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arXiv 1104.0205astro-ph.GA
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低射频下SNR IC443的高分辨射电研究

High-resolution radio study of SNR IC443 at low radio frequencies

G. Castelletti, G. Dubner, T. Clarke, N. E. Kassim

摘要:

我们详细研究了超新星遗迹IC 443在低射频下的形态,并准确地建立了其射电连续谱特性。我们在多种配置中使用VLA,以74和330 MHz的频率生成IC 443的高分辨率无线电图像。射电光谱指数随位置的变化与2 MASS的近红外数据、VERITAS的伽马射线数据和12^CO分子谱线发射数据相关。74 MHz下的新图像HPBW=35”,rms=30 mJy/波束,330 MHz下的新图像HPBW= 17”,rms=1.7 mJy/波束。整个SNR的积分通量密度为S_74MHz=470+/-51 Jy和S_330MHz=248+/-15 Jy。对于与致密源CXOUJ061705.3+222127相关的脉冲星风星云,我们计算出S_330MHz=0.23+/-0.05 Jy,S_1420MHz=0.20+/-0.04 Jy,α ~0.0。在74和330 MHz之间的整个IC 443的频谱指数观察到的实质性变化。最平坦的光谱分量(-0.25<α <-0.05)与东部边界SNR最亮的部分一致,与2 MASS J和H波段观察到的离子线一致。这一结果有力地表明,一个快速离解的J型激波穿过相互作用的分子云使分子离解并使气体电离。因此,我们得出结论,在74 MHz的热吸收是负责的局部光谱指数平坦沿东部边界的IC 443。IC 443内部的漫反射光谱比SNR中的任何地方都要陡峭(-0.85<alpha<-0.6),而南部的脊又有一个平坦的光谱(alpha -0.4),这是强激波/分子云相互作用的结果。在现有的统计数据的VERITAS伽马射线发射惊人地匹配CO分布,但没有明确的证据被发现的TeV分布和无线电发射之间的形态相关性。

英文摘要:

We investigated in detail the morphology at low radio frequencies of the supernova remnant IC443 and accurately established its radio continuum spectral properties. We used the VLA in multiple configurations to produce high resolution radio images of IC443 at 74 and 330 MHz. The changes with position in the radio spectral index were correlated with data in near infrared from 2MASS, in gamma-rays from VERITAS, and with the molecular 12^CO line emission. The new image at 74 MHz has HPBW=35", rms=30 mJy/beam and at 330 MHz HPBW= 17" and rms=1.7 mJy/beam. The integrated flux densities for the whole SNR are S_74MHz=470+/-51 Jy and S_330MHz=248+/-15 Jy. For the pulsar wind nebula associated with the compact source CXOUJ061705.3+222127, we calculated S_330MHz=0.23+/-0.05 Jy, S_1420MHz=0.20+/-0.04 Jy, and alpha~0.0. Substantial variations are observed in spectral index between 74 and 330 MHz across IC443. The flattest spectral components (-0.25< alpha<-0.05) coincide with the brightest parts of the SNR along the eastern border, with an impressive agreement with ionic lines as observed in the 2MASS J and H bands. This result strongly suggests that the passage of a fast dissociating J-type shock across the interacting molecular cloud dissociated the molecules and ionized the gas. We therefore conclude that thermal absorption at 74 MHz is responsible for the localized spectral index flattening observed along the eastern border of IC443. The diffuse interior of IC443 has a spectrum steeper than found anywhere in the SNR (-0.85<alpha<-0.6), while the southern ridge again has a flatter spectrum (alpha -0.4), consequence in this case of the strong shock/molecular cloud interaction. At the available statistics the VERITAS gamma-ray emission strikingly matches the CO distribution, but no clear evidence is found for a morphological correlation between the TeV distribution and radio emission.

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