A global view on star formation: The GLOSTAR Galactic plane survey. VII. Supernova remnants in the Galactic longitude range 28° < l < 36°

Context. While over 1000 supernova remnants (SNRs) are estimated to exist in the Milky Way, fewer than 400 have been found

to date. In the context of this apparent deficiency, more than 150 SNR candidates were recently identified in the D-configuration

Very Large Array (VLA-D) continuum images of the 4–8 GHz Global View on Star Formation (GLOSTAR) survey, in the Galactic

longitude range −2° < l < 60°.

Aims. We attempt to find evidence of nonthermal synchrotron emission from 35 SNR candidates in the Galactic longitude range

28° < l < 36°, and to study the radio continuum emission from the previously confirmed SNRs in this region.

Methods. Using the short-spacing-corrected GLOSTAR VLA-D+Effelsberg images, we measured the ∼6 GHz total and linearly

polarized flux densities of the SNR candidates and the confirmed SNRs. We also attempted to determine the spectral indices by

measuring flux densities from complementary Galactic plane surveys and from the temperature-temperature plots of the GLOSTAREffelsberg images.

Results. We provide evidence of nonthermal emission from four candidates that have spectral indices and polarization consistent with

a SNR origin, and, considering their morphology, we are confident that three of these (G28.36+0.21, G28.78-0.44, and G29.38+0.10)

are indeed SNRs. However, about 25% of the candidates (8 out of 35) have spectral index measurements that indicate thermal emission,

and the rest of them are so faint that is not possible to place a good constraint on the spectral index.

Conclusions. Additional observations at longer wavelengths and higher sensitivities will shed more light on the nature of these

candidates. A simple Monte Carlo simulation reiterates the view that future studies must persist with the current strategy of searching

for SNRs with small angular sizes to solve the problem of the Milky Way’s missing SNRs.