1. A Pulsar Wind Nebula Origin for Luminous TeV Source HESS J1640-465 Joseph Gelfand (NYUAD / CCPP) Eric Gotthelf, Jules Halpern (Columbia University), Dean Shaff (NYUAD) 2015 December 14 1 28th Texas Symposium on Relativistic Astrophysics

2. Outline Why study Galactic TeV sources? TeV  -rays → >PeV particles Normally SNR or PWN. Why HESS J1640-465? Most luminous TeV  -ray source in Milky Way Associated with a radio SNR, X-ray PWN, and a pulsar If HESS J1640-465 is a PWN… pulsar spun down very rapidly Initial spin period P 0 ~ 20 – 35 ms 2015 December 14 28th Texas Symposium on Relativistic Astrophysics2

3. Sources of TeV  -ray emission Numerous discrete TeV  -ray sources in Milky Way Main source classes: Supernova Remnants (SNRs) Pulsar Wind Nebulae (PWNe) Often associated with each other 2015 December 14 28th Texas Symposium on Relativistic Astrophysics3 (Carrigan et al. 2013, arXiv:1307.4690)

4. HESS J1640 – 465 2015 December 14 28th Texas Symposium on Relativistic Astrophysics4 (HESS Collaboration et al. 2014, MNRAS, 439, 2828) (A. Abramowski et al. 2014, ApJ, 794, L1) Luminous TeV source in a crowded region Borders HESS J1641-463 MeV and GeV emission detected as well GeV  -rays predominantly from HESS J1640-465 (Lemoine-Goumard et al. 2014, ApJ,794, L16)

5. Radio Supernova Remnant Crowded region Coincident with SNR G338.3-0.0 Located behind massive star cluster Electrons and protons accelerated to high energy in SNR shell Inverse Compton emission from high- energy electrons CR protons + Ambient protons →  0 →  (“hadronic”) 2015 December 14 28th Texas Symposium on Relativistic Astrophysics5 (Castelleti et al. 2011, A&A, 536, A98)

6. SNR Interpretation of HESS J1640-465  -rays predominantly hadronic CR energy ~5×10 48 ergs HESS J1641-463: diffusing CRs interacting with nearby molecular cloud Problem: No direct evidence for interaction between SNR G338.3–0.0 No thermal X-rays No OH masers CO nearby, but not coincident 2015 December 14 28th Texas Symposium on Relativistic Astrophysics6 (Tang et al. 2015, ApJ, 812, 32) (HESS Collaboration et al. 2014, MNRAS, 439, 2828)

7. X-ray Pulsar PSR J1640-4631 Fairly high Ė, fairly low characteristic age Properties consistent with that observed from other  -ray PWNe 2015 December 14 28th Texas Symposium on Relativistic Astrophysics7 (Gotthelf et al. 2014, ApJ, 788, 155) (Mattana et al. 2009, ApJ, 694, 12)

8. X-ray Pulsar Wind Nebula Discovered before pulsar X-ray size «  -ray size Chandra spectrum Uncertain due to high N H → limited bandwidth  = 1.4±0.4 dependent on abundance models NuSTAR spectrum Contaminated by pulsar  = 2.3±1.0 2015 December 14 28th Texas Symposium on Relativistic Astrophysics8 (Funk et al. 2007, ApJ, 662, 517) (Gotthelf et al. 2014, ApJ, 788, 155)

9. Is HESS J1640 ‒ 465 a Pulsar Wind Nebula? Observed Properties SNR radius PWN radius = TeV radius Radio upper-limit Chandra X-ray spectrum Fermi spectrum HESS spectrum Current pulsar Ė, characteristic age Uncertainties Initial kinetic energy E sn and mass M ej of supernova ejecta Density of surrounding ISM n ism Pulsar braking index p and spin- down timescale  sd Magnetization  B and particle spectrum (E min, E break, E max, p 1, p 2 ) Temperature and energy density of background photon field(s) Distance 2015 December 14 28th Texas Symposium on Relativistic Astrophysics9

10. 10 Schematic of a Pulsar Wind Nebula inside a Supernova Remnant Neutron Star Pulsar Wind Termination Shock Magnetic Field:  B Ė Electrons: (1-  B )Ė Injection Spectrum Pulsar Wind Nebula Pressure: P pwn Magnetic Field: B pwn Swept-up Material Mass: M sw,pwn Velocity: v pwn Supernova Remnant Pressure: P snr (R pwn ) Velocity: v snr (R pwn ) Density:  snr (R pwn ) Ejecta mass: M ej Kinetic energy: E sn Density ISM: n ism (Gelfand et al. 2009, ApJ, 703,2051) 2015 December 14 28th Texas Symposium on Relativistic Astrophysics

11. 11 Evolutionary Model for a Pulsar Wind Nebula Inside a Supernova Remnant Homogeneous ISM, Pulsar Wind Nebula (PWN) One-zone model Dynamical evolution determined by motion of swept-up material Net force from pressure difference between PWN and Supernova Remnant (SNR) Emission dominated by synchrotron radiation and Inverse Compton scattering of electrons off background photons (Figure 6; Gelfand et al. 2007) Pulsar Wind Nebula 4πR pwn 2 P pwn 4πR pwn 2 P snr (R pwn ) Supernova Remnant 2015 December 14 28th Texas Symposium on Relativistic Astrophysics (Gelfand et al. 2009, ApJ, 703,2051)

12. Model Results MCMC algorithm to identify combinations of model parameters which minimize  2 22 degrees of freedom Lowest reduced  2 ≈3 2015 December 14 28th Texas Symposium on Relativistic Astrophysics12 Prefers X-ray  > 2 “Noisy” Fermi spectrum

13. PSR J1640-4631 properties 2015 December 14 28th Texas Symposium on Relativistic Astrophysics13 (HESS Collaboration et al. 2014, MNRAS, 439. 2828) Pulsar braking index p,spin-down timescale  sd largely unconstrained … but  sd ≤ 100 years Why? PWN size ≈ SNR size Occurs IF NS rotational energy ≈ SN energy Ė much higher in the past PRELIMINARY!

14. Initial Spin Period of PSR J1640- 4631 Initial spin period P 0 « P≈206 ms now P 0 ~ 20 – 35 ms Compare with models / other pulsars Somewhat lower than other pulsars Inconsistent with P 0 limited by GW emission? 2015 December 14 28th Texas Symposium on Relativistic Astrophysics14 PRELIMINARY!

15. Summary Can reproduce properties of HESS J1640-465 with PWN model IF PSR J1641-4631 spun down rapidly Need to: Determine MeV spectrum from additional Fermi data Better measure X-ray extent, spectrum of PWN Utilize possible pulsar braking index measurement by NuSTAR Detect PWN in radio (SKA?) Add SNR component to modeling Include effects of cosmic ray acceleration on SNR evolution 2015 December 14 28th Texas Symposium on Relativistic Astrophysics15 Thank You!

16. 2015 December 14 28th Texas Symposium on Relativistic Astrophysics16

17. Background Photon Field 2015 December 14 28th Texas Symposium on Relativistic Astrophysics17

18. Pulsar Wind Properties 2015 December 14 28th Texas Symposium on Relativistic Astrophysics18

19. Combined Emission from Pulsar & Pulsar Wind Nebula? Pulsar Power-law with exponential cut off Constant  -ray efficiency   Pulsar Wind Nebula One-zone evolutionary model Broken power- law injection spectrum 2015 December 14 28th Texas Symposium on Relativistic Astrophysics19 (Abdo et al. 2013, ApJS, 208, 17) (Gelfand et al. 2009, ApJ, 703,2051)