Long X-ray burst monitoring with INTEGRAL

1. Long X-ray burst monitoring with INTEGRAL Jérôme Chenevez

2. Low Mass X-ray Binaries Type I X-ray bursts are thermonuclear explosions in the surface layers of a neutron star accreting H and/or He from the envelope of a companion star. Their emission is described by blackbody radiation with peak temperature ~2 keV and X-ray softening during the decay. DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 2

3. More or less long bursts Ordinary H bursts Unusual long bursts Ordinary He bursts Superbursts After Kuulkers, 2003 DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 3

4. MOTIVATIONIntermediate duration (~10 min) X-ray bursts like, e.g., GX 3+1 long X-ray burst on 31st August 2004 are rare events.They may reveal new nuclear burning processes. The long term goal is to interpret the various types of bursts into a consistent picture of the nuclear burning in the surface layers of accreting neutron stars. DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 4

5. 2˚ N GP X-ray binaries in the GC region (48 bursters/ 85 known) JEM-X mosaic (10 - 25 keV) DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 5

6. X-ray burst detection in JEM-X images Before After DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 6

7. DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 7

8. Spectral analysis Type I X-ray bursts are characterized by blackbody emission (T ≈ 25∙106 K) showing a fast rise time followed by exponential decay with cooling. The time resolved spectral analysis of GX 3+1 long X-ray burst reveals variations in the temperature and inferred blackbody radius which indicate expansion and contraction of the emission region. Chenevez et al. 2006, A&A, 449, L5 Bolometric luminosity (assuming d = 5 kpc) Blackbody temperature Inferred blackbody radius DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 8

9. JEM-X detector light curve (3-20 keV) of KP 484 (30s bins) DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 9

10. JEM-X source-extracted LC 2nd known long burst from SLX 1737-282 with photospheric radius expansion  D  7.5 kpc. 1st burst (long) on 20000327 (in ‘t Zand et al, 2002) 3rd long burst in recent INTEGRAL data! DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 10

11. Paper in prep. DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 11

12. Nuclear burning regimes H unstability • : Mixed H/He burning triggered by thermally unstable H ignition. Long burst duration (> 100s - 1000s) due to rp- process. a150. • : H stable burning (hot CNO cycle) to He  Pure He flash (3-a). Frequent PRE. a200. • : Mixed H/He burning triggered by thermally unstable He ignition. Burst duration > 10s due to rp- process. a~20-100. • : No bursts (e.g. pulsars). • Pure He accretion (e.g. from white dwarf)  powerful pure He bursts. • Deep Carbon burning in superbursts. He unstability DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 12

13. Back to observations Two phase long burst from GX 3+1 He flash H/He tail DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 13

14. Long term persistent flux of GX 3+1 Relation with accretion rate long burst Superburst DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 14

15. IGR J17254-3257 short and long bursts 5s bins Different lasting bursts from IGR J17254-3257 can be explained by a transition between two slightly different accretion rates. Burst 1 is a mixed H/He burst triggered by a weak H flash, while burst 2 is the result of the burning of a large He pile at a slightly higher accretion rate. Chenevez et al. 2007, A&A, 469, L27 20s bins DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 15

16. SUMMARY Long X-ray bursts observed with INTEGRAL / JEM-X DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 16

17. Intermediate duration bursts Only 9 known bursts have shown a duration of a few tens of minutes Unusually long bursts seem generally to be associated with mixed H/He burning at low accretion rate. Depending on the actual accretion rate, either the burning of a large amount of H is triggered by an He flash, or a large column of He is triggered by H ignition. Long pure He bursts involving an even larger column depth are also possible, especially if no H is accreted. An aborted superburst due to the premature ignition of a carbon layer triggered by an He detonation may also be considered. Superbursts that last several hours and release about 1000 times more energy are thought to arise from carbon shell flashes in the layers below the surface of the neutron star. DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 17

18. PERSPECTIVES X-ray bursts as probes of: • Compact object as neutron star  LMXB • Neutron stars properties (MNS, RNS, TNS, spin) • Actual accretion rate • Metallicity and/or nature of the companion • Nuclear lines Future prospect:  It is worth continuing to monitor long X-ray bursts! Start of a new campaign from August 2007 in INTEGRAL AO-5 DFS annual meeting | Nyborg, 19 June 2007 | L-XrB monitoring with INTEGRAL | page 18