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Register a new userInvestigating Galactic supernova remnant candidates with LOFAR
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We investigate six supernova remnant (SNR) candidates --- G51.21+0.11, G52.37-0.70, G53.07+0.49, G53.41+0.03, G53.84-0.75, and the possible shell around G54.1-0.3 --- in the Galactic Plane using newly acquired LOw-Frequency ARray (LOFAR) High-Band Antenna (HBA) observations, as well as archival Westerbork Synthesis Radio Telescope (WSRT) and Very Large Array Galactic Plane Survey (VGPS) mosaics. We find that G52.37-0.70, G53.84-0.75, and the possible shell around pulsar wind nebula G54.1+0.3 are unlikely to be SNRs, while G53.07+0.49 remains a candidate SNR. G51.21+0.11 has a spectral index of $alpha=-0.7pm0.21$, but lacks X-ray observations and as such requires further investigation to confirm its nature. We confirm one candidate, G53.41+0.03, as a new SNR because it has a shell-like morphology, a radio spectral index of $alpha=-0.6pm0.2$ and it has the X-ray spectral characteristics of a 1000-8000 year old SNR. The X-ray analysis was performed using archival XMM-Newton observations, which show that G53.41+0.03 has strong emission lines and is best characterized by a non-equilibrium ionization model, consistent with an SNR interpretation. Deep Arecibo radio telescope searches for a pulsar associated with G53.41+0.03 resulted in no detection, but place stringent upper limits on the flux density of such a source if it is beamed towards Earth.
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Narrow passband optical images of the large Galactic supernova remnant G179.0+2.6 reveal a faint but nearly complete emission shell dominated by strong [O III] 4959,5007 A line emission. The remnants optical emission, which consists of both diffuse and filamentary features, is brightest along its southern and northeastern limbs. Deep H-alpha images detect little coincidence emission indicating an unusually high [O III]/H-alpha emission ratio for such a large and apparently old remnant. Low-dispersion optical spectra of several regions confirm large [O III]/H-alpha line ratios with typical values around 10. The dominance of [O III] emission for the majority of the remnants optical filaments suggests shock velocities above 100 km/s are present throughout most of the remnant, likely reflecting a relatively low density ambient ISM. The remnants unusually strong [O III] emission adds to the remnants interesting set of properties which include a thick radio emission shell, radial polarization of its radio emission like that typically seen in young supernova remnants, and an unusually slow-rotating gamma-ray pulsar with a characteristic spin-down age ~50 kyr.
G1.9+0.3 is the youngest known Galactic supernova remnant (SNR), with an estimated supernova (SN) explosion date of about 1900, and most likely located near the Galactic Center. Only the outermost ejecta layers with free-expansion velocities larger than about 18,000 km/s have been shocked so far in this dynamically young, likely Type Ia SNR. A long (980 ks) Chandra observation in 2011 allowed spatially-resolved spectroscopy of heavy-element ejecta. We denoised Chandra data with the spatio-spectral method of Krishnamurthy et al., and used a wavelet-based technique to spatially localize thermal emission produced by intermediate-mass elements (IMEs: Si and S) and iron. The spatial distribution of both IMEs and Fe is extremely asymmetric, with the strongest ejecta emission in the northern rim. Fe Kalpha emission is particularly prominent there, and fits with thermal models indicate strongly oversolar Fe abundances. In a localized, outlying region in the northern rim, IMEs are less abundant than Fe, indicating that undiluted Fe-group elements (including 56Ni) with velocities larger than 18,000 km/s were ejected by this SN. But in the inner west rim, we find Si- and S-rich ejecta without any traces of Fe, so high-velocity products of O-burning were also ejected. G1.9+0.3 appears similar to energetic Type Ia SNe such as SN 2010jn where iron-group elements at such high free-expansion velocities have been recently detected. The pronounced asymmetry in the ejecta distribution and abundance inhomogeneities are best explained by a strongly asymmetric SN explosion, similar to those produced in some recent 3D delayed-detonation Type Ia models.
We present X-ray and radio observations of the new Galactic supernova remnant (SNR) G306.3-0.9, recently discovered by Swift. Chandra imaging reveals a complex morphology, dominated by a bright shock. The X-ray spectrum is broadly consistent with a young SNR in the Sedov phase, implying an age of 2500 yr for a distance of 8 kpc, plausibly identifying this as one of the 20 youngest Galactic SNRs. Australia Telescope Compact Array (ATCA) imaging reveals a prominent ridge of radio emission that correlates with the X-ray emission. We find a flux density of ~ 160 mJy at 1 GHz, which is the lowest radio flux recorded for a Galactic SNR to date. The remnant is also detected at 24microns, indicating the presence of irradiated warm dust. The data reveal no compelling evidence for the presence of a compact stellar remnant.
Deep H$alpha$ images of a faint emission complex 4.0 x 5.5 degrees in angular extent and located far off the Galactic plane at l = 70.0 degrees, b=-21.5 degrees reveal numerous thin filaments suggestive of a supernova remnants shock emission. Low dispersion optical spectra covering the wavelength range 4500 - 7500 A show only Balmer line emissions for one filament while three others show a Balmer dominated spectrum along with weak [N I] 5198, 5200 A, [O I] 6300, 6364 A, [N II] 6583 A, [S II] 6716, 6731 A and in one case [O III] 5007 A line emission. Many of the brighter H$alpha$ filaments are visible in near UV GALEX images presumably due to C III] 1909 A line emission. ROSAT All Sky Survey images of this region show a faint crescent shaped X-ray emission nebula coincident with the portion of the H$alpha$ nebulosity closest to the Galactic plane. The presence of long, thin Balmer dominated emission filaments with associated UV emission and coincident X-ray emission suggests this nebula is a high latitude Galactic supernova remnant despite a lack of known associated nonthermal radio emission. Relative line intensities of the optical lines in some filaments differ from commonly observed [S II]/H$alpha$ > 0.4 radiative shocked filaments and typical Balmer filaments in supernova remnants. We discuss possible causes for the unusual optical SNR spectra.
G349.7 + 00.2 is a young Galactic supernova remnant (SNR) with a mushroom morphology in radio and X-rays, and it has been detected across the entire electromagnetic spectrum from radio to high energy $gamma$-rays. Moreover, the remnant is interacting with a molecular cloud based on the observations in the radio and infrared band. The reason for the formation of the periphery and the dynamical evolution of the remnant are investigated using 3D hydrodynamical (HD) simulations. Under the assumption that the supernova ejecta is evolved in the medium with a density gradient, the shell is composed of two hemispheres with different radiuses, and the smaller hemisphere is in relatively dense media. The resulting periphery of remnant is consistent with detected ones, and it can be concluded that the peculiar periphery of G349.7+00.2 can be reproduced as the remnants interacting with the medium with a density gradient.
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