The discovery of the white dwarf binary system AR Scorpii (AR Sco) with its fascinating non-thermal dominated multi-frequency emission has sparked renewed interest in potential high energy gamma-ray emission from white dwarf pulsars. The Spectral Energy Distribution (SED) below and above optical shows evidence of non-thermal synchrotron emission, with pulsed emission in optical and X-ray bands at the white dwarf spin period ($P_{*} = 117 \, \mbox{s}$) as well as a beat period ($P_{\rm b} = 118.1 \, \mbox{s}$) with the binary period. From an energy perspective, the highly magnetic rotating white dwarf can accelerate particles to TeV energies. In this study, a search for high energy gamma-ray emission was conducted between 100 MeV - 500 GeV by analysing the newly available Fermi-LAT Pass 8 data with the new Fermi 1.0.1 Science Tools. Binned likelihood analysis was done using power law, broken power law and log parabola models. From the selected Region of Interest (ROI) centred on AR Sco's position, we calculated a significance of $\sqrt{TS}\leq$ 3.87$σ$ for the integrated gamma-ray activity between 100 MeV - 500 GeV at a photon flux level of 0.486 $\pm$ 0.261 x 10$^{-8}$ photons cm$^{-2}$ s$^{-1}$ using the broken power law model. This resulted in a 3$σ$ upper-limit detection from the position of AR Sco. The location of AR Sco inside the Rho Ophiuchi (Rho Oph) molecular cloud complex combined with the poor spatial resolution of Fermi-LAT, complicates any positive identification of low-level gamma-ray activity at the location that coincides with the position of AR Sco.
We present high-speed optical photometric observations, spanning ~2 years, of the recently-discovered white dwarf pulsar AR Scorpii. The amplitudes of the orbital, spin and beat modulations appear to be remarkably stable and repeatable over the time span of our observations. It has been suggested that the polarized and non-polarized emission from AR Scorpii is powered by the spin-down of the white dwarf. However, we find that our new data is inconsistent with the published spin-down ephemeris. Whilst our data is consistent with a constant spin period further observations over an extended time-…
We present detailed optical photo-polarimetric observations of the recently-discovered white dwarf pulsar AR Scorpii. Our extensive dataset reveals that the polarized emission is remarkably stable and repeatable with spin, beat and orbital modulations. This has enabled us to construct a simple geometrical model which assumes that all of the optically polarized emission emanates from two diametrically opposed synchrotron emission regions on the white dwarf magnetosphere. We suggest that the observed polarimetric modulations occur as a result of an enhanced injection of relativistic electrons in…
The binary system AR Scorpii hosts an M-type main sequence cool star orbiting around a magnetic white dwarf in the Milky Way Galaxy. The broadband non-thermal emission over radio, optical and X-ray wavebands observed from AR Scorpii indicates strong modulations on the spin frequency of the white dwarf as well as the spin-orbit beat frequency of the system. Therefore, AR Scorpii is also referred to as a white dwarf pulsar wherein a fast spinning white dwarf star plays very crucial role in the broadband non-thermal emission. Several interpretations for the observed features of AR Scorpii appear …
AR Scorpii (AR Sco), the only-known radio-pulsing white dwarf binary, shows unusual pulsating emission at the radio, infrared, optical and ultraviolet bands. To determine its astrometric parameters at the radio band independently, we conducted multi-epoch Very Long Baseline Interferometry (VLBI) phase-referencing observations with the European VLBI Network (EVN) at 5 GHz and the Chinese VLBI Network (CVN) plus the Warkworth 30-metre telescope (New Zealand) at 8.6 GHz. By using the differential VLBI astrometry, we provide high-precision astrometric measurements on the parallax ($π=8.52_{-0.07}^…
We analyze rapid-cadence, multiwavelength photometry of AR Scorpii from three observatories, covering five observing seasons. We measure the arrival times of the system's beat pulses and use them to compute an updated ephemeris. The white dwarf spin-down rate is estimated with an uncertainty of only 4%. These results confirm, beyond any doubt, that the white dwarf's spin period is increasing at the rate consistent with by that of Stiller et al. (2018). We study the evolution of the beat pulse's color index across the orbit. The color of the primary pulse maxima varies significantly across the …
In this work, we have analyzed the $γ$-ray data in the energy range 100 MeV to 500 GeV from the \emph{Fermi}-Large Area Telescope (LAT) observations for the period August 4, 2008 to March 31, 2019. The $γ$-ray emission from AR Scorpii over the last decade is not statistically significant and therefore 2$σ$ upper limit on the integral flux above 100 MeV has been estimated. We reproduce the non-thermal broadband spectral energy distribution of AR Scorpii using an emission model having two synchrotron components due to the relativistic electrons in very high magnetic fields. The first component (…
Marsh et al. detected radio and optical pulsations from the binary system AR Scorpii (AR Sco). This system, with an orbital period of 3.56 h, is composed of a cool, low-mass star and a white dwarf with a spin period of 1.95 min. Optical observations by Buckley et al. showed that the polarimetric emission from the white dwarf is strongly linearly polarised ( up to $\sim40\%$) with periodically changing intensities. This periodic non-thermal emission is thought to be powered by the highly magnetised ($ 5 \times 10^{8} $ G) white dwarf that is spinning down. The morphology of the polarisation sig…
The LOw-Frequency ARray (LOFAR) has recently conducted a survey (LOFAR Tied-Array All-sky Survey; LOTAAS) for pulsars in the Northern hemisphere that resulted in discoveries of 73 new pulsars. For the purpose of studying the properties of these pulsars, we search for their $γ$-ray counterparts using the all-sky survey data obtained with the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope (Fermi).We analyze the LAT data for 70 LOTAAS pulsars (excluding two millisecond pulsars and one with the longest known spin period of 23.5s). We find one candidate counterpart to PSRJ10…
We describe an image-based method that uses two radio criteria, compactness and spectral index, to identify promising pulsar candidates among Fermi Large Area Telescope (LAT) unassociated sources. These criteria are applied to those radio sources from the Giant Metrewave Radio Telescope all-sky survey at 150 MHz (TGSS ADR1) found within the error ellipses of unassociated sources from the 3FGL catalog and a preliminary source list based on 7 years of LAT data. After follow-up interferometric observations to identify extended or variable sources, a list of 16 compact, steep-spectrum candidates i…
Pulsar Discoveries from the TRAPUM UHF Survey of Fermi-LAT Sources
The University of Manchester（曼彻斯特大学）；National Astronomical Research Institute of Thailand（泰国国家天文研究所）；Max Planck Institute for Gravitational Physics (Albert Einstein Institute)（马克斯·普朗克引力物理研究所（爱因斯坦研究所））；Leibniz Universität Hannover（汉诺威莱布尼茨大学）；INAF – Osservatorio Astronomico di Cagliari（意大利国家天体物理研究所卡利亚里天文台）
Taking advantage of 10 years of Fermi-LAT data, we perform a new and deep analysis of the pulsar wind nebula (PWN) HESS J1825-137. We present the results of the spectral analysis and of the first energy-resolved morphological study of the PWN HESS J1825-137 from 1 GeV to 1 TeV. This PWN is an archetypal system making it a perfect laboratory for studying particle transport mechanisms. Combining this analysis with recent H.E.S.S. results enables a more complete picture of the nebula to emerge.
Search for gamma-ray variability around Fermi-LAT pulsar glitches
Friedrich-Alexander Universität Erlangen-Nürnberg（弗里德里希·亚历山大埃尔朗根-纽伦堡大学）；Istituto Nazionale di Fisica Nucleare, Sezione di Pisa（意大利国家核物理研究所比萨分部）；Università di Pisa, Dipartimento di Fisica E. Fermi（比萨大学E.费米物理系）；Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz（加州大学圣克鲁兹分校粒子物理研究所、物理系和天文与天体物理系）
We report on the analysis of 13 gamma-ray pulsars discovered in the Einstein@Home blind search survey using Fermi Large Area Telescope (LAT) Pass 8 data. The 13 new gamma-ray pulsars were discovered by searching 118 unassociated LAT sources from the third LAT source catalog (3FGL), selected using the Gaussian Mixture Model (GMM) machine learning algorithm on the basis of their gamma-ray emission properties being suggestive of pulsar magnetospheric emission. The new gamma-ray pulsars have pulse profiles and spectral properties similar to those of previously-detected young gamma-ray pulsars. Fol…
