Observations of t hermonuclear X-ray bursts - an overview

1. Observations ofthermonuclear X-ray bursts-an overview Jean in ‘t Zand

2. The X-ray burst phenomenon is omnipresent 1 day looking at 40x40 degrees around the Galactic center (BeppoSAX WFC) The X-ray burst is the brightest phenomenom from the NS surface Observations of thermonuclear X-ray bursts / EWASS 2013

3. Talk outline • Introduction • History • Principles • 'Recent' discoveries • Textbook burster • Burst oscillations • Superbursts • Intermediate duration bursts • Superexpansion/absorption edges • Etc. • Summary & Outlook Observations of thermonuclear X-ray bursts / EWASS 2013

4. History: observations 44 years First one detected in 1969 with Vela 5b Still the brightest X-ray burst ever: 1.4 x 10-6 erg s-1 cm-2 (50 x Crab !; bright enough to disturb earth’s ionosphere) Published in 1972 (Belian et al.), explained as an accretion event First cited in 1976 From Cen X-4, the nearest LMXB 1975: first promptly followed-on burst detection with Astronomical Netherlands Satellite (Grindlay & Heise 1975) Observations of thermonuclear X-ray bursts / EWASS 2013

5. History: theory 40 years ago • Rosenbluth, Ruderman, Dyson, Bahcall, Shaham, Ostriker (1973) predict for first time nuclear fusion on accreting NSs • Van Horn and Hansen (1974) predict unstable fusion to explain what we now know are BH transients • Maraschi & Cavaliere (1976), after first acknowledged burst detection, connect burst phenomenon to theoretical prediction by Van Horn & Hansen (1974) • Woosley & Taam (1976) first model for X-ray burst, although proposed as model for Gamma-Ray Bursts, using carbon as fuel • Joss (1977) and Lamb & Lamb (1978) first to propose helium as dominant fuel • Wallace & Woosley (1981) explained hydrogen/helium flashes Observations of thermonuclear X-ray bursts / EWASS 2013

6. Local accretion rate in low-B NSs 10 to 105 gr s-1 cm-2 • After hours to days, accumulate columns of y=108 gr cm-2 (cf, 103 for earth atmosphere) • Pressure (y*g) builds up to ignition condition for runaway triple-alpha and CNO processes • Can result in thermonuclear shell flash if • Layer heats up to 109 K and then cools radiativelythrough 107 K photosphere  X-ray burst Based on slide from Andrew Cumming Observations of thermonuclear X-ray bursts / EWASS 2013

7. Spectra  pure black body Strohmayer & Bildsten 2006 Strohmayer & Brown 2002 Observations of thermonuclear X-ray bursts / EWASS 2013

8. Nuclear reactions: CNO cycle and 3-alpha • Hot CNO cycle: for solar metal, takes 1 d to burn H Observations of thermonuclear X-ray bursts / EWASS 2013

9. Nuclear reactions: the rp-process Observations of thermonuclear X-ray bursts / EWASS 2013

10. Courtesy Andrew Cumming Observations of thermonuclear X-ray bursts / EWASS 2013

11. Burning regimes Fujimoto et al. 1981 Observations of thermonuclear X-ray bursts / EWASS 2013

12. H-poor donor? (UCXB?) n y M-dot>10% Edd? M-dot>3% Edd? y n n M-dot<1% Edd? M-dot>10%? M-dot>1% Edd? y y y n n M-dot > 100%? y n y n Short H flash + long He flash Mixed H/He flash Short pure He flash Mixed H/He flash Short pure He flash Long He flash No flash No flash Observations of thermonuclear X-ray bursts / EWASS 2013

13. Courtesy Andrew Cumming Observations of thermonuclear X-ray bursts / EWASS 2013

14. Basic inferences • Fluence amount of energy  amount of fuel burnt • Decay time  thickness of fuel layer • If at Eddington limit: peak flux  distance (d=√Ledd/4πFpeak) • Peak luminosity  amount of fuel X production rate of nuclear energy • Flux + distance  radius (r=d √F/σT4 = Stefan Boltzmann) • Alpha  fuelcomposition Observations of thermonuclear X-ray bursts / EWASS 2013

15. History: observations of X-ray bursts *not all 102discoveries in this table White: past missions; red: current missions Observations of thermonuclear X-ray bursts / EWASS 2013

16. Burst peak fluxes & fluences >pf/Ntot < 0,2 Crab 10% > 1 Crab 60% Observations of thermonuclear X-ray bursts / EWASS 2013

17. Burst durations  intermediate duration bursts (UCXBs)  ‘superbursts’ (carbon) He bursts mixed H/He bursts  Observations of thermonuclear X-ray bursts / EWASS 2013

18. Discoveries in 1996-2013 Observations of thermonuclear X-ray bursts / EWASS 2013

19. Textbook burster (Kong et al. 2007) Observations of thermonuclear X-ray bursts / EWASS 2013

20. Textbook burster (Galloway et al. 2004) Observations of thermonuclear X-ray bursts / EWASS 2013

21. Textbook burster (Ubertini et al. 1999; Galloway et al. 2004) Observations of thermonuclear X-ray bursts / EWASS 2013

22. Why?  accretion histories of prolific bursters RXTE-PCA Gal. Bulge scans, courtesy Craig Markwardt Observations of thermonuclear X-ray bursts / EWASS 2013

23. Texbookburster (in 't Zand et al. 2009) Observations of thermonuclear X-ray bursts / EWASS 2013

24. Burning regimes in transient KS 1731-260 (Cornelisse et al. 2003) Observations of thermonuclear X-ray bursts / EWASS 2013

25. Bursts with too short recurrence times • 150 hours over 7 observations • 76 bursts, 15 in 5 triples, 28 in doubles Boirin et al. 2007 Keek et al. 2010 Observations of thermonuclear X-ray bursts / EWASS 2013

26. Burst oscillations (Strohmayer et al. 1996/7, review by Watts 2012, cc Zhang et al. 2012) Observations of thermonuclear X-ray bursts / EWASS 2013

27. Superbursts (Cornelisse et al. 2000, Cumming & Bildsten 2001, Strohmayer & Brown 2002, Strohmayer & Markwardt 2002, in 't Zand et al. 2003) Observations of thermonuclear X-ray bursts / EWASS 2013

28. Superburstpopulation 21 superburstsfrom 14 superbursters (3/2 questionable) All superbursters are normal bursters as well 4recurrent superbursters (few months to 10 years recurrence time) Observations of thermonuclear X-ray bursts / EWASS 2013

29. Observations of thermonuclear X-ray bursts / EWASS 2013

30. Superburst – normal burst quenching (Kuulkers et al. 2004, Cumming & Macbeth 2004, Keek et al. 2011) Observations of thermonuclear X-ray bursts / EWASS 2013

31. Observations of thermonuclear X-ray bursts / EWASS 2013

32. Superburst - problem • 4/12 superbursters accrete at low average values (<1% Eddington). • Implied recurrence time is ~20 yrs, inconsistent with number detected • Impliedcrustalheatingmuchhigher • Chemical freeze out at bottomocean? 1.8 MeV/nucl (Keek et al. 2008, Medin & Cumming 2010) Observations of thermonuclear X-ray bursts / EWASS 2013

33. Superburst problem (Altamirano et al. 2012) Observations of thermonuclear X-ray bursts / EWASS 2013

34. Also: normal burst problem (in 't Zand et al. 2002, Wijnands et al. 2009) Observations of thermonuclear X-ray bursts / EWASS 2013

35. Intermediate duration bursts (in 't Zand et al. 2005, 2007, Falanga et al. 2008) Observations of thermonuclear X-ray bursts / EWASS 2013

36. Intermediate duration bursts • Half look like UCXBs (in 't Zand et al. 2007) Observations of thermonuclear X-ray bursts / EWASS 2013

37. Superexpansion (Galloway et al. 2008) Observations of thermonuclear X-ray bursts / EWASS 2013

38. Superexpansion Hoffman et al. 1977 Observations of thermonuclear X-ray bursts / EWASS 2013

39. Superexpansion Van Paradijs et al. 1990 Observations of thermonuclear X-ray bursts / EWASS 2013

40. Superexpansion Van Paradijs et al. 1990 Observations of thermonuclear X-ray bursts / EWASS 2013

41. Superexpansion in 4U 1722-24 Flux drops to below pre-burst levels (Molkov et al. 2000) Observations of thermonuclear X-ray bursts / EWASS 2013

42. Compilation of 37 cases from 10 sources (24 WFC, 8PCA, 1 INTEGRAL, 4 literature) All continue to show small expansion factors after the superexpansion ALL from hydrogen-deficient UCXBs (in 't Zand et al. 2010, 2011, 2012) Observations of thermonuclear X-ray bursts / EWASS 2013

43. SE and ME durations versus burst duration Moderate expansion duration tme Superexpansion duration tse Why flat?? Burst ‘duration’ τ (in 't Zand et al. 2010) Observations of thermonuclear X-ray bursts / EWASS 2013

44. Explanation: expulsion of shell • κ = κ0 / (1+(T/4.5x108K)0.86)  Leddincreases ~5 times from photosphere to ignition depth • Transition initially blows away column/shell where L>Ledd • On energetic arguments shell thickness can be up to 1% of yb , or 106-8 g cm-2 • Shell will dilute as (r/10 km)2 and become optically thin after a time (vt/10)2=106 or t=104/v km s-1 • t < 10 s  v>103 km s-1 • Consistent with preliminary measurements • This needs to be confirmed by time-dependent model calculations Like a classical nova (RS Oph simulation by A. Beardmore) (in 't Zand et al. 2010) Observations of thermonuclear X-ray bursts / EWASS 2013

45. Superexpansion (in 't Zand et al. 2012) Observations of thermonuclear X-ray bursts / EWASS 2013

46. (Weinberg et al. 2008) Observations of thermonuclear X-ray bursts / EWASS 2013

47. Most beautiful data set (bright 7 Crab burst, 5 PCUs on):4U 0614+091 – a very short 50 msprecursor (Kuulkers et al. 2010) Observations of thermonuclear X-ray bursts / EWASS 2013

48. Time-resolved spectroscopy of 4U 0614+09 (in 't Zand et al. 2010) Observations of thermonuclear X-ray bursts / EWASS 2013

49. Improvement by including reflection against disk(end of burst) (in 't Zand et al. 2010) Observations of thermonuclear X-ray bursts / EWASS 2013

50. Improvement by including edges(end of superexpansion) (in 't Zand et al. 2010) Observations of thermonuclear X-ray bursts / EWASS 2013