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Register a new userIs the Cygnus Superbubble a Hypernova Remnant?
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We present here the observation of the Cygnus Superbubble (CSB) using the Solid-state slit camera (SSC) aboard the Monitor of All-sky X-ray Image. The CSB is a large diffuse structure in the Cygnus region with enhanced soft X-ray emission. By utilizing the CCD spectral resolution of the SSC, we detect Fe, Ne, Mg emission lines from the CSB for the first time. The best fit model implies thin hot plasma of kT ~ 0.3 keV with depleted abundance of 0.26 +/- 0.1 solar. Joint spectrum fitting of the ROSAT PSPC data and MAXI/SSC data enables us to measure precise values of NH and temperature inside the CSB. The results show that all of the regions in the CSB have similar NH and temperature, indicating that the CSB is single unity. The energy budgets calculation suggests that 2-3 Myrs of stellar wind from the Cyg OB2 is enough to power up the CSB, whereas due to its off center position, the origin of the CSB is most likely a Hypernova.
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The nature of the synchrotron superbubble in the IC 10 galaxy is discussed using the results of our investigation of its ionized gas structure, kinematics, and emission spectrum from observations made with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, and based on our analysis of the radio emission of the region. The hypernova explosion is shown to be a more plausible mechanism of the formation of the synchrotron superbubble compared with the earlier proposed model of multiple supernova explosions. A compact remnant of this hypernova may be identified with the well known X-ray binary X-1 -- an accreting black hole.
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We present the analysis of Suzaku observations of the young open cluster Westerlund 2, which is filled with diffuse X-ray emission. We found that the emission consists of three thermal components or two thermal and one non-thermal components. The upper limit of the energy flux of the non-thermal component is smaller than that in the TeV band observed with H.E.S.S. This may indicate that active particle acceleration has stopped in this cluster, and that the accelerated electrons have already cooled. The gamma-ray emission observed with H.E.S.S. is likely to come from high-energy protons, which hardly cool in contrast with electrons. Metal abundances of the diffuse X-ray gas may indicate the explosion of a massive star in the past.
Using a deep Chandra AO-1 observation of the face-on spiral galaxy M101, we examine three of five previously optically-identified X-ray sources which are spatially correlated with optical supernova remnants (MF54, MF57, and MF83). The X-ray fluxes from these objects, if due to diffuse emission from the remnants, are bright enough to require a new class of objects, with the possible attribution by Wang to diffuse emission from hypernova remnants. Of the three, MF83 was considered the most likely candidate for such an object due to its size, nature, and close positional coincidence. However, we find that MF83 is clearly ruled out as a hypernova remnant by both its temporal variability and spectrum. The bright X-ray sources previously associated with MF54 and MF57 are seen by Chandra to be clearly offset from the optical positions of the supernova remnants by several arc seconds, confirming a result suggested by the previous work. MF54 does have a faint X-ray counterpart, however, with a luminosity and temperature consistent with a normal supernova remnant of its size. The most likely classifications of the sources are as X-ray binaries. Although counting statistics are limited, over the 0.3--5.0 keV spectral band the data are well fit by simple absorbed power laws with luminosities in the 10^38 to 10^39 ergs/s range. The power law indices are softer than those of Milky Way LMXB of similar luminosities, and are more consistent with those of the Large Magellanic Cloud. Both the high luminosity and the soft spectral shape favor these being accreting black hole binaries in high soft states.
Underlying nearly every quantitative discussion of the Cygnus Loop supernova remnant is uncertainty about its distance. Here we present optical images and spectra of nebulosities around two stars whose mass-loss material appears to have interacted with the remnants expanding shock front and thus can be used to estimate the Cygnus Loops distance. Narrow passband images reveal a small emission-line nebula surrounding an M4 red giant near the remnants eastern nebula NGC 6992. Optical spectra of the nebula show it to be shock-heated with significantly higher electron densities than seen in the remnants filaments. This along with a bow-shaped morphology suggests it is likely red giant mass-loss material shocked and accelerated by passage of the Cygnus Loops blast wave. We also identify a B7 V star located along the remnants northwestern limb which also appears to have interacted with the remnants shock wave. It lies within a small arc of nebulosity in an unusually complex region of highly curved and distorted filaments along the remnants northern shock front suggestive of a localized disturbance of the shock front due to the B stars stellar winds. Based on the assumption that these two stars lie inside the remnant, combined with an estimated distance to a molecular cloud situated along the remnants western limb, we propose a distance to the Cygnus Loop of 1.0 +/- 0.2 kpc. Although larger than several recent estimates of 500 - 800 pc, a distance ~1 kpc helps resolve difficulties with the remnants postshock cosmic ray and gas pressure ratio and estimated supernova explosion energy.
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