SNR G034.6-00.5

SNR G034.6-00.5, also known as W44, 3C 392, and CTB 60, is a supernova remnant listed in the Cambridge catalog as G34.7−0.4, which notes the object has been called G34.6−0.5.¹ It lies in a dense molecular environment and has a mixed morphology, with a radio shell surrounding centrally concentrated thermal X-rays and a pulsar with an associated pulsar wind nebula within its boundary.¹ The remnant has a flux density of 240 Jy at 1 GHz and a spectral index of 0.37, making it one of the brighter radio remnants in the Galactic plane.¹ Distance estimates span roughly 2 to 3 kpc, with H I absorption suggesting 3.0 kpc, optical absorption 2.1 or 2.7 kpc, and H₂ emission 2.8 kpc.¹

Discovery and naming

Its Galactic-coordinate name is written both G34.6−0.5 and G34.7−0.4 in different catalogs; the Cambridge Galactic supernova remnant catalog notes that the object "has been called G34.6−0.5."¹

Radio morphology

In the radio band W44 appears as an asymmetric, nearly elliptical bright shell. The Cambridge catalog describes the shell as distorted and brighter to the east, with a pulsar and associated nebula within it.¹ Early mapping work traced the source at successively higher resolution: Molonglo observations at 408 MHz with 3 arcminute resolution measured a flux density of 299 Jy, Arecibo measurements gave 540 ± 187 Jy at 430 MHz, and later Parkes, Effelsberg, and other maps resolved the shell structure at 2.7, 4.9, and 5 GHz.¹

The integrated radio spectrum is relatively flat for a shell remnant, with a spectral index of 0.37 (flux density falling as frequency to a low power) and a flux density of 240 Jy at 1 GHz, making it one of the brighter radio remnants in the Galactic plane.¹

X-ray properties

X-ray emission from W44 is centrally concentrated with a thermal spectrum, and includes a pulsar wind nebula around the remnant's pulsar.¹ Early Einstein Observatory observations found that the X-ray emission appears to be anticorrelated with the radio emission, consistent with the interior-filled X-ray morphology, and noted increased low-energy absorption toward the dense molecular cloud associated with the remnant.²

Environment and pulsar

A pulsar lies within the boundary of the remnant, with an associated nebula seen in radio and X-ray observations.¹

Distance estimates from different methods span roughly 2 to 3 kpc: H I absorption suggests 3.0 kpc, optical absorption suggests 2.1 or 2.7 kpc, and H₂ emission suggests 2.8 kpc.¹ At these distances the 35 × 27 arcmin shell corresponds to a remnant tens of light-years across.¹

As a mixed-morphology remnant

W44 belongs to the class of mixed-morphology supernova remnants, objects showing considerable overlap in their properties, in which a radio shell surrounds bright interior thermal X-rays.³ This combination contrasts with the more common shell-type remnants, whose X-ray emission follows the radio limb brightening. The centrally filled thermal X-rays, radiative recombination continua, and molecular-cloud association shown by W44 are the characteristics that define this class.³

The remnant remains a target of ongoing observation: amateur radio-telescope groups have recorded it repeatedly, with observations on 5 and 8 December 2022 and again in 2023, and it appears as a calibrated source in modern survey catalogs such as GLOSTAR, which lists its extent as Galactic longitude 34.390 to 34.930 and latitude −0.760 to −0.093.^{4 • 5}

References

1. G34.7-0.4 (W44), A Catalogue of Galactic Supernova Remnants, Mullard Radio Astronomy Observatory, Cambridge
2. Einstein Observations of the SNRs IC 443, W44 and W49B
3. Notes on type: mixed morphology supernova remnants, Berkeley SETI Research Center Exotica catalog
4. Activité en 2023, Radiotélescope du Parc de La Villette
5. GLOSTAR: Radio Source Catalog IV, Astronomy & Astrophysics

Initially written Oct 15, 2026 · Edited: Oct 25, 2026

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