Deep optical imaging of the γ-ray pulsar J1048–5832 with the VLT^⋆,⋆⋆

¹ Ioffe Physical Technical Institute, Politekhnicheskaya 26, 194021 St. Petersburg, Russia
e-mail: danila@astro.ioffe.ru; shib@astro.ioffe.ru
² St. Petersburg State Polytechnical Univ., Politekhnicheskaya 29, 195251 St. Petersburg, Russia
e-mail: aida.taylor@gmail.com; da.zyuzin@gmail.com
³ The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden

Received: 3 August 2012
Accepted: 31 January 2013

Abstract

Context. PSR J1048–5832 is a young radio-pulsar that has recently been detected in γ-rays with Fermi, and also in X-rays with Chandra and XMM-Newton. It powers a compact pulsar wind nebula visible in X-rays and is in many ways similar to the Vela pulsar.

Aims. We present deep optical observations made with the ESO Very Large Telescope to search for optical counterparts of the pulsar and its nebula and to explore their multi-wavelength emission properties.

Methods. The data were obtained in the V and R bands and were compared with archival data in other spectral domains.

Results. We do not detect the pulsar in the optical and derive informative upper limits of R  ≳  28.^m1 and V  ≳  28.^m4 for its brightness. Using a red-clump star method, we estimate an interstellar extinction towards the pulsar of A_V  ≈  2 mag, which is consistent with the absorbing column density derived from X-rays. The respective distance agrees with the dispersion measure distance. We reanalysed the Chandra X-ray data and compared the dereddened upper limits with the unabsorbed X-ray spectrum of the pulsar. We find that regarding its optical-X-ray spectral properties this γ-ray pulsar is not distinct from other pulsars detected in both ranges. However, like the Vela pulsar, it is very inefficient in the optical and X-rays. Among a dozen optical sources overlapping with the pulsar X-ray nebula we find one with V  ≈  26.^m9 and R  ≈  26.^m3, whose colour is slightly bluer than that of the field stars and is consistent with the peculiar colours typical for pulsar nebula features. It positionally coincides with a relatively bright feature of the pulsar X-ray nebula, resembling the Crab wisp and is located in  ~2 from the pulsar. We suggest this source as a counterpart candidate to the feature.

Conclusions. Based on the substantial interstellar extinction towards the pulsar and its optical inefficiency, additional optical studies should be carried out at longer wavelengths.