COBE Constraints on a Local group X-ray Halo

We investigate the effect of a putative X-ray emitting halo surrounding the Local Group of galaxies, and specifically the possible temperature anisotropies induced in the COBE-DMR four-year sky maps by an associated Sunyaev-Zel'dovich effect. By fitting the isothermal spherical halo model proposed by Suto et.al. (1996) to the coadded four-year COBE-DMR 53 and 90 GHz sky maps in Galactic coordinates, we find no significant evidence of a contribution. We therefore reject the claim that such a halo can affect the estimation of the primordial spectral index and amplitude of density perturbations as inferred from the DMR data. We find that correlation with the DMR data imposes constraints on the plausible contribution of such an X-ray emitting halo to a distortion in the CMB spectrum (as specified by the Compton-y parameter), up to a value for R -- the ratio of the core radius of the isothermal halo gas distribution to the distance to the Local Group centroid -- of 0.68. For larger values of R, the recent cosmological upper limit derived by COBE-FIRAS provides stronger constraints on the model parameters. Over the entire parameter space for R, we find an upper limit to the inferred sky-RMS anisotropy signal of 14 microKelvin (95% c.l.), a negligible amount relative to the 35 microKelvin signal observed in the COBE-DMR data.Comment: 4 pages, 3 figures; accepted for publication in MNRAS pink page

Testing the Gaussianity of the COBE-DMR data with spherical wavelets

We investigate the Gaussianity of the 4-year COBE-DMR data (in HEALPix pixelisation) using an analysis based on spherical Haar wavelets. We use all the pixels lying outside the Galactic cut and compute the skewness, kurtosis and scale-scale correlation spectra for the wavelet coefficients at each scale. We also take into account the sensitivity of the method to the orientation of the input signal. We find a detection of non-Gaussianity at $> 99$ per cent level in just one of our statistics. Taking into account the total number of statistics computed, we estimate that the probability of obtaining such a detection by chance for an underlying Gaussian field is 0.69. Therefore, we conclude that the spherical wavelet technique shows no strong evidence of non-Gaussianity in the COBE-DMR data.Comment: latex file 7 pages, 6 figures, submitted to MNRA

Technology Corner: Analysing E-Mail Headers for Forensic Investigation

Electronic Mail (E-Mail), which is one of the most widely used applications of Internet, has become a global communication infrastructure service. However, security loopholes in it enable cybercriminals to misuse it by forging its headers or by sending it anonymously for illegitimate purposes, leading to e-mail forgeries. E-mail messages include transit handling envelope and trace information in the form of structured fields which are not stripped after messages are delivered, leaving a detailed record of e-mail transactions. A detailed header analysis can be used to map the networks traversed by messages, including information on the messaging software and patching policies of clients and gateways, etc. Cyber forensic e-mail analysis is employed to collect credible evidence to bring criminals to justice. This paper projects the need for e-mail forensic investigation and lists various methods and tools used for its realization. A detailed header analysis of a multiple tactic spoofed e-mail message is carried out in this paper. It also discusses various possibilities for detection of spoofed headers and identification of its originator. Further, difficulties that may be faced by investigators during forensic investigation of an e-mail message have been discussed along with their possible solutions

On the Non-Gaussianity Observed in the COBE-DMR Sky Maps

In this paper we pursue the origin of the non-Gaussianity determined by a bispectrum analysis of the COBE-DMR 4-year sky maps. The robustness of the statistic is demonstrated by the rebinning of the data into 12 coordinate systems. By computing the bispectrum statistic as a function of various data partitions - by channel, frequency, and time interval, we show that the observed non-Gaussian signal is driven by the 53 GHz data. This frequency dependence strongly rejects the hypothesis that the signal is cosmological in origin. A jack-knife analysis of the coadded 53 and 90 GHz sky maps reveals those sky pixels to which the bispectrum statistic is particularly sensitive. We find that by removing data from the 53 GHz sky maps for periods of time during which a known systematic effect perturbs the 31 GHz channels, the amplitudes of the bispectrum coefficients become completely consistent with that expected for a Gaussian sky. We conclude that the non-Gaussian signal detected by the normalised bispectrum statistic in the publicly available DMR sky maps is due to a systematic artifact. The impact of removing the affected data on estimates of the normalisation of simple models of cosmological anisotropy is negligible.Comment: 14 pages, plus 8 Postscript and 3 GIF figures. LaTeX2e document using AASTeX v5.0 macros. Revised version accepted for publication in the Astrophysical Journal: small changes to the text, minor modifications to figures 1 and