SARAS 2 Constraints on Global 21 cm Signals from the Epoch of Reionization

Spectral distortions in the cosmic microwave background over the 40--200~MHz band are imprinted by neutral hydrogen in the intergalactic medium prior to the end of reionization. This signal, produced in the redshift range $z = 6-34$ at the rest frame wavelength of 21 cm, has not been detected yet; and poor understanding of high redshift astrophysics results in a large uncertainty in the expected spectrum. The SARAS~2 radiometer was purposely designed to detect the sky-averaged 21-cm signal. The instrument, deployed at the Timbaktu Collective (Southern India) in April--June 2017, collected 63~hr of science data, which were examined for the presence of the cosmological 21-cm signal. In our previous work the first-light data from SARAS~2 radiometer were analyzed with Bayesian likelihood-ratio tests using $264$ plausible astrophysical scenarios. In this paper we re-examine the data using an improved analysis based on the frequentist approach and forward modeling. We show that SARAS~2 data rejects 27 models, out of which 25 are rejected at a significance $>5\sigma$. All the rejected models share the scenario of inefficient heating of the primordial gas by the first population of X-ray sources along with rapid reionization

First Results on the Epoch of Reionization from First Light with SARAS 2

Long wavelength spectral distortions in the Cosmic Microwave Background arising from the 21-cm transition in neutral Hydrogen are a key probe of Cosmic Dawn and the Epoch of Reionization. These features may reveal the nature of the first stars and ultra-faint galaxies that transformed the spin temperature and ionization state of the primordial gas. SARAS~2 is a spectral radiometer purposely designed for precision measurement of these monopole or all-sky global 21-cm spectral distortions. We use 63~hr night time observing of the radio background in the frequency band 110-200~MHz with the radiometer deployed at the Timbaktu Collective in Southern India to derive likelihoods for plausible redshifted 21-cm signals predicted by theoretical models. First light with SARAS 2 disfavors the class of models that feature weak X-ray heating (with $f_X \leq 0.1$) and rapid reionization (with peak $\frac{dT_b}{dz} \geq 120~\textrm{mK per unit redshift interval}$ )

The Murchison Widefield Array Transients Survey (MWATS). A search for low-frequency variability in a bright Southern hemisphere sample

We report on a search for low-frequency radio variability in 944 bright (>4 Jy at 154 MHz) unresolved, extragalactic radio sources monitored monthly for several years with the Murchison Widefield Array. In the majority of sources, we find very low levels of variability with typical modulation indices 2.8 yr) with time-averaged modulation indices M¯¯¯¯¯=3.1−7.1M¯=3.1−7.1 per cent. With 7/15 of these variable sources having peaked spectral energy distributions, and only 5.7 per cent of the overall sample having peaked spectra, we find an increase in the prevalence of variability in this spectral class. We conclude that the variability seen in this survey is most probably a consequence of refractive interstellar scintillation and that these objects must have the majority of their flux density contained within angular diameters less than 50 milliarcsec (which we support with multiwavelength data). At 154 MHz, we demonstrate that interstellar scintillation time-scales become long (∼decades) and have low modulation indices, while synchrotron-driven variability can only produce dynamic changes on time-scales of hundreds of years, with flux density changes less than one milli-jansky (without relativistic boosting). From this work, we infer that the low-frequency extragalactic southern sky, as seen by SKA-Low, will be non-variable on time-scales shorter than 1 yr

Landscape Analysis: Connected Lighting System

The lighting industry has gone under major transformations in recent decades. These changes are both at components/luminaires and system level. In 1999, Haitz stated that lumen per package will increase by a factor of 30 and the cost per lumen will decrease by factor of 10 [1]. This is also known as Haitz’s law [2]. In 2011, Haitz’s law is revisited; though the cost per lumen decremental rate remained the same, lumen per package incremental rate dropped to 20 [3]. According to revised Haitz’s law, LED has entered to era that can overcome its adoption barrier—high lamp price and low light output per emitter [2, 4]—in general lighting section. Next Generation Lighting Industry Alliance (NGLIA)’s presentation to the Department of Energy (DOE) shows that LED would disrupt the traditional lighting resource and dominate the lighting market by 2020 [5]

The radio spectral energy distribution of infrared-faint radio sources

Context.Infrared-faint radio sources (IFRS) are a class of radio-loud (RL) active galactic nuclei (AGN) at high redshifts (z ≥ 1.7) that are characterised by their relative infrared faintness, resulting in enormous radio-to-infrared flux density ratios of up to several thousand. Aims. Because of their optical and infrared faintness, it is very challenging to study IFRS at these wavelengths. However, IFRS are relatively bright in the radio regime with 1.4 GHz flux densities of a few to a few tens of mJy. Therefore, the radio regime is the most promising wavelength regime in which to constrain their nature. We aim to test the hypothesis that IFRS are young AGN, particularly GHz peaked-spectrum (GPS) and compact steep-spectrum (CSS) sources that have a low frequency turnover. Methods. We use the rich radio data set available for the Australia Telescope Large Area Survey fields, covering the frequency range between 150 MHz and 34 GHz with up to 19 wavebands from different telescopes, and build radio spectral energy distributions (SEDs) for 34 IFRS. We then study the radio properties of this class of object with respect to turnover, spectral index, and behaviour towards higher frequencies. We also present the highest-frequency radio observations of an IFRS, observed with the Plateau de Bure Interferometer at 105 GHz, and model the multi-wavelength and radio-far-infrared SED of this source. Results. We find IFRS usually follow single power laws down to observed frequencies of around 150 MHz. Mostly, the radio SEDs are steep (α < −0.8; 74+6-9%), but we also find ultra-steep SEDs (α < −1.3; 6+7-2%). In particular, IFRS show statistically significantly steeper radio SEDs than the broader RL AGN population. Our analysis reveals that the fractions of GPS and CSS sources in the population of IFRS are consistent with the fractions in the broader RL AGN population. We find that at least 18+8-5% of IFRS contain young AGN, although the fraction might be significantly higher as suggested by the steep SEDs and the compact morphology of IFRS. The detailed multi-wavelength SED modelling of one IFRS shows that it is different from ordinary AGN, although it is consistent with a composite starburst-AGN model with a star formation rate of 170 M⊙ yr-1