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!