Observations of the Corona Borealis supercluster with the superextended Very Small Array: further constraints on the nature of the non-Gaussian cosmic microwave background cold spot

We present interferometric imaging at 33GHz, with the new superextended configuration of the Very Small Array (VSA), of a very deep decrement inthe cosmic microwave background (CMB) temperature. This decrement islocated in the direction of the Corona Borealis supercluster, at aposition with no known galaxy clusters, and was discovered by a previousVSA survey. A total area of 3deg2 has now been imaged, withan angular resolution of 7arcmin and a flux sensitivity of5mJybeam-1.These observations confirm the presence of this strong and resolvednegative spot at -37 +/- 5mJybeam-1 (-229 +/- 32muK). Thisstructure is also present in the Wilkinson Microwave Anisotropy Probe5-year data. The temperature of the W-band (94GHz) data at the positionof the decrement agrees within 0.3sigman with that observedby the VSA at 33GHz and within 0.2sigman with theSunyaev-Zel'dovich (SZ) spectrum.Our analyses show that it is a non-Gaussian feature in the CMB at alevel of 4.4sigma, where sigma accounts for primordial CMBfluctuations, thermal noise and residual radio source contributions. Theprobability of finding such a deviation or larger in simulationsincluding Gaussian CMB is only 0.63per cent. Therefore, an explanationother than primordial Gaussian CMB is required. We have considered thepossibility of an SZ effect generated in a diffuse, extended warm/hotgas distribution. This hypothesis is especially relevant, as thepresence of such structures, if confirmed, could provide the locationfor a significant fraction of the missing baryons in the Local Universe.However, from the absence of X-ray emission in this region we concludethat the whole decrement cannot be generated solely via the SZ effect insuch structure. Therefore, the most plausible scenario is a combinationbetween a negative CMB feature and a SZ effect, probably generated by awarm/hot gas distribution.