1 Locating PeV Cosmic-Ray Accelerators: Future Detectors in Multi-TeV Gamma-Ray Astronomy Adelaide, 6-8 December 2006 Josep M. Paredes HE AND VHE EMISSION FROM X-RAY BINARIES

2 1.X-ray binaries 2.How many microquasars we know 3.µqs as HE and VHE γ -ray sources: Theoretical point of view Observational point of view 4. µqs, gamma-ray binaries,…….. 5. Summary OUTLINE

3 XB: A binary system containing a compact object (NS or a stellar-mass BH) accreting matter from the companion star. The accreted matter forms an accretion disc, responsible for the X-ray emission. A total of 280 XB (Liu et al. 2000, 2001). HMXBs: (131) Optical companion with spectral type O or B. Mass transfer via decretion disc (Be stars) or via strong wind or Roche-lobe overflow. LMXBs: (149) Optical companion with spectral type later than B. Mass transfer via Roche- lobe overflow. Microquasars: X-ray binaries with relativistic jets At least 15 microquasars Maybe the majority of RXBs are microquasars (Fender 2001) 280 XB 43 (15%) REXBs 8 HMXBs 35 LMXBs

4 MICROQUASARS IN OUR GALAXY High Energy Detections Name M comp Radio Jet INTEGRAL BATSE COMPTEL EGRET Others (M  ) p/t  app Size Note keV keV keV keV 1-30 MeV >100 MeV (AU) (significance) (count/s) (significance) (mCrab) High Mass X-ray Binaries LS I  p   700 Prec ? ± ± 2.1 yes? 3EGJ MAGIC V4641 Sgr 9.6 t  9.5        LS p  1000 Prec ? ± ± 1.8 yes? 3EGJ1824  1514 HESS SS ±5? p 0.26 ~10 4  10 6 Prec ± ± 2.8   Hadronic, X-ray jet Cygnus X p  ~ ± ± 2.5 yes  Cygnus X-3  p 0.69 ~10 4 Radio outb ± ± 2.1   Low Mass X-ray Binaries Circinus X-1  t > 15 > ± ± 2.6   XTE J t  2 ~10 3 X-ray jet ± ± 2.5   Scorpius X p 0.68 ~ ± ± 2.2   GRO J t Prec? ± ± 3.9   GX ± 0.5 t  < ± ± 3.5   1E  p  ~ ± ± 3.7   XTE J > 4.5? t 1.3 > 10 4      GRS  p  ~ ± ± 3.0   GRS ± 4 t 1.2  1.7 ~10  10 4 Prec? ± ± 2.7   The 3rd IBIS/ISGRI soft gamma-ray survey catalog (Bird et al. 2006, ApJ, in press, astro-ph/ ) BATSE Earth Occultation Catalog, Deep Sample Results (Harmon et al. 2004, ApJS, 154, 585)

5 Donor star IR  UV (thermal) Dust ? IR  mm (thermal) Large scale ejection Radio & X gamma? Interaction with environment Disc + corona ? X  IR therm + non therm Compacts jets Radio  IR  X?  gamma? (synchrotron) Wind Visible  radio (free-free) M Adapted from Chaty (Ph.D. Thesis) MULTIFREQUENCY EMISSION IN MICROQUASARS

6 Black holes display different X-ray spectral states: - Low/hard state (a.k.a. power-law state). Compact radio jet. - High/soft state (a.k.a. steep power-law state). No radio emission. - Intermediate and very high states  transitions. Transient radio emission. BLACK HOLE STATES Fender 2001, ApSSS 276, 69

7 Low/Hard High/Soft Corbel et al. 2000, A&A 359, 251 Grebenev et al. 1993, A&ASS 97, 281

8 Leptonic models: SSC Atoyan & Aharonian 1999, MNRAS 302, 253 Latham et al. 2005, AIP CP745, 323 EC Kaufman Bernadó et al. 2002, A&A 385, L10 Georganopoulos et al. 2002, A&A 388, L25 SSC+EC Bosch-Ramon et al A&A 417, 1075 Synchrotron jet emission Markoff et al. 2003, A&A 397, 645 Hadronic models: Pion decay Romero et al. 2003, A&A 410, L1 Bosch-Ramon et al. 2005, A&A 432, 609 MQs as high-energy γ -ray sources Theoretical point of view

9 Leptonic high energy models Non-thermal flares GRS (Atoyan & Aharonian 1999, MNRAS 302, 253)  Flares are caused by synchrotron radiation of relativistic e  suffering radiative, adiabatic and energy-dependent escape losses in fast-expanding plasmoids (radio clouds) Synchrotron self Compton model Rodríguez et al. 1995, ApJS 101, 173  Continuous supply or in-situ acceleration of radio e 

10 GRS G 0.2 G 0.1G Exponential cutoff energies: 20 TeV _____ 1 TeV _ _ _ _ 30 GeV _. _. _ B = 0.05 G IC scattering or maybe even direct synchrotron emission from the jets could dominate the high-energy emission above an MeV or so Atoyan & Aharonian 1999, MNRAS 302, 253, and 2001 BATSE IR sub-mm radio  After limiting, from the radio data, the basic parameter characterizing the expanding plasmoids, the e  may be accelerated up to TeV energies, and the fluxes of synchrotron radiation could then extend beyond the X-ray region and the fluxes of the IC γ-rays to HE and VHE.

11 Radiation absorbed in the local field trough pair creation The recurrent and relatively rapid variability could be explained by the precession of the jet, which results in a variable Doppler amplification External Compton Scattering - HMXB Jet exposed to star, disk and corona photon fields. Applied to Cygnus X-1 (Romero, Kaufman Bernadó & Mirabel 2002, A&A 393, L61)  Corona (Klein-Nishina regime), disk and companion star (Thomson)  The Compton losses in the different regions will modify the injected electron spectrum, introducing a break in the power law at the energy at which the cooling time equals the escape time. Up-scattering of star photons (A) disk (B) corona (C) Viewing angle of 30 º Bulk Lorentz factor Γ=5

12 Hadronic models (only) for gamma γ -ray emission: ➢ Conical jet eV protons interacting with strong stellar wind protons, assuming efficient wind proton diffusion inside the jet. ➢ Protons are injected in the base of the jet and evolve adiabaticaly. ➢ Applied to explain gamma-ray emission from high mass microquasars ( Romero et al. 2003, A&A 410, L1 ).  The γ-ray emission arises from the decay of neutral pions created in the inelastic collisions between relativistic protons ejected by the compact object and the ions in the stellar wind. Hadronic jet models for microquasars

13 Romero,Torres, Kaufman, Mirabel 2003, A&A 410, L1 Interactions of hadronic beams with moving clouds in the context of accreting pulsars have been previously discussed in the literature by Aharonian & Atoyan ( 1996, Space Sci. Rev. 75, 357 ). The only requisites for the model are a windy high-mass stellar companion and the presence of multi-TeV protons in the jet. Spherically symmetric wind and circular orbit

14 1) 100 yr 2) 1000 yr, 3) yr d MQ/cloud =10pc M cloud =10 5 Msun L jet =10 37 erg/s Models from radio to VHE: ➢ Released eV protons from the jet that diffuse through and interact with the ISM. ➢ Computed the broadband spectrum of the emission coming out from the pp primary interactions (γ-rays produced by neutral pion decay) as well as the emission (synchrotron, bremsstrahlung and IC scattering) produced by the secondary particles produced by charged pion-decay. ➢ All the respective energy losses have been taken unto account. ➢ Applied to impulsive and permanent microquasar ejections. Bosch-Ramon et al. 2005, A&A 432, 609

15 MQs as high-energy γ -ray sources Observational point of view

16 Jet parameters:  > 0.15,  < 81  T B = 9.4 x 10 7 K It is the only simultaneous X-ray/radio source within the 3EG J statistical contours. Paredes et al. 2000, Science 288, 2340 VLBA, 5 GHz EGRET candidate: LS 5039 Equipartition: E e = 5 x erg B = 0.2 G LS 5039 could be related to the high energy gamma-ray source 3EG J The photon spectral index is steeper than the  < 2 values usually found for pulsars Merk et al.1996, A&ASS 120, 465 L γ (>100 MeV)=4  erg·s  1 Orbital phase 0.2

17 O6.5V((f)) Inverse Compton Scattering Synchrotron Radiation e-e- e-e- e-e- v jet  0.15c L opt ~ 1  erg/s  -ray, E > 100 MeV, L  ~ 4  erg/s  e ~ 10 3 Radio, L GHz ~ 1  erg/s X-ray L 3-30 keV ~ 5  erg/s UV, E ~ 10 eV e-e- e-e- e-e- Proposed scenario

18 3EG J EG J EG J EG J GRO J µ-quasar LS 5039 GRO J (l/b: 17.5/-0.5) Summary complicated source region possible counterparts: - 3 known  -sources (unid. EGRET) (MeV emission: superposition ?) - micro quasar RX J /LS 5039 (sug. counterpart of 3EG J ; Paredes et al. 2000) work in progress Collmar 2003, Proc. 4th Agile Science Workshop

19 Discovery of the TeV counterpart by HESS (Aharonian et al. 2005). Good position agreement with LS Good extrapolation of the EGRET spectrum.

20 Radial velocity curve of LS 5039 Casares et al., 2005, MNRAS, 364, 899 P = ± d e = 0.35 ± 0.04 Periastron at phase 0.0 And assuming pseudo-synchronisation at periastron: i = 20.3˚ ± 4.0 M compact = 5.4 ( ) M  New orbital ephemeris!! New spectroscopic observations of LS 5039 INT 2.5 m telescope (July 2002 and 2003) A black hole in LS 5039 ?

21 With the new orbital ephemerides → correlated TeV and X-ray orbital variability. HESS RXTE (Casares et al. 2005),

22 VHE γ-rays can be absorbed by optical photons of energy hν ε, when their scattering angle θ exceeds zero. Aharonian et al. 2006, A&A, in press (astro-ph/ ) 3.9 day orbital modulation in the TeV gamma-ray flux

23 We have enough information to build up a Spectral Energy Distribution that can be modeled to extract physical information (Paredes et al. 2006, A&A 451, 259).

24 Harrison et al. 2000, ApJ 528, 454 The EGRET angular resolution is sufficient to exclude the quasar QSO as the source of γ-ray emission. The radio emitting X-ray binary LSI , since its discovery, has been proposed to be associated with the γ-ray source 2CG (= 3EG J ) Periodic emission Radio (P= d) ↔ accretion at periastron passage Taylor&Gregory 1982, ApJ 255, 210 Optical and IR Mendelson&Mazeh 1989, MNRAS 239, 733; Paredes et al A&A 288, 519 X-rays Paredes et al A&A 320, L25 γ-rays ??? The broadband 1 keV-100 MeV spectrum remains uncertain (OSSE and COMPTEL observations were likely dominated by the QSO emission) Strickman et al. 1998, ApJ 497, 419 EGRET candidate: LSI Hartman et al. 1999, ApJS 123, 79

25 EGRET observations of 3EG J shows variability on short (days) and long (months) timescales 3EG J variability Tavani et al. 1998, ApJ 497, L89 Massi et al (astro-ph/ ) INTEGRAL variability Hermsen et al Rome, “keV to TeV connection”Workshop, 18 October 2006

26 Chandra Image of LSI+61303Chandra PSF Obtained using the Chandra simulator 5” LSI PSF Surface brightness distribution Flux changes on timescales of few hours. Factor of two variability Paredes et al. 2006

J. Rico (IFAE)Results of MAGIC fist observation cycle on Galactic sources Flux time variability Albert et al MAGIC has observed LSI during 6 orbital cycles A variable flux (probability of statistical fluctuation 3  ) detected Marginal detections at phases Maximum flux detected at phase with a 16% of the Crab Nebula flux Strong orbital modulation  the emission is produced by the interplay of the two objects in the binary No emission at periastron, two maxima in consecutive cycles at similar phases  hint of periodicity!

J. Rico (IFAE)Results of MAGIC fist observation cycle on Galactic sources LS I : the film Albert et al The average emission has a maximum at phase 0.6. Search for intra-night flux variations (observed in radio and x-rays) yields negative result Marginal detections occur at lower phases. We need more observation time at periastron passage Parts of the orbit not covered due to similarities between orbital period (26.5 days) and Moon period

29 Radio 15 GHz /Ryle, simultaneous with MAGIC obs. The TeV flux maximum is detected at phases , overlapping with the X-ray outburst and the onset of the radio outburst. Concerning energetics, a relativistic power of several erg s -1 could explain the non thermal luminosity of the source from radio to VHE gamma-rays. This power can be extracted from accretion in a slow inhomogeneous wind along the orbit (Bednarek 2006, MNRAS 268, 579). This spectrum is consistent with that of EGRET for a spectral break between 10 and 100 GeV. The flux above 200 GeV corresponds to an isotropic luminosity of ~7 x erg s -1, at a distance of 2 kpc. The intrinsic luminosity of LS I at its maximum is a factor ~6 higher than that of LS 5039, and a factor ~2 lower than the combined upper limit (<8.8 x cm -2 s -1 above 500 GeV) obtained by Whipple (Fegan et al. 2005, ApJ 624, 638). Spectrum for phases 0.4 and 0.7

3.6cm images ~3d apart. Beam 1.5x1.1mas 3x2.2 AU. Contours +_0.2mJy, increment sqrt(2). Orbital Phase AU Dhawan et al. 2006, VI MIcroquasars Workshop, Como, Setember 2006 LSI VLBA images over full orbit New VLBI observations show a rotating jet-like structure

32 Mirabel 2006, (Perspective) Science 312, 1759 A possible scenario comes from the application of the pulsar wind nebulae formed with the interaction of a relativistic pulsar wind with the ISM but where the wind of the companion plays the role of the ISM. The stagnation point, where the pressure from the two winds is balanced, is within the binary system. Particles are accelerated at the termination shock and produce the non-thermal synchrotron emission (Dubus 2006, A&A 456, 801).

33 UV photons from the companion star suffer inverse Compton scattering by the same population of non-thermal particles, leading to emission in the GeV-TeV energy range. Particles move downstream away from the pulsar at a speed v (initially ≈c/3). A cometary nebula of radio emitting particles is formed. It rotates with the orbital period of the binary system. We see this nebula projected (Dubus 2006, A&A 456, 801).

34 PSR B / SS 2883 is a binary system containing a B2Ve donor and a 47.7 ms radio pulsar orbiting it every 3.4 years, in a very eccentric orbit with e=0.87. No radio pulses are observed when the NS is behind the circumstellar disk (free-free absorption). VHE gamma-rays are detected when the NS is close to periastron or crosses de disk (Aharonian et al. 2005). PSR B

35 The VHE spectrum can be fit with a power-law and explained by IC scattering processes. The lightcurve shows significant variability and a puzzling behavior not predicted by previously available models (Aharonian et al. 2005).

36 Three TeV sources (all HMXBs) discovered up to now: LS 5039 O+BH? LS I Be+NS? PSR B Be+NS Detection of new VHE sources? Since these sources are located in the Galactic plane, a sensitivity better by a factor X with respect to current instruments means detecting ~3X sources. Binaries with short orbital periods, difficult for Be but likely for O donors, should be ‘on’ all the time, although strong variability due to absorption is an issue. Detectable in deep enough surveys. Binaries with long orbital periods and high eccentricities should display an ‘on/off’ behavior, more with higher values. Detectable in long monitorings.

37 IC spectra of WR 147 A. Reimer et al. 2006, A&SS (astro-ph/ ) Gamma-ray emission should be expected either through: Leptonic processes (IC) (Chen & White 1991, ApJ 366, 512) Relativistic bremsstrahlung (Pollock 1987, A&A 171, 135) Hadronic interactions of co-accelerated ions with the dense wind material (White & Chen 1992, ApJ 387, 81) but what about gamma-rays from Colliding winds of massive stars ? Binary pulsars ?

38 Unidentified TeV source: TeV J2032 SIGNIFICANCE  by HEGRA STEADY in flux over 4 years of data taking EXTENDED with radius ~ (6.2  1.2  0.9) arcmin HARD SPECTRUM with index -1.9  0.1 stat  0.3 sys INTEGRAL FLUX > 1 TeV at the level of ~ 5% Crab Aharonian et al. 2002, A&A 293, L37

39 Paredes et al. 2006, ApJ Letters, in press VLA, 20 cm

40 GMRT, 45cm At 10 kpc, these objects would present luminosities likely requiring the presence of a compact object, and thus pointing to an X-ray binary nature. (for a model of microquasars -X-ray binaries with jets- powering extended TeV hadronic emission, see Bosch-Ramon et al. (2005)).

41  Microquasars are among the most interesting sources in the galaxy from the viewpoint of high-energy astrophysics.  Models predict that radio jets could be natural sites for the production of high energy photons via both Compton scattering and maybe direct synchrotron emission.  Leptonic and hadronic processes could be behind TeV emission.  Up to now, above ~ 500 keV, a handful of µqs have been detected: Cygnus X-1 at  1 MeV, GRO J at ~1 MeV, GRS and Cygnus X-3 at TeV? LS 5039 and LSI+61303: 100 MeV - few TeV  More microquasars will be detected soon with the Cherenkov telescopes and GLAST. This will bring more constraints to the physics of these systems.  Multiwavelength (multi-particle) campaigns are of primary importance. Summary