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The X-ray/hard X-ray/gamma-ray connection of gamma-ray binaries and possible propeller states Diego F. Torres Special thanks to Daniela Hadasch, Jian Li, Alessandro Papitto, & Nanda Rea Research done with the support of www.ice.csic.es/research/map LS I +61 303 Is it a neutron star binary? • There are no detected pulsations • But there were two flares, ~0.1 s, with ‘high’ Lx (orders of magnitude beyond bolometric lum.) • The bursts were in all aspects similar to SGR ones. • LS I +61 303 relate gamma-ray binaries with magnetar systems • Take into account that magnetar phenomenology is related to the inner magnetic field of neutron stars, not the dipolar: two (relatively) low-B magnetars are know. We are not necessarily speaking of >1014 G NS. Super-orbital variability • Known in radio and Hα (e.g. Gregory 2002) • Discovered in X-rays after DFT, et al. 2012 5+ years of monitoring with RXTE (Li et el. 2012, Chernyakova et al. 2012) • Today, hints of superorbital variability in hard X-rays (INTEGRAL/IBIS) Due to the large (4 years) super-orbital period: • Yet unclear with MAGIC/VERITAS @ TeV Li, et al. 2012 • …and with LAT @ GeV 2 Hints of inter-relation Peak flux per orbit in TeV shown in red (all of them happening in the 0.6–1.0 orbital phase range) as a function of super-orbital phase, together with radio, Hα (black, Zamanov et al. 2000) and X-ray data Li, DFT, et al. 2012 3 Changes of state in a pulsar binary EjectorPropellerAccretor (and sometimes backwards) Ideas go back up to Gnusareva & Lipunov 1985, application to LSI +61 303 in Zamanov et al. 1995; DFT et al. 2012; Papitto, DFT, Rea 2012 4 Idea: changes of state in a pulsar binary EjectorPropellerAccretor (and sometimes backwards) see e.g., Bednarek 2009 for ability of propellers to accelerate particles up to HE 5 Idea: changes of state in a pulsar binary EjectorPropellerAccretor (and sometimes backwards) 6 Mass accreted change a lot along eccentric orbits apastron e.g., for Be stars, with winds of 2 components, poloidal and equatorial, changes can reach up to 3-4 orders of magnitude See Papitto, DFT, Rea 2012, ApJ 7 Flip-flop between states is possible depending on the pulsar period Papitto, DFT, Rea 2012 Example for a fixed magnetic field of B=1013 G 8 Flip-flop between states is possible depending on the pulsar period Papitto, DFT, Rea 2012 Example for a fixed magnetic field of B=1013 G 9 Flip-flop life is larger than the ejector’s The time it takes for a NS to reach a period P under the action of a spindown torque N (P) is obtained from the integration of the equation See Papitto, DFT, Rea 2012, ApJ 10 Flip-flop life is larger than the ejector’s The time it takes for a NS to reach a period P under the action of a spindown torque N (P) is obtained from the integration of the equation (conservative scenario) See Papitto, DFT, Rea 2012, ApJ 11 Parameter space limited by bolometric luminosity If the apastron luminosity is all ejector-generated the system must be to the left of the red curves It could always be an ejector or stay flip-flopping along the orbit depending on (P,B) Papitto, DFT, Rea 2012, ApJ 12 Parameter space limited by bolometric luminosity i.e.,: in periastron is a propeller, in apastron is an ejector If the apastron luminosity is all ejector-generated the system must be to the left of the red curves It could always be an ejector or stay flip-flopping along the orbit depending on (P,B) Papitto, DFT, Rea 2012, ApJ 13 Parameter space limited by imposing superorbital variability If the disc dominates the apastron (suppose: having grown larger at the maximum of the superorbital variability); the transition to the propeller moves to the left, and depending on (P,B) the system could be a permanent propeller (to the right of the green line) or a flipflopper (to the left) Papitto, DFT, Rea 2012, ApJ 14 Parameter space limited by imposing superorbital variability At such enlarged mass accretion rates, the disc may not reach the apastron but may reach intermediate phases of the orbit. The mass accretion rate at these intermediate orbital phases is larger than at apastron, and the system is more likely to be flip-flopping for a given (P,B). Papitto, DFT, Rea 2012, ApJ 15 LS I +61 303: significant increase in the hard X-ray dataset Data published by Zhang, DFT, 2010 16 LS I +61 303: significant increase in the hard X-ray dataset 2 counts/s (18-60 keV) Binned lightcurve departs from a constant behavior 1 0 -1 53000 54000 MJD 55000 56000 17 LS I +61 303: significant increase in the hard X-ray dataset Folded in the superorbital phase The hard X-ray profile coincides with the soft X-ray one. Both have maxima at the Superorbital phase where Halpha is maximal too. counts/s (18-60 keV) 1 0.5 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Super-orbital Phase 1.6 1.8 2 Li, DFT et al. 2011 18 LS I +61 303: significant increase in the hard X-ray dataset 0.5 0 0 0.2 0.4 0.6 0.8 1 1.2 Super-orbital Phase 1.4 1.6 1.8 2 0.2 0.4 0.6 0.8 1 1.2 Super-orbital Phase 1.4 1.6 1.8 2 300 exposure (ks) Folded in the superorbital phase The hard X-ray profile coincides with the soft X-ray one. Both have maxima at the Superorbital phase where Halpha is maximal too. counts/s (18-60 keV) 1 200 100 0 0 19 XSS J12270-4859: a LMXB emitting at GeV? A faint low mass X-ray binary with a γ-ray counterpart [De Martino+ 2010,2012; Hill+ 2011; Saitou+ 2009,2011]; 140 off the Galactic plane. Steady gamma-ray emission, no orbital or spin period. L(0.2-100keV) = L(> 100MeV) = 2 x 1034 d2kpc2 erg/s → comparable X-ray and γ-ray output Flares and dips in soft X-rays also suggesting variations by an optically thick absorber Steady in hard X-rays and GeV No pulsations detected in radio and X-rays either (but loose upper limit in X-rays) Optical continuum: K2-K5 star + disc Broad Hα, Hβ and He II detected indicate accretion 21 XSS J12270-4859 Possible interpretations: • Is a jet involved? -Lradio/Lgamma implies B~10-8 G, much lower than typical µG fields in extended radio structures -Steady γ-ray emission never observed from accreting BH • An isolated pulsar? -No pulsation found, and steep spectrum / high cutoff would be uncommon. -Rotation powered pulsar are not bright X-ray emitters (LX/Lγ~10-3; instead of 1 like for XSS) • A pulsar in a binary? -Galactic latitude would suggest a MSP acting as an ejector (recycling scenario). -Signature of accretion down to the NS are not observed. -But optical emission suggests accretion. No steady hard X-ray emission expected if it is non-accreting. -Propeller? 22 XSS J12270-4859: INTEGRAL analysis IBIS/ISGRI data (18-60 keV): Left, the whole dataset (553 ks) since 2003 (~14σ) Right: only at the Fermi-LAT period detection (2008-2010), 73ks in IBIS (~5σ) The source is steady along the whole dataset (2003-2012), and thus it is not seen to vary between accretor and ejector phases along the last 10 years (as in the case of J1023+0038). 23 XSS J12270-4859: the source is stable in hard X-rays (2003-2012) The 553.7 ks IBIS/ISGRI exposure is cut into 7 time spans of 79 ks each. XSS J12270-4859 is detected with similar significance around 4σ in all but one, there is no long-term variability of XSS J12270-4859 in 18–60 kev band. The 3rd time span has the lowest significance. Though with similar exposure time, only a short time period (15 days) is covered compared to the others (each with ~600 days). XSS J12270-4859 may have experienced a short time low state there. Dips observed in soft X-rays too. 24 XSS J12270-4859: energetics Luminosity of 1035 erg s-1 For P=2.5 ms, fastness = 2 (ms) 25 Concluding remarks • On long timescales (due to pulsar spin down) a NS in a binary must pass through ejector, propeller, and accretor phases. • On short timescales, this is governed by the accretion rate; this is large if the orbit is eccentric. Alternating systems are a natural consequence. • For LS I +61 303, at relatively high spin-down (few 1035- few 1036 erg s-1), the time spent in flip-flop mode exceeds by a factor of 3 the time spent as ejector. • Changes in the mass accretion rate can also come from the superorbital behavior, and these could be enough to induce MW long term behavior. • The X-rays / hard X-rays holds interesting keys to understand the emission properties and the long-term behavior of gamma-ray binaries. • LS I 61 303 and XSS J12270-4859 are insteresting cases of possible propeller states in neutron star binaries. 26