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An unidentified γ-ray source 4FGL J1838.2+3223 has been proposed as a pulsar candidate. We present optical time-series multiband photometry of its likely optical companion obtained with the 2.1-m telescope of Observatorio Astronómico Nacional San Pedro Mártir, Mexico. The observations and the data from the Zwicky Transient Facility revealed the source brightness variability with a period of ≈4.02 h likely associated with the orbital motion of the binary system. The folded light curves have a single sine-like peak per period with an amplitude of about three magnitudes accompanied by fast sporadic flares up to one magnitude level. We reproduce them modelling the companion heating by the pulsar. As a result, the companion side facing the pulsar is strongly heated up to 11300 ± 400 K, while the temperature of its back side is only 2300 ± 700 K. It has a mass of 0.10 ± 0.05 M⊙ and underfills its Roche lobe with a filling factor of |$0.60^{+0.10}_{-0.06}$|⁠. This implies that 4FGL J1838.2+3223 likely belongs to the 'spider' pulsar family. The estimated distance of ≈3.1 kpc is compatible with Gaia results. We detect a flare from the source in X-rays and ultraviolet using Swift archival data and another one in X-rays in the eROSITA all-sky survey. Both flares have X-ray luminosity of ∼1034 erg s−1 which is two orders of magnitude higher than the upper limit in quiescence obtained from eROSITA assuming spectral shape typical for spider pulsars. If the spider interpretation is correct, these flares are among the strongest observed from non-accreting spider pulsars. [ABSTRACT FROM AUTHOR]

PSR J1641+8049 is a 2 ms black widow pulsar with the 2.2 h orbital period detected in the radio and γ-rays. We performed new phase-resolved multiband photometry of PSR J1641+8049 using the OSIRIS instrument at the Gran Telescopio Canarias. The obtained data were analysed together with the new radio-timing observations from the Canadian Hydrogen Intensity Mapping Experiment (CHIME), the X-ray data from the Spectrum-RG/ eROSITA all-sky survey, and all available optical photometric observations. An updated timing solution based on CHIME data is presented, which accounts for secular and periodic modulations in pulse dispersion. The system parameters obtained through the light-curve analysis, including the distance to the source 4.6–4.8 kpc and the orbital inclination 56–59 deg, are found to be consistent with previous studies. However, the optical flux of the source at the maximum brightness phase faded by a factor of ∼2 as compared to previous observations. Nevertheless, the face of the J1641+8049 companion remains one of the most heated (8000–9500 K) by a pulsar among the known black widow pulsars. We also report a new estimation on the pulsar proper motion of ≈2 mas yr−1, which yields a spin-down luminosity of ≈4.87 × 1034 erg s−1 and a corresponding heating efficiency of the companion by the pulsar of 0.3–0.7. The pulsar was not detected in X-rays implying its X-ray-luminosity was |$\lesssim$| 3 × 1031 erg s−1 at the date of observations. [ABSTRACT FROM AUTHOR]

We present the results of optical spectroscopy of stellar companions to three binary millisecond pulsars, PSRs J0621+2514, J2317+1439, and J2302+4442, obtained with the Gran Telescopio Canarias. The spectrum of the J0621+2514 companion shows a blue continuum and prominent Balmer absorption lines. The latter are also resolved in the spectrum of the J2317+1439 companion, showing that both are DA-type white dwarfs. No spectral features are detected for the J2302+4442 companion; however, its broad-band magnitudes and the spectral shape of the continuum emission imply that this is also a DA-type white dwarf. Based on the spectral analyses, we conclude that the companions of J0621+2514 and J2317+1439 are relatively hot, with effective temperatures T eff = 8600 ± 200 and 9600 ± 2000 K, respectively, while the J2302+4442 companion is significantly cooler, T eff<6000 K. We also estimated the distance to J0621+2514 of 1.1 ± 0.3 kpc and argue that its companion and the companion of J2317+1439 are He-core white dwarfs providing constraints on their cooling ages of |$\lesssim$| 2 Gyr. [ABSTRACT FROM AUTHOR]

The Fermi catalogue contains about 2000 unassociated γ-ray sources. Some of them were recently identified as pulsars, including so-called redbacks and black widows, which are millisecond pulsars in tight binary systems with non- and partially-degenerate low-mass stellar companions irradiated by the pulsar wind. We study a likely optical and X-ray counterpart of the Fermi source 4FGL J2054.2+6904 proposed earlier as a pulsar candidate. We use archival optical data as well as Swift /XRT and SRG / eROSITA X-ray data to clarify its nature. Using Zwicky Transient Facility data in g and r bands spanning over 4.7 yr, we find a period of ≈7.5 h. The folded light curve has a smooth sinusoidal shape with the peak-to-peak amplitude of ≈0.4 mag. The spectral fit to the optical spectral energy distribution of the counterpart candidate gives the star radius of 0.5 ± 0.1 R⊙ and temperature of 5500 ± 300 K implying a G2–G9-type star. Its X-ray spectrum is well fitted by an absorbed power law with the photon index of 1.0 ± 0.3 and unabsorbed flux of ≈2 × 10−13 erg s−1 cm−2. All the properties of 4FGL J2054.2+6904 and its presumed counterpart suggest that it is a member of the redback family. [ABSTRACT FROM AUTHOR]

We report the results of XMM–Newton observations of the Galactic mixed-morphology supernova remnant G350.0−2.0. Diffuse thermal X-ray emission fills the north-western part of the remnant surrounded by radio shell-like structures. We did not detect any X-ray counterpart of the latter structures, but found several bright blobs within the diffuse emission. The X-ray spectrum of the most part of the remnant can be described by a collisionally ionized plasma model vapec with solar abundances and a temperature of ≈0.8 keV. The solar abundances of plasma indicate that the X-ray emission comes from the shocked interstellar material. The overabundance of Fe was found in some of the bright blobs. We also analysed the brightest point-like X-ray source 1RXS J172653.4−382157 projected on the extended emission. Its spectrum is well described by the two-temperature optically thin thermal plasma model mekal typical for cataclysmic variable stars. The cataclysmic variable source nature is supported by the presence of a faint (g ≈ 21) optical source with non-stellar spectral energy distribution at the X-ray position of 1RXS J172653.4−382157. It was detected with the XMM–Newton optical/UV monitor in the U filter and was also found in the archival Hα and optical/near-infrared broad-band sky survey images. On the other hand, the X-ray spectrum is also described by the power law plus thermal component model typical for a rotation powered pulsar. Therefore, the pulsar interpretation of the source cannot be excluded. For this source, we derived the upper limit for the pulsed fraction of 27 per cent. [ABSTRACT FROM AUTHOR]

PSR J1357-6429 is a young radio pulsar that has been detected in the X-ray and γ -ray bands. We present high spatial resolution near-infrared imaging of the pulsar field in the J, H and Ks bands obtained using the VLT/NaCo with the Adaptive Optic system. We found a faint source at the most precise pulsar radio position, which we propose as the pulsar near-infrared counterpart candidate. It is confidently detected in the J and Ks bands, with J=23.51±0.24 and Ks =21.82±0.25. There is a hint of the source in theHband, with an upper limitH>22.8. The dereddened source fluxes are compatible with the extrapolation of the pulsar X-ray spectrum towards the near-infrared. If the candidate is the true counterpart, this property means that PSR J1357-6429 would be similar to the nearby middle-age pulsar PSR B0656+14. In this case, both pulsars demonstrate an unusually high near-infrared efficiency relative to the X-ray efficiency as compared with other pulsars detected in these two ranges. [ABSTRACT FROM AUTHOR]

We present spectral and timing analyses of the X-ray emission from the pulsar wind nebula DA 495 and its central object, J1952.2+2925, suggested to be the pulsar, using archival Chandra and XMM-Newton data. J1952.2+2925 has a pure thermal spectrum which is equally well fitted either by the blackbody model with a temperature of 215 eV and an emitting area radius of 0.6 km or by magnetized neutron star atmosphere models with temperatures of 80-90 eV. In the latter case, the thermal emission can come from the entire neutron star surface which temperature is consistent with standard neutron star cooling scenarios. We place also an upper limit on the J1952.2+2925 non-thermal flux. The derived spectral parameters are generally compatible with published ones based only on the Chandra data, but they are much more accurate due to the inclusion of XMM-Newton data. No pulsations were found and we placed an upper limit for the J1952.2+2925 pulsed emission fraction of 40 per cent. Utilizing the interstellar absorption-distance relation, we estimated the distance to DA 495, which can be as large as 5 kpc if J1952.2+2925 emission is described by the atmosphere models. We compiled possible multiwavelength spectra of the nebula including radio data; they depend on the spectral model of the central object. Comparing the results with other pulsar plus wind nebula systems, we set reasonable constraints on the J1952.2+2925 spin-down luminosity and age. We suggest that the Fermi source 3FGL J1951.6+2926 is the likely -ray counterpart of J1952.2+2925. [ABSTRACT FROM AUTHOR]

PSR J1357-6429 is a young and energetic radio pulsar detected in X-rays and Y -rays. It powers a compact pulsar wind nebula with a jet visible in X-rays and a large-scale plerion detected in X-ray and TeV ranges. Previous multiwavelength studies suggested that the pulsar has a significant proper motion of about 180 mas yr-1, implying an extremely high transverse velocity of about 2000 km s-1. In order to verify this, we performed radio-interferometric observations of PSR J1357-6429 with the Australia Telescope Compact Array (ATCA) in the 2.1-GHz band. We detected the pulsar with a mean flux density of 212 ± 5 | J y and obtained the most accurate pulsar position: RA = 13h57m028.525(14),Dec. = -64°29'29/./89(15). Using both new and archival ATCA data, we did not find any proper motion and estimated its 90 per cent upper limit as μ < 106 mas yr-1. The pulsar shows a highly polarized single pulse, as was observed earlier at 1.4 GHz. Spectral analysis revealed a shallow spectral index av = 0.5 ± 0.1. Based on our new radio position of the pulsar, we discount the claim of an optical counterpart candidate reported previously. [ABSTRACT FROM AUTHOR]