arXiv subjects

P. Reich

Publications and source records attributed to P. Reich.

At least 37 records · Page 2Linked to original sources

arXiv2010

A Sino-German 6 cm polarization survey of the Galactic plane III. The region from 10 degree to 60 degree longitude

(Abridged) We have conducted a total intensity and polarization survey of the Galactic plane at 6 cm using the Urumqi 25 m telescope for the Galactic longitude range of 10 deg<l<60 deg and the Galactic latitude range of |b|<5 deg. Missing absolute zero levels of Stokes U and Q maps were restored by extrapolating the WMAP five-year K-band polarization data. For total intensities we recovered missing large-scale components by referring to the Effelsberg 11 cm survey. Total intensity and polarization maps are presented with an angular resolution of 9.5 arcmin and a sensitivity of 1 mK and 0.5 mK in total and polarized intensity, respectively. The 6 cm polarized emission in the Galactic plane originates within about 4 kpc distance, which increases for polarized emission out of the plane. The polarization map shows "patches", "canals" and "voids" with no correspondence in total intensity. We attribute the patches to turbulent magnetic field cells. Canals are caused by abrupt variation of polarization angles at the boundaries of patches rather than by foreground Faraday Screens. The superposition of foreground and Faraday Screen rotated background emission almost cancels polarized emission locally, so that polarization voids appear. By modelling the voids, we estimate the Faraday Screen's regular magnetic field along the line-of-sight to be larger than about 8 microG. We separated thermal (free-free) and non-thermal (synchrotron) emission according to their different spectral indices. The spectral index for the synchrotron emission was based on WMAP polarization data. The fraction of thermal emission at 6 cm is about 60% in the plane.

astro-ph.GA↗

arXiv2010

A Sino-German 6 cm polarization survey of the Galactic plane II. The region from 129 degree to 230 degree longitude

Linearly polarized Galactic synchrotron emission provides valuable information about the properties of the Galactic magnetic field and the interstellar magneto-ionic medium, when Faraday rotation along the line of sight is properly taken into account. We aim to survey the Galactic plane at 6 cm including linear polarization. At such a short wavelength Faraday rotation effects are in general small and the Galactic magnetic field properties can be probed to larger distances than at long wavelengths. The Urumqi 25-m telescope is used for a sensitive 6 cm survey in total and polarized intensities. WMAP K-band (22.8 GHz) polarization data are used to restore the absolute zero-level of the Urumqi U and Q maps by extrapolation. Total intensity and polarization maps are presented for a Galactic plane region of 129 degree < l < 230 degree and |b| < 5 degree in the anti-centre with an angular resolution of 9'5 and an average sensitivity of 0.6 mK and 0.4 mK Tb in total and polarized intensity, respectively. We briefly discuss the properties of some extended Faraday Screens detected in the 6 cm polarization maps. The Sino-German 6 cm polarization survey provides new information about the properties of the magnetic ISM. The survey also adds valuable information for discrete Galactic objects and is in particular suited to detect extended Faraday Screens with large rotation measures hosting strong regular magnetic fields.

astro-ph.GA↗

arXiv2010

A Survey of the Polarized Emission from the Galactic Plane at 1420 MHz with Arcminute Angular Resolution

Context: Observations of polarized emission are a significant source of information on the magnetic field that pervades the Interstellar Medium of the Galaxy. Despite the acknowledged importance of the magnetic field in interstellar processes, our knowledge of field configurations on all scales is seriously limited. Aims: This paper describes an extensive survey of polarized Galactic emission at 1.4 GHz that provides data with arcminute resolution and complete coverage of all structures from the broadest angular scales to the resolution limit, giving information on the magneto-ionic medium over a wide range of interstellar environments. Methods: Data from the DRAO Synthesis Telescope, the Effelsberg 100-m Telescope, and the DRAO 26-m Telescope have been combined. Angular resolution is ~1' and the survey extends from l = 66 deg to l = 175 deg over a range -3 deg < b < 5 deg along the northern Galactic plane, with a high-latitude extension from l = 101 deg to l = 116 deg up to b = 17.5 deg. This is the first extensive polarization survey to present aperture-synthesis data combined with data from single antennas, and the techniques developed to achieve this combination are described. Results: The appearance of the extended polarized emission at 1.4 GHz is dominated by Faraday rotation along the propagation path, and the diffuse polarized sky bears little resemblance to the total-intensity sky. There is extensive depolarization, arising from vector averaging on long lines of sight, from HII regions, and from diffuse ionized gas seen in H-alpha images. Preliminary interpretation is presented of selected polarization features on scales from parsecs (the planetary nebula Sh 2-216) to hundreds of parsecs (a supperbubble GSH 166-01-17) to kiloparsecs (polarized emission in the direction of Cygnus X).

astro-ph.GA↗

arXiv2008

The radio spectrum and magnetic field structure of SNR HB3

Evidence for a spectral flattening of the supernova remnant (SNR) HB3 (G132.7+1.3) was recently claimed in literature based on previously published total flux density data, and the flattening was further interpreted as the discovery of thermal bremsstrahlung emission in the shell of HB3. A spectral flattening has never been observed from any SNR before. Reliable observations of HB3 at frequencies above 3000 MHz are crucial to confirm such a spectral behaviour. We extracted 4800 MHz total intensity and polarisation data of HB3 from the Sino-German 6 cm polarisation survey of the Galactic plane made with the Urumqi 25 m telescope, and analysed the spectrum of HB3, together with Effelsberg data at 1408 MHz and 2675 MHz. We found an overall spectral index of HB3 of alpha=-0.61+-0.06 between 1408 MHz and 4800 MHz, similar to the index at lower frequencies. There is no spectral flattening at high frequencies. We detected strong polarised emission from HB3 at 4800 MHz. Our 4800 MHz data show a tangential field orientation in the HB3 shell.

astro-ph↗

arXiv2008

The impact of Galactic synchrotron emission on CMB anisotropy measurements. I. Angular power spectrum analysis of total intensity all-sky surveys

Galactic foreground emission is a limiting factor for precise cosmic microwave background (CMB) anisotropy measurements. We perform an angular power spectrum analysis (APS) of all-sky total intensity maps at 408 MHz and 1420 MHz, which are dominated by synchrotron emission out of the Galactic plane. We subtract the brighter sources from the maps. We study the APS as a function of Galactic latitude by considering various cuts and as a function of sky position by dividing the sky into patches of about 15 deg x 15 deg in size. The APS of the Galactic radio diffuse synchrotron emission is best fitted by a power law, $C_{\ell} \sim k \ell^α$, with $α\in [-3.0,-2.6]$, where the lower values of $α$ typically correspond to the higher latitudes. Nevertheless, the analysis of the patches reveals that strong local variations exist. The mean APS for $\ell \in [20,40]$ is used to determine the mean spectral index between 408 MHz and 1420 MHz, which is then adopted to extrapolate the synchrotron APS results to the microwave range. A simple extrapolation to 23 GHz of the synchrotron emission APS found at 408 and 1420 MHz does not explain all the power in the WMAP synchrotron component even at middle/high Galactic latitudes. This suggests a significant microwave contribution (of about 50% of the signal) by other components such as free-free or spinning dust emission. The comparison between the extrapolated synchrotron APS and the CMB APS shows that a mask excluding the regions with $|b_{gal}| \lesssim 5^{\circ}$ would reduce the foreground fluctuations to about half of the cosmological ones at 70 GHz even at the lowest multipoles. We discuss the main implications of our analysis for the cosmological exploitation of microwave temperature anisotropy maps.

astro-ph↗

arXiv2007

Polarization observations of SNR G156.2+5.7 at lambda 6cm

G156.2+5.7 is a large supernova remnant (SNR) first discovered in the ROSAT X-ray survey but radio observations are rare because of its low surface brightness and large size. Radio continuum and polarization images of the SNR G156.2+5.7 at lambda 6 cm are presented for the first time to be discussed in the context with available data to investigate its physical properties. We obtained an integrated flux density for G156.2+5.7 of S6cm= 2.5+-0.5Jy. The spectral index of the integrated emission is alpha=-0.48+-0.08 between lambda 74 cm and 6 cm excluding compact radio sources. We also obtained a spectral index map, which shows little variation between the shells and the central area of the SNR. This is consistent with the constant integrated flux density spectrum. Highly polarized radio emission has been detected from the SNR shell, but also from a central patch, which probably originates in the front part of the spherical SNR shell. We derived the distribution of rotation measure from polarization data at 11 cm and 6 cm and found RM gradients of opposite direction in the SNR shell. The SNR G156.2+5.7 is unusual by its exceptionally high X-ray brightness and very low surface-brightness in the radio range. The magnetic field is very well ordered along the shell periphery as expected for a compressed ambient magnetic field. A toroidal magnetic field component is indicated by the RM distribution. (abridged)

astro-ph↗

arXiv2006

A Sino-German lambda6 cm polarization survey of the Galactic plane I. Survey strategy and results for the first survey region

(Abridged) Polarization measurements of the Galactic plane at lambda6 cm probe the interstellar medium (ISM) to larger distances compared to measurements at longer wavelengths, hence enable us to investigate properties of the Galactic magnetic fields and electron density. We are conducting a new lambda6 cm continuum and polarization survey of the Galactic plane covering 10degr < l < 230degr and |b|<5degr. Missing large-scale structures in the U and Q maps are restored based on extrapolated polarization K-band maps from the WMAP satellite. The lambda6 cm data are analyzed together with maps at other bands. We discuss some results for the first survey region, 7degr X 10degr in size, centered at (l,b)=(125.5degr, 0degr). Two new passive Faraday screens, G125.6-1.8 and G124.9+0.1, were detected. They cause significant rotation of background polarization angles but little depolarization. G124.9+0.1 was identified as a new faint HII region at a distance of 2.8 kpc. G125.6-1.8, with a size of about 46 pc, has neither correspondence in enhanced Halpha emission nor a counterpart in total intensity. A model combining foreground and background polarization modulated by the Faraday screen was developed. Using this model, we estimated the strength of the ordered magnetic field along the line of sight to be 3.9 microGauss for G124.9+0.1, and exceeding 6.4 microGauss for G125.6-1.8. We obtained an estimate of 2.5 and 6.3 mK/kpc for the average polarized and total synchrotron emissivity towards G124.9+0.1. The synchrotron emission beyond the Perseus arm is quite weak.

astro-ph↗

arXiv2006

An angular power spectrum analysis of the DRAO 1.4 GHz polarization survey: implications for CMB observations

The aim of the present analysis is to improve the knowledge of the statistical properties of the Galactic diffuse synchrotron emission, which constrains sensitive CMB anisotropy measurements. We have analysed the new DRAO 1.4 GHz polarization survey together with the Stockert 1.4 GHz total intensity survey and derived the angular power spectra (APSs) of the total intensity, the polarized emission, and their cross-correlation for the entire surveys and for three low-intensity regions. The APSs of the diffuse synchrotron emission are modelled by power laws. For the $E$ and $B$ modes, a slope of $α\sim [-3.0,-2.5]$ for the multipole range $\sim [30,300]$ is found. By the extrapolation of these results to 70 GHz, we can estimate the Galactic synchrotron contamination of CMB anisotropies, and we find results that are compatible with the ones coming from WMAP 3-yr data. In the low-intensity regions, the cosmological primordial B~mode peak at $\ell \sim 100$ should be clearly observable for a tensor-to-scalar ratio $T/S \gsim 0.5$ and a synchrotron temperature spectral index $β\sim -3$. Its detection is also possible for $T/S \gsim 0.005$ and $β\sim -3$, in case a separation of the foreground from the CMB signal could be achieved with an accuracy of $\sim 5-10%$. For the TE mode, a mask excluding $|b_{gal}| \le 5^{\circ}$ (for $β\sim -3.0$) or $|b_{gal}| \le 20^{\circ}$ (for $β\sim -2.8$) from the surveys is sufficient to render the foreground contamination negligible, thus confirming the ability of WMAP to have a clear view of the temperature-polarization correlation peak and antipeak series.

astro-ph↗

arXiv2006

A statistical analysis of a Galactic all sky survey at 1.4 GHz

Radio surveys at frequencies of about 1 GHz allow to map the synchrotron emission in a frequency range where (except for very low Galactic latitudes or towards localized regions) it dominates over the other radio components. New all sky total intensity and polarization data at 1.4 GHz have been recently collected. We focus on the Galactic radio emission correlation properties described in terms of angular power spectrum (APS). We present for the first time the APS, in both total intensity and polarization modes, for some representative Galactic cuts and suitable APS power law parametrizations.

astro-ph↗

arXiv2005

Deep 1.4-GHz observations of diffuse polarized emission

Polarized diffuse emission observations at 1.4-GHz in a high Galactic latitude area of the northern Celestial hemisphere are presented. The 3.2 X 3.2 deg^2 field, centred at RA = 10h 58m, Dec = +42deg 18' (B1950), has Galactic coordinates l~172deg, b~+63deg and is located in the region selected as northern target of the BaR-SPOrt experiment. Observations have been performed with the Effelsberg 100-m telescope. We find that the angular power spectra of the E- and B-modes have slopes of beta_E = -1.79 +/- 0.13 and beta_B = -1.74 +/- 0.12, respectively. Because of the very high Galactic latitude and the smooth emission, a weak Faraday rotation action is expected, which allows both a fair extrapolation to Cosmic Microwave Background Polarization (CMBP) frequencies and an estimate of the contamination by Galactic synchrotron emission. We extrapolate the E-mode spectrum up to 32-GHz and confirm the possibility to safely detect the CMBP E-mode signal in the Ka band found in another low emission region (Carretti et al. 2005b). Extrapolated up to 90-GHz, the Galactic synchrotron B-mode looks to compete with the cosmic signal only for models with a tensor-to-scalar perturbation power ratio T/S < 0.001, which is even lower than the T/S value of 0.01 found to be accessible in the only other high Galactic latitude area investigated to date. This suggests that values as low as T/S = 0.01 might be accessed at high Galactic latitudes. Such low emission values can allow a significant red-shift of the best frequency to detect the CMBP B-mode, also reducing the contamination by Galactic dust, and opening interesting perspectives to investigate Inflation models.

astro-ph↗

arXiv2005

New lambda6cm observations of the Cygnus Loop

Radio continuum and polarization observations of the entire Cygnus Loop at 6cm wavelength were made with the Urumqi 25m telescope. The 6cm map is analysed together with recently published maps from the Effelsberg 100m telescope at 21cm and 11cm. The integrated flux density of the Cygnus Loop at 6cm is 90+/-9Jy, which implies a spectral index of -0.40+/-0.06 being consistent with that of Uyaniker et al. (2004) in the wavelength range up to 11cm. This rules out any global spectral steepening up to 6cm. However, small spectral index variations in some regions of the source are possible, but there are no indications for any spectral curvature. The linear polarization data at 6cm show percentage polarizations up to 35% in some areas of the Cygnus Loop, exceeding those observed at 11cm. The Rotation Measure is around -21rad/m^2 in the southern area, which agrees with previous observations. However, the distribution of Rotation Measures is rather complex in the northern part of the Cygnus Loop, where the 21cm emission is totally depolarized. Rotation Measures based on 11cm and 6cm data are significantly larger than in the southern part. The difference in the polarization characteristic between the northern and southern part supports previous ideas that the Cygnus Loop consists of two supernova remnants.

astro-ph↗

arXiv2003

Synchrotron Polarization at High Galactic Latitude

We present preliminary results from mapping the high-latitude Galactic polarization with the Effelsberg Telescope at $λ$21 cm. Structures on the resulting maps are mostly on the scale of several degrees. The results show detection of polarization over most of the field, at the level of tens of percent of the synchrotron emission. The evidence of more structure in Stokes Q and U rather than in $\sqrt{Q^2+U^2}$ suggests the existence of Faraday rotation.

astro-ph↗

arXiv2001

Polarization surveys of the Galaxy

We report on sensitive 21cm and 11cm polarization surveys of the Galactic plane carried out with the Effelsberg 100-m telescope at arcmin angular resolution and some related work. Highly structured polarized emission is seen along the Galactic plane as well as up to very high Galactic latitudes. These observations reflect Faraday effects in the interstellar medium. Polarized foreground and background components along the line of sight, modified by Faraday rotation and depolarization, add in a complex way. The amplitudes of polarized emission features are highly frequency dependent. Small-scale components decrease in amplitude rapidly with increasing frequency. We stress the need for sensitive absolutely calibrated polarization data. These are essential for baseline setting and a correct interpretation of small-scale structures. Absolutely calibrated data are also needed to estimate the high-frequency polarized background. A recent study of polarized emission observed across the local Taurus-Auriga molecular cloud complexes indicates excessive synchrotron emission within a few hundred parsecs. These results suggest that possibly a large fraction of the Galactic high latitude total intensity and polarized emission is of local origin.

astro-ph↗

arXiv2001

A radio continuum survey of the southern sky at 1420 MHz. Observations and data reduction

We describe the equipment, observational method and reduction procedure of an absolutely calibrated radio continuum survey of the South Celestial Hemisphere at a frequency of 1420 MHz. These observations cover the area 0h < R.A. < 24h for declinations less than -10 degree. The sensitivity is about 50 mK T_B (full beam brightness) and the angular resolution (HPBW) is 35.4', which matches the existing northern sky survey at the same frequency.

astro-ph↗

arXiv1999

A 1.4 GHz radio continuum and polarization survey at medium Galactic latitudes: II. First section

We present the first section of a radio continuum and polarization survey at medium Galactic latitudes carried out with the Effelsberg 100-m telescope at 1.4 GHz. Four large fields have been observed, which all together cover an area of about 1100 square degree. The rms-sensitivity is about 15 mK TB (about 7 mJy/beam area) in total intensity and is limited by confusion. A sensitivity of 8 mK TB is obtained in linear polarization. The angular resolution of the observations is 9.35 arcminute. The maps in total intensity and linear polarization have been absolutely calibrated by low resolution data where available. Significant linear polarization is seen in all the maps. In general, the intensity fluctuations measured in linear polarization are not correlated with total intensity structures. Areas of high polarization of some degrees extent are seen, again with no apparent corresponding total intensity feature. Modulation of polarized background emission by spatially varying Faraday rotation seems the most likely explanation. Quite unexpected is the detection of filamentary and ring-like depolarization structures in the direction of the anticentre region, whose extents are up to about 3 degree.

astro-ph↗

arXiv1998

A 1.4 GHz radio continuum and polarization survey at medium Galactic latitudes: I. Observation and reduction technique

A radio continuum survey at medium Galactic latitudes with the Effelsberg 100-m telescope is being carried out at a centre frequency of 1.4 GHz in total power and linear polarization. Areas up to +/- 20 degree of Galactic latitude are now being observed at a sensitivity of 15 mK TB total intensity and 8 mK TB in linear polarization with an angular resolution of 9'35. This paper describes the observing and reduction technique applied which results in absolutely calibrated maps. The methods are illustrated by examples of images from the survey.

astro-ph↗

arXiv1996

Radio observations of gamma-ray blazars

Starting in 1991 we have performed a regular monitoring of EGRET sources with the Effelsberg 100-m telescope and the IRAM 30-m at Pico Veleta. In comparison with data on a sample of flat-spectrum quasars which have not been seen by EGRET we search for correlations of any kind in the behaviour of FSRQ's in the radio and gamma-ray regime. While there is no radio-to-gamma-ray luminosity correlation for these sources, it seems that gamma-ray high states coincide with increased activity in the radio regime with a strong tendency that gamma-ray outbursts precede radio outbursts. The gamma-ray spectra seem to harden with increasing flux level.

astro-ph↗

arXiv1996

Is there a correlation between radio and gamma ray luminosities of AGN ?

The possibility of a correlation between the radio (cm)- and $γ$-ray luminosity of variable AGN seen by EGRET is investigated. We performed Monte-Carlo simulations of typical data sets and applied different correlation techniques (partial correlation analysis, $χ^2$-test applied on flux-flux relations) in view of a truncation bias caused by sensitivity limits of the surveys. For K-corrected flux densities, we find that with the least squares method only a linear correlation can be recovered. Partial correlation analysis on the other side provides a robust tool to detect correlations even in flux-limited samples if intrinsic scatter does not exceed $\sim 40$ \% of the original $γ$-ray luminosity. The analysis presented in this paper takes into account redshift bias and truncation effects simultaneously which was never considered in earlier papers. Applying this analysis to simultaneously observed radio- and $γ$-ray data, no correlation is found. However, an artificial correlation appears when using the mean flux. This is probably due to the reduction of the dynamical range in the flux-flux relation. Furthermore, we show that comparing the emission in both spectral bands at a high activity state leads to no convincing correlation. In conclusion, we can not confirm a correlation between radio and $γ$-ray luminosities of AGN which is claimed in previous works.

astro-ph↗