G181.1+9.5, a new high-latitude low-surface brightness supernova remnant

Abstract

Context. More than 90% of the known Milky Way supernova remnants (SNRs) are within 5• of the Galactic plane. The discovery of the new high-latitude SNR G181.1+9.5 will give us the opportunity to learn more about the environment and magnetic field at the interface between disk and halo of our Galaxy. Aims. We present the discovery of SNR G181.1+9.5, a new high-latitude SNR, serendipitously discovered in an ongoing survey of the Galactic anti-centre High-Velocity Cloud complex, observed with the DRAO Synthesis Telescope in the 21 cm radio continuum and H i spectral line.Methods. We use radio continuum observations (including the linearly polarized component) at 1420 MHz (observed with the DRAO ST) and 4850 MHz (observed with the Effelsberg 100-m radio telescope) to map G181.1+9.5 and determine its nature as a SNR. High-resolution 21 cm H i line observations and H i emission and absorption spectra reveal the physical characteristics of its local interstellar environment. Finally, we estimate the basic physical parameters of G181.1+9.5 using models for highly-evolved SNRs. Results. G181.1+9.5 has a circular shell-like morphology with a radius of about 16 pc at a distance of 1.5 kpc some 250 pc above the mid-plane. The radio observations reveal highly linearly polarized emission with a non-thermal spectrum. Archival ROSAT X-ray data reveal high-energy emission from the interior of G181.1+9.5 indicative of the presence of shock-heated ejecta. The SNR is in the advanced radiative phase of SNR evolution, expanding into the HVC inter-cloud medium with a density of n HI ≈ 1 cm −3 . Basic physical attributes of G181.1+9.5 calculated with radiative SNR models show an upper-limit age of 16 000 yr, a swept-up mass of more than 300 M , and an ambient density in agreement with that estimated from H i observations. Conclusions. G181.1+9.5 shows all characteristics of a typical mature shell-type SNR, but its observed faintness is unusual and requires further study.

Hoinga: a supernova remnant discovered in the SRG/eROSITA All-Sky Survey eRASS1

“…We note that other high-latitude SNRs have also been found to have unusually low brightness compared to those at low latitudes; see e.g. G181.1+9.5 (Kothes et al 2017) and G 0.1−9.7 (Hurley-Walker et al 2019b).…”

A revised catalogue of 294 Galactic supernova remnants

“…• G181.1+9.5, another high-latitude remnant, identified from radio observations by Kothes et al (2017).…”

Discovery of a new supernova remnant G21.8−3.0

“…In the case that G21.8−3.0 is not young, the small physical size requires a low initial explosion energy and/or a high ambient density into which it expands (Sedov 1959). However, as we failed to identify any related H i structures, it is difficult to estimate the initial ambient number density and further the age of G21.8−3.0 as done by Su et al (2017) and Kothes et al (2017). For the shell-type SNRs, distance and diameter can also be estimated from the empirical radio surface brightness -diameter (Σ-D) relation.…”

“…A number of new SNRs have also been identified through very careful inspections in arcmin-resolution images of very sensitive large-scale radio surveys (e.g. Foster et al 2013;Kothes et al 2014; ⋆ E-mail: xygao@nao.cas.cn (XYG) Gerbrandt et al 2014;Kothes et al 2017) and occasionally from deep Hα observations (e.g. Fesen & Milisavljevic 2010;Fesen et al 2015).…”