The radio emission from the Galaxy at 22 MHz

Roger, R. S.; Costain, C. H.; Landecker, T. L.; Swerdlyk, C. M.

doi:10.1051/aas:1999239

Cited by 167 publications

(183 citation statements)

References 13 publications

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“…This emission has a strong frequency dependence (ν −2.6 , Lawson et al 1987;Reich & Reich 1988) and can thus be a significant component, or even dominate, the system temperature, T sys , at low frequencies. We note however that this spectral index does vary over the sky and especially in the low band it may turn over (Roger et al 1999). Moreover, as the effect of the sky temperature on sensitivity can have a frequency dependence that is steeper than that of the flux density of some pulsars, pulsars located in regions of bright synchrotron emission, such as along the Galactic plane, become more difficult to detect at low radio frequencies.…”

Section: Galactic Backgroundmentioning

confidence: 87%

Observing pulsars and fast transients with LOFAR

Stappers

Hessels

Alexov

et al. 2011

A&A

215

160

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Low frequency radio waves, while challenging to observe, are a rich source of information about pulsars. The LOw Frequency ARray (LOFAR) is a new radio interferometer operating in the lowest 4 octaves of the ionospheric "radio window": 10-240 MHz, that will greatly facilitate observing pulsars at low radio frequencies. Through the huge collecting area, long baselines, and flexible digital hardware, it is expected that LOFAR will revolutionize radio astronomy at the lowest frequencies visible from Earth. LOFAR is a next-generation radio telescope and a pathfinder to the Square Kilometre Array (SKA), in that it incorporates advanced multi-beaming techniques between thousands of individual elements. We discuss the motivation for low-frequency pulsar observations in general and the potential of LOFAR in addressing these science goals. We present LOFAR as it is designed to perform high-time-resolution observations of pulsars and other fast transients, and outline the various relevant observing modes and data reduction pipelines that are already or will soon be implemented to facilitate these observations. A number of results obtained from commissioning observations are presented to demonstrate the exciting potential of the telescope. This paper outlines the case for low frequency pulsar observations and is also intended to serve as a reference for upcoming pulsar/fast transient science papers with LOFAR.

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Section: Galactic Backgroundmentioning

confidence: 87%

Observing pulsars and fast transients with LOFAR

Stappers

Hessels

Alexov

et al. 2011

A&A

215

160

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“…Starting with lower frequencies, Roger et al (1999) used the 22 MHz and 408 MHz surveys to derive average high latitude…”

Section: Appendix A: Radio Spectral Index Datamentioning

confidence: 99%

The interstellar cosmic-ray electron spectrum from synchrotron radiation and direct measurements

Strong

Orlando

Jaffe

2011

A&A

195

249

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Aims. We exploit synchrotron radiation to constrain the low-energy interstellar electron spectrum, using various radio surveys and connecting with electron data from Fermi-LAT and other experiments. Methods. The GALPROP programme for cosmic-ray propagation, gamma-ray and synchrotron radiation is used. Secondary electrons and positrons are included. Propagation models based on cosmic-ray and gamma-ray data are tested against synchrotron data from 22 MHz to 94 GHz. Results. The synchrotron data confirm the need for a low-energy break in the cosmic-ray electron injection spectrum. The interstellar spectrum below a few GeV has to be lower than standard models predict, and this suggests less solar modulation than usually assumed. Reacceleration models are more difficult to reconcile with the synchrotron constraints. We show that secondary leptons are important for the interpretation of synchrotron emission. We also consider a cosmic-ray propagation origin for the low-energy break. Conclusions. Exploiting the complementary information on cosmic rays and synchrotron gives unique and essential constraints on electrons, and has implications for gamma rays. This connection is especially relevant now in view of the ongoing Planck and Fermi missions.

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“…Higher resolution surveys in this frequency range have been obtained with single-dish antennas at 1.4 MHz (Reich et al 1990a(Reich et al , 1997, 2.4 MHz (Duncan et al 1995), and 2.7 MHz (Reich et al 1984Fürst et al 1990); but their sky coverage has been limited to within a few degrees of the Galactic plane. At lower frequencies, low-resolution antenna arrays have been used to conclude three other major surveys with 69% and 95% of total sky coverage, respectively, at 22 MHz (Roger et al 1999) and 45 MHz (Alvarez et al 1997;Maeda et al 1999).…”

Section: Large-scale Galactic Emission and The Gem Projectmentioning

confidence: 99%

The 2.3 GHz continuum survey of the GEM project

Tello¹,

Villela²,

Torres³

et al. 2013

A&A

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Context. Determining the spectral and spatial characteristics of the radio continuum of our Galaxy is an experimentally challenging endeavour for improving our understanding of the astrophysics of the interstellar medium. This knowledge has also become of paramount significance for cosmology, since Galactic emission is the main source of astrophysical contamination in measurements of the cosmic microwave background (CMB) radiation on large angular scales. Aims. We present a partial-sky survey of the radio continuum at 2.3 GHz within the scope of the Galactic Emission Mapping (GEM) project, an observational program conceived and developed to reveal the large-scale properties of Galactic synchrotron radiation through a set of self-consistent surveys of the radio continuum between 408 MHz and 10 GHz. Methods. The GEM experiment uses a portable and double-shielded 5.5-m radiotelescope in altazimuthal configuration to map 60-degree-wide declination bands from different observational sites by circularly scanning the sky at zenithal angles of 30 • from a constantly rotating platform. The observations were accomplished with a total power receiver, whose front-end high electron mobility transistor (HEMT) amplifier was matched directly to a cylindrical horn at the prime focus of the parabolic reflector. The Moon was used to calibrate the antenna temperature scale and the preparation of the map required direct subtraction and destriping algorithms to remove ground contamination as the most significant source of systematic error. Results. We used 484 h of total intensity observations from two locations in Colombia and Brazil to yield 66% sky coverage from δ = −51.• 73 to δ = +34.• 78. The observations in Colombia were obtained with a horizontal HPBW of 2.• 30 ± 0.• 13 and a vertical HPBW of 1.• 92 ± 0.• 18. The pointing accuracy was 6. 84 and the RMS sensitivity was 11.42 mK. The observations in Brazil were obtained with a horizontal HPBW of 2.• 31 ± 0.• 03 and a vertical HPBW of 1.• 82 ± 0.• 12. The pointing accuracy was 5. 26 and the RMS sensitivity was 8.24 mK. The zero-level uncertainty of the combined survey is 103 mK with a temperature scale error of 5% after direct correlation with the Rhodes/HartRAO survey at 2326 MHz on a T -T plot. Conclusions. The sky brightness distribution into regions of low and high emission in the GEM survey is consistent with the appearance of a transition region as seen in the Haslam 408 MHz and WMAP K-band surveys. Preliminary results also show that the temperature spectral index between 408 MHz and the 2.3 GHz band of the GEM survey has a weak spatial correlation with these regions; but it steepens significantly from high to low emission regions with respect to the WMAP K-band survey.

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The radio emission from the Galaxy at 22 MHz

Cited by 167 publications

References 13 publications

Observing pulsars and fast transients with LOFAR

Observing pulsars and fast transients with LOFAR

The interstellar cosmic-ray electron spectrum from synchrotron radiation and direct measurements

The 2.3 GHz continuum survey of the GEM project

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