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Published March 1, 2016 | Submitted + Published
Journal Article Open

A recent change in the optical and γ-ray polarization of the Crab nebula and pulsar


We report on observations of the polarization of optical and γ-ray photons from the Crab nebula and pulsar system using the Galway Astronomical Stokes Polarimeter (GASP), the Hubble Space Telescope, Advanced Camera for Surveys and the International Gamma-Ray Astrophysics Laboratory satellite (INTEGRAL). These, when combined with other optical polarization observations, suggest that the polarized optical emission and γ-ray polarization changes in a similar manner. A change in the optical polarization angle has been observed by this work, from 109.5 ± 0∘.7 in 2005 to 85.3 ± 1∘.4 in 2012. On the other hand, the γ-ray polarization angle changed from 115 ± 11° in 2003–2007 to 80 ± 12° in 2012–2014. Strong flaring activities have been detected in the Crab nebula over the past few years by the high-energy γ-ray missions Agile and Fermi, and magnetic reconnection processes have been suggested to explain these observations. The change in the polarized optical and γ-ray emission of the Crab nebula/pulsar as observed, for the first time, by GASP and INTEGRAL may indicate that reconnection is possibly at work in the Crab nebula. We also report, for the first time, a non-zero measure of the optical circular polarization from the Crab pulsar+knot system.

Additional Information

© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 November 24. Received 2015 November 23. In original form 2015 January 27. First published online December 31, 2015. The authors are grateful for time allocated for GASP observations at Palomar. Work partly based on observations with INTEGRAL, a European Space Agency (ESA) project with instruments and science data centre funded by ESA member states (especially the Principal Investigator countries: Denmark, France, Germany, Italy, Switzerland, and Spain), Czech Republic and Poland, and with the participation of Russia and the United States. The HST/ACS data used in this paper were obtained from MAST. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Science Foundation Ireland is acknowledged for its support in the development of GASP under grant number 09/RFP/AST2391. PM thanks the Irish Research Council for support. This work was made possible in part through support of the Ulysses Ireland–France collaborative funding research programme.

Attached Files

Published - MNRAS-2016-Moran-2974-81.pdf

Submitted - 1511.07641v1.pdf


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