The population of Galactic X-ray bursters as seen by JEMX onboard INTEGRAL

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1 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

2 Introduction C. Sanchez-Fernandez 19th Nov, 2013, 6th IDSW, Aranjuez, Spain INTEGRAL

3 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 s burst of X-rays. Rise time sec Decay time 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

4 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: days orbital separations: AU s Accretion rate: M Sun /yr ( kg/s/cm 2 )

5 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: ( ) kg/m 3 Surface gravity ~ 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

6 The physics of type-i X-ray bursts Accretion flowl( 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

7 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 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

8 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 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

9 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

10 Data Analysis and preliminary results

11 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) - ( s/pointing)

12 Data Analysis All public JEMX data in the INTEGRAL archive processed Initially up to rev 900 Currently up to rev 1200 (~ 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)

13 Results 2500 type-i X-ray bursts detected from 75 Galactic bursters (102 bursters known) ~500+ weak burst candidates

14 Results SAX J SAX J AX J SAX J AX J SAX J XMM J SWIFT J SWIFT J SWIFT J MXB MAXI J Cyg X-2 XB U XTE J XB XB Aql X-1 XB HETE J U Ser X-1 XB GS U GX U GX 13+1 XTE J SAX J XTE J SAX J S SAX J IGR J AX J SAX J SAX J IGR J GRS EXO SAX J U IGR J IGR J Swift J EXO SAX J A IGR J GX 3+1 SLX SLX IGR J IGR J SAX J A A GRS KS SLX XTE J U SLX IGR J SLX RXH J KS MXB U U IGR J XTE J IGR J H RX J S SAX J U U XTE J XTE J U U U MXB XTE J XTE J MAXI J U U UW CrB Cir X-1 Cen X-4 4U U U S U EXO U U IGR J IGR J IGR J RXS J

15 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

16 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

17 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

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