Astron. Astrophys. 335, L21-L24 (1998)

Letter to the Editor

Possible pulsed optical emission from Geminga ^*

A. , Shearer ¹, A. , Golden ², S. , Harfst ², R. , Butler ², R.M. , Redfern ², C.M.M. , O'Sullivan ², G.M. , Beskin ³, S.I. , Neizvestny ³, V.V. , Neustroev ³, V.L. , Plokhotnichenko ³, M. , Cullum ⁴, A. and Danks <sup>5

1</sup> Information Technology Centre, National University of Ireland, Galway, Galway City, Ireland
² Department of Physics, National University of Ireland, Galway, Galway City, Ireland
³ SAO, Nizhnij Arhyz, Karachai-Cherkessia, Russia
⁴ European Southern Observatory, Garching bei München, Germany
⁵ STX/Goddard Space Flight Centre, Greenbank, Maryland, USA

Received 20 January 1998 / Accepted 12 May 1998

Abstract

We present optical data which suggests that G", the optical counterpart of the -ray pulsar Geminga, possibly pulses in B with a period of 0.237 seconds. The similarity between the optical pulse shape and the -ray light curve indicates that a large fraction of the optical emission is non-thermal in origin - contrary to recent suggestions based upon the total optical flux. The derived magnitude of the pulsed emission is . Whilst it is not possible to give an accurate figure for the pulsed fraction (due to variations in the sky background) we can give an 1 upper limit of for the unpulsed fraction.

Key words: pulsars: individual (Geminga) techniques: 2-d photon-counting detectors

* Based on Observations taken at ESO, La Silla, Chile and SAO, Nizhnij Arhyz, Russia

Send offprint requests to: A. Shearer (e-mail: andy.shearer@ucg.ie)

© European Southern Observatory (ESO) 1998

Online publication: June 12, 1998

helpdesk@link.springer.de