Is the Cygnus Superbubble a Hypernova Remnant

We present here an observation of the Cygnus Superbubble (CSB) using the Solid-state slit camera (SSC) aboard the Monitor of All-sky X-ray Image (MAXI). 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 detected Fe, Ne, Mg emission lines from the CSB for the first time. The best-fit model implies a thin hot plasma of kT � 0.3 keV with a depleted abundance of 0.26 ˙ 0.1 solar. Joint spectrum fittings of the ROSAT/PSPC data and MAXI/SSC data enabled us to measure precise values of NH and the temperature inside the CSB. The results show that all of the regions in the CSB have a similar NH and temperature, indicating that the CSB is a single unity. An energy budgets calculation suggests that (2–3) � 10 6 yr of stellar wind from the Cyg OB2 is sufficient to power up the CSB, whereas due to its off-center position, the origin of the CSB is most likely to be a Hypernova.