NIKA 150 GHz polarization observations of the Crab nebula and its spectral energy distribution

¹ Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble Alpes, CNRS/IN2P3, 53 avenue des Martyrs, Grenoble, France
² Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Blvd de l’Observatoire, CS 34229, 06304 Nice cedex 4, France
³ Institut de RadioAstronomie Millimétrique (IRAM), Grenoble, France
⁴ Laboratoire AIM, CEA/IRFU, CNRS/INSU, Université Paris Diderot, CEA-Saclay, 91191 Gif-Sur-Yvette, France
⁵ Astronomy Instrumentation Group, University of Cardiff, Cardiff, Whales, UK
⁶ Institut d’Astrophysique Spatiale (IAS), CNRS and Université Paris Sud, Orsay, France
⁷ Institut Néel, CNRS and Université Grenoble Alpes, France
⁸ Institut de RadioAstronomie Millimétrique (IRAM), Granada, Spain
e-mail: ritaccoa@iram.es
⁹ Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Roma, Italy
¹⁰ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, Grenoble, France
¹¹ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
¹² School of Earth and Space Exploration, and Department of Physics, Arizona State University, Tempe AZ 85287, USA
¹³ Université de Toulouse, UPS-OMP, Institut de Recherche en Astrophysique et Planétologie (IRAP), Toulouse, France
¹⁴ CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse cedex 4, France
¹⁵ University College London, Department of Physics and Astronomy, Gower Street, London WC1E 6BT, UK
¹⁶ Institut d’Astrophysique de Paris, Sorbonne Université, UPMC Univ. Paris 06, CNRS UMR 7095, 75014 Paris, France
¹⁷ LERMA, CNRS, Observatoire de Paris, 61 avenue de l’Observatoire, Paris, France
¹⁸ Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Plaza San Juan, 1, planta 2, 44001 Teruel, Spain
¹⁹ Joint ALMA Observatory & European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
²⁰ Max Planck Institute for Radio Astronomy, 53111 Bonn, Germany
²¹ Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, 10691 Stockholm, Sweden

Received: 11 July 2017
Accepted: 24 April 2018

Abstract

The Crab nebula is a supernova remnant exhibiting a highly polarized synchrotron radiation at radio and millimetre wavelengths. It is the brightest source in the microwave sky with an extension of 7 by 5 arcmin, and is commonly used as a standard candle for any experiment which aims to measure the polarization of the sky. Though its spectral energy distribution has been well characterized in total intensity, polarization data are still lacking at millimetre wavelengths. We report in this paper high resolution observations (18′′ FWHM) of the Crab nebula in total intensity and linear polarization at 150 GHz with the NIKA camera. NIKA, operated at the IRAM 30 m telescope from 2012 to 2015, is a camera made of Lumped Element Kinetic Inductance Detectors (LEKIDs) observing the sky at 150 and 260 GHz. From these observations we are able to reconstruct the spatial distribution of the polarization degree and angle of the Crab nebula, which is found to be compatible with previous observations at lower and higher frequencies. Averaging across the source and using other existing data sets we find that the Crab nebula polarization angle is consistent with being constant over a wide range of frequencies with a value of − 87.7° ± 0.3 in Galactic coordinates. We also present the first estimation of the Crab nebula spectral energy distribution polarized flux in a wide frequency range: 30–353 GHz. Assuming a single power law emission model we find that the polarization spectral index β_pol = – 0.347 ± 0.026 is compatible with the intensity spectral index β = – 0.323 ± 0.001.