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Characterizing the diffuse Galactic synchrotron emission (DGSE) at arcminute angular scales is needed to remove this foregrounds in cosmological 21-cm measurements. Here, we present the angular power spectrum (Cℓ) measurement of the diffuse Galactic synchrotron emission using two fields observed by the TIFR GMRT Sky Survey (TGSS). We apply 2D Tapered Gridded Estimator (TGE) to estimate the Cℓ from the visibilities. We find that the residual data after subtracting the point sources is likely dominated by the diffuse Galactic synchrotron radiation across the angular multipole range 240 ≤ ℓ ≲ 500. We fit a power law to the measured Cℓ over this ℓ range. We find that the slopes in both fields are consistent with earlier measurements. For the second field, however, we interpret the measured Cℓ as an upper limit for the DGSE as there is an indication of a significant residual point source contribution.

High-resolution radio measurements of air showers—cascades of secondary particles in the atmosphere initiated by cosmic rays—reveal that cosmic rays with energies of 10 17 –10 17.5 electronvolts have a mixed composition, with light elements (protons and helium nuclei) making up 80 per cent of their mass. Mass composition of cosmic rays Stijn Buitink et al . report on the mass composition of cosmic rays in the energy range 10 17 to 10 17.5 electron volts, derived from LOFAR radio telescope measurements of cosmic ray initiated cascades of secondary particles (air showers) in the atmosphere. They find a mixed composition, containing a light-mass fraction of approximately 80%. Unless the extragalactic cosmic ray component becomes significant below 10 17.5 electron volts, these findings indicate an additional Galactic component dominating in this energy range. Cosmic rays are the highest-energy particles found in nature. Measurements of the mass composition of cosmic rays with energies of 10 17 –10 18 electronvolts are essential to understanding whether they have galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal 1 comes from accelerators capable of producing cosmic rays of these energies 2 . Cosmic rays initiate air showers—cascades of secondary particles in the atmosphere—and their masses can be inferred from measurements of the atmospheric depth of the shower maximum 3 ( X max ; the depth of the air shower when it contains the most particles) or of the composition of shower particles reaching the ground 4 . Current measurements 5 have either high uncertainty, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays 6 , 7 , 8 is a rapidly developing technique 9 for determining X max (refs 10 , 11 ) with a duty cycle of, in principle, nearly 100 per cent. The radiation is generated by the separation of relativistic electrons and positrons in the geomagnetic field and a negative charge excess in the shower front 6 , 12 . Here we report radio measurements of X max with a mean uncertainty of 16 grams per square centimetre for air showers initiated by cosmic rays with energies of 10 17 –10 17.5 electronvolts. This high resolution in X max enables us to determine the mass spectrum of the cosmic rays: we find a mixed composition, with a light-mass fraction (protons and helium nuclei) of about 80 per cent. Unless, contrary to current expectations, the extragalactic component of cosmic rays contributes substantially to the total flux below 10 17.5 electronvolts, our measurements indicate the existence of an additional galactic component, to account for the light composition that we measured in the 10 17 –10 17.5 electronvolt range.

The infrared-radio correlation (IRRC) offers a way to assess star formation from radio emission. Multiple studies found the IRRC to decrease with increasing redshift. This may in part be due to the lack of knowledge about the possible radio spectral energy distributions (SEDs) of star-forming galaxies. We constrain the radio SED of a complete sample of highly star-forming galaxies (SFR > 100 M⊙/ yr) based on the VLA-COSMOS 1.4 GHz Joint and 3 GHz Large Project catalogs. We reduce archival GMRT 325 MHz and 610 MHz observations, broadening the rest-frame frequency range to 0.3-15 GHz. Employing survival analysis and fitting a double power law SED, we find that the slope steepens from a spectral index of α1 = 0.51±0.04 below 4.5 GHz to α2 = 0.98±0.07 above 4.5 GHz. Our results suggest that the use of a K-correction assuming a single power-law radio SED for star forming galaxies is likely not the root cause of the IRRC trend.

We present deep low radio frequency (230-470 MHz) observations from the Karl G. Jansky Very Large Array of the Perseus cluster, probing the non-thermal emission from the old particle population of the AGN outflows. Our observations of this nearby relaxed cool core cluster have revealed a multitude of new structures associated with the mini-halo, extending to hundreds of kpc in size. Its irregular morphology seems to have been influenced both by the AGN activity and by the sloshing motion of the cluster’ gas. In addition, it has a filamentary structure similar to that seen in radio relics found in merging clusters. These results illustrate the high-quality images that can be obtained with the new JVLA at low radio-frequencies.

Cosmic rays are the highest-energy particles found in nature. Measurements of the mass composition of cosmic rays with energies of 10(17)-10(18) electronvolts are essential to understanding whether they have galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal comes from accelerators capable of producing cosmic rays of these energies. Cosmic rays initiate air showers--cascades of secondary particles in the atmosphere-and their masses can be inferred from measurements of the atmospheric depth of the shower maximum (Xmax; the depth of the air shower when it contains the most particles) or of the composition of shower particles reaching the ground. Current measurements have either high uncertainty, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays is a rapidly developing technique for determining Xmax (refs 10, 11) with a duty cycle of, in principle, nearly 100 per cent. The radiation is generated by the separation of relativistic electrons and positrons in the geomagnetic field and a negative charge excess in the shower front. Here we report radio measurements of Xmax with a mean uncertainty of 16 grams per square centimetre for air showers initiated by cosmic rays with energies of 10(17)-10(17.5) electronvolts. This high resolution in Xmax enables us to determine the mass spectrum of the cosmic rays: we find a mixed composition, with a light-mass fraction (protons and helium nuclei) of about 80 per cent. Unless, contrary to current expectations, the extragalactic component of cosmic rays contributes substantially to the total flux below 10(17.5) electronvolts, our measurements indicate the existence of an additional galactic component, to account for the light composition that we measured in the 10(17)-10(17.5) electronvolt range.

An upgrade of the low frequency observing system of the VLA developed by NRL and NRAO, called low band (LB), will open a new era of Galactic center (GC) transient monitoring. Our previous searches using the VLA and GMRT have revealed a modest number of radio-selected transients, but have been severely sensitivity and observing time limited. The new LB system, currently accessing the 236--492 MHz frequency range, promises ≥5 × improved sensitivity over the legacy VLA system. The new system is emerging from commissioning in time to catch any enhanced sub-GHz emission from the G2 cloud event, and we review existing limits based on recent observations. We also describe a proposed 24/7 commensal system, called the LOw Band Observatory (LOBO). LOBO offers over 100 VLA GC monitoring hours per year, possibly revealing new transients and helping validate ASTRO2010's anticipation of a new era of transient radio astronomy. A funded LOBO pathfinder called the VLA Low Frequency Ionosphere and Transient Experiment (VLITE) is under development. Finally, we consider the impact of LB and LOBO on our GC monitoring program.