Discovery of hard X-ray delays in the X-ray emission of the Seyfert 1 galaxy Mrk~110: possible evidence for Comptonization

We report the discovery of hard X-ray delays in the X-ray emission of the Seyfert 1 galaxy Mrk 110, based on a long XMM-Newton observation. Cross correlation between the X-ray light curves of different energy bands reveals an energy dependent delay ranging from a few minutes to an hour. We find that the energy spectrum can be modeled by Comptonization of disk blackbody photons. The energy dependent delay can be modeled as due to the effect of Comptonization in a hot plasma confined within 10 Schwarzschild radius of the black hole. We discuss our results in the context of inverse Comptonization of the soft photons by highly energetic plasma.Comment: 4 pages, 4 figures, To appear in Astrophysical Journal Lette

Infiltration under two contrasting hydrologic scenarios in Texas

Investigation of infiltration provides insights about the flow of water and transport of contaminants through the vadose zone. Infiltration is governed by prevailing environmental conditions like soil characteristics, plant cover and geologic settings. The main objective was to study preferential flow dominated infiltration at two contrasting hydrologic settings in Texas. For the first study, artificial rainfall was simulated within a plot covered with juniper trees at a karst region of the Edwards Plateau and sub-surface flow was monitored using TDR probes. Sub-surface flow was simulated using HYDRUS-2D. Results demonstrated that sub-surface flow occurred in a tri-modal manner, consisting of flow in karst conduits, planar fractures in the limestone, and soil matrix. Both fracture and matrix flow responses increased with increase in rainfall intensity. During large rainfall events, water exchange was observed between the fractures and matrix. Dye studies indicated that fractures and juniper roots were primary pathways for preferential flow occurring within the plot. The model simulated flow characteristics like exchange processes and differentiated between preferential and conduit flow besides determining approximate van Genuchten parameters for each geologic unit.For the second study, tension infiltrometers were used to conduct infiltration experiments at six soil water pressures (?? = -0.2 to 0 m) in an agricultural field near College Station over a 21 month period. The aim was to determine steady infiltration rate, if, saturated hydraulic conductivity, Ksat, unsaturated hydraulic conductivity, K(??) and unsaturated flux density ??(??). Moreover, the effect of varying disc diameters on steady state infiltration rates (if) was also studied. Results demonstrated that infiltration occurred in a bi-modal fashion consisting of preferential flow and matrix flow. Macropores and roots present in the soil resulted in gravity dominated flow at ?? = -0.05 to 0 m for all experiments. Statistical analysis suggested that the soil did not exhibit spatial variability within the plot and the five different disc diameters had no effect on if. Statistically significant differences in if were observed between 0.2 and 0.24 m disc diameters at saturation over the 21 month period. The if values illustrated strong temporal variations based on natural conditions over the 21 month period

Wrinkles, folds and ripplocations: unusual deformation structures of confined elastic sheets at non-zero temperatures

We study the deformation of a fluctuating crystalline sheet confined between two flat rigid walls as a simple model for layered solids where bonds among atoms {\it within} the same layer are much stronger than those {\it between} layers. When subjected to sufficiently high loads in an appropriate geometry, these solids deform and fail in unconventional ways. Recent experiments suggest that configurations named {\it ripplocations}, where a layer folds backwards over itself, are involved. These structures are distinct and separated by large free energy barriers from smooth {\it ripples} of the atomic layers that are always present at any non-zero temperature. We use Monte Carlo simulation in combination with an umbrella sampling technique to obtain conditions under which such structures form and study their specific experimental signatures.Comment: 8 pages, 7 figure

XMM observations of the narrow-line QSO PHL 1092: Detection of a high and variable soft component

We present results based on an XMM-Newton observation of the high luminosity narrow-line QSO PHL 1092 performed in 2003 January. The 0.3 - 10 keV spectrum is well described by a model which includes a power-law (Gamma ~ 2.1) and two blackbody components (kT ~ 130 eV and kT ~ 50 eV). The soft X-ray excess emission is featureless and contributes ~ 80% to the total X-ray emission in the 0.3 - 10 keV band. The most remarkable feature of the present observation is the detection of X-ray variability at very short time scale: the X-ray emission varied by 35% in about 5000 s. We find that this variability can be explained by assuming that only the overall normalization varied during the observation. There was no evidence for any short term spectral variability and the spectral shape was similar even during the ASCA observation carried out in 1997. Considering the high intrinsic luminosity (~ 2x10^45 erg/s) and the large inferred mass of the putative black hole (~ 1.6x10^8 M_sun), the observed time scale of variability indicates emission at close to Eddington luminosity arising from very close to the black hole. We suggest that PHL 1092 in particular (and narrow line Seyfert galaxies in general) is a fast rotating black hole emitting close to its Eddington luminosity and the X-ray emission corresponds to the high-soft state seen in Galactic black hole sources.Comment: 7 figures, 8 pages, emulateapj style, ApJ in pres

Detection of absorption features in the X-ray spectrum of the narrow-line Quasar PG 1404+226 : Possible evidence for accretion disk winds

We present the results of an analysis of data from XMM-Newton and CHANDRA observations of the high luminosity narrow-line quasar PG 1404+226. We confirm a strong soft X-ray excess in the X-ray spectrum and we find rapid variability (a factor of two in about 5000 s). When the X-ray spectrum is fit with a two component model which 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 about 26000 km/s 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 (EW) 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 constraints the physical size of the absorbing medium within 100 Schwartzschild radius (Rg) of the putative supermassive black hole. We also find a marginal evidence for a correlation between the strength of the absorption line and the X-ray luminosity.Comment: 4 pages, 4 figures, Astrophysical Journal Letter (in press

An investigation of the origin of soft X-ray excess emission from Narrow-line Seyfert 1 galaxies Akn564 and Mrk1044

We investigate the origin of the soft X-ray excess emission from narrow-line Seyfert 1 galaxies Akn564 and Mrk1044 using XMM-Newton observations. We find clear evidence for time delays between the soft and hard X-ray emission from Akn564 based on a 100ks long observation. The variations in the 4-10keV band lag behind that in the 0.2-0.5keV band by 1768+/-122s. The full band power density spectrum (PDS) of Akn~564 has a break at ~1.2e-3Hz with power-law indices of ~1 and ~3 below and above the break. The hard (3-10keV) band PDS is stronger and flatter than that in the soft (0.2-0.5keV) band. Based on a short observation of Mrk1044, we find no correlation between the 0.2-0.3keV and 5-10keV bands at zero lag. These observations imply that the soft excess is not the reprocessed hard X-ray emission. The high resolution spectrum of Akn564 obtained with the RGS shows evidence for a highly ionized and another weakly ionized warm absorber medium. The smeared wind and blurred ionized reflection models do not describe the pn data adequately. The spectrum is consistent with a complex model consisting of optically thick Comptonization in a cool plasma for the soft excess and a steep power-law, modified by two warm absorber media as inferred from the RGS data and the foreground Galactic absorption. The smeared wind and optically thick Comptonization models both describe the spectrum of Mrk1044 satisfactorily, but the ionized reflection model requires extreme parameters. The data suggest two component corona -- a cool, optically thick corona for the soft excess and a hot corona for the power-law component. The existence of a break in the soft band PDS suggests a compact cool corona that can either be an ionized surface of the inner disk or an inner optically thick region coupled to a truncated disk.Comment: Accepted for publication in ApJ, 19 page

An Investigation of Suicidal Ideation from Social Media Using Machine Learning Approach

  Despite improvements in the detection and treatment of severe mental disorders, suicide remains a significant public health concern. Suicide prevention and control initiatives can benefit greatly from a thorough comprehension and foreseeability of suicide patterns. Understanding suicide patterns, especially through social media data analysis, can help in suicide prevention and control efforts. The objective of this study is to evaluate predictors of suicidal behavior in humans using machine learning. It is crucial to create a machine learning model for detection of suicide thoughts by monitoring a user's social media posts to identify warning signs of mental health issues. Through the analysis of social media posts, our research intends to develop a machine learning model for identifying suicide ideation and probable mental health problems. This study will help immensely to comprehend the environmental risk factors that influence suicidal thoughts and conduct across time. In this research the use of machine learning on social media data is an exciting new direction for understanding the environmental risk factors that impact an individual's susceptibility to suicide ideation and conduct over time. The machine learning algorithms showed high accuracy, precision, recall, and F1-score in detecting suicide patterns on social media data whereas SVM has the highest performance with an accuracy of 0.886.    

Pseudo-Schwarzschild Spherical Accretion as a Classical Black Hole Analogue

We demonstrate that a spherical accretion onto astrophysical black holes, under the influence of Newtonian or various post-Newtonian pseudo-Schwarzschild gravitational potentials, may constitute a concrete example of classical analogue gravity naturally found in the Universe. We analytically calculate the corresponding analogue Hawking temperature as a function of the minimum number of physical parameters governing the accretion flow. We study both the polytropic and the isothermal accretion. We show that unlike in a general relativistic spherical accretion, analogue white hole solutions can never be obtained in such post-Newtonian systems. We also show that an isothermal spherical accretion is a remarkably simple example in which the only one information--the temperature of the fluid, is sufficient to completely describe an analogue gravity system. For both types of accretion, the analogue Hawking temperature may become higher than the usual Hawking temperature. However, the analogue Hawking temperature for accreting astrophysical black holes is considerably lower compared with the temperature of the accreting fluid.Comment: Final Version to appear in the journal General Relativity & Gravitation, Volume 27, Issue 11, 2005. 17 pages, Two colour and one black and white figures. Typos corrected. Recent reference on analogue effect in relativistic accretion disc adde