ROSAT survey observations of the Monogem Ring

Details ROSAT survey observations of the Monogem Ring ROSAT survey observations of the Monogem Ring

Jan 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........30p&link_type=abstract

PhD Dissertation, Wisconsin Univ. Madison, WI United States

Astronomy and Astrophysics

Astronomy

2

Supernova Remnants, Nebulae, X Ray Astronomy, Infrared Astronomy Satellite, Rosat Mission, Distance, Clouds, Temperature, Rings

Scientific paper

Maps of the 'Monogem Ring' in the R1 (110-284 eV), R2 (140-284 eV), and R4 + R5 (500-1100 eV) bands from the ROSAT All-Sky survey are presented. The Monogem Ring is a large region (diameter approximately 25 deg) of diffuse, soft X-ray emission centered at 1 approximately 203 deg and b approximately +12 deg. The ring is brightest in the R1 and R2 bands and extends across the galactic plane with no sign of absorption, indicating that the X-ray emitting region is in front of most of the neutral hydrogen in this direction. Spectral fits indicate that the most-likely value of the neutral hydrogen column density (NH) is 5.0 x 1019 cm-2. There are intrinsic spectral variations within the remnant, most notably from the low longitude side to the high longitude side, which would be consistent with a temperature increase from T = 105.95 K to T = 106.34 K, assuming a constant N(H) of 5.0 x 1019 cm-2. The flux in the R1 + R2 band was calculated to be 3.28 x 10-9 ergs cm-2 s-1 assuming this N(H) value. The X-ray maps have been compared with the total N(H) and IRAS 100 micron maps of the same region. The IRAS map reveals a cloud which is located along the line of sight to the central region of the ring. There is an anti-correlation between the X-ray intensity and the IRAS 100 micron intensity; however there is no change in the R2/R1 ratio in the region encompassing the cloud. We conclude that this is most likely a chance coincidence of the cloud overlapping the line of sight to the the X-ray emitting region which is truly ring-like in structure. The Monogem Ring is modelled as a supernova remnant (SNR) in the adiabatic stage at various distances between 100 and 850 pc. If the distance to the ring is 300 pc and the average temperature is T = 106.15 K, the initial ambient density is 5.2 x 10-3 cm-3, the initial explosion energy is 0.19 x 1051 ergs, and the age is approximately 86,000 yrs. The thermal pressure of the X-ray emitting gas is only 4.5 x 104 K cm-3, which is comparable to estimates of the pressure of the undisturbed interstellar medium (ISM). As this remnant continues to evolve, it will most likely reach pressure equilibrium with the ISM before it reaches the radiative stage of SNR evolution.

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