Possible optical detection of a fast, nearby radio pulsar PSR B1133+16^*

¹ Observatorio Astronómico Nacional SPM, Instituto de Astronomía, Universidad Nacional Autónomia de México, Ensenada, BC, México e-mail: zhar@astrosen.unam.mx
² Ioffe Physical Technical Institute, Politekhnicheskaya 26, St. Petersburg 194021, Russia e-mail: shib@astro.ioffe.ru
³ Departamento de Fisica, Universidad de Concepcion, Casilla 160-C, Concepcion, Chile e-mail: rmennick@stars.cfm.udec.cl
⁴ Special Astrophysical Observatory, Russian Academy of Science, Nizhnii Arkhyz, Russia, 369167 e-mail: vkom@sao.ru
⁵ Isaac Newton Institute of Chile, SAO Branch, Russia

Received: 26 April 2007
Accepted: 1 November 2007

Abstract

Aims.We performed deep optical observations of the field of an old, fast-moving radio pulsar PSR B1133+16 in an attempt to detect its optical counterpart and a bow shock nebula.

Methods.The observations were carried out using the direct imaging mode of FORS1 at the ESO VLT/UT1 telescope in the B, R, and H_α bands. We also used archival images of the same field obtained with the VLT in the B band and with the Chandra/ACIS in X-rays.

Results. In the B band we detected a faint (B = 281 ± 03) source that may be the optical counterpart of PSR B1133+16, as it is positionally consistent with the radio pulsar and with the X-ray counterpart candidate published earlier. Its upper limit in the R band implies a color index 05, which is compatible with the index values for most pulsars identified in the optical range. The derived optical luminosity and its ratio to the X-ray luminosity of the candidate are consistent with expected values derived from a sample of pulsars detected in both spectral domains. No Balmer bow shock was detected, implying a low density of ambient matter around the pulsar. However, in the X-ray and H_α images we found the signature of a trail extending ~ behind the pulsar and coinciding with the direction of its proper motion. If confirmed by deeper studies, this is the first time such a trail has been seen in the optical and X-ray wavelengths.

Conclusions.Further observations at later epochs are necessary to confirm the identification of the pulsar by the candidate's proper motion measurements.