LS 5039 is a high-mass gamma-ray binary hosting a compact object of unknown type. NuSTAR observed LS 5039 during its entire 3.9 day binary period. We performed a periodic signal search up to 1000 Hz which did not produce credible period candidates. W
e do see the 9.05 s period candidate, originally reported by Yoneda et al. 2020 using the same data, in the Fourier power spectrum, but we find that the statistical significance of this feature is too low to claim it as a real detection. We also did not find significant bursts or quasi-periodic variability. The modulation with the orbital period is clearly seen and remains unchanged over a decade long timescale when compared to the earlier Suzaku light curve. The joint analysis of the NuSTAR and Suzaku XIS data shows that the 0.7-70 keV spectrum can be satisfactory described by a single absorbed power-law model with no evidence of cutoff at higher energies. The slope of the spectrum anti-correlates with the flux during the binary orbit. Therefore, if LS 5039 hosts a young neutron star, its X-ray pulsations appear to be outshined by the intrabinary shock emission. The lack of spectral lines and/or an exponential cutoff at higher energies suggests that the putative neutron star is not actively accreting. Although a black hole scenario still remains a possibility, the lack of variability or Fe K$alpha$ lines, which typically accompany accretion, makes it less likely.
We have obtained a deep 670 ks CXO ACIS image of the remarkable pulsar wind nebula (PWN) of PSR J1709-4429, in 4 epochs during 2018-2019. Comparison with an archival 2004 data set provides a pulsar proper motion mu = 13 pm 3 mas/yr at a PA of 86 pm 9
degree (1 sigma combined statistical and systematic uncertainties), precluding birth near the center of SNR G343.1-2.3. At the pulsars characteristic age of 17 kyr, the association can be preserved through a combination of progenitor wind, birth kick and PWN outflow. Associated TeV emission may, however, indicate explosion in an earlier supernova. Inter-epoch comparison of the X-ray images shows that the PWN is dynamic, but we are unable to conclusively measure flow speeds from blob motion. The pulsar has generated a radio/X-ray wind bubble, and we argue that the PWNs long narrow jets are swept back by shocked pulsar wind venting from this cavity. These jets may trace the polar magnetic field lines of the PWN flow, an interesting challenge for numerical modeling.
The soft gamma-ray repeater (SGR) 0526-66 is the first-identified magnetar, and is projected within the supernova remnant N49 in the Large Magellanic Cloud. Based on our ~50 ks NuSTAR observation, we detect the quiescent-state 0526-66 for the first t
ime in the 10-40 keV band. Based on the joint analysis of our NuSTAR and the archival Chandra ACIS data, we firmly establish the presence of the nonthermal component in the X-ray spectrum of 0526-66 in addition to the thermal emission. In the best-fit blackbody (BB) plus power law (PL) model, the slope of the PL component (photon index Gamma = 2.1) is steeper than those (Gamma > ~1.5) for other magnetars. The soft part of the X-ray spectrum can be described with a BB component with the temperature of kT = 0.43 keV. The best-fit radius (R = 6.5 km) of the X-ray-emitting area is smaller than the canonical size of a neutron star. If we assume an underlying cool BB component with the canonical radius of R = 10 km for the neutron star in addition to the hot BB component (2BB + PL model), a lower BB temperature of kT = 0.24 keV is obtained for the passively cooling neutron starssurface, while the hot spot emission with kT = 0.46 keV dominates the thermal spectrum (~85% of the thermal luminosity in the 0.5-5 keV band). The nonthermal component (Gamma ~ 1.8) is still required.
We report on the energy-resolved timing and phase-resolved spectral analysis of X-ray emission from PSR J0659+1414 observed with XMM-Newton and NuSTAR. We find that the new data rule out the previously suggested model of the phase-dependent spectrum
as a three-component (2 blackbodies + power-law) continuum, which shows large residuals between $0.3-0.7$ keV. Fitting neutron star atmosphere models or several blackbodies to the spectrum does not provide a better description of the spectrum, and requires spectral model components with unrealistically large emission region sizes. The fits improve significantly if we add a phase-dependent absorption feature with central energy $0.5-0.6$ keV and equivalent width up to $approx 50$ eV. We detected the feature for about half of the pulse cycle. Energy-resolved pulse profiles support the description of the spectrum with a three-component continuum and an absorption component. The absorption feature could be interpreted as an electron cyclotron line originating in the pulsar magnetosphere and broadened by the non-uniformity of the magnetic field along the line of sight. The significant phase-variability in the thermal emission from the entire stellar surface may indicate multi-polar magnetic fields and a non-uniform temperature distribution. The strongly pulsed non-thermal spectral component detected with NuSTAR in the $3-20$ keV range is well fit by a power-law model with a photon index $Gamma=1.5pm0.2$.
PSR J1809-1917 is a young ($tau=51$ kyr) energetic ($dot{E}=1.8times10^{36}$ 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 $Gamma_{rm jet}=1.2pm0.1$. The more extended emission and CN share the same symmetry axis, which is also aligned with the direction toward the TeV $gamma$-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, $Gamma_{rm CN}approxGamma_{rm EN}=1.55pm0.09$; no spectral changes across the ENs 2 pc extent are seen. The total PWN 0.5-8 keV luminosity is $L_{rm PWN}approx 9times10^{32}$ erg s$^{-1}$, about half of which is due to the EN.
We review observations of several classes of neutron-star-powered outflows: pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe interacting directly with interstellar medium (ISM), and magnetar-powered outflows. We describe radio,
X-ray, and gamma-ray observations of PWNe, focusing first on integrated spectral-energy distributions (SEDs) and global spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering array of morphologies, with jets, trails, and other structures. Several of the 23 so far identified magnetars show evidence for continuous or sporadic emission of material, sometimes associated with giant flares, and a few possible magnetar-wind nebulae have been recently identified.
We present a joint analysis of optical emission-line and X-ray observations of the archetypical Galactic mixed-morphology supernova remnant (MMSNR) W28 (G6.4-0.1). MMSNRs comprise a class of sources whose shell-like radio morphology contrasts with a
filled center in X-rays; the origin of these contrasting morphologies remains uncertain. Our CTIO images reveal enhanced [S II] emission relative to H-alpha along the northern and eastern rims of W28. Hydroxyl (OH) masers are detected along these same rims, supporting prior studies suggesting that W28 is interacting with molecular clouds at these locations, as observed for several other MMSNRs. Our ROSAT HRI mosaic of W28 provides almost complete coverage of the SNR. The X-ray and radio emission is generally anti-correlated, except for the luminous northeastern rim, which is prominent in both bands. Our Chandra observation sampled the X-ray-luminous central diffuse emission. Spectra extracted from the bright central peak and from nearby annular regions are best fit with two over-ionized recombining plasma models. We also find that while the X-ray emission from the central peak is dominated by swept-up material, that from the surrounding regions shows evidence for oxygen-rich ejecta, suggesting that W28 was produced by a massive progenitor. We also analyze the X-ray properties of two X-ray sources (CXOU J175857.55-233400.3 and 3XMM J180058.5-232735) projected into the interior of W28 and conclude that neither is a neutron star associated with the SNR. The former is likely to be a foreground cataclysmic variable or a quiescent low-mass X-ray-binary while the latter is likely to be a coronally-active main sequence star.
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 prope
rties 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 pulsars 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.
Pulsars traveling at supersonic speeds are often accompanied by cometary bow shocks seen in Halpha. We report on the first detection of a pulsar bow shock in the far-ultraviolet (FUV). We detected it in FUV images of the nearest millisecond pulsar J0
437-4715 obtained with the Hubble Space Telescope. The images reveal a bow-like structure positionally coincident with part of the previously detected Halpha bow shock, with an apex at 10 ahead of the moving pulsar. Its FUV luminosity, L(1250-2000 A) ~ 5x10^28 erg/s, exceeds the Halpha luminosity from the same area by a factor of 10. The FUV emission could be produced by the shocked ISM matter or, less likely, by relativistic pulsar wind electrons confined by strong magnetic field fluctuations in the bow shock. In addition, in the FUV images we found a puzzling extended (~3 in size) structure overlapping with the limb of the bow shock. If related to the bow shock, it could be produced by an inhomogeneity in the ambient medium or an instability in the bow shock. We also report on a previously undetected X-ray emission extending for about 5 ahead of the pulsar, possibly a pulsar wind nebula created by shocked pulsar wind, with a luminosity L(0.5-8 keV) ~ 3x10^28 erg/s.
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 a
ddition 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.
