1. About the discovery of X-ray bursts 35 years ago John Heise’s After Dinner speech X-ray burst workshop Leiden 2010 SRON-Utrecht

2. many high-energy satellites in the period 1960-1975 UHURU 1971 Vela-5 1969 SAS-3 1975 ANS 1974 1960 1975

3. Mostly “scanning” satellites small fraction of time “on source” but seeing large fraction of the sky rare phenomenae better seen while pointing ANS, the Astronomical Netherlands Satellite the first X-ray pointing satellite

4. ANS, 1974-1976, the first 3-axis stabilized X-ray satellite for X-ray & UV with unfavorable orbit: ANS Instruments: SRON-Utrecht SXX 0.2 – 0.25 keV 1-7 keV Harvard+MIT HXX 2-25 keV bragg-crystal spectr. Groningen UV-telescope SXX: John Heise HXX: Gursky, Grindlay bragg: Schnopper,

5. X-ray bursts discovered for the wrong reason NGC 6624, a centrally condensed globular cluster errorbox 3U1820-30 In 1974 thought (Bahcall) to contain a Central Black Hole of ~100-1000 M sun characteristics of BHs were thought to be ● soft spectrum ● variability

6. 1974 Rothschild et al. ~millisec bursts (for ~1 M sun ) so possibly Expecting ~sec bursts (for ~1000 M sun ) In 1974: 1 candidate Black Hole: Cyg X-1 exhibiting millisec bursts

7. summer 1974 (after visit John Bahcall) Heise planned observations for 3U1820-30 around 28 september 1974 swapping time with the UV-experiment t maximize exposure time with window ANS planning: visibility per source ~1 day/cos(lat)

8. Data analysis nov 1975 35 years ago

9. nov 1975 discovery of 2 X-ray Bursts in 3U 1820-30 ANS-data NGC6624 3U1820-30 ANS data arrived in nov 1975 Data reduction with Josh Grindlay, Harvard: Grindlay & Heise, 1975 (IAU-circular) Grindlay et al, 1976 10 s

10. dec 1975: energy explosions in space Dutch press: sensational discovery with “ANS” “ANS” Astronomical Netherlands Satellite 1974-1976

11. main concern in the beginning: background particle events? SXX and HXX different respons to high-energy particles collimators were slightly offset and ratio was consistent with celestial source NO:

12. others were less concerned about the possibility of bg-events COSMOS 428 1960 1975

13. Background events? Hard “bursts” seen everywhere since 1971! But these were background Kosmos 428 satellite, IKI, Moscow Babushkina Kudryavtsev Melioranskii Walter Lewin 1977: correlated with geoposition (all near van Allen belts)

14. Thermonuclear explanation of X-ray bursts ● 1975, Hansen and van Horn “Nuclear fusion in accreting neutron star envelopes” ● 1976, first mentioned in the context of X-ray bursts by Laura Maraschi (Milaan) ● 1976, Woosley and Taam Thermonuclear explosions on Neutron Stars ● 1976, Jean Swank BB emission size consistent with NS

15. What about the Vela-5A/B short transients? Including the “Norma burster” position accuracy ~6 degree Walter Lewin in reviews: ignored by definition (Def. : X-ray bursts have rise times ~1 sec, not seen in Vela-bursts)

16. Other Fast Transients in X-rays ● Other satellites (Ariel V etc) discovered fast Transients also at high galactic latitude ● What is the nature of these sources? some may be Gamma Ray Bursts some may be related with flare stars ● The study required the use of wide field imaging in X-rays with long exposure times: just sit and wait till a transient occurred within the FOV

17. Wide Field Cameras in X-rays To localize new fast Transients and establish there nature SRON-Utrecht invested in Coded Mask Camera’s

18. Wide Field Cameras in X-rays 1980 5 WFCs? new Dutch satellite TIXTE? TIXTE: S/C concept WFC’s 1982 4 WFCs? new ESA satellite X80? 1981 COMIS/TTM om MIR-station a pilot study with 1 WFC? YES! Launched 1987 1983 3 WFCs? Dutch-Italian satellite 1985 2 WFCs! Dutch-Italian SAX satellite

19. biggest succes: arcmin localization of GRBs Cyg X-1 Burst 40 o significance→ exposure 52 ksec 30 sec 48 ksec 3 o x3 o GRB960720 GRB970228 WFC GRB

20. WFC view on the Galactic Center discovery of new neutron stars SAXJ1808-36

21. WFC discovery of superbursts a new thermonuclear burning regime 4U1735-44 Cornelisse et al. 2001 KS1731-26 X-ray intensity → hardness → E~10 39 ergs E~10 42 ergs X-ray Burst Superburst Röntgen-intensiteit → time →

22. Xray-burst publications per year 1976 1985 1995 2005 Tod’s discovery of burst oscillations data Jean in ‘t Zand

23. Top of most cited papers Wallace & Woosley (1981): 372 (TH, Explosive hydrogen burning) Lewin et al. (1993): 284 (Space Science Review) Strohmayer et al (1996): 283 (OBS, Discovery burst oscillations) Grindlay et al. (1976) 198 (OBS, discovery paper) Lewin et al. (1981): 181 (Space Science Review) Woosley & Taam (1976): 174 (TH, 1st interpretation) Fujimoto et al. (1981): 165 (TH, Accretion regimes for bursting) Chakrabarty et al. (2003): 164 (OBS, burst.osc. pulsar in J1808) Schatz et al. (2001): 158 (TH, endpoint of rp process) Ayasli et al. (1982): 152 (TH) Kuulkers et al. (2003): 125 (OBS, PRE bursts in Globular clusters) Swank et al. (1977): 116 (BB emission size consistent with NS) Joss et al. (1977): 107 (TH) Strohmayer et al. (2002): 104 (OBS, Superburst from 4U 1820-30)

24. most productive authors nr as first author (Citation score) Lewin: 41 (20) van Paradijs: 21 (23) Strohmayer: 34 (29) Grindlay: 15 (26) in 't Zand: 14 (23) Kuulkers: 13 (19) Taam: 13 (23) Swank: 10 (17) Hoffman: 10 (21) Cumming: 11 (18)

25. Conclusion X-ray burst astronomy is a thriving field with a promise to extract fundamental NS-data