On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

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The Observation of Gravitational Waves from a Binary Black Hole Merger

Monthly Notices is one of the three largest general primary astronomical research publications. It is an international journal, published by the Royal Astronomical Society. This article 1 describes its publication policy and practice.

Monthly Notices of the Royal Astronomical Society

LOFAR, the LOw-Frequency ARray, is a new-generation radio interferometer constructed in the north of the Netherlands and across europe. Utilizing a novel phased-array design, LOFAR covers the largely unexplored low-frequency range from 10-240 MHz and provides a number of unique observing capabilities. Spreading out from a core located near the village of Exloo in the northeast of the Netherlands, a total of 40 LOFAR stations are nearing completion. A further five stations have been deployed throughout Germany, and one station has been built in each of France, Sweden, and the UK. Digital beam-forming techniques make the LOFAR system agile and allow for rapid repointing of the telescope as well as the potential for multiple simultaneous observations. With its dense core array and long interferometric baselines, LOFAR achieves unparalleled sensitivity and angular resolution in the low-frequency radio regime. The LOFAR facilities are jointly operated by the International LOFAR Telescope (ILT) foundation, as an observatory open to the global astronomical community. LOFAR is one of the first radio observatories to feature automated processing pipelines to deliver fully calibrated science products to its user community. LOFAR's new capabilities, techniques and modus operandi make it an important pathfinder for the Square Kilometre Array (SKA). We give an overview of the LOFAR instrument, its major hardware and software components, and the core science objectives that have driven its design. In addition, we present a selection of new results from the commissioning phase of this new radio observatory.

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LOFAR: The LOw-Frequency ARray

Many problems in the experimental estimation of parameters for models can be solved through use of the likelihood ratio test. Applications of the likelihood ratio, with particular attention to photon counting experiments, are discussed. The procedures presented solve a greater range of problems than those currently in use, yet are no more difficult to apply. The procedures are proved analytically, and examples from current problems in astronomy are discussed.

Parameter estimation in astronomy through application of the likelihood ratio. [satellite data analysis techniques

After the All-Sky Automated Survey for SuperNovae discovered a significant brightening of the inner region of NGC 2617, we began a ∼70 day photometric and spectroscopic monitoring campaign from the X-ray through near-infrared (NIR) wavelengths. We report that NGC 2617 went through a dramatic outburst, during which its X-ray flux increased by over an order of magnitude followed by an increase of its optical/ultraviolet (UV) continuum flux by almost an order of magnitude. NGC 2617, classified as a Seyfert 1.8 galaxy in 2003, is now a Seyfert 1 due to the appearance of broad optical emission lines and a continuum blue bump. Such 'changing look active galactic nuclei (AGNs)' are rare and provide us with important insights about AGN physics. Based on the Hβ line width and the radius-luminosity relation, we estimate the mass of central black hole (BH) to be (4 ± 1) × 10{sup 7} M {sub ☉}. When we cross-correlate the light curves, we find that the disk emission lags the X-rays, with the lag becoming longer as we move from the UV (2-3 days) to the NIR (6-9 days). Also, the NIR is more heavily temporally smoothed than the UV. This can largely be explained bymore » a simple model of a thermally emitting thin disk around a BH of the estimated mass that is illuminated by the observed, variable X-ray fluxes.« less

https://iopscience.iop.org/article/10.1088/0004-637X/788/1/48/pdf

The man behind the curtain: x-rays drive the uv through nir variability in the 2013 active galactic nucleus outburst in ngc 2617

In this work, we study the synthetic explosions of a massive star. We take a 100 M$_{\odot}$ zero--age main--sequence (ZAMS) star and evolve it until the onset of core-collapse using {\tt MESA}. Then, the resulting star model is exploded using the publicly available stellar explosion code, {\tt STELLA}. The outputs of {\tt STELLA} calculations provide us the bolometric light curve and photospheric velocity evolution along with other physical properties of the underlying supernova. In this paper, the effects of having large Hydrogen-envelope on the supernova light curve have been explored. We also explore the effects of the presence of different amounts of nickel mass and the effect of changing the explosion energy of the resulting supernovae from such heavy progenitors, on their bolometric light curves and photospheric velocities. 

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Core-collapse supernova from a possible progenitor star of 100 
 
 
 
 $$M_{\odot }$$
 
 
 M
 ⊙
 
 


Discovery of a Supernova Candidate

BOOTES‐IR is the natural evolution of BOOTES (Burst Observer and Optical Transient Exploring System) towards the near‐infrared (NIR). Using the experience gathered during the last 7 years, we are developing a powerful tool for the detection and study of Gamma‐Ray Burst (GRB) afterglows. The system includes a custom developed robotic observatory software (RTS2) that manages all the instruments and devices of the observatory to make them work together in an optimal way. Additionally we have created a package of real time reduction and analysis tools (JIBARO) that allow us to automatically identify GRB afterglow candidates. The telescope, a 0.6m Ritchey‐Chretien, now in commissioning phase, is capable of pointing with a typical delay of 5 seconds between arrival of the alert and start of the first exposure. The NIR camera, with 1024 × 1024 pixels and a field of view of 12′ × 12′ will see first light in Spring 2006 and is expected to be in normal operation during the Summer. An optical camera working in parallel will complement observations.

BOOTES‐IR: The extension of BOOTES towards the near‐IR

We present an analysis of long-term X-ray and optical observations of the Wolf-Rayet binary WR 25. Using archival data from observations with the XMM-Newton and the Swift observatories spanning over ~10 yr, we show that WR 25 is a periodic variable in X-rays with a period of $208 \pm 3$ days. X-ray light curves in the 0.5-10.0 keV energy band show phase-locked variability, where the flux increased by a factor of ~2 from minimum to maximum, being maximum near periastron passage. The light curve in the soft energy band (0.5-2.0 keV) shows two minima indicating the presence of two eclipses. However, the light curve in the hard energy band (2.0-10.0 keV) shows only one minimum during the apastron passage. The X-ray spectra of WR 25 were explained by a two-temperature plasma model. Both the cool and the hot plasmas were constant at 0.628+/-0.008 and 2.75+/-0.06 keV throughout an orbital cycle, where the cooler plasma could be due to the small scale shocks in a radiation-driven outflow and the high temperature plasma could be due to the collision of winds. The column density varied with the orbital phase and was found to be maximum after the periastron passage, when the WN star is in front of the O star. The abundances of WR 25 were found to be non-solar. Optical V-band data of WR 25 also show the phase-locked variability, being at maximum near periastron passage. The results based on the present analysis indicate that WR 25 is a colliding wind binary where the presence of soft X-rays is attributed to individual components; however, hard X-rays are due to the collision of winds.

Phase-resolved XMM-Newton and swift observations of WR 25

By the introduction of micro processors and resolution in power electronics devices, power quality becomes a major issue. Uninterrupted and best power quality is the current demand of every consumer for their sensitive devices. In the resolution in the field of renewable energy sources particularly solar and wind, grid integrated with these renewable system is the primarily need of future. The major challenge with these renewable sources is their variability in power supply. Use of power electronic devices in making the output supply of the renewable sources as per the grid requirement introduces harmonics into the system which degrade the power quality. Installation of custom power devices such as DVR and DSTATCOM is an effective solution of such problem. These devices are capable of maintaining the active and reactive power flow of the system. In this paper the operation of DVR in mitigating the dominant harmonics and improve the power quality.

Shashi B. Pandey

Papers

Core-collapse supernova from a possible progenitor star of 100 $$M_{\odot }$$ M ⊙

Discovery of a Supernova Candidate

BOOTES‐IR: The extension of BOOTES towards the near‐IR

Phase-resolved XMM-Newton and swift observations of WR 25

A Remedy for Elimination of Harmonics in Solar Integrated Grid System