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Register a new userOptical Emission Associated with the Galactic Supernova Remnant G179.0+2.6
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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.
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Wide-field Halpha images of the radio faint Galactic supernova remnant G182.4+4.2 reveal a surprisingly extensive and complex emission structure, with an unusual series of broad and diffuse filaments along the remnants southwestern limb. Deep [O III] 5007 images reveal no appreciable remnant emission with the exception of a single filament coincident with the westernmost of the broad southwest filaments. The near total absence of [O III] emission suggests the majority of the remnants optical emission arises from relatively slow shocks (<70 km/s), consistent with little or no associated X-ray emission. Low-dispersion optical spectra of several regions in the remnants main emission structure confirm a lack of appreciable [O III] emission and indicate [S II]/Halpha line ratios of 0.73 - 1.03, consistent with a shock-heated origin. We find G182.4+4.2 to be a relatively large (d~50 pc at 4 kpc) and much older (age ~40 kyr) supernova remnant than previously estimated, whose weak radio and X-ray emissions are related to its age, low shock velocity, and location in a low density region some 12 kpc out from the Galactic centre.
We report the VLA detection of the radio counterpart of the X-ray object referred to as the Cannonball, which has been proposed to be the remnant neutron star resulting from the creation of the Galactic Center supernova remnant, Sagittarius A East. The radio object was detected both in our new VLA image from observations in 2012 at 5.5 GHz and in archival VLA images from observations in 1987 at 4.75 GHz and in the period from 1990 to 2002 at 8.31 GHz. The radio morphology of this object is characterized as a compact, partially resolved point source located at the northern tip of a radio tongue similar to the X-ray structure observed by Chandra. Behind the Cannonball, a radio counterpart to the X-ray plume is observed. This object consists of a broad radio plume with a size of 30arcsec$times$15arcsec, followed by a linear tail having a length of 30arcsec. The compact head and broad plume sources appear to have relatively flat spectra ($propto u^alpha$) with mean values of $alpha=-0.44pm0.08$ and $-0.10pm0.02$, respectively; and the linear tail shows a steep spectrum with the mean value of $-1.94pm0.05$. The total radio luminosity integrated from these components is $sim8times10^{33}$ erg s$^{-1}$, while the emission from the head and tongue amounts for only $sim1.5times10^{31}$ erg s$^{-1}$. Based on the images obtained from the two epochs observations at 5 GHz, we infer the proper motion of the object: $mu_alpha = 0.001 pm0.003$ arcsec yr$^{-1}$ and $mu_delta = 0.013 pm0.003$ arcsec yr$^{-1}$. With an implied velocity of 500 km s$^{-1}$, a plausible model can be constructed in which a runaway neutron star surrounded by a pulsar wind nebula was created in the event that produced Sgr A East. The inferred age of this object, assuming that its origin coincides with the center of Sgr A East, is approximately 9000 years.
We present evidence that the very-high-energy (VHE, E > 100 GeV) gamma-ray emission coincident with the supernova remnant IC 443 is extended. IC 443 contains one of the best-studied sites of supernova remnant/molecular cloud interaction and the pulsar wind nebula CXOU J061705.3+222127, both of which are important targets for VHE observations. VERITAS observed IC 443 for 37.9 hours during 2007 and detected emission above 300 GeV with an excess of 247 events, resulting in a significance of 8.3 standard deviations (sigma) before trials and 7.5 sigma after trials in a point-source search. The emission is centered at 06 16 51 +22 30 11 (J2000) +- 0.03_stat +- 0.08_sys degrees, with an intrinsic extension of 0.16 +- 0.03_stat +- 0.04_sys degrees. The VHE spectrum is well fit by a power law (dN/dE = N_0 * (E/TeV)^-Gamma) with a photon index of 2.99 +- 0.38_stat +- 0.3_sys and an integral flux above 300 GeV of (4.63 +- 0.90_stat +- 0.93_sys) * 10^-12 cm^-2 s^-1. These results are discussed in the context of existing models for gamma-ray production in IC 443.
Hadronic gamma-ray emission from supernova remnants (SNRs) is an important tool to test shock acceleration of cosmic ray protons. Tycho is one of nearly a dozen Galactic SNRs which are suggested to emit hadronic gamma-ray emission. Among them, however, it is the only one in which the hadronic emission is proposed to arise from the interaction with low-density (~0.3 cm^{-3}) ambient medium. Here we present an alternative hadronic explanation with a modest conversion efficiency (of order 1%) for this young remnant. With such an efficiency, a normal electron-proton ratio (of order 10^{-2}) is derived from the radio and X-ray synchrotron spectra and an average ambient density that is at least one-order-of-magnitude higher is derived from the hadronic gamma-ray flux. This result is consistent with the multi-band evidence of the presence of dense medium from the north to the east of the Tycho SNR. The SNR-cloud association, in combination with the HI absorption data, helps to constrain the so-far controversial distance to Tycho and leads to an estimate of 2.5 kpc.
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.
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