This paper explores the feasibility of applying genetic programming (GP) to multicategory pattern classification problem for the first time. GP can discover relationships among observed data and express them mathematically. Multicategory pattern classification has been done traditionally by using the maximum likelihood classifier (MLC). GP-based techniques have an advantage over statistical methods because they are distribution free, i.e., no prior knowledge is needed about the statistical distribution of the data. GP also has the ability to automatically discover the discriminant features for a class. GP has been applied for two-category (class) pattern classification. In this paper, a methodology for GP-based -class pattern classification is developed. The given -class problem is modeled as two-class problems, and a genetic programming classifier expression (GPCE) is evolved as a discriminant function for each class. The GPCE is trained to recognize samples belonging to its own class and reject samples belonging to other classes. A strength of association (SA) measure is computed for each GPCE to indicate the degree to which it can recognize samples belonging to its own class. The higher the value of SA, the better is the ability of a GPCE to recognize samples belonging to its own class and reject samples belonging to other classes. The SA measure is used for uniquely assigning a class to an input feature vector. Heuristic rules are used to prevent a GPCE with a higher SA from swamping a GPCE with a lower SA. Experimental results are presented to demonstrate the applicability of GP for multicategory pattern classification, and the results obtained are found to be satisfactory, and are compared with those of the MLC. We also discuss the various issues that arise in our approach to GP-based classification, such as the creation of training sets, the role of incremental learning, and the choice of function set in the evolution of GPCEs, as well as conflict resolution for uniquely assigning a class.

We present the results of a systematic investigation of spectral evolution in the Z source GX 349+2, using data obtained during 1998 with Proportional-Counter-Array (PCA) on-board the RXTE satellite. The source traced a extended normal branch (NB) and flaring branch (FB) in the color-color diagram (CD) and hardness-intensity diagram (HID) during these observations. The spectra at different positions of Z-track were best fitted by a model consisting of a disk blackbody and a comptonized spectrum. A broad (gaussian) iron line at $\sim 6.7$ keV is also required to improve the fit. The spectral parameters showed a systematic and significant variation with the position along the Z-track. The evolution in spectral parameters is discussed in the view of increasing mass accretion rate scenario, proposed to explain the motion of Z sources in the CD and HID.Comment: 7 pages, 5 figures, 2 tables, accepted for the publication in the MNRA

In this paper, we present the first results of spectral and timing properties of the atoll source 4U 1705-44 using ∼ 100 ks data obtained with Large Area X-ray Proportional Counter (LAXPC) onboard AstroSat. The source was in the high-soft state during our observations and traced out a banana track in the Hardness Intensity Diagram (HID). We study the evolution of the Power Density Spectra (PDS) and the energy spectra along the HID. PDS show presence of a broad Lorentzian feature (Peaked Noise or PN) centered at 1 − 13 Hz and a very low frequency noise (VLFN). The energy spectra can be described by sum of a thermal Comptonized component, a power-law and a broad iron line. The hard tail seen in the energy spectra is variable and contribute 4 − 30% of the total flux. The iron line seen in this source is broad (FWHM ∼ 2 keV) and strong (EW ∼ 369 − 512 eV). Only relativistic smearing in the accretion disc can not explain the origin of this feature and requires other mechanism such as broadening by Comptonization process in the external part of the 'Comptonized Corona'. A subtle and systematic evolution of the spectral parameters (optical depth, electron temperature etc.) is seen as the source moves along the HID. We study the correlation between frequency of the PN and the spectral parameters. PN frequency seems to be correlated with the strength of the corona. We discuss the implication of the results in the paper.

We present the results of an analysis of data from XMM-Newton and Chandra observations of the highluminosity narrow-line quasar PG 1404ϩ226. We confirm a strong soft X-ray excess in the X-ray spectrum, and we find rapid variability (a factor of 2 in about 5000 s). When the X-ray spectrum is fitted with a two-component model that includes a power-law and a blackbody component, we find that low-energy absorption lines are required to fit the data. If we interpret these lines as due to highly ionized species of heavy elements in an outflowing accretion disk wind, an outflow velocity of ∼26,000 km s Ϫ1 could be derived. One interesting feature of the present observation is the possible detection of variability in the absorption features: the absorption lines are visible only when the source is bright. From the upper limits of the equivalent widths of the absorption lines during the low-flux states and also from the model-independent pulse-height ratios, we argue that the strength of absorption is lower during the low-flux states. This constrains the physical size of the absorbing medium within 100 Schwarzschild radius (R S ) of the putative supermassive black hole. We also find a marginal evidence of a correlation between the strength of the absorption line and the X-ray luminosity.

We examine the dynamical behavior of accretion flow around XTE J1859+226 during the 1999 outburst by analyzing the entire outburst data (∼ 166 days) from RXTE Satellite. Towards this, we study the hysteresis behavior in the hardness intensity diagram (HID) based on the broadband (3−150 keV) spectral modeling, spectral signature of jet ejection and the evolution of Quasiperiodic Oscillation (QPO) frequencies using the twocomponent advective flow model around a black hole. We compute the flow parameters, namely Keplerian accretion rate (ṁ d ), sub-Keplerian accretion rate (ṁ h ), shock location (r s ) and black hole mass (M bh ) from the spectral modeling and study their evolution along the q-diagram. Subsequently, the kinetic jet power is computed as L obs jet ∼ 3 − 6 × 10 37 erg s −1 during one of the observed radio flares which indicates that jet power corresponds to 8 − 16% mass outflow rate from the disc. This estimate of mass outflow rate is in close agreement with the change in total accretion rate (∼ 14%) required for spectral modeling before and during the flare. Finally, we provide a mass estimate of the source XTE J1859+226 based on the spectral modeling that lies in the range of 5.2 − 7.9M ⊙ with 90% confidence.