1. C. Venter Centre for Space Research NWU Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013 Constraining the properties of millisecond pulsars in globular clusters through multiwavelength modelling http://blogs.agu.org/wildwildscience/files/2009/07/globular-800.jpg with A. Kopp, D.J. van der Walt, S. Casanova, P. Eger, W. Domainko, I. Buesching

2. Motivation Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013 Theoretical NXNX  N X ~  0.74 GCs are very old (~10 10 yr) Expected to harbour large density of evolved stellar products Large central density: large stellar interaction rates Large density of LMXRBs in GCs – MSP progenitors Many MSPs Cluster models: < 200 MSPs “Ingredients” to create photons: Sources of rel. particles (Additional) acceleration B-fields – SR E-fields – CR Photon fields – ICS (Stellar populations other than MSPs – alternative sources of particles) Pooley et al. (2003)

3. Hui et al. (2009) ~50% 1. Motivation Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013 Obervational... Bogdanov et al. (2006) 2. Freire et al. (2011) 2. 3. 1. 144 radio MSPs in 28 GCs * 2. X-ray,  -ray GC MSPs; optical companions 3. Diffuse radio emission (Clapson et al. 2011) * www.naic.edu/~pfreire/GCpsr.html

4. Motivation Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013 Obervational... 1. Diffuse X-ray emission (Eger et al. 2010) 2. GeV emission (Fermi): ~12 GCs (Abdo et al. 2010) 3. VHE emission (H.E.S.S.): Ter5 (Abramowski et al. 2010) 3. 2. 1.

5. HISTORY OF GC MODELS Bednarek & Sitarek (2007) Zajczyk et al. (2013) Leptons accelerated at shock waves originating from collisions of pulsar winds and / or inside the pulsar magnetosphere: PL injection spectra ICS on CMB and stellar photons Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013 PSPC model for acceleration of leptons in MSP magnetospheres Bohm diffusion CR & ICS on CMB and stellar photons (see also Harding et al. 2005)

6. HISTORY OF GC MODELS Cheng et al. (2010) Hui et al. (2011) ICS of relativistic e + on CMB, stellar photons, galactic background (IR, optical) 2-step  from spatial  -ray info Mono-energetic injection spectrum Explain HE spectra using IC, not CR IC emission > 10 pc Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013 Probe correlations between : - HE L  and  c, [Fe/H] -> N MSP - HE L  and u i -> IC origin of HE  -rays (u i and [Fe/H] may not be independent) Degeneracy w.r.t. u i may be alleviated by TeV observations.

7. HISTORY OF GC MODELS (Venter & de Jager 2008) CR Fermi LAT Pulsed CR 100 GC MSPs Randomize over geometry and P, P PSPC E-field Lessons: Using population decreases uncertainty Depends on P, P EOS: small effect F  ~ N vis Constrain E ||, I PC, N vis Approximate CR calculation – improve Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013

8. HISTORY OF GC MODELS (Venter & de Jager 2010) Full CR calculation vs. delta approximation Lessons: Correct CR power previously used Smoother spectrum “Tails” important for Fermi LAT range Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013

9. 47 Tuc HISTORY OF GC MODELS (Venter & de Jager 2009; Venter et al. 2009) PSPC E-field: Q e randomized over  Basic particle transport Bohm diffusion ICS on CMB / stellar photons 2-zone model; crude u(r) SR (constant B) Lessons: No reacceleration: lower limit  p important 47 Tuc visible for Fermi LAT (x2) 47 Tuc; Ter5 visible for H.E.S.S. Constraints on N MSP, B Difficult to test SR: unresolved sources (cf. Aharonian et al. 2009) Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013

10. Ter5 HISTORY OF GC MODELS (Venter et al. 2011) Pulsed & unpulsed flux predictions for Ter5 Fermi data: N MSP ~ 60 Updated GC parameters 2 zones Lessons: J1823–3021A: CR dominates ICS in GeV range for NGC 6624 N MSP ~ N vis ~ N tot ~ 60 (B,  ) PSPC not generally applicable? Reacc. – PL injection spectrum Structural parameters, d, L GC, N *, R,T determine u(r) Add outer zone / more zones Use X-rays to constrain  Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013

11. HISTORY OF GC MODELS (Prinsloo et al. 2013) 3-zone model; improved u(r) Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013

12. REFINED GC MODEL (Kopp et al., submitted) PL injection spectrum Diffusion IC & SR losses u(r); CMB; Galactic background Many zones Spherical symmetry Transport B(r) will influence E SR, f, and thus IC spectrum Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013

13. LINE-OF-SIGHT INTEGRATION (Kopp et al., submitted) Constraining  using diffuse X-rays Source size Bohm diffusion  =  0 E 0.6  0 = 8e28 cm 2 /s, B = 12  G,  = 2.0  0 = 3e28 cm 2 /s, B = 5  G,  = 1.8 Preliminary B = 4  G B = 10  G B = 5  G Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013

14. BACK-OF-THE-ENVELOPE  Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013

15. SED & PARAMETER CONSTRAINTS (Kopp et al., submitted) Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013  0 = 8e28 cm 2 /s, B = 12  G,  = 2.0  0 = 3e28 cm 2 /s, B = 5  G,  = 1.8 E min = 3.8e-3 TeV E min = 0.1 TeV Preliminary IC parameters: Diffusion parameters:  =  0 E  Cluster parameters: R c, R h, R t  d F g  d 2 u(r)  N * R 2 T 4  R c, R h, R t  SR parameters: u(r), u CMB, u BG N e (u i,B)  N MSP  p E  B 2 N e (u i, B,  )  N MSP  p CR parameters: E || (r, , , P, P, M, R) N MSP Injection spectrum: E min, E max, , N MSP  N MSP  p

16. OFFSET VHE SOURCE Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013  MSPs born near tidal radius (?)  Small population of MSPs skewing  -ray source (?)  Non-uniform energy density profile (local optical / IR sources)  Other contributions to u(r) (e.g. Galactic) (small effect?) E.g., Cheng et al. (2010); Tam et al. (2011)  GC proper motion      Non-MSP sources of particles  VHE source not associated with GC (?) Preliminary

17. GC POPULATION MODELLING H.E.S.S. searched for TeV emission from 15 GGs (Abramowski et al. 2013) Targets: 47 Tuc, NGC 6388, M 15, HP 5, Terzan 10, M 54, NGC 362, Pal 6, NGC 6256, Djorg 2, NGC 6749, NGC 6144, NGC 288, HP 1, Terzan 9 Total exposure: 195 h of good quality data Results: - No individual GC detected - No signal detected in a stacking analysis Comparison to Terzan 5: -Stacking upper limits much below expectation from IC (scaled model) Good project for detailed modelling! Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013

18. ALTERNATIVE MODELS Due to the extreme stellar densities in GC: mergers of compact stars can happen (e.g. white dwarfs, neutron stars) Remnants of merger-driven explosions in GC e.g. SN Ia, short GRBs (Abramowski et al. 2011, Domainko 2011) CR acceleration in shocks; Hadronic scenario - could explain the VHE offset Recent catastrophic event in Terzan 5 could explain the non- detection of any other GCs in VHE  -rays and non-thermal X-rays Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013 GRB Remnant Scenario Large numbers of non-accreting WDs Similar energetics for total released particles (rotation-powered) ICS on CMB Few thousand WDs formed within GC lifetime may be detectable for CTA (Bednarek 2012) White dwarfs

19. CONCLUSIONS Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013 GC age / density facilitate binary, LMXRB, & MSP formation GCs are multi- objects – use e.g. diffuse radio, diffuse X-rays, GeV  -rays / MSPs & VHE  -rays to constrain parameters Continued development of MSP GC model Refined model: LOS integration, transport, u(r) Constrain underlying source population / particle acceleration / radiation mechanisms / cluster parameters Open questions: - Relative amount of CR vs. IC in GeV band - Large / no GeV cutoffs? - Offset, asymmetric VHE source in Terzan 5  (r,  ), u(r,  ), B(r) ? - No X-ray emission in many sources (low GC B-field?) - No known MSPs in some HE GCs! (Beaming? Faintness?) - Detailed acceleration of injected particles unknown - Contributions from other sources Stacking of GCs

20. THANK YOU! “You are worthy, O Lord, to receive glory and honour and power; for You created all things, and by Your will they exist and were created” (Rev. 4:11).