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!