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We have obtained the polarization data cube of the supernova remnant (SNR) VRO 42.05.01 at 1240 MHz using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). Three-dimensional Faraday synthesis is applied to the FAST data to derive the Faraday depth spectrum. The peak Faraday depth map shows a large area of enhanced foreground rotation measure (RM) of ∼60 rad m−2 extending along the remnant's "wing" section, which coincides with a large-scale H i shell at −20 km s−1. The two depolarization patches within the "wing" region with RMs of 97 rad m−2 and 55 rad m−2 coincide with two H i structures in the H i shell. Faraday screen model fitting on the Canadian Galactic Plane Survey 1420 MHz full-scale polarization data reveals a distance of (0.7–0.8) d SNR in front of the SNR with enhanced regular magnetic field there. The highly piled-up magnetic field indicates that the H i shell at −20 km s−1 could originate from an old evolved SNR. [ABSTRACT FROM AUTHOR]

The investigation of very high energy (VHE) γ‐ray sources by any methods, including mirror Cherenkov telescopes, touches on the problem of the cosmic‐ray origin and, accordingly, the role of the Galaxy in their generation. The SHALON observations have yielded the results on Galactic supernova remnants (SNR) of different ages. Among them are: the shell‐type SNRs Tycho's SNR, Cas A, IC 443, γCygni SNR, G166.0+4.3. For each of SNRs, the observation results are presented with spectral energy distribution by SHALON in comparison with other experiment data and images by SHALON in together with data from X‐ray by Chandra and radio‐data by CGPS. The experimental data presented here have confirmed the prediction of the theory about the hadronic generation mechanism of VHE 800 GeV–100 TeV γ‐rays in Tycho's SNR, Cas A and IC 443, and also the collected experimental data help to make clear the origin of TeV γ‐ray emission in the older SNRs like γCygni SNR and G166.0+4.3. [ABSTRACT FROM AUTHOR]

We present the detections of shocked molecular hydrogen (H2) gas in near- and mid-infrared and broad CO in millimeter from the mixed-morphology supernova remnant (SNR) HB 3 (G132.7+1.3) using the Palomar Wide-field InfraRed Camera, the Spitzer GLIMPSE360 and Wide-field Infrared Survey Explorer (WISE) surveys, and the Heinrich Hertz Submillimeter Telescope. Our near-infrared narrow-band filter H2 2.12 μm images of HB 3 show that both Spitzer Infrared Array Camera and WISE 4.6 μm emission originates from shocked H2 gas. The morphology of H2 exhibits thin filamentary structures and a large scale of interaction sites between the HB 3 and nearby molecular clouds. Half of HB 3, the southern and eastern shell of the SNR, emits H2 in a shape of a butterfly or W, indicating the interaction sites between the SNR and dense molecular clouds. Interestingly, the H2 emitting region in the southeast is also co-spatial to the interacting area between HB 3 and the H ii regions of the W3 complex, where we identified star-forming activity. We further explore the interaction between HB 3 and dense molecular clouds with detections of broad CO(3-2) and CO(2-1) molecular lines from the southern and southeastern shell along the H2 emitting region. The widths of the broad lines are 8–20 km s−1; the detection of such broad lines is unambiguous, dynamic evidence of the interactions between the SNR and clouds. The CO broad lines are from two branches of the bright, southern H2 shell. We apply the Paris–Durham shock model to the CO line profiles, which infer the shock velocities of 20–40 km s−1, relatively low densities of 103–4 cm−3, and strong (>200 μG) magnetic fields. [ABSTRACT FROM AUTHOR]

In the current decade, GeV/TeV gamma-ray observations of several supernova remnants (SNRs) have implied that accelerated particles are escaping from their acceleration sites. However, when and how they escape from the SNR vicinities are yet to be understood. Recent studies have suggested that the particle escape might develop with thermal plasma ages of the SNRs. We present a systematic study on the time evolution of particle escape using thermal X-ray properties and gamma-ray spectra using 38 SNRs associated with GeV/TeV gamma-ray emissions. We conducted spectral fittings on the gamma-ray spectra using exponential cutoff power-law and broken power-law models to estimate the exponential cutoff or the break energies, both of which are indicators of particle escape. Plots of the gamma-ray cutoff/break energies over the plasma ages show similar tendencies to those predicted by analytical/numerical calculations of particle escape under conditions in which a shock is interacting with thin interstellar medium or clouds. The particle escape timescale is estimated as ∼100 kyr from the decreasing trends of the total energy of the confined protons with the plasma age. The large dispersions of the cutoff/break energies in the data may suggest an intrinsic variety of particle escape environments. This might be the cause of the complicated Galactic cosmic ray spectral shape measured on Earth. [ABSTRACT FROM AUTHOR]

Context. The environment of supernova remnants (SNRs) is a key factor in their evolution, particularly at later stages of their existence. Mixed-morphology (MM) SNRs have a peculiar centre-filled X-ray shape that remains enigmatic. It is often assumed that they evolve in very dense environments, and that the X-ray morphology is due to interactions between the SNRs and their surroundings. Aims. We aim to determine whether VRO 42.05.01 is embedded in, and interacting with, a dense molecular environment. We also aim to understand the multi-wavelength emission from the environment of this SNR, and whether the interstellar material can be responsible for the the MM nature of the source, and for its strange radio and optical shape. Methods. We used the IRAM telescope in Pico Veleta, Spain, to search for signs of interaction between the SNR and neighbouring molecular clouds. We observed a region of 26′ × 14′ towards the west of VRO 42.05.01 and a region of 8′ × 4′ towards the north of the remnant in the 12CO J = 1−0, 13CO J = 1−0, and 12CO J = 2−1 transitions with the EMIR receiver. We made maps of the properties of the observed molecular clouds (peak temperatures, central velocities, velocity dispersions), as well as maps of column density along the line of sight, and ratio of the 12CO J = 2−1 to 12CO J = 1−0 transitions. We also analyse archival optical, infrared, and radio spectroscopic data for other hints on the nature of the medium. Results. We do not find conclusive physical proof that the SNR is interacting with the few, clumpy molecular clouds that surround it in the region of our observations, although there is some suggestion of such interaction (in a region outside our map) from infrared emission. We find that there is a velocity gradient in one of the molecular clouds that is consistent with a stellar wind blown by a 12−14 M⊙ progenitor star. We reassess the literature distance to VRO 42.05.01, and propose that it has a local standard of rest velocity of − 6 km s−1, and that it is located 1.0 ± 0.4 kpc away (the earlier distance value was 4.5 ± 1.5 kpc). We find that a dust sheet intersects VRO 42.05.01 and is possibly related to its double shell-shaped morphology. [ABSTRACT FROM AUTHOR]

Context. The Galactic plane is the brightest source of γ rays in the sky. It should also be one of the brightest very-high-energy neutrino sources, if a neutrino flux comparable to the γ-ray flux is produced by the cosmic ray interactions in the interstellar medium. Aims. We explore the detectability of the neutrino flux from the entire Galactic plane or from a part of it with the IceCube neutrino detector. Methods. We calculated the normalization and the spectral index of the neutrino power-law spectrum from different regions of the Galactic plane, based on the observed spectral characteristics of the pion decay γ-ray diffuse emission observed by the Fermi/LAT telescope in the energy band above 100 GeV.We compared the neutrino flux calculated in this way with the sensitivity of IceCube for the detection of extended sources. Results. Assuming a binned extended source analysis method, we find that the only possible evidence of neutrino emission for sources located in the northern hemisphere after 20 years of exposure is from the Cygnus region. For other parts of the Galactic plane even a 20 year exposure with IceCube is not sufficient for the detection. Taking into account marginal significance of the detectable source in the Cygnus region, we find a precise position and size of the source region that optimizes the signal-to-noise ratio for neutrinos. We also calculated the low-energy threshold above which the neutrino signal can be detected with the highest signal-to-noise ratio. This calculation of precise source position, size, and energy range, based on the γ-ray data, can be used to remove the so-called trial factor in the analysis of the real neutrino data of IceCube. We notice that the diffuse neutrino emission from the inner Galactic plane in the southern hemisphere is much brighter. A neutrino detector with characteristics equivalent to IceCube, but placed at the northern hemisphere (such as KM3NeT), would detect several isolated neutrino sources in the Galactic plane with just a five-year exposure at the 5σ level. Their discovery would identify the cosmic ray sources in the Galaxy that have been active during the last 104 years. Conclusions. The detection of the diffuse neutrino emission from cosmic ray interactions in the Galactic disk is challenging, but marginally feasible with a 20 year exposure by IceCube. Dramatically shorter (2-5 yr) exposure times would be required for the Galactic plane signal detection with an IceCube-like neutrino detector in the northern hemisphere. [ABSTRACT FROM AUTHOR]

Context. A growing number of researchers present evidence that the pulsar wind nebula 3C 58 is much older than predicted by its proposed connection to the historical supernova of A.D. 1181. There is also a great diversity of arguments. The strongest of these arguments rely heavily on the assumed distance of 3.2 kpc determined with H i absorption measurements. Aims. This publication aims at determining a more accurate distance for 3C58 and at re-evaluating the arguments for an older age. Methods. I have re-visited the distance determination of 3C 58 based on new H i data from the Canadian Galactic Plane Survey and our recent improvements in the knowledge of the rotation curve of the outer Milky Way Galaxy. I also used newly determined distances to objects in the neighbourhood, which are based on direct measurements by trigonometric parallax. Results. I have derived a new more reliable distance estimate of 2 kpc for 3C 58. This makes the connection between the pulsar wind nebula and the historical event from A.D. 1181 once again much more viable. [ABSTRACT FROM AUTHOR]

By combining the photometric, spectroscopic, and astrometric information of the stars in the sightline of supernova remnants (SNRs), the distances to and the extinctions of 32 Galactic SNRs are investigated. The stellar atmospheric parameters are from the Sloan Digital Sky Survey−DR14/Apache Point Observatory Galaxy Evolution Experiment and Large sky Area Multi-Object fiber Spectroscopic Telescope−DR5/LEGUE spectroscopic surveys. The multiband photometry, from optical to infrared, are collected from the Gaia, APASS, Pan-STARRS1, Two Micron All Sky Survey, and Wide-field Infrared Survey Explorer surveys. With the calibrated Gaia distances of individual stars, the distances to 15 of 32 SNRs are well determined from their produced extinction and association with molecular clouds. The upper limits of distance are derived for three SNRs. The color excess ratios of 32 SNRs are calculated, and their variation with wavebands is fitted by a simple dust model. The inferred dust grain size distribution bifurcates: while the graphite grains have comparable size to the average interstellar medium dust, the silicate grains are generally larger. Along the way, the average extinction law from optical to near-infrared of the Milky Way is derived from the 1.3-million-star sample and found to agree with the CCM89 law with . [ABSTRACT FROM AUTHOR]

Reports on a highly-ordered Faraday-rotation structure of elliptical shape, with its long axis parallel to the plane of the Milky Way galaxy. Detection of magnetic fields which could be involved in the formation of such structures; Location; Possible origin.

Recent hydrodynamical models of supernova remnants (SNRs) demonstrate that their evolution depends heavily on the inhomogeneities of the surrounding medium. As SNRs expand, their morphologies are influenced by the nonuniform and turbulent structure of their environments, as reflected in their radio continuum emission. In this paper, we measure the asymmetries of 96 SNRs in radio continuum images from three surveys of the Galactic plane and compare these results to the SNRs’ radii, which we use as a proxy for their age. We find that larger (older) SNRs are more elliptical/elongated and more mirror asymmetric than smaller (younger) SNRs, though the latter vary in their degrees of asymmetry. This result suggests that SNR shells become more asymmetric as they sweep up the interstellar medium (ISM), as predicted in hydrodynamical models of SNRs expanding in a multiphase or turbulent ISM. [ABSTRACT FROM AUTHOR]

Supernova remnants (SNRs) have been considered to be the dominant contributors to Galactic cosmic rays. However, the relation between high-energy particles trapped in SNRs and cosmic rays observed at the Earth remains obscure. In this paper, we fit the spectral energy distributions of 35 SNRs with a simple one-zone emission model and analyze correlations of model parameters to uncover the evolution of high-energy particle distribution in SNRs. We find that (1) the particle distribution in general can be described by a broken power-law function with a high-energy cutoff for all SNRs; (2) the low-energy spectrum becomes harder and the break energy decreases with aging of SNRs, (3) for most middle-age SNRs, the energy loss timescale of electrons at the high-energy cutoff is approximately equal to the age of the corresponding remnant implying quenching of very-high-energy electron acceleration; for young SNRs, this energy loss timescale is shorter than the age of SNRs implying continuous electron acceleration at the cutoff energy; and for a few old age SNRs, the energy loss timescale is longer than the corresponding age, which may suggest escaping of higher energy particles from SNRs. Finally, we comment on the implications of these results on the SNR origin of Galactic cosmic rays. [ABSTRACT FROM AUTHOR]

We carried out 12CO(J = 1–0) observations of the Galactic gamma-ray supernova remnant (SNR) Kesteven 79 using the Nobeyama Radio Observatory 45 m radio telescope, which has an angular resolution of ∼20 arcsec. We identified molecular and atomic gas interacting with Kesteven 79, whose radial velocity is ∼80 km s−1. The interacting molecular and atomic gases show good spatial correspondence with the X-ray and radio shells, which have an expanding motion with an expanding velocity of ∼4 km s−1. The molecular gas associated with the radio and X-ray peaks also exhibits a high intensity ratio of CO 3–2/1–0 > 0.8, suggesting a kinematic temperature of ∼24 K, owing to heating by the supernova shock. We determined the kinematic distance to the SNR to be ∼5.5 kpc and the radius of the SNR to be ∼8 pc. The average interstellar proton density inside of the SNR is ∼360 cm−3, of which atomic protons comprise only ∼10%. Assuming a hadronic origin for the gamma-ray emission, the total cosmic-ray proton energy above 1 GeV is estimated to be ∼5 × 1048 erg. [ABSTRACT FROM AUTHOR]

We present an X-ray study of the GeV gamma-ray supernova remnant (SNR) HB 21 with Suzaku. HB 21 is interacting with molecular clouds, and is the faintest in the GeV band among known GeV SNRs. We discovered strong radiative recombination continua of Si and S from the center of the remnant, which provide direct evidence of a recombining plasma (RP). The total emission can be explained with the RP and ionizing plasma components. The electron temperature and recombination timescale of the RP component were estimated as 0.17 (0.15–0.18) keV and 3.2 (2.0–4.8) × 1011 s cm−3, respectively. The estimated age of the RP (∼170 kyr) is the longest among known recombining GeV SNRs, because of a very low density of electrons (∼0.05 cm−3). We have examined the dependencies of GeV spectral indices on each of RP ages and SNR diameters for nine recombining GeV SNRs. Both showed possible positive correlations, indicating that both the parameters can be good indicators of properties of accelerated protons, for instance the degree of escape from SNR shocks. A possible scenario for a process of proton escape is introduced: interaction with molecular clouds makes weaker magnetic turbulence and cosmic-ray protons escape, simultaneously cooling down the thermal electrons and generating an RP. [ABSTRACT FROM AUTHOR]

We performed millimeter observations of CO lines toward the supernova remnant (SNR) HB 3. Substantial molecular gas around −45 km s−1 is detected in the conjunction region between the SNR HB 3 and the nearby W3 complex. This molecular gas is distributed along the radio continuum shell of the remnant. Furthermore, the shocked molecular gas indicated by line wing broadening features is also distributed along the radio shell and inside it. By both morphological correspondence and dynamical evidence, we confirm that the SNR HB 3 interacts with the −45 km s−1 molecular cloud (MC), in essence, with the nearby H ii region/MC complex W3. The redshifted line wing broadening features indicate that the remnant is located at the nearside of the MC. With this association, we could place the remnant at the same distance as the W3/W4 complex, which is 1.95 ± 0.04 kpc. The spatial distribution of aggregated young stellar object candidates shows a correlation with the shocked molecular strip associated with the remnant. We also find a binary clump of CO at (l = 132.°94, b = 1.°12) around −51.5 km s−1 inside the projected extent of the remnant, and it is associated with significant mid-infrared emission. The binary system also has a tail structure resembling the tidal tails of interacting galaxies. According to the analysis of CO emission lines, the larger clump in this binary system is about stable, and the smaller clump is significantly disturbed. [ABSTRACT FROM AUTHOR]

We report the discovery of extended gamma-ray emission measured by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the region of the supernova remnant (SNR) HB 3 (G132.7+1.3) and the W3 II complex adjacent to the southeast of the remnant. W3 is spatially associated with bright 12CO (J = 1–0) emission. The gamma-ray emission is spatially correlated with this gas and the SNR. We discuss the possibility that gamma rays originate in interactions between particles accelerated in the SNR and interstellar gas or radiation fields. The decay of neutral pions produced in nucleon–nucleon interactions between accelerated hadrons and interstellar gas provides a reasonable explanation for the gamma-ray emission. The emission from W3 is consistent with irradiation of the CO clouds by the cosmic rays accelerated in HB 3. [ABSTRACT FROM AUTHOR]

We present molecular spectroscopy toward 50 Galactic supernova remnants (SNRs) taken at millimeter wavelengths in 12CO J = 2 − 1. These observations are part of a systematic survey for broad molecular line (BML) regions indicative of interactions with molecular clouds (MCs). We detected BML regions toward 19 SNRs, including 9 newly identified BML regions associated with SNRs (G08.3–0.0, G09.9–0.8, G11.2–0.3, G12.2+0.3, G18.6–0.2, G23.6+0.3, 4C–04.71, G29.6+0.1, and G32.4+0.1). The remaining 10 SNRs with BML regions confirm previous evidence for MC interaction in most cases (G16.7+0.1, Kes 75, 3C 391, Kes 79, 3C 396, 3C 397, W49B, Cas A, and IC 443), although we confirm that the BML region toward HB 3 is associated with the W3(OH) H ii region, not the SNR. Based on the systemic velocity of each MC, molecular line diagnostics, and cloud morphology, we test whether these detections represent SNR–MC interactions. One of the targets (G54.1+0.3) had previous indications of a BML region, but we did not detect broadened emission toward it. Although broadened 12CO J = 2 − 1 line emission should be detectable toward virtually all SNR–MC interactions, we find relatively few examples; therefore, the number of interactions is low. This result favors mechanisms other than supernova feedback as the basic trigger for star formation. In addition, we find no significant association between TeV gamma-ray sources and MC interactions, contrary to predictions that SNR–MC interfaces are the primary venues for cosmic ray acceleration. [ABSTRACT FROM AUTHOR]