Agnieszka Slowikowska

Optical Polarimetry of the Inner Crab Nebula and Pulsar

Time-resolved polarisation measurements of pulsars oer an unique insight into the geometry of their emission regions. Such measurements provide observational constraints on the dierent models proposed for the pulsar emission mechanisms. Optical polarisation data of the Crab Nebula was obtained from the HST archive. The dataset consists of a series of observations of the nebula taken with the HST/ACS. We produced polarisation vector maps of the inner nebula and measured, for the rst time, the degree of linear polarisation (P.D.) and the position angle (P.A.) of the pulsar’s integrated pulse beam, and of its nearby synchrotron knot. This yielded P:D: = 5:2 0:3% and P:A: = 105:1 1:6 for the pulsar, and P:D: = 59:0 1:9% and P:A: = 124:7 1:0 for the synchrotron knot. This is the rst high-spatial resolution multi-epoch study of the polarisation of the inner nebula and pulsar. None of the main features in the nebula show evidence of signicant polarisation evolution in the period covered by these observations. The results for the pulsar are consistent with those obtained by S lowikowska et al. (2009) using the high-time resolution photo-polarimeter OPTIMA, once the DC component has been subtracted. Our results clearly prove that the knot is the main source of the DC component.

A Multiwavelength Study of the Pulsar PSR B1929+10 and Its X-Ray Trail

We report on the emission properties of PSR B1929+10 and its putative trail from a multiwavelength study performed using optical, X-ray, and radio data. XMM-Newton observations confirm the existence of the diffuse emission with a trail morphology lying in a direction opposite to the transverse motion of the pulsar. The trail spectrum is nonthermal and produced by electron-synchrotron emission in the shock between the pulsar wind and the surrounding medium. Radio data from the Effelsberg 11 cm radio continuum survey show an elongated feature that roughly coincides with the X-ray trail. Three not fully resolved radio sources seen in the NVSS survey data at 1.4 GHz match with part of the elongated radio feature seen at 11 cm. The emission properties observed from PSR B1929+10 are in excellent agreement with a nonthermal, and thus magnetospheric-radiation-dominated, emission scenario. The pulsars X-ray spectrum is best described by a single power-law model with a photon index of 2.72. A flux contribution from the thermal emission of heated polar caps of at most ~7% is inferred from a best-fitting composite Planckian and power-law spectral model. A pure thermal emission spectrum consisting of two Planckian spectra is regarded as unlikely. A broken power-law spectral model with Ebreak = 0.83 keV and the photon indexes α1 = 1.12 and α2 = 2.48 can describe the optical and X-ray data entirely in terms of a nonthermal magnetospheric origin. The X-ray pulse profile observed in the 0.2-10 keV band is found to be markedly different from the broad sinusoidal pulse profile seen in the low statistic Rontgensatellit (ROSAT) data. Fitting Gaussians to the X-ray light curve indicates the possible existence of three pulse components. A small narrow pulse, characterized by energies greater than 1 keV, is found to lead the radio main pulse by ~20°. The fraction of pulsed photons in the 0.2-10 keV band is 32% ± 4%. For the subbands 0.2-1.0 and 1.0-2.1 keV the pulsed fraction is 24% ± 5% and 44% ± 6%, respectively, indicating a mild energy dependence at a ~2 σ level. Simulations in the framework of an outer gap emission model are able to reproduce the observed X-ray pulse profile and its phase shift relative to the radio pulse.

The Pulsar Shadow as the Origin of Double Notches in Radio Pulse Profiles

We present a model of the eclipsing of a rotating, spatially extended source of directional emission by a central absorber and apply it to the pulsar magnetosphere. The model assumes the radially extended inward radio emission along the local direction of the magnetic field, and the pulsar as the absorber. The geometry of the magnetic field lines of the rotating dipole is favorable for double-eclipse events, which we identify with the double notches observed in pulse profiles of nearby pulsars. For pulsars with large dipole inclinations 70° α 110°, the double notches are predicted to occur within a narrow phase range of 20°-30° before the main radio peak. Application of the model to PSR B0950+08 establishes it as a nearly orthogonal rotator (α 75°, β -10°) with many pulse components naturally interpreted in terms of the inward radio emission from a large range of altitudes. The inward components include the intermittently strong, leading component of the main pulse, which would traditionally have been interpreted as a conal emission in the outward direction. The model also identifies the magnetic field lines along which the radially extended inward radio emission occurs in B0950+08. These have a narrow range of the footprint parameter s close to ~1.1 (closed field line region, near the last open field lines). We describe directional characteristics of inward emission from the radially extended region and compare them with characteristics of extended outward emission. Our work shows that pulse profiles of at least some pulsars may be a superposition of both inward and outward emission.

The HU Aqr planetary system hypothesis revisited

We study the mid-egress eclipse timing data gathered for the cataclysmic binary HU Aquarii during the years 1993-2014. The (O-C) residuals were previously attributed to a single ~7 Jupiter mass companion in ~5 au orbit or to a stable 2-planet system with an unconstrained outermost orbit. We present 22 new observations gathered between June, 2011 and July, 2014 with four instruments around the world. They reveal a systematic deviation of ~60 - 120 seconds from the older ephemeris. We re-analyse the whole set of the timing data available. Our results provide an erratum to the previous HU Aqr planetary models, indicating that the hypothesis for a third and fourth body in this system is uncertain. The dynamical stability criterion and a particular geometry of orbits rule out coplanar 2-planet configurations. A putative HU Aqr planetary system may be more complex, e.g., highly non-coplanar. Indeed, we found examples of 3-planet configurations with the middle planet in a retrograde orbit, which are stable for at least 1Gyr, and consistent with the observations. The (O-C) may be also driven by oscillations of the gravitational quadrupole moment of the secondary, as predicted by the Lanza et al. modification of the Applegate mechanism. Further systematic, long-term monitoring of HU Aqr is required to interpret the (O-C) residuals.

The near-infrared detection of PSR B0540–69 and its nebula

Context. The ∼1700 year old PSR B0540−69 in the Large Magellanic Clouds (LMC) is considered the twin of the Crab pulsar because of its similar spin parameters, magnetic field, and energetics. PSR B0540−69 (V ∼ 22.5) is also one of the very few pulsars for which both optical pulsations and polarised emission have been measured. Its optical spectrum is fit by a power-law, ascribed to synchrotron radiation, like for the young Crab and Vela pulsars. At variance with them, however, a double break is required to join the X-ray and optical power-law spectra, with the first one possibly occurring in the near ultraviolet (nUV). Aims. Near-infrared (nIR) observations, never performed for PSR B0540−69, are crucial to determine whether the optical power-law spectrum extends to longer wavelengths or a new break occurs, like it happens for both the Crab and Vela pulsars in the mid-infrared (mIR), hinting at an even more complex particle energy and density distribution in the pulsar magnetosphere. Methods. We observed PSR B0540−69 in the J, H ,a ndKS bands with the Very Large Telescope (VLT) to detect it, for the first time, in the nIR and characterise its optical-to-nIR spectrum. To disentangle the pulsar emission from that of its pulsar wind nebula (PWN), we obtained high-spatial resolution adaptive optics images with the NAOS-CONICA instrument (NACO). Results. We could clearly identify PSR B0540−69 in our J, H ,a ndKS-band images and measure its flux (J = 20.14, H = 19.33, KS = 18.55, with an overall error of ±0.1 mag in each band). The joint fit to the available optical and nIR photometry with a powerlaw spectrum Fν ∝ ν −α gives a spectral index α = 0.70 ± 0.04, slightly more precise than measured in the optical only. This clearly implies that there is no spectral break between the optical and the nIR. We also detected, for the first time, the PSR B0540−69 PWN in the nIR. The comparison between our NACO images and Hubble Space Telescope (HST) optical ones does not reveal any apparent difference in the PWN morphology as a function of wavelength. The PWN optical-to-nIR spectrum is also fit by a single power-law, with spectral index α = 0.56 ± 0.03, slightly flatter than the pulsar’s. Conclusions. Using NACO at the VLT, we obtained the first detection of PSR B0540−69 and its PWN in the nIR. Due to the small angular scale of the PWN (∼4 �� ) only the spatial resolution of the James Webb Space Telescope (JWST) will make it possible to extend the study of the pulsar and PWN spectrum towards the mid-IR.

High-Time-Resolution Measurements of the Polarization of the Crab Pulsar at 1.38 GHz

Using the Westerbork Synthesis Radio Telescope, we obtained high-time-resolution measurements of the full polarization of the Crab pulsar. At a resolution of 1/8192 of the 34 ms pulse period (i.e., 4.1 μs), the 1.38 GHz linear-polarization measurements are in general agreement with previous lower-time-resolution 1.4 GHz measurements of linear polarization in the main pulse (MP), in the interpulse (IP), and in the low-frequency component (LFC). We find the MP and IP to be linearly polarized at about 24% and 21% with no discernible difference in polarization position angle. However, contrary to theoretical expectations and measurements in the visible, we find no evidence for significant variation (sweep) in the polarization position angle over the MP, the IP, or the LFC. We discuss the implications, which appear to be in contradiction to theoretical expectations. We also detect weak circular polarization in the MP and IP, and strong (≈20%) circular polarization in the LFC, which also exhibits very strong (≈98%) linear polarization at a position angle of 40° from that of the MP or IP. The properties are consistent with the LFC, which is a low-altitude component, and the MP and IP, which are high-altitude caustic components. Current models for the MP and IP emission do not readily account for the absence of pronounced polarization changes across the pulse. We measure IP and LFC pulse phases relative to the MP consistent with recent measurements, which have shown that the phases of these pulse components are evolving with time.

VLT polarimetry observations of the middle-aged pulsar PSR B0656+14

Optical polarisation measurements are key tests for different models of the pulsar magnetosphere. Furthermore, comparing the relative orientation of the phase-averaged linear polarisation direction and the pulsar proper motion vector may unveil a peculiar alignment, clearly seen in the Crab pulsar. Our goal is to obtain the first measurement of the phase-averaged optical linear polarisation of the fifth brightest optical pulsar, PSR\, B0656+14, which has also a precisely measured proper motion, and verify a possible alignment between the polarisation direction and the proper motion vector. We carried out observations with the Very Large Telescope (VLT) to measure the phase-averaged optical polarisation degree (P.D.) and position angle (P.A.) of PSR B0656+14. We measured a P.D. of

Very fast photometric and X‐ray observations of the intermediate polar V2069 Cygni (RX J2123.7+4217)

11.9\%\pm5.5\%

Analysis of single pulse radio flux measurements of PSR B1133+16 at 4.85 and 8.35 GHz

and a P.A. of

Optical polarization of the Crab pulsar: precision measurements and comparison to the radio emission

125.8\degr\pm13.2\degr