The Crab Nebula, thought for decades to be a "standard candle", has recently seen this status challenged by the observation of intense high-energy gamma rays flares. An Irish and French team (centre for Astronomy of the Université of Galway and Service d’Astrophysique from CEA–Irfu ) has stressed this finding by observing for the first time a change of polarization in visible and gamma-ray light in the central region of the nebula from 2005 to 2012. This results from a programme combining observations made at the Mount Palomar 5 meter telescope with the GASP polarimeter from the University of Galway, by the astronomical gamma-ray satellite Integral and archival data from the Hubble Space Telescope. The polarization changes could be related according to the researchers to a rearrangement process of the magnetic field and effects induced on energetic particles in a region near the central pulsar. This work is published in the journal Monthly Notices of the Royal Astronomical Society and object of the Picture Of the Month (POM) from the European Space Agency (ESA).
On the left, this HST image shows the inner part of the Crab nebula with the Crab pulsar and its near-by knot located 0.65" (1300 AU) south-east of the pulsar inside the red box. On the right, a zoomed view of the image is shown. The arrows indicate at different periods in time the polarization angle in the optical (HST in 2005 and GASP in 2012) and in hard X-rays (Integral in the period 2003-2007 and 2012-2014). Also indicated are the directions of the proper motion (PM) and spin axis (SA) of the pulsar.
" A recent change in the optical and gamma-ray polarization of the Crab nebula and pulsar "
P. Moran, G. Kyne, C. Gouiffès, P. Laurent, G. Hallinan, R. M. Redfern and A. Shearer
publié dans la revue Monthly Notices of the Royal Astronomical Society 2015 456 (3): 2974-2981
Acces to the electronic version
See - POM (ESA, 2016 Juanuary 1)
This work was made possible in part through support of the Ulysses Ireland-France collaborative funding research program.
Rédaction : C. Gouiffès