Narrow Results

We discuss observational constrains coming from supernovae imposed on the behaviour of the Randall–Sundrum models. We test the models using the Perlmutter SNIa data as well as the new Knop and Tonry/Barris samples. The data indicates that, under the assumption that we admit zero pressure dust matter on the brane, the cosmological constant is still needed to explain current observations. We estimate the model parameters using the best-fitting procedure and the likelihood method. The observations from supernovae give a large value of the density parameter for brane matter Ω_λ,0≃0.01 as the best fit. For high redshifts z>1.2, the difference between the brane model and the ΛCDM (Perlmutter) model becomes detectable observationally. From the maximum likelihood method we obtained the favored value of Ω_λ,0=0.004±0.016 for Ω_k,0=0 and Ω_m,0=0.3. This gives the limit Ω_λ,0<0.02 at 1σ level. While the model with brane effects is preferred by the supernovae type Ia data, the model without brane fluid is still statistically admissible. We also discuss how fit depends on restrictions of the sample, especially with respect to redshift criteria. We also pointed out the property of sensitive dependence of results with respect to the choice of ℳ parameter. For comparison the limit on brane effects which comes from CMB anisotropies and BBN is also obtained. The uncertainty in the location of the first peak gives a stronger limit Ω_λ,0<1.0×10^-12, whereas from BBN we obtain that Ω_λ,0<1.0×10^-27. However, both very strict limits are obtained with the assumption that brane effects do not change the physics in the pre-recombination era, while the SNIa limit is model independent.

We demonstrate that the fit to supernovae data can also be obtained if we admit the phantom matter p=-(4/3)ϱ on the brane, where this matter mimics the influence of the cosmological constant. We show that phantom matter enlarges the age of the universe on the brane which is demanded in cosmology. Finally, we propose to check for dark radiation and brane tension by the application of the angular diameter of galaxies minimum value test.

Radio astronomy observatories with high throughput back end instruments require real-time data processing. While computing hardware continues to advance rapidly, development of real-time processing pipelines remains difficult and time-consuming, which can limit scientific productivity. Motivated by this, we have developed Bifrost: an open-source software framework for rapid pipeline development.^(a) Bifrost combines a high-level Python interface with highly efficient reconfigurable data transport and a library of computing blocks for CPU and GPU processing. The framework is generalizable, but initially it emphasizes the needs of high-throughput radio astronomy pipelines, such as the ability to process data buffers as if they were continuous streams, the capacity to partition processing into distinct data sequences (e.g. separate observations), and the ability to extract specific intervals from buffered data. Computing blocks in the library are designed for applications such as interferometry, pulsar dedispersion and timing, and transient search pipelines. We describe the design and implementation of the Bifrost framework and demonstrate its use as the backbone in the correlation and beamforming back end of the Long Wavelength Array (LWA) station in the Sevilleta National Wildlife Refuge, NM.

Tata Institute of Fundamental Research (TIFR) Near Infrared Imaging Camera-II (TIRCAM2) is a closed-cycle Helium cryo-cooled imaging camera equipped with a Raytheon 512$\times$512 pixels InSb Aladdin III Quadrant focal plane array (FPA) having sensitivity to photons in the 1–5$\mu \text{m}$ wavelength band. In this paper, we present the performance of the camera on the newly installed 3.6m Devasthal Optical Telescope (DOT) based on the calibration observations carried out during 2017 May 11–14 and 2017 October 7–31. After the preliminary characterization, the camera has been released to the Indian and Belgian astronomical community for science observations since 2017 May. The camera offers a field-of-view (FoV) of $\sim 86.5^{\prime \prime }\times 86.5^{\prime \prime }$ on the DOT with a pixel scale of 0.169${}^{\prime \prime }$. The seeing at the telescope site in the near-infrared (NIR) bands is typically sub-arcsecond with the best seeing of $\sim 0.45^{\prime \prime }$ realized in the NIR $K$-band on 2017 October 16. The camera is found to be capable of deep observations in the $J$, $H$ and $K$ bands comparable to other 4m class telescopes available world-wide. Another highlight of this camera is the observational capability for sources up to Wide-field Infrared Survey Explorer (WISE) W1-band (3.4$\mu$m) magnitudes of 9.2 in the narrow $L$-band ($nbL$; ${\lambda }_{\mathrm{\text{cen}}}\sim$ 3.59$\mu$m). Hence, the camera could be a good complementary instrument to observe the bright $nbL$-band sources that are saturated in the Spitzer-Infrared Array Camera (IRAC) ([3.6] $\lesssim$ 7.92 mag) and the WISE W1-band ([3.4] $\lesssim$ 8.1 mag). Sources with strong polycyclic aromatic hydrocarbon (PAH) emission at 3.3$\mu$m are also detected. Details of the observations and estimated parameters are presented in this paper.

This paper presents an observing methodology for calibrated measurements of radio interference levels and compares these with threshold interference limits that have been established for interference entering the bands allocated to the Radio Astronomy Service. The measurement time and bandwidth intervals for these observations may be commensurate with the time and frequency variability characteristic of the interfering signals and the threshold levels may be appropriately scaled from the values presented in ITU-R RA.769 using a 2000s reference time interval. The data loss for astronomical instruments may be measured as a percentage of occupancy in the time–frequency domain both for short and long measurement intervals. The observed time–frequency occupancy characteristics for non-geostationary satellite systems and earth stations in the mobile–satellite service may be incorporated into an effective power flux density simulation to obtain the effective data loss and sky blockage due to these services.

Distance measurement is crucial to astronomy. Here, we suggest a new conceptual method to measure the distance by using a local instrument. By engaging the double-slit interference and by considering the phase information of the light, the position of the intensity maximum is related to the distance of the source. Consequently, the precise measurement of the position can be used to measure the distance of the remote source.

The Mexican Array Radio Telescope (MEXART), located in the state of Michoacan in Mexico, has been operating in an analog fashion, utilizing a Butler Matrix to generate fixed beams on the sky, since its inception. Calibrating this instrument has proved difficult, leading to loss in sensitivity. It was also a rigid setup, requiring manual intervention and tuning for different observation requirements. The Radio Frequency (RF) system has now been replaced with a digital one. This digital backend is a hybrid system utilizing both FPGA-based technology and GPU acceleration, and is capable of automatically calibrating the different rows of the array, as well as generating a configurable number of frequency-domain synthesized beams to towards selected locations on the sky. A monitoring and control system, together with a full-featured web-based front-end, has also been developed, greatly simplifying the interaction with the instrument. This paper presents the design, implementation and deployment of the new digital backend, including preliminary analysis of system performance and stability.

TIRCAM2 is the facility near-infrared Imager at the Devasthal 3.6-m telescope in northern India, equipped with an Aladdin III InSb array detector. We have pioneered the use of TIRCAM2 for very fast photometry, with the aim of recording Lunar Occultations (LO). This mode is now operational and publicly offered. In this paper, we describe the relevant instrumental details, provide references to the LO method and the underlying data analysis procedures, and list the LO events recorded so far. Among the results, we highlight a few which have led to the measurement of one small-separation binary star and of two stellar angular diameters. We conclude with a brief outlook on further possible instrumental developments and an estimate of the scientific return. In particular, we find that the LO technique can detect sources down to $K\approx 9$mag with $\mathrm{\text{SNR}}=1$ on the Devasthal Optical Telescope telescope. Angular diameters larger than $\approx 1$ milliarcsecond (mas) could be measured with SNR above 10, or $K\approx 6$mag. These numbers are only an indication and will depend strongly on observing conditions such as lunar phase and rate of lunar limb motion. Based on statistics alone, there are several thousands LO events observable in principle with the given telescope and instrument every year.

Gamma-ray bursts (GRBs) are cosmological explosions which carry valuable information from the distant past of the expanding universe. One of the greatest discoveries in modern cosmology is the finding of the accelerated expansion of the universe using Type Ia supernovae (SN Ia) as standard candles. However, due to the interstellar extinction SN Ia can be seen only up to a redshift z ∼ 1.5. GRBs are considered as the potential alternative to push this limit to as high as z ∼ 10, a redshift regime corresponding to an epoch when the universe just started to form the first structures. There exist several correlations between the energy and an observable of a GRB which can be used to derive luminosity distance. In recent works, we have studied spectral evolution within the individual pulses and obtained such correlations within the pulses. Here we summarize our results of the pulse-wise GRB correlation study. It is worth mentioning that all GRB correlations are still empirical, and we cannot use them in cosmology unless we understand the basic physics of GRBs. To this end, we need to investigate the prompt emission spectrum which is so far generally described by the empirical Band function. We shall discuss our current understanding of the radiation process particularly the finding of two blackbodies and a powerlaw (the 2BBPL model) as the generic spectral model and its implication. This is a work in progress and we expect to obtain the most fundamental GRB correlation based on our improved spectral model.