Ultraluminous X-Ray Bursts: a challenge to high energy astrophysics lore

as presented at Journal Club, 4 November 2016

Transcript

1. Ultraluminous X-Ray Bursts: a challenge to high energy astrophysics lore Anna Ho Journal Club 4 November 2016 1
2. The landscape of x-ray bursts includes magnetars and accretion onto neutron stars and black holes. 2
3. The landscape of x-ray bursts includes magnetars and accretion onto neutron stars and black holes. Bursts from magnetars: Soft Gamma Repeaters (SGRs), Anomalous X-ray Pulsars (AXPs) 2
4. The landscape of x-ray bursts includes magnetars and accretion onto neutron stars and black holes. Bursts from magnetars: Soft Gamma Repeaters (SGRs), Anomalous X-ray Pulsars (AXPs) Bursts from x-ray binaries: Type I bursts (thermonuclear burning) Type II bursts (accretion instability) 2
5. Within that landscape, there are mysteries and unusual phenomena. 3
6. Within that landscape, there are mysteries and unusual phenomena. SGR giant flares (1043-44 erg/s) 3
7. Within that landscape, there are mysteries and unusual phenomena. SGR giant flares (1043-44 erg/s) 3 “…on December 27, 2004…a GRB from a…soft gamma-ray repeater (SGR) hit the Earth's atmosphere. The disturbance of the Earth's atmosphere caused VLF radio signals transmitted from Hawaii to Antarctica, to decrease in amplitude by over 20 dB”
8. Within that landscape, there are mysteries and unusual phenomena. 4 SGR giant flares (1043-44 erg/s) The Rapid Burster (Type I & Type II bursts) Superbursts: long durations (hours), long recurrence times (years) The Bursting Pulsar (Type II bursts & coherent pulsations) Ultraluminous x-ray bursts (e.g. Sivakoff et al. 2005)
9. The Sivakoff et al. (2005) ultraluminous burst has no clear analog in our galaxy, and the nature of the source is unknown. 5
10. The Sivakoff et al. (2005) ultraluminous burst has no clear analog in our galaxy, and the nature of the source is unknown. 5 No clear optical counterpart Elliptical galaxy NGC 4697 Lpeak = 5.5 x 1039 erg/s (> 8 LEdd,NS) Two ~minute flares separated by ~four years
11. Irwin et al. 2016 (Nature) searched Chandra archival data for 70 nearby elliptical galaxies and found two ultraluminous x-ray bursts. 6
12. Irwin et al. 2016 (Nature) searched Chandra archival data for 70 nearby elliptical galaxies and found two ultraluminous x-ray bursts. Luminosity (erg/s) ~ 3 hours 1039 1040 1041 Figure adapted from Irwin et al. (2016) ~1 hour 1039 1040 1038 6
13. These bursts have an unusual combination of energetics, timescale, and location. 7
14. These bursts have an unusual combination of energetics, timescale, and location. Their energetics & timescales are similar to magnetar bursts, but… 7
15. These bursts have an unusual combination of energetics, timescale, and location. Their energetics & timescales are similar to magnetar bursts, but… …they are located in old stellar populations. 7
16. In globular clusters, luminous x-ray sources tend to be x-ray binaries. 8
17. In globular clusters, luminous x-ray sources tend to be x-ray binaries. Mass segregation drives neutron stars to the core, increasing the rate of stellar encounters… 8
18. In globular clusters, luminous x-ray sources tend to be x-ray binaries. Mass segregation drives neutron stars to the core, increasing the rate of stellar encounters… …and captures 8
19. In globular clusters, luminous x-ray sources tend to be x-ray binaries. Mass segregation drives neutron stars to the core, increasing the rate of stellar encounters… …and captures 8 However, these ultraluminous bursts are more luminous & shorter than Type I/II bursts
20. There are at least three ways to explain a (super-Eddington) peak luminosity of 1040 erg/s: 9
21. There are at least three ways to explain a (super-Eddington) peak luminosity of 1040 erg/s: 1) relativistic beaming 9
22. There are at least three ways to explain a (super-Eddington) peak luminosity of 1040 erg/s: 1) relativistic beaming 2) the central object is an intermediate-mass black hole 9
23. There are at least three ways to explain a (super-Eddington) peak luminosity of 1040 erg/s: 1) relativistic beaming 3) the accretion disk transports material at a super-Eddington rate 2) the central object is an intermediate-mass black hole 9
24. A central intermediate-mass black hole would be interesting, because these are conspicuously absent. 10 1) relativistic beaming 3) the accretion disk transports material at a super-Eddington rate 2) the central object is an intermediate-mass black hole
25. An accretion disk can transport material at a super-Eddington rate… 3) the accretion disk transports material at a super-Eddington rate 11 1) relativistic beaming 2) the central object is an intermediate-mass black hole
26. An accretion disk can transport material at a super-Eddington rate… 3) the accretion disk transports material at a super-Eddington rate 11 1) relativistic beaming 2) the central object is an intermediate-mass black hole …but conventional lore says that you can get 3x, but “thou shalt not get 100x Eddington” (—Sterl)
27. An accretion disk can transport material at a super-Eddington rate… 3) the accretion disk transports material at a super-Eddington rate 11 1) relativistic beaming 2) the central object is an intermediate-mass black hole …but conventional lore says that you can get 3x, but “thou shalt not get 100x Eddington” (—Sterl) An accretion disk can transport material at a super-Eddington rate with a strong B field…
28. All of the possibilities are interesting. Magnetar: how can you get a magnetar in an old stellar population? Accretion disk: something is wrong or missing with our physics. IMBH: if not, the arguments in favor of these are in trouble. 12
29. Could there be a magnetar in an old stellar population? 13
30. Could there be a magnetar in an old stellar population? there are young neutron stars in globular clusters, from the accretion-induced collapse of a white dwarf 13
31. Could there be a magnetar in an old stellar population? there are young neutron stars in globular clusters, from the accretion-induced collapse of a white dwarf we should search star-forming galaxies: are there comparable bursts there as well? 13
32. Could there be a magnetar in an old stellar population? there are young neutron stars in globular clusters, from the accretion-induced collapse of a white dwarf we should search star-forming galaxies: are there comparable bursts there as well? 13 thank you to: Sterl Phinney, Vikram Ravi, Dan Stern (NuSTAR)