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

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/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.

ṁ=accreted mass/time/area(Eddington-normalized: ṁ/ṁEdd)

Pic: Horowitz; Refs: Woosley & Taam (1976); Fujimoto ea (1981); Taam (1981); Bildsten (1998); Cumming & Bildsten (2000); Woosley ea (2004)

Incr

easi

ng

ṁ

Burning regimes (a shell flash in a nutshell)

BU

RS

T R

AT

E I

NC

RE

AS

ES

!•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.

Incr

easi

ng

ṁ

Bursting regimes (observational status until 2010)

Where are the bursts at ṁ > 0.1 ṁEdd?? 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?

RX

TE

PC

A

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 monitorWorld 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: 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)

Burst recurrence time in 4U 0614+09 (2010-2011): 12 +/- 3 d

Shortest burst pair ever seen from the source: 2.8 days apart.

GBM & thermonuclear bursts: 4U0614+09

Linares et al. (2012)

GBM & thermonuclear bursts: 4U0614+09

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.

Che

neve

z et

al.

(200

8)

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 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?

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 0614+09 (Linares et al. 2012, ApJ, to be submitted)

Refs.

Thanks!