High-Resolution VLA Imaging of the Supernova Remnant W28 at 328 and 1415 MH[CLC]z[/CLC]

Dubner, G.; Velázquez, P. F.; Goss, W. M.; Holdaway, M. A.

doi:10.1086/301583

Cited by 65 publications

(78 citation statements)

References 24 publications

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“…The flat spectrum of the region traced by SgrA-E at radio frequencies provides an insight as what the cause might be. This flat spectrum is reminiscent of the W28 SNR which is known to be interacting with an adjacent molecular cloud (Dubner et al 2002). The flat spectral index distribution is consistent with the Fermi acceleration mechanism predicting a flatter spectrum when a shock wave drives through a molecular cloud (Bykov et al 2000).…”

Section: The Sgra-e Filament: Synchrotron Mechanismsupporting

confidence: 67%

The nature of nonthermal X-ray filaments near the galactic center

Yusef‐Zadeh

Wardle

Muno

et al. 2005

Advances in Space Research

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Recent Chandra and XMM-Newton observations reported evidence of two Xray filaments G359.88-0.08 (SgrA-E) and G359.54+0.18 (the ripple filament) near the Galactic center. The X-ray emission from these filaments has a nonthermal spectrum and coincides with synchrotron emitting radio sources. Here, we report the detection of a new X-ray feature coincident with a radio filament G359.90-0.06 (SgrA-F) and show more detailed VLA, Chandra and BIMA observations of the radio and X-ray filaments. In particular, we show that radio emission from the nonthermal filaments G359.90-0.06 (SgrA-F) and G359.54+0.18 (the ripple) has a steep spectrum whereas G359.88-0.08 (SgrA-E) has a flat spectrum. The X-ray emission from both these sources could be due to synchrotron radiation. However, given that the 20 km s −1 molecular cloud, with its intense 1.2mm dust emission, lies in the vicinity of SgrA-F, it is possible that the X-rays could be produced by inverse Compton scattering of far-infrared photons from dust by the relativistic electrons responsible for the radio synchrotron emission. The production of X-ray emission from ICS allows an estimate of the magnetic field strength of 0.08 mG within the

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Section: The Sgra-e Filament: Synchrotron Mechanismsupporting

confidence: 67%

The nature of nonthermal X-ray filaments near the galactic center

Yusef‐Zadeh

Wardle

Muno

et al. 2005

Advances in Space Research

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“…11 we have identified with open white diamonds the regions with OH (1720 MHz) maser emission as detected by Hewitt (2009). In the case of SNR W28, Dubner et al (2000) demonstrated a clear correspondence between regions of flat spectral index and OH maser emission. We search for a similar correlation in IC 443.…”

Section: Comparison With the Molecular Distributionmentioning

confidence: 71%

High-resolution radio study of SNR IC 443 at low radio frequencies

Castelletti

Dubner

Kassim

2011

A&A

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Aims. We investigate the morphology at low radio frequencies of the supernova remnant (SNR) IC 443 in detail and accurately establish its radio continuum spectral properties. Methods. We used the VLA in multiple configurations to produce high-resolution radio images of IC 443 at 74 and 330 MHz. From these data we produced the first sensitive, spatially resolved spectral analysis of the radio emission at long wavelengths. The changes with position in the radio spectral index were correlated with data in near infrared (NIR) from 2MASS, in gamma-rays from VERITAS, and with the molecular 12 CO (J = 1−0) line emission. With the available statistics the VERITAS γ-ray emission strikingly matches the CO distribution, but no clear evidence is found for a morphological correlation between the TeV distribution and radio emission. Conclusions. The excellent correspondence between the eastern radio flattest spectrum region and NIR ionic lines 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 (τ 74 up to ∼0.3) is responsible for the localized spectral index flattening observed along the eastern border of IC 443. Towards the interior of IC 443, the spectrum is consistent with those expected from linear diffusive shock acceleration, while the flatter spectrum in the southern ridge is a consequence of the strong shock/molecular cloud interaction.

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“…HESS J1801−233 can be seen to overlap the northeastern shell of the SNR, coinciding with a strong peak in the 90 cm continuum emission. We note that a thermal component is likely present in this peak, given its spectral index α ∼ −0.2 (for S ∝ ν α ) between 90 and 20 cm (Dubner et al 2000). Outlines of the SNRs traced by non-thermal radio emission, G6.67−0.42 and G7.06−0.12 (Yusef-Zadeh et al 2000;Helfand et al 2006; labelled as G6.51−0.48 and G7.0−0.1 by Brogan et al 2006) are also indicated.…”

Section: Nanten and Other Observations Of Molecular Cloudsmentioning

confidence: 95%

Discovery of very high energy gamma-ray emission coincident with molecular clouds in the W 28 (G6.4-0.1) field

Aharonian

Akhperjanian

Bazer‐Bachi

et al. 2008

A&A

239

238

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Aims. Observations of shell-type supernova remnants (SNRs) in the GeV to multi-TeV γ-ray band, coupled with those at millimetre radio wavelengths, are motivated by the search for cosmic-ray accelerators in our Galaxy. The old-age mixed-morphology SNR W 28 (distance ∼2 kpc) is a prime target due to its interaction with molecular clouds along its northeastern boundary and other clouds situated nearby. Methods. We observed the W 28 field (for ∼40 h) at very high energy (VHE) γ-ray energies (E > 0.1 TeV) with the HESS. Cherenkov telescopes. A reanalysis of EGRET E > 100 MeV data was also undertaken. Results from the NANTEN 4 m telescope Galactic plane survey and other CO observations were used to study molecular clouds. Results. We have discovered VHE γ-ray emission (HESS J1801−233) coincident with the northeastern boundary of W 28 and a complex of sources (HESS J1800−240A, B and C) ∼0.5 • south of W 28 in the Galactic disc. The EGRET source (GRO J1801−2320) is centred on HESS J1801−233 but may also be related to HESS J1800−240 given the large EGRET point spread function. The VHE differential photon spectra are well fit by pure power laws with indices Γ ∼ 2.3 to 2.7. The spectral indices of HESS J1800−240A, B, and C are consistent within statistical errors. All VHE sources are ∼10 in intrinsic radius except for HESS J1800−240C, which appears pointlike. The NANTEN 12 CO(J = 1−0) data reveal molecular clouds positionally associating with the VHE emission, spanning a ∼15 km s −1 range in local standard of rest velocity. Conclusions. The VHE/molecular cloud association could indicate a hadronic origin for HESS J1801−233 and HESS J1800−240, and several cloud components in projection may contribute to the VHE emission. The clouds have components covering a broad velocity range encompassing the distance estimates for W 28 (∼2 kpc) and extending up to ∼4 kpc. Assuming hadronic origin and distances of 2 and 4 kpc for cloud components, the required cosmic-ray density enhancement factors (with respect to the solar value) are in the range ∼10 to ∼30. If situated at 2 kpc distance, such cosmic-ray densities may be supplied by SNRs like W 28. Additionally and/or alternatively, particle acceleration may come from several catalogued SNRs and SNR candidates, the energetic ultra compact HII region W 28A2, and the HII regions M 8 and M 20, along with their associated open clusters. Further sub-mm observations would be recommended to probe in detail the dynamics of the molecular clouds at velocites >10 km s −1 and their possible connection to W 28. Key words. gamma rays: observationsEnergy spectra are only available in electronic form at

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High-Resolution VLA Imaging of the Supernova Remnant W28 at 328 and 1415 MH[CLC]z[/CLC]

Cited by 65 publications

References 24 publications

The nature of nonthermal X-ray filaments near the galactic center

The nature of nonthermal X-ray filaments near the galactic center

High-resolution radio study of SNR IC 443 at low radio frequencies

Discovery of very high energy gamma-ray emission coincident with molecular clouds in the W 28 (G6.4-0.1) field

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