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We carry out a dedicated study of 3XMM J181923.7–170616 with an approximate pulsation period of 400 s using the XMM-Newton and Swift observations spanning across nine years. We have refined the period of the source to 407.904(7) s (at epoch MJD 57142) and constrained the 1σ upper limit on the period derivative . The source radiates hard, persistent X-ray emission during the observation epochs, which is best described by an absorbed power-law model (Γ ∼ 0.2–0.8) plus faint Fe lines at 6.4 and 6.7 keV. The X-ray flux revealed a variation within a factor of 2, along with a spectral hardening as the flux increased. The pulse shape is sinusoid-like and the spectral properties of different phases do not present significant variation. The absorption () is similar to the total Galactic hydrogen column density along the direction, indicating that it is a distant source. A search for the counterpart in optical and near-infrared surveys reveals a low-mass K-type giant, while the existence of a Galactic OB supergiant is excluded. A symbiotic X-ray binary (SyXB) is the favored nature of 3XMM J181923.7–170616 and can essentially explain the low luminosity of , slow pulsation, hard X-ray spectrum, and possible K3 III companion. An alternative explanation of the source is a persistent Be X-ray binary (BeXB) with a companion star no earlier than B3-type. [ABSTRACT FROM AUTHOR]

The physical nature of thermal composite supernova remnants (SNRs) remains controversial. We have revisited the archival XMM-Newton and Chandra data of the thermal composite SNR Kesteven 41 (Kes 41 or G337.8–0.1) and performed a millimeter observation toward this source in the 12CO, 13CO, and C18O lines. The X-ray emission, mainly concentrated toward the southwestern part of the SNR, is characterized by distinct S and Ar He-like lines in the spectra. The X-ray spectra can be fitted with an absorbed nonequilibrium ionization collisional plasma model at a temperature of 1.3-2.6 keV and an ionization timescale of 0.1-1.2 × 1012 cm–3 s. The metal species S and Ar are overabundant, with 1.2-2.7 and 1.3-3.8 solar abundances, respectively, which strongly indicate the presence of a substantial ejecta component in the X-ray-emitting plasma of this SNR. Kes 41 is found to be associated with a giant molecular cloud (MC) at a systemic local standard of rest velocity of –50 km s–1 and confined in a cavity delineated by a northern molecular shell, a western concave MC that features a discernible shell, and an H I cloud seen toward the southeast of the SNR. The birth of the SNR in a preexisting molecular cavity implies a mass of ≳ 18 M☼ for the progenitor if it was not in a binary system. Thermal conduction and cloudlet evaporation seem to be feasible mechanisms to interpret the X-ray thermal composite morphology, and the scenario of gas reheating by the shock reflected from the cavity wall is quantitatively consistent with the observations. An updated list of thermal composite SNRs is also presented in this paper. [ABSTRACT FROM AUTHOR]