The population of Galactic X-ray bursters as seen by JEMX onboard INTEGRAL Celia Sánchez-Fernández ISOC ESAC, Madrid, Spain In collaboration with: E. Kuulkers, D. Galloway, J. Chenevez C. Sanchez-Fernandez In collaboration with: E. Kuulkers. E. Aranzana, J. Chenevez, D. Galloway 1
Introduction C. Sanchez-Fernandez 19th Nov, 2013, 6th IDSW, Aranjuez, Spain INTEGRAL
Type-I X-ray bursts Thermonuclear instabilities on the surface of low magnetic field accreting Neutron Stars (NS) in Low Mass X-Ray Binary Systems Accreted hydrogen (H) and helium (He) on the NS surface undergoes a thin-shell instability, giving rise to a 10 100 s burst of X-rays. Rise time 0.5-5 sec Decay time 10-100 sec Recurrence hours days Energy release: 1039 ergs Burst X-ray spectrum consistent with a blackbody (kt ~2 3 kev; 107 K) that cools down during decay first record of an X-ray burst in 1969 with Vela5b (Belian et al. 1972) discovery paper 7 years later (Grindlay et al. 1976) Currently 102 X-ray bursters known C. Sanchez-Fernandez (for reviews, see Lewin et al. 1993, 1995; Strohmayer & Bildsten 2006) 19th Nov, 2013, 6th IDSW, Aranjuez, Spain INTEGRAL
Low Mass X-ray binaries Accretion disc Accretion disk NS Companion Low mass star + Compact object (neutron star or black hole) accreting matter from companion Accretion converts gravitational potential energy to radiation ΔE acc = GM R orbital periods: 0.01-100 days orbital separations: 0.001-1 AU s Accretion rate: 10-8 -10-10 M Sun /yr (0.5-50 kg/s/cm 2 )
Neutron Stars One of the possible ends for a massive star (4-8 M sun ) when they explode as a Supernovae Some facts Mass: ~1.4M sun, Radius: 10km Density: (3.7-5.9 ) 10 17 kg/m 3 Surface gravity ~5 10 12 m/s² escape velocity from the surface of a NS is around 0.3c magnetic fields ~10 12 Gauss Recent simulations suggest that neutron star crust is around 10 billion times as strong as steel
The physics of type-i X-ray bursts Accretion flowl(10-10 5 gr s -1 cm -2 ) Pressure builds up to ignition condition for explosive triple-α, CNO cycle and rp-capture processes if heating is faster than radiative cooling, runaway process or thermonuclear shell flash occurs Layer heats up to 10 9 K within milliseconds and then cools radiatively over tens of seconds
Local accretion rate determines burning regime Stable H&He burning: #ṁ/ṁ Edd >1 #Both H and He burn stably. No bursts. Mixed H/He ignition: 0.04<ṁ/ṁ Edd <1 He ignites in a mix of H&He. Pure He ignition: 0.01<ṁ/ṁ Edd <0.04 He ignites in the absence of H. Unstable H burning: #ṁ/ṁ Edd <0.01 #Thermally unstable H burning. (Fujimoto et al. 1981) For a neutron star M Edd 2 10 8 M yr 1 for H-rich accretion H-Rich bursts 7 Limited by b-decays in CNO cycle: Slower He-Rich bursts Via triple-a process: faster and more intense
Local accretion rate determines burning regime asic 1D theory Stable H&He burning: #ṁ/ṁ Edd >1 #Both H and He burn stably. No bursts. Mixed H/He ignition: 0.04<ṁ/ṁ Edd <1 He ignites in a mix of H&He. Pure He ignition: 0.01<ṁ/ṁ Edd <0.04 He ignites in the absence of H. Unstable H burning: #ṁ/ṁ Edd <0.01 #Thermally unstable H burning. (Fujimoto et al. 1981) For a neutron star M Edd 2 10 8 M yr 1 for H-rich accretion H-Rich bursts 8 Limited by b-decays in CNO cycle: Slower He-Rich bursts Via triple-a process: faster and more intense
What can we learn from type-i X-ray bursts? use them to constrain neutron star mass, radius, core temperature and therefore dense matter EOS binary evolution: donor composition, using XRBs to light up the surrounding gas combustion physics: how does the burning front spread? stellar physics: mixing, settling nuclear physics: properties of nuclei near the drip Lines (rp-process, neutron rich nuclei in the crust) Exhibition of nuclear reactions seen nowhere else Probe of densest matter in Universe > General Relativity in the strong field regime
Data Analysis and preliminary results
INTEGRAL: The INTErnational Gamma-ray Astrophysics Laboratory Payload: 2 prime gamma-ray coded-mask instruments SPI - Spectrograph 18keV - 8MeV IBIS - Imager with spectral capabilities 15 kev 10 MeV 2 concurrent monitors (X-rays, optical) JEM-X - Imager with spectral capabilities (3-35 kev) Fully coded FoV: 4.8x4.8 deg OMC optical camera (V-band, 550 nm) Observing strategy: - dithering pattern around nominal target position (Hex, 5x5) - (1800-3600 s/pointing)
Data Analysis All public JEMX data in the INTEGRAL archive processed Initially up to rev 900 Currently up to rev 1200 (~120000 pointings) 10 years of INTEGRAL data; ~ 240 Msec of data) 50 % of them in Gal. Plane regions, where most galactic X-ray bursters are located standard processing routines (OSA 10.0) used to generate source light curves (3-25 kev; time resolution: 5s) own burst searching (IDL) procedures then applied, allowing: - Burst detection - Fit to burst profile - Determination of burst params - peak count rates - duration - Rise, decay times - integrated count rate -recurrence time s)
Results 2500 type-i X-ray bursts detected from 75 Galactic bursters (102 bursters known) ~500+ weak burst candidates
Results 1000 100 10 1 SAX J2224.9+5421 SAX J1828.5-1037 AX J1824.5-2451 SAX J1818.7+1424 AX J1745.6-2901 SAX J1324.5-6313 XMM J174457-2850.3 SWIFT J1922.7-1716 SWIFT J185003.2-0056 SWIFT J174805.3-2446 MXB 1716-31 MAXI J1647-227 Cyg X-2 XB 2129+47 4U 2129+12 XTE J2123-058 XB 1940-04 XB 1916-053 Aql X-1 XB 1905+000 HETE J1900.1-2455 4U 1850-086 Ser X-1 XB 1832-330 GS 1826-24 4U 1820-303 GX 17+2 4U 1812-12 GX 13+1 XTE J1814-338 SAX J1810.8-2609 XTE J1810-189 SAX J1808.4-3658 2S 1803-245 SAX J1806.5-2215 IGR J17597-2201 AX J1754.2-2754 SAX J1753.5-2349 SAX J1752.3-3138 IGR J17511-3057 GRS 1747-312 EXO 1747-214 SAX J1750.8-2900 4U 1746-37 IGR J17498-2921 IGR J17498-2921 Swift J1749.4-2807 EXO 1745-248 SAX J1748.9-2021 1A 1744-361 IGR J17480-2446 GX 3+1 SLX 1744-299 1000 100 10 1 SLX 1744-300 IGR J17473-2721 IGR J17464-2811 SAX J1747.0-2853 1A 1742-294 1A 1742-289 GRS 1741.9-2853 KS 1741-293 SLX 1737-282 XTE J1739-285 4U 1735-444 SLX 1735-269 IGR J17364-2711 SLX 1732-304 1RXH J173523.7-35401 KS 1731-260 MXB 1730-335 4U 1728-34 4U 1722-30 IGR J17254-3257 XTE J1723-376 IGR J17191-2821 1H 1715-321 RX J1718.4-4029 2S 1711-339 SAX J1712.6-3739 4U 1708-40 4U 1708-23 XTE J1710-281 XTE J1709-267 4U 1705-44 4U 1705-32 4U 1702-429 MXB 1658-298 XTE J1701-407 XTE J1701-462 MAXI J1647-227 4U 1636-536 4U 1608-522 UW CrB Cir X-1 Cen X-4 4U 1323-62 4U 1254-69 4U 1246-588 2S 0918-549 4U 0836-429 EXO 0748-676 4U 0614+09 4U 0513-40 IGR J18245-2452 IGR J17062-6143 IGR J17380-3749 1RXS J180408.9-34205
Intermediate Duration bursts: Burst tails of minutes Some non-standard cases Thick He Layer? Double, triple Bursts Low recurrence for fuel accretion Turbulent mixing? Rapid burster activity Clumpy accretion
Burst activity vs persistent emission: GX 3+1 Persistent source, in GC field frequently observed by INTEGRAL Distance: ~4.5 kpc (Kuulkers & van der Klis 2000) Long term burst peak variations (den Hartog et al. 2003) 142 bursts detected in our sample, one of intermediate duration
Ongoing work.. Scientific analysis of these data is on progress Basic burst parameters derived from light curve (DONE!) Detailed burst spectral analysis being carried out (done for a few systems) # #- Brightest bursts time resolved spectroscopy # #- Weaker ones: burst averaged spectra Broad-band fits to continuum emission, combining JEM-X and ISGRI data Determination of system parameters