All-sky Galactic radiation at 45 MHz and spectral index between 45 and 408 MHz

Guzmán, Andrés E.; May, J.; Álvarez, H.; Maeda, Keiichi

doi:10.1051/0004-6361/200913628

Cited by 136 publications

(164 citation statements)

References 57 publications

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“…8 that beam correction has a significant impact on the recovered spectral index. Without correction, the beam effects mask the flattening that is expected near the Galactic Centre (de Oliveira-Costa et al 2008;Guzmán et al 2011).…”

Section: Spectral Indexmentioning

confidence: 99%

“…Both the Haslam map and the GSM have become widely used and cited in both simulations and data reduction pipelines for redshifted 21 cm observations (Bowman, Morales, & Hewitt 2009;Patra et al 2013;Subrahmanyan & Cowsik 2013;Thyagarajan et al 2015;Bernardi et al 2016). Guzmán et al 2011 created an all-sky temperature map at 45 MHz based upon the surveys of Alverez et al (1997) and Maeda et al (1999). In addition, they produced an allsky Galactic spectral index map based upon two frequency points by using their 45 MHz and the Haslam 408 MHz map after corrections for zero-level, extragalactic non-thermal emission, and CMB factors.…”

Section: Introductionmentioning

confidence: 99%

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Improved measurement of the spectral index of the diffuse radio background between 90 and 190 MHz

Mozdzen¹,

Bowman²,

Monsalve³

et al. 2016

Mon. Not. R. Astron. Soc.

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We report absolutely calibrated measurements of diffuse radio emission between 90 and 190 MHz from the Experiment to Detect the Global EoR Signature (EDGES). EDGES employs a wide beam zenith-pointing dipole antenna centred on a declination of −26.7 • . We measure the sky brightness temperature as a function of frequency averaged over the EDGES beam from 211 nights of data acquired from July 2015 to March 2016. We derive the spectral index, β, as a function of local sidereal time (LST) and find −2.60 > β > − 2.62 ±0.02 between 0 and 12 h LST. When the Galactic Centre is in the sky, the spectral index flattens, reaching β = −2.50 ±0.02 at 17.7 h. The EDGES instrument is shown to be very stable throughout the observations with night-to-night reproducibility of σ β < 0.003. Including systematic uncertainty, the overall uncertainty of β is 0.02 across all LST bins. These results improve on the earlier findings of by reducing the spectral index uncertainty from 0.10 to 0.02 while considering more extensive sources of errors. We compare our measurements with spectral index simulations derived from the Global Sky Model (GSM) of de Oliveira-Costa et al. (2008) and with fits between the Guzmán et al. (2011) 45 MHz andHaslam et al. (1982) 408 MHz maps. We find good agreement at the transit of the Galactic Centre. Away from transit, the GSM tends to over-predict (GSM less negative) by 0.05 < ∆ β = β GSM − β EDGES < 0.12, while the 45-408 MHz fits tend to over-predict by ∆ β < 0.05.

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Section: Spectral Indexmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Improved measurement of the spectral index of the diffuse radio background between 90 and 190 MHz

Mozdzen¹,

Bowman²,

Monsalve³

et al. 2016

Mon. Not. R. Astron. Soc.

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“…A correction factor (Tgal+Tsys)/Tsys is used to scale the flux densities at these frequencies where Tsys corresponds to the system temperature associated with the flux calibrators. Tgal is estimated by extrapolating the sky temperature value at 408 MHz (Haslam et al 1982) to 325 and 610 MHz assuming a spectral index of −2.6 (Roger et al 1999; Guzmán et al 2011) for the Galactic plane emission. The correction factors estimated this way are used to scale the images.…”

Section: Gmrt Observations and Data Reductionmentioning

confidence: 99%

Detection of non-thermal emission from the massive protostellar jet HH80-81 at low radio frequencies using GMRT

Vig

Veena

Mandal

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Low radio frequencies are favourable for the identification of emission from non-thermal processes such as synchrotron emission. The massive protostellar jet associated with IRAS 18162-2048 (also known as the HH80-81 system) has been imaged at low radio frequencies: 325, 610 and 1300 MHz, using the Giant Metrewave Radio Telescope, India. This is the first instance of detection of non-thermal emission from a massive protostellar jet at such low radio frequencies. The central region displays an elongated structure characteristic of the jet. In addition, the associated Herbig-Haro objects such as HH80, HH81, HH80N, and other condensations along the inner regions of the jet exhibit negative spectral indices. The spectral indices of most condensations are ∼ −0.7, higher than the value of −0.3 determined earlier using high frequency measurements. The magnetic field values derived using radio flux densities in the present work, under the assumption of equipartition near minimum energy condition, lie in the range 116 − 180 µG. We probe into the hard X-ray nature of a source that has been attributed to HH80, in an attempt to reconcile the non-thermal characteristics of radio and X-ray measurements. The flux densities of condensations at 610 MHz, measured nearly 11 yrs apart, display variability that could be ascribed to the cooling of condensations, and emphasize the importance of coeval or nearly-coeval measurements for estimation of spectral indices.

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“…Thus the constancy of the mean spectral index between 408 MHz and the 2300 MHz can be given directly for the entire GEM strip, irrespective of emission region, and results in −2.64 ± 0.11 according to the Rhodes survey and −2.63 ± 0.21 according to the GEM survey. Guzman et al (2011) have also recently reported a temperature spectral index of −2.5 to −2.6 over most of the sky between 45 MHz and 408 MHz. On the other hand, when the mean spectral index of the GEM and Rhodes surveys is obtained with respect to the WMAP K-band, the steepening of the spectral index increases toward the low-emission region, as expected for relativistic electrons of higher energies propagating to the larger scale heights that characterize these regions at high Galactic latitudes.…”

Section: Temperature Spectral Indexmentioning

confidence: 86%

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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All-sky Galactic radiation at 45 MHz and spectral index between 45 and 408 MHz

Cited by 136 publications

References 57 publications

Improved measurement of the spectral index of the diffuse radio background between 90 and 190 MHz

Improved measurement of the spectral index of the diffuse radio background between 90 and 190 MHz

Detection of non-thermal emission from the massive protostellar jet HH80-81 at low radio frequencies using GMRT

The 2.3 GHz continuum survey of the GEM project

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