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We perform a molecular (CO and CN) line observation using the IRAM 30 m telescope toward two small regions near the western edge of supernova remnant (SNR) W50/SS 433. CO observation reveals spatial correspondence of two molecular clumps at the local-standard-of-rest (LSR) velocity around +53 , with multiwavelength local features of the W50/SS 433 system. One of the two clumps appears to be embedded in a void of diffuse radio and X-ray emission. Toward the two clumps, asymmetric broad-line profiles of the 12CO lines are obtained, which provide kinematic evidence of the association between the clumps and the jet-related gas. The 12CO J = 2–1/J = 1–0 line ratios (≳0.9) and the kinetic temperatures (∼30 K) of the clumps are distinctively higher than all those of the clumps at other LSR velocities along the same line of sight, which may be physical signatures of the association. We show that the clump coincident with the void can survive the thermal heating if it is surrounded by hot gas, with an evaporation timescale much larger than the age of SNR W50. We also show that the thermal equilibrium in the high-temperature clumps can be maintained by the heating of the penetrating environmental cosmic rays. CN (J = 3/1–1/2) line emission is detected in the two clumps, and the CN abundances derived are much higher than that in the interstellar molecular clouds (MCs) and that in the SNR-interacting MCs. [ABSTRACT FROM AUTHOR]

The mixed-morphology class of supernova remnants (MMSNRs) comprises a substantial fraction of observed remnants, but there is no consensus on their origin as yet. A clue to their nature is the presence of regions that show X-ray evidence of recombining plasmas. Recent calculations of remnant evolution in a cloudy interstellar medium that included thermal conduction but not nonequilibrium ionization (NEI) showed promise in explaining observed surface brightness distributions but could not determine whether recombining plasmas were present. In this paper, we present numerical hydrodynamic models of MMSNRs in 2D and 3D, including explicit calculation of NEI effects. Both the spatial ionization distribution and temperature–density diagrams show that recombination occurs inside the simulated MMSNR and that both adiabatic expansion and thermal conduction cause recombination, albeit in different regions. Features created by the adiabatic expansion stand out in the spatial and temperature–density diagrams, but thermal conduction also plays a role. Thus, thermal conduction and adiabatic expansion both contribute significantly to the cooling of high-temperature gas. Realistic observational data are simulated with both spatial and spectral input from various regions. We also discuss the possibility of analyzing the sources of recombination and dominant hydrodynamic processes in observations using temperature–density diagrams and spatial maps. [ABSTRACT FROM AUTHOR]

We mapped 12CO J = 1–0, 12CO J = 2–1, 13CO J = 1–0, and 13CO J = 2–1 lines toward supernova remnant (SNR) Cassiopeia A with the IRAM 30 m telescope. The molecular clouds (MCs) along the line of sight of Cas A do not show optically thin, shock-broadened 12CO lines ( toward Cas A), or high-temperature features from shock heating ( toward Cas A). Therefore, we suggest that there is no physical evidence to support that the SNR is impacting the molecular gas. All the detected MCs are likely in front of Cas A, as implied by the HCO+ absorption line detected in the same velocity ranges. These MCs contribute H2 column densities of , , and in the west, south, and center of the SNR, respectively. The 20 K warm gas at is distributed along a large-scale molecular ridge in the south of Cas A. Part of the gas is projected onto Cas A, providing a foreground H2 mass of , consistent with the mass of cold dust (15–20 K; 2–4 ) found in front of the SNR. We suggest that the 20 K warm gas is heated by background cosmic rays with an ionization rate of . The cosmic rays and X-ray emission from Cas A are excluded as the heating sources of the clouds. [ABSTRACT FROM AUTHOR]

We present ∼400 ks NuSTAR observations of the northeast (NE) and southwest (SW) nonthermal limbs of the Galactic SNR SN1006. We discovered three sources with X-ray emission detected at ≳50 keV. Two of them are identified as background active galactic nuclei. We extract the NuSTAR spectra from a few regions along the nonthermal limbs and jointly analyze them with the XMM-Newton spectra and the radio data. The broadband radio/X-ray spectra can be well described with a synchrotron emission model from a single population of CR electrons with a power-law energy distribution and an exponential cutoff. The power-law index of the electron particle distribution function (PDF) is ≈1.88–1.95 for both the NE and SW limbs, and we do not find significant evidence for a variation of this index at different energy (curvature). There are significant spatial variations of the synchrotron emission parameters. The highest energy electrons are accelerated in regions with the lowest expansion velocity, which is opposite to what has been found in Tycho’s supernova remnant. In addition to a gradual steepening of synchrotron emission from the center of the nonthermal limbs to larger azimuthal angles, we also find that both the emission spectrum and the PDF are significantly flatter in three regions in the SW limb where the shock encounters a higher density ambient medium. The NE limb also shows significantly higher cutoff energy in the PDF than the SW limb. By comparing with the roughly symmetric TeV emission and largely asymmetric GeV emission from the two nonthermal limbs, we conclude that the asymmetry in the ambient medium and magnetic fields may have largely modified the acceleration and emission of CR leptons. [ABSTRACT FROM AUTHOR]

The matter state inside neutron stars (NSs) is an exciting problem in astrophysics, nuclear physics, and particle physics. The equation of state (EOS) of NSs plays a crucial role in the present multimessenger astronomy, especially after the event of GW170817. We propose a new NS EOS, “QMF18,” from the quark level, which describes robust observational constraints from a free-space nucleon, nuclear matter saturation, heavy pulsar measurements, and the tidal deformability of the very recent GW170817 observation. For this purpose, we employ the quark mean-field model, which allows us to tune the density dependence of the symmetry energy and effectively study its correlations with the Love number and the tidal deformability. We provide tabulated data for the new EOS and compare it with other recent EOSs from various many-body frameworks. [ABSTRACT FROM AUTHOR]

We present a new millimeter CO-line observation toward supernova remnant (SNR) CTB 87, which was regarded purely as a pulsar wind nebula (PWN), and an optical investigation of a coincident surrounding superbubble. The CO observation shows that the SNR delineated by the radio emission is projectively covered by a molecular cloud (MC) complex at to . Both the symmetric axis of the radio emission and the trailing X-ray PWN appear projectively to be along a gap between two molecular gas patches at −58 to . Asymmetric broad profiles of 12CO lines peaked at are found at the eastern and southwestern edges of the radio emission. This represents a kinematic signature consistent with an SNR–MC interaction. We also find that a superbubble, ∼37′ in radius, appears to surround the SNR from H i 21 cm ( to ), WISE mid-IR, and optical extinction data. We build a multi-band photometric stellar sample of stars within the superbubble region and find 82 OB star candidates. The likely peak distance in the stars’ distribution seems consistent with the distance previously suggested for CTB 87. We suggest the arc-like radio emission is mainly a relic of the part of the blast wave that propagates into the MC complex and is now in a radiative stage while the other part of the blast wave has been expanding into the low-density region in the superbubble. This scenario naturally explains the lack of X-ray emission related to the ejecta and blast wave. The SNR–MC interaction also favors a hadronic contribution to the γ-ray emission from the CTB 87 region. [ABSTRACT FROM AUTHOR]

We report our independent GeV γ-ray study of the young shell-type supernova remnant (SNR) Kes 73, which harbors a central magnetar, and CO-line millimeter observations toward the SNR. Using 7.6 years of Fermi-LAT observation data, we detected an extended γ-ray source (“source A”) with centroid on the west of the SNR, with a significance of 21σ in 0.1–300 GeV and an error circle of 5.′4 in angular radius. The γ-ray spectrum cannot be reproduced by a pure leptonic emission or a pure emission from the magnetar, and thus a hadronic emission component is needed. The CO-line observations reveal a molecular cloud (MC) at VLSR ∼ 90 km s−1, which demonstrates morphological correspondence with the western boundary of the SNR brightened in multiwavelength. The 12CO (J = 2 − 1)/12CO (J = 1 − 0) ratio in the left (blue) wing 85–88 km s−1 is prominently elevated to ∼1.1 along the northwestern boundary, providing kinematic evidence of the SNR-MC interaction. This SNR-MC association yields a kinematic distance 9 kpc to Kes 73. The MC is shown to be capable of accounting for the hadronic γ-ray emission component. The γ-ray spectrum can be interpreted with a pure hadronic emission or a magnetar+hadronic hybrid emission. In the case of pure hadronic emission, the spectral index of the protons is 2.4, very similar to that of the radio-emitting electrons, essentially consistent with the diffusive shock acceleration theory. In the case of magnetar+hadronic hybrid emission, a magnetic field decay rate ≳1036 erg s−1 is needed to power the magnetar’s curvature radiation. [ABSTRACT FROM AUTHOR]

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]

Kes 79 (G33.6+0.1) is an aspherical thermal composite supernova remnant (SNR) observed across the electromagnetic spectrum and showing an unusual highly structured morphology, in addition to harboring a central compact object (CCO). Using the CO J = 1–0, J = 2–1, and J = 3–2 data, we provide the first direct evidence and new morphological evidence to support the physical interaction between the SNR and the molecular cloud in the local standard of rest velocity . We revisit the 380 ks XMM-Newton observations and perform a dedicated spatially resolved X-ray spectroscopic study with careful background subtraction. The overall X-ray-emitting gas is characterized by an under-ionized () cool ( keV) plasma with solar abundances, plus an under-ionized () hot ( keV) plasma with elevated Ne, Mg, Si, S, and Ar abundances. The X-ray filaments, spatially correlated with the 24 IR filaments, are suggested to be due to the SNR shock interaction with dense gas, while the halo forms from SNR breaking out into a tenuous medium. Kes 79 appears to have a double-hemisphere morphology viewed along the symmetric axis. Projection effect can explain the multiple-shell structures and the thermal composite morphology. The high-velocity, hot ( keV) ejecta patch with high metal abundances, together with the non-uniform metal distribution across the SNR, indicate an asymmetric SN explosion of Kes 79. We refine the Sedov age to 4.4–6.7 kyr and the mean shock velocity to 730 . Our multi-wavelength study suggests a progenitor mass of ∼15–20 solar masses for the core-collapse explosion that formed Kes 79 and its CCO, PSR J1852+0040. [ABSTRACT FROM AUTHOR]

Whether the progenitors of SNe Ia are single-degenerate or double-degenerate white dwarf (WD) systems is a highly debated topic. To address the origin of Tycho’s Type Ia supernova remnant (SNR), SN 1572, we have carried out a 12CO J = 2–1 mapping and a 3 mm line survey toward the remnant using the IRAM 30 m telescope. We show that Tycho is surrounded by a clumpy molecular bubble at a local standard of rest velocity of , which expands at a speed of and has a mass of (at the distance of 2.5 kpc). Enhanced 12CO J = 2–1 line emission relative to 12CO J = 1–0 emission and possible line broadenings (in velocity range −64 to −60 km s−1) are found at the northeastern boundary of the SNR, where the shell is deformed and decelerated. These features, combined with the morphological correspondence between the expanding molecular bubble and Tycho, suggest that the SNR is associated with the bubble at the velocity range −66 to −57 km s−1. The most plausible origin for the expanding bubble is the fast outflow (with velocity of hundreds km s−1) driven from the vicinity of a WD as it accreted matter from a nondegenerate companion star. The SNR has been expanding in the low-density wind-blown bubble, and the shock wave has just reached the molecular cavity wall. This is the first unambiguous detection of an expanding bubble driven by the progenitor of a Type Ia SNR, which constitutes evidence for a single-degenerate progenitor for this SN Ia. [ABSTRACT FROM AUTHOR]

We present the first dedicated X-ray study of the supernova remnant (SNR) G32.8−0.1 (Kes 78) with Suzaku. X-ray emission from the whole SNR shell has been detected for the first time. The X-ray morphology is well correlated with the emission from the radio shell, while anti-correlated with the molecular cloud found in the SNR field. The X-ray spectrum shows not only conventional low-temperature (kT ∼ 0.6 keV) thermal emission in a non-equilibrium ionization state, but also a very high-temperature (kT ∼ 3.4 keV) component with a very low ionization timescale (∼2.7 × 109 cm−3 s), or a hard nonthermal component with a photon index Γ ∼ 2.3. The average density of the low-temperature plasma is rather low, of the order of 10−3–10−2 cm−3, implying that this SNR is expanding into a low-density cavity. We discuss the X-ray emission of the SNR, also detected in TeV with H.E.S.S., together with multi-wavelength studies of the remnant and other gamma-ray emitting SNRs, such as W28 and RCW 86. Analysis of a time-variable source, 2XMM J185114.3−000004, found in the northern part of the SNR, is also reported for the first time. Rapid time variability and a heavily absorbed hard-X-ray spectrum suggest that this source could be a new supergiant fast X-ray transient. [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]