A Pulsar Wind Nebula Origin for Luminous Te
A Pulsar Wind Nebula Origin for Luminous Te. V Source HESS J 1640 -465 Joseph Gelfand (NYUAD / CCPP) Eric Gotthelf, Jules Halpern (Columbia University), Dean Shaff (NYUAD) 2015 December 14 28 th Texas Symposium on Relativistic Astrophysics 1
Outline n Why study Galactic Te. V sources? n n n Why HESS J 1640 -465? n n n Te. V g-rays → >Pe. V particles Normally SNR or PWN. Most luminous Te. V g-ray source in Milky Way Associated with a radio SNR, X-ray PWN, and a pulsar If HESS J 1640 -465 is a PWN… n n pulsar spun down very rapidly Initial spin period P 0 ~ 20 – 35 ms 2015 December 14 28 th Texas Symposium on Relativistic Astrophysics 2
Sources of Te. V g-ray emission n n Numerous discrete Te. V g-ray sources in Milky Way Main source classes: n n n Supernova Remnants (SNRs) Pulsar Wind Nebulae (PWNe) Often associated with each other (Carrigan et al. 2013, ar. Xiv: 1307. 4690) 2015 December 14 (Carrigan et al. 2013, ar. Xiv: 1307. 4690) 28 th Texas Symposium on Relativistic Astrophysics 3
HESS J 1640 – 465 n Luminous Te. V source in a crowded region n n Borders HESS J 1641 -463 Me. V and Ge. V emission detected as well n Ge. V g-rays predominantly (Lemoine-Goumard et al. 2014, Ap. J, 794, L 16) from HESS (A. Abramowski et al. 2014, Ap. J , 794, L 1) (Lemoine-Goumard 2014, MNRAS Ap. J , 794, L 16)2828) J 1640 -465 (HESS Collaboration etetal. 2014, , 439, 2015 December 14 28 th Texas Symposium on Relativistic Astrophysics 4
Radio Supernova Remnant n Crowded region n Coincident with SNR G 338. 3 -0. 0 Located behind massive star cluster Electrons and protons accelerated to high energy in SNR shell n n Inverse Compton emission from highenergy electrons CR protons + Ambient protons → p 0 → gg (“hadronic”) (Castelleti et al. 2011, A&A, 536, A 98) 2015 December 14 28 th Texas Symposium on Relativistic Astrophysics 5
SNR Interpretation of HESS J 1640 -465 n g-rays predominantly hadronic n n n (HESS Collaboration et al. 2014, MNRAS, 439, 2828) CR energy ~5× 1048 ergs HESS J 1641 -463: diffusing CRs interacting with nearby molecular cloud Problem: No direct evidence for interaction between SNR G 338. 3– 0. 0 n n n No thermal X-rays No OH masers CO nearby, but not coincident (Tang et al. 2015, Ap. J, 812, 32) 2015 December 14 28 th Texas Symposium on Relativistic Astrophysics 6
X-ray Pulsar n PSR J 1640 -4631 n n Fairly high Ė , fairly low characteristic age Properties consistent with that observed from other g-ray PWNe (Gotthelf et al. 2014, Ap. J , 788, 155) (Mattana et al. 2009, Ap. J, 694, 12) (Gotthelf et al. 2014, Ap. J , 788, 155) 2015 December 14 28 th Texas Symposium on Relativistic Astrophysics 7
X-ray Pulsar Wind Nebula n n n Discovered before pulsar X-ray size « g-ray size Chandra spectrum n n n Uncertain due to high NH → limited bandwidth G = 1. 4± 0. 4 dependent on abundance models Nu. STAR spectrum n n Contaminated by pulsar G = 2. 3± 1. 0 2015 December 14 (Gotthelf et al. 2014, (Funk et al. Ap. J, 2007, 788, Ap. J, 155) 662, 517) 28 th Texas Symposium on Relativistic Astrophysics 8
Is HESS J 1640‒ 465 a Pulsar Wind Nebula? n Observed Properties n n n n SNR radius PWN radius = Te. V radius Radio upper-limit Chandra X-ray spectrum Fermi spectrum HESS spectrum Current pulsar Ė, characteristic age 2015 December 14 n Uncertainties n n n Initial kinetic energy Esn and mass Mej of supernova ejecta Density of surrounding ISM nism Pulsar braking index p and spindown timescale tsd Magnetization h. B and particle spectrum (Emin, Ebreak, Emax, p 1, p 2 ) Temperature and energy density of background photon field(s) Distance 28 th Texas Symposium on Relativistic Astrophysics 9
Schematic of a Pulsar Wind Nebula inside a Supernova Remnant Neutron Star Termination Shock Supernova Remnant Pressure: Psnr(Rpwn) Velocity: vsnr(Rpwn) Density: rsnr(Rpwn) Ejecta mass: Mej Kinetic energy: Esn Density ISM: nism (Gelfand et al. 2009, Ap. J, 703, 2051) 2015 December 14 Magnetic Field: BĖ Electrons: (1 - B)Ė Injection Spectrum Pulsar Wind Nebula Pressure: Ppwn Magnetic Field: Bpwn 28 th Texas Symposium on Relativistic Astrophysics Swept-up Material Mass: Msw, pwn Velocity: vpwn 10
Evolutionary Model for a Pulsar Wind Nebula Inside a Supernova Remnant n Homogeneous ISM, Pulsar 4πRpwn 2 Ppwn Wind Nebula (PWN) n n One-zone model Dynamical evolution determined by motion of swept-up material n 4πRpwn 2 Psnr(Rpwn) Net force from pressure difference between PWN and Supernova Remnant (SNR) Pulsar Wind Nebula Emission dominated by synchrotron radiation and Inverse Compton scattering of electrons off background photons (Figure 6; Gelfand et al. 2007) (Gelfand et al. 2009, Ap. J, 703, 2051) Supernova Remnant n 2015 December 14 28 th Texas Symposium on Relativistic Astrophysics 11
Model Results n MCMC algorithm to identify combinations of model parameters which minimize c 2 n n 22 degrees of freedom Lowest reduced c 2≈3 Prefers X -ray G > 2 2015 December 14 28 th Texas Symposium on Relativistic Astrophysics “Noisy” Fermi spectrum 12
PSR J 1640 -4631 properties n n Pulsar braking index p , spin-down timescale tsd largely unconstrained n … but tsd ≤ 100 years n n n PWN size ≈ SNR size Occurs IF NS rotational energy ≈ SN energy Ė much higher in the past R A N I IM Why? L E R P ! Y (HESS Collaboration et al. 2014, MNRAS, 439. 2828) 2015 December 14 28 th Texas Symposium on Relativistic Astrophysics 13
Initial Spin Period of PSR J 16404631 n Initial spin period P 0 « P≈206 ms now n n Compare with models / other pulsars n n N I IM L E R P Somewhat lower than other pulsars Inconsistent with P 0 limited by GW emission? 2015 December 14 ! Y R A P 0 ~ 20 – 35 ms 28 th Texas Symposium on Relativistic Astrophysics 14
Summary n n Can reproduce properties of HESS J 1640 -465 with PWN model IF PSR J 1641 -4631 spun down rapidly Need to: n n n Thank You! Determine Me. V spectrum from additional Fermi data Better measure X-ray extent, spectrum of PWN Utilize possible pulsar braking index measurement by Nu. STAR Detect PWN in radio (SKA? ) Add SNR component to modeling n Include effects of cosmic ray acceleration on SNR evolution 2015 December 14 28 th Texas Symposium on Relativistic Astrophysics 15
2015 December 14 28 th Texas Symposium on Relativistic Astrophysics 16
Background Photon Field 2015 December 14 28 th Texas Symposium on Relativistic Astrophysics 17
Pulsar Wind Properties 2015 December 14 28 th Texas Symposium on Relativistic Astrophysics 18
Combined Emission from Pulsar & Pulsar Wind Nebula? n Pulsar n n n Power-law with exponential cut off Constant g-ray efficiency hg Pulsar Wind Nebula n n One-zone evolutionary model Broken powerlaw injection spectrum (Gelfand et al. 2009, Ap. J, 703, 2051) 2015 December 14 (Abdo et al. 2013, Ap. JS, 208, 17) 28 th Texas Symposium on Relativistic Astrophysics 19
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