Optical follow-up of the Crab pulsar (PSR J0534+2200)
ATel #5976; R. Nesci (INAF/IAPS, Roma), V. Falasca, A. Caravano, A. Moretti (Oss. Cittadino, Foligno)
on 12 Mar 2014; 23:59 UT
Credential Certification: Roberto Nesci (Roberto.Nesci@iaps.inaf.it)
Subjects: Optical, Neutron Star, Pulsar
After the indication of an enhanced Gamma-ray flux from the Crab nebula by Gasparrini et al. (ATel#5971) we observed the Crab with the 30cm telescope of the Foligno Observatory with a Canon 350D (scale 0.89 arcsec/pixel). We obtained two series of unfiltered images, each with 15 minutes exposure. The pulsar was detected just separated from the brighter nearby stellar object 5 arcsec to NE. Aperture photometry was performed with IRAF/apphot using a 2 arcsec radius: the pulsar magnitude was V=16.3 +/-0.2, while the nearby star was 15.65+/-0.07. A large number (130) of comparison stars around the nebula, in the range V=11 to 16.5, were taken from the UCAC4 catalog.
The slope of the linear fit between instrumental and catalog magnitudes is 0.98 with rms deviations 0.15. Evaluation of the background level is tricky, due to the presence of the nebular emission: we made several choices of the inner radius of the coronal area used to define the background, with results always within our formal uncertainty.
We conclude therefore that the pulsar is substantially at its typical optical flux level and does not show an increase of a factor 2 like that reported at Gamma-rays frequencies.