arXiv subjects

Noel Klingler

Publications and source records attributed to Noel Klingler.

26 records · Page 2Linked to original sources

arXiv2018

On the broad-band synchrotron spectra of pulsar wind nebulae

As shown by broad-band observations, pulsar wind nebulae (PWNe) are characterized by a broken power-law spectrum of synchrotron emission. Based on the modern magnetohydrodynamic (MHD) turbulence theories, we investigate the re-acceleration of electrons in the PWN through the adiabatic stochastic acceleration (ASA), which arises from fundamental dynamics of MHD turbulence. The ASA acts to flatten the injected energy spectrum of electrons at low energies, while synchrotron cooling results in a steep spectrum of electrons at high energies. Their dominance in different energy ranges leads to a flat radio spectrum ($F_ν$) and a steep X-ray spectrum. Our analytical spectral shapes generally agree well with the observed synchrotron spectra of radio- and X-ray-bright PWNe. The spectral break corresponding to the balance between the ASA and synchrotron losses provides a constraint on the acceleration timescale of the ASA and the magnetic field strength in the PWN.

astro-ph.HE↗

arXiv2018

The Variable Pulsar Wind Nebula of PSR J1809-1917

PSR J1809-1917 is a young ($τ=51$ kyr) energetic ($\dot{E}=1.8\times10^{36}$ erg s$^{-1}$) radio pulsar powering a pulsar wind nebula (PWN). We report on the results of three Chandra X-ray Observatory observations which show that the PWN consists of a small ($\sim 20''$) bright compact nebula (CN) and faint extended emission seen up to $2'$ from the pulsar. The CN is elongated in the northeast-southwest direction and exhibits morphological and flux variability on a timescale of a few months. We also find evidence of small arcsecond-scale jets extending from the pulsar along the same direction, and exhibiting a hard power-law (PL) spectrum with photon index $Γ_{\rm jet}=1.2\pm0.1$. The more extended emission and CN share the same symmetry axis, which is also aligned with the direction toward the TeV $γ$-ray source HESS J1809--193, supporting their association. The spectrum of the extended nebula (EN) fits an absorbed PL with about the same slope as that of the CN, $Γ_{\rm CN}\approxΓ_{\rm EN}=1.55\pm0.09$; no spectral changes across the EN's 2 pc extent are seen. The total PWN 0.5-8 keV luminosity is $L_{\rm PWN}\approx 9\times10^{32}$ erg s$^{-1}$, about half of which is due to the EN.

astro-ph.HE↗

arXiv2018

The Mouse Pulsar Wind Nebula

The young energetic pulsar J1747-2958 ($τ=26$ kyr, $\dot{E}=2.5\times 10^{36}$ erg s$^{-1}$) powers the Mouse pulsar wind nebula (PWN), famous for its spectacular tail spanning 45$"$ in X-rays and 12$'$ in radio ($d\sim5$ kpc). We present the results of Chandra observations of the PWN and the analysis of archival lower-frequency data. The Chandra HRC image reveals a point-like source at the pulsar position, $\approx$1$'$ behind the bow shock apex of the PWN. The flattened appearance of the compact nebula is consistent with an equatorial outflow deformed by the ram pressure, implying that the angle between the pulsar's spin axis and line of sight is $\sim70^\circ$ (in agreement with the radio and $γ$-ray pulse profiles). The spatially-resolved spectroscopy with Chandra ACIS shows that the power-law (PL) spectrum steepens from $Γ=1.65\pm0.02$ to $3.0\pm0.1$ over the 45$'$ extent of the X-ray tail. However, the tail's X-ray spectrum integrated over its 45$"$ length fits a single absorbed PL with $Γ=2.09\pm0.03$. We also found the Mouse PWN in 150 MHz GMRT data, and a possible counterpart in 24 ${\rm μ}$m Spitzer data. The multiwavelength data suggest that, at low frequencies, the spectrum of the X-ray-emitting tail region can be described by a broken PL with at least one turnover between radio and X-rays. This is consistent with synchrotron cooling of electrons injected at the termination shock (with an SED slope of 2.2) in an equipartition magnetic field $B\sim200$ ${\rm μG}$ and a bulk flow speed $v\sim4000$ km s$^{-1}$.

astro-ph.HE↗

arXiv2018

Kinetic "jets" from fast moving pulsars

Some fast-moving pulsars, like the Guitar and the Lighthouse, exhibit asymmetric non-thermal emission features that extend well beyond their ram pressure confined pulsar wind nebulae (PWNe). Using 3D relativistic simulations we explain these features as kinetically streaming pulsar wind particles that escaped into the interstellar medium (ISM) due to reconnection between the PWN and ISM magnetic fields. The structure of the reconnecting magnetic fields at the incoming and outgoing regions produce highly asymmetric magnetic bottles, and result in asymmetric extended features. For the features to become visible, the ISM magnetic field should be sufficiently high, $B_{\rm ISM}>10$~$μ$G. We also discuss archival observations of PWNe displaying evidence of kinetic jets: the Dragonfly PWN (PSR J2021+3651), G327.1--1.1, and MSH 11--62, the latter two of which exhibit "snail eyes" morphologies. We suggest that in those cases the pulsar is moving along the ambient magnetic field in a frisbee-type configuration.

astro-ph.HE↗

arXiv2017

Toward understanding the physical underpinnings of spatial and spectral morphologies of pulsar wind nebulae

We discuss the observational properties of pulsar wind nebulae (PWNe) linking them to the injected (at the termination shock) electron spectral energy distribution and parameters of pulsar magnetospheres. In particular, we (1) present spatially-resolved Chandra ACIS spectral maps of twelve PWNe and measure the slopes of the uncooled PWN spectra just downstream of the termination shock obtained from these maps, (2) consider the connections between PWN morphologies and predictions of the magnetospheric emission models and (3) discuss the limits on the maximum energies of particles in PWNe from X-ray and gamma-ray observations.

astro-ph.HE↗

arXiv2017

Pulsar Wind Nebulae Created by Fast-Moving Pulsars

We review multiwavelength properties of pulsar wind nebulae (PWNe) created by supersonically moving pulsars and the effects of pulsar motion on the PWN morphologies and the ambient medium. Supersonic pulsar wind nebulae (SPWNe) are characterized by bow-shaped shocks around the pulsar and/or cometary tails filled with the shocked pulsar wind. In the past several years significant advances in SPWN studies have been made in deep observations with the Chandra and XMM-Newton X-ray Observatories as well as the Hubble Space Telescope. In particular, these observations have revealed very diverse SPWN morphologies in the pulsar vicinity, different spectral behaviors of long pulsar tails, the presence of puzzling outflows misaligned with the pulsar velocity, and far-UV bow shocks. Here we review the current observational status focusing on recent developments and their implications.

astro-ph.HE↗

arXiv2016

Deep Chandra Observations of the Pulsar Wind Nebula Created by PSR B0355+54

We report on Chandra X-ray Observatory (CXO) observations of the pulsar wind nebula (PWN) associated with PSR B0355+54 (eight observations with a 395 ks total exposure, performed over an 8 month period). We investigated the spatial and spectral properties of the emission coincident with the pulsar, compact nebula (CN), and extended tail. We find that the CN morphology can be interpreted in a way that suggests a small angle between the pulsar spin axis and our line-of-sight, as inferred from the radio data. On larger scales, emission from the 7' (2 pc) tail is clearly seen. We also found hints of two faint extensions nearly orthogonal to the direction of the pulsar's proper motion. The spectrum extracted at the pulsar position can be described with an absorbed power-law + blackbody model. The nonthermal component can be attributed to magnetospheric emission, while the thermal component can be attributed to emission from either a hot spot (e.g., a polar cap) or the entire neutron star surface. Surprisingly, the spectrum of the tail shows only a slight hint of cooling with increasing distance from the pulsar. This implies either a low magnetic field with fast flow speed, or particle re-acceleration within the tail. We estimate physical properties of the PWN and compare the morphologies of the CN and the extended tail with those of other bow shock PWNe observed with long CXO exposures.

astro-ph.HE↗

arXiv2016

Chandra Observations of Outflows from PSR J1509-5850

PSR J1509-5850 is a middle-aged pulsar with the period P ~ 89 ms, spin-down power Edot = 5.1 x 10^35 erg/s, at a distance of about 3.8 kpc. We report on deep Chandra X-ray Observatory observations of this pulsar and its pulsar wind nebula (PWN). In addition to the previously detected tail extending up to 7' southwest from the pulsar (the southern outflow), the deep images reveal a similarly long, faint diffuse emission stretched toward the north (the northern outflow) and the fine structure of the compact nebula (CN) in the pulsar vicinity. The CN is resolved into two lateral tails and one axial tail pointing southwest (a morphology remarkably similar to that of the Geminga PWN), which supports the assumption that the pulsar moves towards the northeast. The luminosities of the southern and northern outflows are about 1 x 10^33 and 4 x 10^32 erg/s, respectively. The spectra extracted from four regions of the southern outflow do not show any softening with increasing distance from the pulsar. The lack of synchrotron cooling suggests a high flow speed or in-situ acceleration of particles. The spectra extracted from two regions of the northern outflow show a hint of softening with distance from the pulsar, which may indicate slower particle propagation. We speculate that the northern outflow is associated with particle leakage from the bow shock apex into the ISM, while the southern outflow represents the tail of the shocked pulsar wind behind the moving pulsar. We estimate the physical parameters of the observed outflows and compare the J1509-5850 PWN with PWNe of other supersonically moving pulsars.

astro-ph.HE↗