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تسجيل مستخدم جديدG107.0+9.0: A New Large Optically Bright, Radio and X-Ray Faint Galactic Supernova Remnant in Cepheus
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Wide-field H-alpha images of the Galactic plane have revealed a new supernova remnant (SNR) nearly three degrees in diameter centred at l = 107.0, b = +9.0. Deep and higher resolution H-alpha and [O III] 5007 Ang images show dozens of H-alpha filaments along the remnants northern, western, and southwestern limbs, but few [O III] bright filaments. The nebula is well detected in the H-alpha Virginia Tech Spectral-Line Survey images, with many of its brighter filaments even visible on Digital Sky Survey images. Low-dispersion spectra of several filaments show either Balmer dominated, non-radiative filaments or the more common SNR radiative filaments with [S II]/H-alpha ratios above 0.5, consistent with shock-heated line emission. Emission line ratios suggest shock velocities ranging from <70 km/s along its western limb to ~100 km/s along its northwestern boundary. While no associated X-ray emission is seen in ROSAT images, faint 1420 MHz radio emission appears coincident with its western and northern limbs. Based on an analysis of the remnants spatially resolved H-alpha and [O III] emissions, we estimate the remnants distance around 1.5 - 2.0 kpc implying a physically large (dia.= 75 - 100 pc) and old (90 - 110 x 10^3 yr) SNR in its post-Sedov radiative phase of evolution expanding into a low density interstellar medium (n = 0.05 - 0.2 cm^-3) and lying some 250 - 300 pc above the Galactic plane.
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The vast majority of Galactic supernova remnants (SNRs) were detected by their synchrotron radio emission. Recently, the evolved SNR G107.0+9.0 with a diameter of about 3~deg or 75~pc up to 100~pc in size was optically detected with an indication of
faint associated radio emission. This SNR requires a detailed radio study. We aim to search for radio emission from SNR G107.0+9.0 by analysing new data from the Effelsberg 100-m and the Urumqi 25-m radio telescopes in addition to available radio surveys. Radio SNRs outside of the Galactic plane, where confusion is rare, must be very faint if they have not been identified so far. Guided by the H$alpha$ emission of G107.0+9.0, we separated its radio emission from the Galactic large-scale emission. Radio emission from SNR G107.0+9.0 is detected between 22~MHz and 4.8~GHz with a steep non-thermal spectrum, which confirms G107.0+9.0 as an SNR. Its surface brightness is among the lowest known for Galactic SNRs. Polarised emission is clearly detected at 1.4~GHz but is fainter at 4.8~GHz. We interpret the polarised emission as being caused by a Faraday screen associated with G107.0+9.0 and its surroundings. Its ordered magnetic field along the line of sight is below 1~$mu$G. At 4.8~GHz, we identified a depolarised filament along the western periphery of G107.0+9.0 with a magnetic field strength along the line of sight $B{_{||}} sim 15~mu$G, which requires magnetic field compression. G107.0+9.0 adds to the currently small number of known, evolved, large-diameter, low-surface-brightness Galactic SNRs. We have shown that such objects can be successfully extracted from radio-continuum surveys despite the dominating large-scale diffuse Galactic emission.
Wide-field Halpha images of the radio faint Galactic supernova remnant G182.4+4.2 reveal a surprisingly extensive and complex emission structure, with an unusual series of broad and diffuse filaments along the remnants southwestern limb. Deep [O III]
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