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 with A. Kopp, D.J. van der Walt, S. Casanova, P. Eger, W. Domainko, I. Buesching

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)

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) radio MSPs in 28 GCs * 2. X-ray,  -ray GC MSPs; optical companions 3. Diffuse radio emission (Clapson et al. 2011) *

Motivation Latest results from the neutron-star laboratory, Amsterdam, The Netherlands, 6-10 May 2013 Obervational 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)

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)

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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