Observations of three young γ-ray pulsars with the gran telescopio canarias

Abstract

We report the analysis of the first deep optical observations of three isolated gamma-ray pulsars detected by the Fermi Gamma-ray Space Telescope: the radio-loud PSR J0248+6021 and PSR J0631+1036, and the radio-quiet PSR J0633+0632. The latter has also been detected in the X-rays. The pulsars are very similar in their spin-down age (tau similar to 40-60 kyr), spin-down energy (E similar to 10(35) erg s(-1)), and dipolar surface magnetic field (B similar to 3-5 x 10(12) G). These pulsars are promising targets for multiwavelength observations, since they have been already detected in gamma-rays and in radio or X-rays. None of them has been detected yet in the optical band. We observed the three pulsar fields in 2014 with the Spanish 10.4 m Gran Telescopio Canarias (GTC). We could not find any candidate optical counterpart to the three pulsars close to their most recent radio or Chandra positions down to 3 sigma limits of g' similar to 27.3, g' similar to 27, g' similar to 27.3 for PSR J0248+6021, J0631+1036, and J0633+0632, respectively. From the inferred optical upper limits and estimated distance and interstellar extinction, we derived limits on the pulsar optical luminosity. We also searched for the X-ray counterpart to PSR J0248+6021 with Chandra but we did not detect the pulsar down to a 3s flux limit of 5 x 10(-14) erg cm(-2) s(-1) (0.3-10 keV). For all these pulsars, we compared the optical flux upper limits with the extrapolations in the optical domain of the gamma-ray spectra and compared their multiwavelength properties with those of other gamma-ray pulsars of comparable age.