Properties of unique hard X-ray dips observed from GRS 1915+105 and IGR J17091-3624 and their implications

We report a comprehensive study on spectral and timing properties of hard X-ray dips uniquely observed in some so-called variability classes of the micro-quasars GRS 1915+105 and IGR J17091-3624. These dips are characterized by a sudden decline in the 2.0-60.0 keV X-ray intensity by a factor of 4-12 simultaneous with the increase in hardness ratio by a factor of 2-4. Using 31 observations of GRS 1915+105 with RXTE/PCA, we show that different behavior are observed in different types of variability classes, and we find that a dichotomy is observed between classes with abrupt transitions vs those with smoother evolution. For example, both energy-lag spectra and frequency-lag spectra of hard X-ray dips in classes with abrupt transitions and shorter dip intervals show hard-lag (hard photons lag soft photons), while both lag spectra during hard dips in classes with smoother evolution and longer dip intervals show soft-lag. Both lag time-scales are of the order of 100-600 msec. We also show that timing and spectral properties of hard X-ray dips observed in light curves of IGR J17091-3624 during its 2011 outburst are consistent with the properties of the abrupt transitions in GRS 1915+105 rather than smooth evolution. A global correlation between the X-ray intensity cycle time and hard dip time is observed for both abrupt and smooth transition which may be due to two distinct physical processes whose time-scales are eventually correlated. We discuss implications of our results in the light of some generic models.Comment: 17 pages, 5 figures, accepted for publication in the Astrophysical Journa

An Ultra-Low-Power RFID/NFC Frontend IC Using 0.18 μm CMOS Technology for Passive Tag Applications

Battery-less passive sensor tags based on RFID or NFC technology have achieved much popularity in recent times. Passive tags are widely used for various applications like inventory control or in biotelemetry. In this paper, we present a new RFID/NFC frontend IC (integrated circuit) for 13.56 MHz passive tag applications. The design of the frontend IC is compatible with the standard ISO 15693/NFC 5. The paper discusses the analog design part in details with a brief overview of the digital interface and some of the critical measured parameters. A novel approach is adopted for the demodulator design, to demodulate the 10% ASK (amplitude shift keying) signal. The demodulator circuit consists of a comparator designed with a preset offset voltage. The comparator circuit design is discussed in detail. The power consumption of the bandgap reference circuit is used as the load for the envelope detection of the ASK modulated signal. The sub-threshold operation and low-supply-voltage are used extensively in the analog design—to keep the power consumption low. The IC was fabricated using 0.18 μ m CMOS technology in a die area of 1.5 mm × 1.5 mm and an effective area of 0.7 m m 2 . The minimum supply voltage desired is 1.2 V, for which the total power consumption is 107 μ W. The analog part of the design consumes only 36 μ W, which is low in comparison to other contemporary passive tags ICs. Eventually, a passive tag is developed using the frontend IC, a microcontroller, a temperature and a pressure sensor. A smart NFC device is used to readout the sensor data from the tag employing an Android-based application software. The measurement results demonstrate the full passive operational capability. The IC is suitable for low-power and low-cost industrial or biomedical battery-less sensor applications. A figure-of-merit (FOM) is proposed in this paper which is taken as a reference for comparison with other related state-of-the-art researches

Design of a Programmable Passive SoC for Biomedical Applications Using RFID ISO 15693/NFC5 Interface

Low power, low cost inductively powered passive biotelemetry system involving fully customized RFID/NFC interface base SoC has gained popularity in the last decades. However, most of the SoCs developed are application specific and lacks either on-chip computational or sensor readout capability. In this paper, we present design details of a programmable passive SoC in compliance with ISO 15693/NFC5 standard for biomedical applications. The integrated system consists of a 32-bit microcontroller, a sensor readout circuit, a 12-bit SAR type ADC, 16 kB RAM, 16 kB ROM and other digital peripherals. The design is implemented in a 0.18 μ m CMOS technology and used a die area of 1.52 mm × 3.24 mm. The simulated maximum power consumption of the analog block is 592 μ W. The number of external components required by the SoC is limited to an external memory device, sensors, antenna and some passive components. The external memory device contains the application specific firmware. Based on the application, the firmware can be modified accordingly. The SoC design is suitable for medical implants to measure physiological parameters like temperature, pressure or ECG. As an application example, the authors have proposed a bioimplant to measure arterial blood pressure for patients suffering from Peripheral Artery Disease (PAD)

Evidence of two unique variability classes from IGR J17091-3624

IGR J17091-3624 is the second black hole X-ray binary after GRS 1915+105, which showed large and distinct variabilities. The study of these variability classes can be useful to understand the accretion-ejection mechanisms of accreting black holes, and hence to probe the strong gravity regime. We report the discovery of two new variability classes (C1 and C2) from IGR J17091-3624 from the 2011 outburst Rossi X-ray Timing Explorer data. These unique classes will be useful to have complete details about the source, and to learn new aspects about variabilities. For examples, the C1 class shows that the intensity and period of oscillations, energy spectrum and power spectrum can clearly evolve in tens of seconds. Moreover, in such a small time scale, soft-lag becomes hard-lag. The C2 class shows that the variability and the nonvariability can occur at similar energy spectrum, and a soft state is not required for variability to happen.Comment: 5 pages, 6 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society Letter

X-ray spectral state evolution in IGR J17091-3624 and comparison of its heartbeat oscillation properties with those of GRS 1915+105

In this work, we study the X-ray timing and spectral evolution of the transient low mass X-ray binary IGR J17091-3624 during first 66 days of its 2011 outburst. We present results obtained from observations with two instruments, Rossi X-ray Timing Explorer (RXTE)/Proportional Counter Array (PCA) and SWIFT/X-ray telescope (XRT), between 09 February, 2011 and 15 April, 2011. Using quasi-periodic oscillation classifications, power density spectrum characteristics, time-lag behavior and energy spectral properties, we determine source states and their transitions at different times of the outburst. During the first part of the evolution, the source followed trends usually observed from transient black hole X-ray binaries (BHXBs). Interestingly, a gradual transition is observed in IGR J17091-3624 from the low-variability SIMS, commonly seen in BHXBs, to a high-variability state with regular, repetitive and structured pulsations, seen only from GRS 1915+105 (also known as 'rho' class variability/'heartbeat' oscillations). We study the time evolution of characteristic time-scale, quality factor and rms amplitude of heartbeat oscillations in IGR J17091-3624. We also present a detailed comparison of the timing and spectral properties of heartbeat oscillations and their evolution in IGR J17091-3624 and GRS 1915+105.Comment: 23 pages, 10 figures, 3 tables, accepted for publication in the Ap

A passive novel transponder for monitoring leakage in silicone breast implants by using RFID ISO 15693

In this paper, a complete passive transponder device has been discussed which is meant to monitor leakage in silicone breast implants. The passive tag operates in the HF frequency range of 13.56MHz using RFID ISO 15693 standard. The complete system consists of the transponder, reader and a PC. This paper focusses on the development of such a state of the art passive RFID transponder to monitor the wellness of the silicone breast implants periodically in order to detect leakage in the same. Keyword: RFID (Radio frequency identification device), EM (Electromagnetic) field, Passive Transponder, Silicone breast implants