1 / 19

Possible Distance indicators in Gamma-ray Pulsars

Possible Distance indicators in Gamma-ray Pulsars. Wei Wang ( 王 伟 ). May 11 2011 NOAC Beijing. Outline. Distance information for pulsars Gamma-ray emission efficiency ( η ) versus pulsar parameters: P, age, magnetic field at light cylinder (B LC )

ronli
Download Presentation

Possible Distance indicators in Gamma-ray Pulsars

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Possible Distance indicators in Gamma-ray Pulsars Wei Wang ( 王 伟 ) May 11 2011 NOAC Beijing

  2. Outline • Distance information for pulsars • Gamma-ray emission efficiency (η) versus pulsar parameters: P, age, magnetic field at light cylinder (BLC) • Efficiency versus generation order parameters (GOP) • Good correlation between η-GOP, η-BLC are distance indicators for gamma-ray pulsars • Distances of 25 gamma-selected pulsars are estimated

  3. Distance information for pulsars • Trigonometric parallax measurements only available for nearby pulsars, <0.4 kpc mainly for some millisecond pulsars • dispersion measurement (DM) distances for radio pulsars combined with electron density distribution model NE2001 model

  4. Distance for pulsars • kinematic models: the distance of possible associated objects (SNR, PWNe, star clusters, HII regions) could be measured from Doppler shift of absorption or emission lines in HI spectrum together with the rotation curve model of the Galaxy • Estimators according to thermal X-ray spectra or Lx-Edot, Lx-Γ relations Gotthelf 2003 Beck & Truemper 1997

  5. Gamma-ray pulsar family in Fermi/LAT era One-year observations: Gamma-ray all-sky map > 100 MeV >1400 gamma-ray point sources!!! EGRET: 270

  6. Near 100 gamma-ray pulsars 30 radio young pulsars 25 gamma-selected pulsars 13+34 MSPs Gamma-ray pulsar family in Fermi/LAT era

  7. The first gamma-ray pulsar catalog by Fermi/LAT (2010) 21 radio-selected young pulsars 17 gamma-selected young pulsars (most have no any distance information!) 8 millisecond pulsars L- Edot relation : EGRET pulsars L∝ Edot 0.5 (Thompson 2001) In FERMI/LAT Era, not simple case! very large scattering If we fit the data of 21 radio young pulsars, we find a relation of L∝ Edot0.7(0.2) But for MSPs, L∝ 0.1 Edot

  8. Our aims • Find a possible better correlation in gamma-ray pulsars, connecting Lγ and pulsar parameters • Considering Gamma-ray emission efficiency η • η = Lγ/Edot • L γ=4πd2 f Fγ, Fγ is the flux of LAT (>100 MeV) • f is beaming factor, model dependent; could be obtained using pulse profile information, f～ 1 for 8 gamma-ray pulsars estimated by Watters et al. (2009). • For simplicity, f =1 in this work • We show the relations between η and three well-known parameters: P, age and BLC and generation order parameters (GOPs)

  9. 21 radio-selected young gamma-ray pulsars with distance information in the first gamma-ray pulsar catalog (Abdo et al. 2010) are used in the analysis. G magnetic field at light cylinder Age=P/2Pdot no correlation σ= 1.63 σ=1.56 p-value 1.04 e-4 2.90e-5

  10. Generation order parameters • describe pair cascade processes in gamma-ray pulsars based on the RS model (Ruderman & Sutherland 1975; Lu & Shi 1990; Zhao et al. 1989) • The first generation photon with very high energy • The primary photon will be absorbed in magnetosphere, into e-/e+ pairs, the production condition is: • The e-/e+ can emit the second-generation gamma-ray photons, if the energy is high enough. In the similar conditions, the photon will be absorbed again, converted into e-/e+, to emit third-generation photons. • Then pair cascade processes occur

  11. Generation order parameters • ThreeGOPs defined by: • Absorbed through electron fields (Lu et al. 1994) • Absorbed through magnetic and electron fields (Wei et al. 1997) • Absorbed through magnetic fields (Wang & Zhao 2004)

  12. GOPs describe gamma-ray properties of pulsars • Main gamma-ray photon (first generation) must be produced: so GOPs must >1, then gamma-rays can be emitted. For gamma-ray pulsars, GOPs >1 • Larger values of GOPs, more generations of photons, then photon energy become lower, even to X-ray bands • The correlation of GOPs and photon index in gamma-rays are found based on EGRET pulsars • Then lager GOPs, softer in gamma-ray bands, i.e., given a total emitting rate, larger GOPs imply a smaller gamma-ray efficiency !

  13. Better correlation for η-ζ3 implies the magnetic fields dominate the absorption in pair cascade processes. In all correlations, η-ζ3 are the best one (σ, p-value smallest), η-BLC correlation is also acceptable. No correlation σ= 1.69 σ=1.34

  14. Possible distance indicators • Two fundamental parameters P and Pdot are relatively easily obtained • ζ3and BLC: thefunctions of P and Pdot • Good correlations between η-ζ3 and η-BLCexist for radio-selected young gamma-ray pulsars • ηdepends on pulsar distance • With known P and Pdot, and detected gamma-ray flux, pulsar distance will be evaluated • 17 gamma-selected pulsars in the first gamma-ray pulsar catalog (Abdo et al. 2010), 8 new gamma-selected pulsars in blind search (Saz Parkinson et al. 2010): most of they have no any distance information • Distances of 25 gamma-selected pulsar are estimated

  15. Distance estimate for 25 gamma-selected pulsars ζ3 BLC

  16. Distance indicators of gamma-selected pulsars • Geminga: d=0.25+0.12_0.06 kpc from trigonometric parallax on possible optical counterpart Our prediction: d=0.19±0.07 kpc • Many gamma-selected pulsars have too large (non-physical) emission efficiency, e.g.η>1 from other distanceestimation. • Like PSR J2021+4026, d=1-2 kpc from kinematics model on possible association , η=100-400%. Our prediction: d=0.4±0.1 kpc, η=16%.

  17. Millisecond pulsars ? • In parameter spaces of P, τ, MSPs are quite different from young pulsars; and ζ1 and ζ2 of MSPs is below 1 or near 1, may be not suitable for gamma-ray MSPs • But in parameter spaces of BLC and ζ3, MSPs and young pulsars are still similar MSPs may have constant efficiency of 10%; though they still follow behavior: larger BLC and ζ3 inducesmaller η,

  18. Distance distribution of three classes of gamma-ray pulsars The large population of nearby gamma-ray radio-quiet pulsars (or MSPs) could significantly contribute to e-/e+ background flux and diffuse gamma-ray background.

  19. Summary • Good correlations between η-ζ3 and η-BLCare found • Gamma-ray luminosity of pulsars depends on two fundamental parameters: P and Pdot • The relations would be the distance indicators for gamma-ray pulsars, specially radio-quiet pulsars • Gamma-selected pulsars are closer to us compared to radio-selected young pulsars • Our GOPs models are originally proposed based on polar-cap scenario, the possible GOPs applied in outer-gap or slot-gap models may be more complicated, which can be studied furthermore.

More Related