Simultaneous X-ray and optical observations of thermonuclear bursts in the LMXB EXO 0748-676

We report the detection of a large number of optical bursts in the Low Mass X-ray Binary (LMXB) EXO 0748-676 simultaneous with the thermonuclear X-ray bursts. The X-ray and the optical bursts are detected in a long observation of this source with the XMM-Newton observatory. This has increased the number of thermonuclear X-ray bursts in the LMXBs with simultaneous optical detection by several factors. The optical bursts are found to have a linear rise followed by a slow, somewhat exponential decay. Most of the optical bursts have longer rise and decay timescale compared to the corresponding X-ray bursts. We have determined the X-ray and optical excess photon counts in the bursts that allow us to look at the optical to X-ray burst fluence ratio for each burst and the ratio as a function of the X-ray burst intensity and as a function of the orbital phase. The delay between the onset of the X-ray bursts and the onset of the optical bursts have also been measured and is found to have an average value of 3.25 seconds. We do not find any convincing evidence of orbital phase dependence of the following parameters: X-ray to optical delay, rise time of the optical bursts, and optical to X-ray burst intensity ratio as would be expected if the optical bursts were produced by reprocessing from the surface of the secondary star that is facing the compact star. On the other hand, if the optical bursts are produced by reprocessing of the X-rays in the accretion disk, the onset of the bursts is not expected to have a sharp, linear shape as is observed in a few of the bursts in EXO 0748-676. We emphasise the fact that simultaneous optical observations of the X-ray bursts in multiple wavelength bands will enable further detailed investigations of the reprocessing phenomena, including any non-linear effect of the X-ray irradiation.Comment: 12 pares, 5 figures (Submitted to the Bulletin of the Astronomical Society of India

Exploring Short-GRB afterglow parameter space for observations in coincidence with gravitational waves

Short duration Gamma Ray Bursts(SGRB) and their afterglows are among the most promising electro-magnetic (EM) counterparts of Neutron Star (NS) mergers. The afterglow emission is broadband, visible across the entire electro-magnetic window from $\gamma$-ray to radio frequencies. The flux evolution in these frequencies is sensitive to the multi-dimensional afterglow physical parameter space. Observations of gravitational wave (GW) from BNS mergers in spatial and temporal coincidence with SGRB and associated afterglows can provide valuable constraints on afterglow physics. We run simulations of GW-detected BNS events and assuming all of them are associated with a GRB jet which also produces an afterglow, investigate how detections or non-detections in X-ray, optical and radio frequencies can be influenced by the parameter space. We narrow-down the regions of afterglow parameter space for a uniform top-hat jet model which would result in different detection scenarios. We list inferences which can be drawn on the physics of GRB afterglows from multi-messenger astronomy with coincident GW-EM observations.Comment: Published in MNRA

Implementation of low-loss superinductances for quantum circuits

The simultaneous suppression of charge fluctuations and offsets is crucial for preserving quantum coherence in devices exploiting large quantum fluctuations of the superconducting phase. This requires an environment with both extremely low DC and high RF impedance. Such an environment is provided by a superinductance, defined as a zero DC resistance inductance whose impedance exceeds the resistance quantum $R_Q = h/(2e)^2 \simeq 6.5\ \mathrm{k\Omega}$ at frequencies of interest (1 - 10 GHz). In addition, the superinductance must have as little dissipation as possible, and possess a self-resonant frequency well above frequencies of interest. The kinetic inductance of an array of Josephson junctions is an ideal candidate to implement the superinductance provided its phase slip rate is sufficiently low. We successfully implemented such an array using large Josephson junctions ($E_J >> E_C$), and measured internal losses less than 20 ppm, self-resonant frequencies greater than 10 GHz, and phase slip rates less than 1 mHz

Non-degenerate, three-wave mixing with the Josephson ring modulator

The Josephson ring modulator (JRM) is a device, based on Josephson tunnel junctions, capable of performing non-degenerate mixing in the microwave regime without losses. The generic scattering matrix of the device is calculated by solving coupled quantum Langevin equations. Its form shows that the device can achieve quantum-limited noise performance both as an amplifier and a mixer. Fundamental limitations on simultaneous optimization of performance metrics like gain, bandwidth and dynamic range (including the effect of pump depletion) are discussed. We also present three possible integrations of the JRM as the active medium in a different electromagnetic environment. The resulting circuits, named Josephson parametric converters (JPC), are discussed in detail, and experimental data on their dynamic range are found to be in good agreement with theoretical predictions. We also discuss future prospects and requisite optimization of JPC as a preamplifier for qubit readout applications.Comment: 21 pages, 16 figures, 4 table

Effect of different potato varieties and tuber sizes on physiological changes under ambient storage performance

The storability and sprouting behavior of three grades (small, medium and large tubers) from four Indian potato cultivars was studied under ambient conditions to assess the quality changes due to physiological losses and sprouting bhaviour of potato tubers. It was found that physiological loss in weight (%), decay loss on number and weight basis (%), sprout loss on number and weight basis (%), total loss (%), general appearance, presence of black or hollow heart were affected significantly by the different varieties as well as by the size. The loss in weight of tubers due to physiological activities, decaying and sprouting increased with the increased in storage period and the loss was more in larger than smaller and medium tubers. Kufri Badshah showed the best control over sprouting, whereas, 100% sprouting was observed in Kufri Bahar with all possible combinations during storage. The maximum value for cumulative physiological loss in weight was observed in variety Kufri Bahar (12.07%), whereas, minimum was in Kufri Pushkar (7.44%). The maximum decay loss was observed in variety Kufri Pushkar (7.89 and 8.72%) and minimum in Kufri Bahar (0.00 and 4.58%) on 80th and 90th day of storage period. Black or hollow heart was absent completely in all the possible treatments. So far general appearance of the tubers was concerned, the larger tubers shrivelled more and earlier than the medium and small sized tubers. Different varieties behaved differently during the entire storage period

Signal-to-pump back-action and self-oscillation in Double-Pump Josephson Parametric Amplifier

We present the theory of a Josephson parametric amplifier employing two pump sources. Our calculations are based on Input-Output Theory, and can easily be generalized to any coupled system involving parametric interactions. We analyze the operation of the device, taking into account the feedback introduced by the reaction of the signal and noise on the pump power, and in this framework, compute the response functions of interest - signal and idler gains, internal gain of the amplifier, and self-oscillation signal amplitude. To account for this back-action between signal and pump, we adopt a mean-field approach and self-consistently explore the boundary between amplification and self-oscillation. The coincidence of bifurcation and self-oscillation thresholds reveals that the origin of coherent emission of the amplifier lies in the multi-wave mixing of the noise components. Incorporation of the back-action leads the system to exhibit hysteresis, dependent on parameters like temperature and detuning from resonance. Our analysis also shows that the resonance condition itself changes in the presence of back-action and this can be understood in terms of the change in plasma frequency of the junction. The potential of the double pump amplifier for quantum-limited measurements and as a squeezer is also discussed.Comment: 25 pages, 20 figures, three appendice

Effect of phytohormones on shoot apex and leaf explants of Withania somnifera (Ashwagandha)

An efficient protocol for callus induction of Withania somnifera through in vitro culture of shoot apex and leaf explant was standardized. Of the various combinations of phytohormones evaluated, MS media supplemented with 6-furfuryl aminopurine (KIN) 0.5 mg/l + 2,4-dichlorophenoxy acetic acid (2, 4-D) 2.0 mg/l was found to be bestfor mean callus induction (86%) in leaf explants after 6 weeks of culture and in case of shoot apex expant the best response and growth of callusing was observed on MS medium supplemented with 2,4-D 1.0 mg/l + BAP 2.0 mg/l (77%).The response of callus growth increases gradually with the reductions in concentration of KIN in culturemedium of both the explants. This protocol might be used in further research for mass propagation of W. somnifera via indirect regeneration methods

In vitro propagation of Withania somnifera (L.) Dunal. from shoot apex explants

In vitro rapid micropropagation of Withania somnifera; has been achieved using shoot apex explants, when cultured on MS medium with different auxins: Indole Butyric Acid (IBA) 0.5-4 mg/l, Indole Acetic Acid (IAA) 2 mg/l and Naphthalene Acetic Acid (NAA) 0.5-3 mg/l and cytokinin: Benzyl Amino Purine (BAP) 0.5-4 mg/l. NAA and BAP stimulated direct as well as callus mediated multiple shoot. IBA alone and in combination with IAA stimulated rhizogenesis, while IBA with NAA proliferated callus-mediated rhizogenesis. The rooted plantlets through sequential hardening process could be established in the field