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Register a new userA high frequency radio study of G11.2-0.3, a historical supernova remnant with a flat spectrum core
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We present radio maps of the historical supernova remnant G11.2-0.3 in the frequency range from 4.85 GHz to 32 GHz. The integrated spectrum with alpha = -0.50 (S ~ u^alpha) is dominated by its steep spectrum shell emission (alpha ~ -0.57), although a flat spectrum core structure classifies G11.2-0.3 as a composite supernova remnant. A radial magnetic field structure is observed. An analysis of the multi-frequency polarization data results in highly varying rotation measures along the shell. The percentage polarization is rather low (~2%) and we conclude that G11.2-0.3 is in the transient phase from free to adiabatic expansion. The central flat spectrum component is partly resolved. A compact radio source with an inverted spectrum likely coincides with the previously detected X-ray pulsar (Torii et al. (1997). Two symmetric structures with flat radio spectra possibly indicate a bipolar outflow. Combining available X-ray and radio data we conclude that G11.2-0.3 is likely the remnant of a type II supernova explosion with an early type B progenitor star.
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We compare recent observations of the supernova remnant G11.2-0.3 taken with the VLA during 2001-02 with images from VLA archives (1984-85) to detect and measure the amount of expansion that has occurred during 17 years. The bright, circular outer shell shows a mean expansion of (0.71 +/- 0.15)% and (0.50 +/- 0.17)%, from 20- and 6-cm data, respectively, which corresponds to a rate of 0.057 +/- 0.012/yr at 20 cm and 0.040 +/- 0.013/yr at 6 cm. From this result, we estimate the age of the remnant to be roughly between 960 and 3400 years old, according to theoretical models of supernova evolution. This is highly inconsistent with the 24000 yr characteristic age of PSR J1811-1925, located at the remnants center, but, rather, is consistent with the time since the historical supernova observed in 386 AD. We also predict that G11.2-0.3 is currently in a pre-Sedov evolutionary state, and set constraints on the distance to the remnant based on Chandra X-ray spectral results.
We present results of a 400-ks Chandra observation of the young shell supernova remnant (SNR) G11.2-0.3, containing a pulsar and pulsar-wind nebula (PWN). We measure a mean expansion rate for the shell since 2000 of 0.0277+/-0.0018% per yr, implying an age between 1400 and 2400 yr, and making G11.2-0.3 one of the youngest core-collapse SNRs in the Galaxy. However, we find very high absorption ($A_V sim 16^m pm 2^m$), confirming near-IR determinations and ruling out a claimed association with the possible historical SN of 386 CE. The PWN shows strong jets and a faint torus within a larger, more diffuse region of radio emission and nonthermal X-rays. Central soft thermal X-ray emission is anticorrelated with the PWN; that, and more detailed morphological evidence, indicates that the reverse shock has already reheated all ejecta and compressed the PWN. The pulsar characteristic energy-loss timescale is well in excess of the remnant age, and we suggest that the bright jets have been produced since the recompression. The relatively pronounced shell and diffuse hard X-ray emission in the interior, enhanced at the inner edge of the shell, indicate that the immediate circumstellar medium into which G11.2-0.3 is expanding was quite anisotropic. We propose a possible origin for G11.2-0.3 in a stripped-envelope progenitor that had lost almost all its envelope mass, in an anisotropic wind or due to binary interaction, leaving a compact core whose fast winds swept previously lost mass into a dense irregular shell, and which exploded as a Type cIIb or Ibc supernova.
We present a high-resolution radio study of the supernova remnant (SNR) G11.2-0.3 using archival VLA data. Spectral tomography is performed to determine the properties of this composite-type SNRs individual components, which have only recently been distinguished through X-ray observations. Our results indicate that the spectral index of the pulsar wind nebula (PWN), or plerion, is alpha_P ~ 0.25. We observe a spectral index of alpha_S ~ 0.56 throughout most of the SNR shell region, but also detect a gradient in alpha in the south-eastern component. We compare the spectral index and flux density with recent single-dish radio data of the source. Also, the radio efficiency and morphological properties of this PWN are found to be consistent with results for other known PWN systems.
Supernova remnants (SNRs) have a variety of overall morphology as well as rich structures over a wide range of scales. Quantitative study of these structures can potentially reveal fluctuations of density and magnetic field originating from the interaction with ambient medium and turbulence in the expanding ejecta. We have used $1.5$GHz (L band) and $5$GHz (C band) VLA data to estimate the angular power spectrum $C_{ell}$ of the synchrotron emission fluctuations of the Kepler SNR. This is done using the novel, visibility based, Tapered Gridded Estimator of $C_{ell}$. We have found that, for $ell = (1.9 - 6.9) times 10^{4}$, the power spectrum is a broken power law with a break at $ell = 3.3 times 10^{4}$, and power law index of $-2.84pm 0.07$ and $-4.39pm 0.04$ before and after the break respectively. The slope $-2.84$ is consistent with 2D Kolmogorov turbulence and earlier measurements for the Tycho SNR. We interpret the break to be related to the shell thickness of the SNR ($0.35 $ pc) which approximately matches $ell = 3.3 times 10^{4}$ (i.e., $0.48$ pc). However, for $ell > 6.9 times 10^{4}$, the estimated $C_{ell}$ of L band is likely to have dominant contribution from the foregrounds while for C band the power law slope $-3.07pm 0.02$ is roughly consistent with $3$D Kolmogorov turbulence like that observed at large $ell$ for Cas A and Crab SNRs.
We present 1 to 10GHz radio continuum flux density, spectral index, polarisation and Rotation Measure (RM) images of the youngest known Galactic Supernova Remnant (SNR) G1.9+0.3, using observations from the Australia Telescope Compact Array (ATCA). We have conducted an expansion study spanning 8 epochs between 1984 and 2017, yielding results consistent with previous expansion studies of G1.9+0.3. We find a mean radio continuum expansion rate of ($0.78 pm 0.09$) per cent year$^{-1}$ (or $sim8900$ km s$^{-1}$ at an assumed distance of 8.5 kpc), although the expansion rate varies across the SNR perimeter. In the case of the most recent epoch between 2016 and 2017, we observe faster-than-expected expansion of the northern region. We find a global spectral index for G1.9+0.3 of $-0.81pm0.02$ (76 MHz$-$10 GHz). Towards the northern region, however, the radio spectrum is observed to steepen significantly ($sim -$1). Towards the two so called (east & west) ears of G1.9+0.3, we find very different RM values of 400-600 rad m$^{2}$ and 100-200 rad m$^{2}$ respectively. The fractional polarisation of the radio continuum emission reaches (19 $pm$ 2)~per~cent, consistent with other, slightly older, SNRs such as Cas~A.
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