lt?/?Eddlt0.04
• He ignites in the absence of H.
• Mixed H/He ignition
• 0.04lt?/?Eddlt1
• He ignites in a mix of HHe.
• Stable HHe burning
• ?/?Eddgt1
• Both H and He burn stably. No bursts.

BURST RATE INCREASES!
Increasing ?
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Bursting regimes (observational status until 2010)
Linares et al. (2011)
Where are the bursts at ? gt 0.1 ?Edd?? Cornelisse
ea (03) in t Zand ea (07) Galloway ea (08)
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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)
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PART I high-? bursts
Or how we finally found them, in a slowly
rotating neutron star. ? Sensitive to neutron
star spin?
PART II low-? 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)
? mass accretion rate per unit area
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Low-? bursts (how frequent are they?)
Low-? bursts recur on week-months timescales,
but such recurrence times are ill-constrained
using pointed observations.
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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 2010June 2012) 1490
XRB candidates (1.8/day).
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GBM thermonuclear bursts 4U061409
15 GBM bursts from 4U 061409 in the 1st year!
(33 bursts detected in the previous gt30 years
Kuulkers et al. 2010)
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GBM thermonuclear bursts 4U061409
Linares et al. (2012)
Burst recurrence time in 4U 061409 (2010-2011)
12 /- 3 d Shortest burst pair ever seen from the
source 2.8 days apart.
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GBM thermonuclear bursts 4U061409
Chenevez et al. (2008)
Does the long burst population reflect a distinct
ignition regime or a selection effect?
Burst energies in 4U 061409 overlap with normal
and long burst populations.
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PART I high-? bursts
Summary Conclusions

• 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-? bursts

• Burst recurrence time in 4U 061409 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?

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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 061409 (Linares et
al. 2012, ApJ, to be submitted)