2001/02/28 by L. Homer, P. A. Charles, D. Chakrabarty +1 · 4 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Flux (metallurgy) #Gravitational wave #Light curve #Millisecond pulsar #Modulation (music) #Optical depth #Pulsar #Pulsars and Gravitational Waves Research #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1046/j.1365-8711.2001.04567.x
published as Mon.Not.Roy.Astron.Soc. 325 (2001) 1471 · 7 pages, 5 figures, accepted version with very minor changes (after ref's report), to appear in MNRAS
arxiv created 2001/04/07 · openalex publication_date 2001/08/21 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We report the first extensive set of optical photometric observations of the counterpart to SAX J1808.4−3658 (V4580 Sagittarii) in quiescence. The source was detected at V∼21, 5 mag fainter than at the peak of its 1998 outburst. However, a comparable ∼6 per cent semi-amplitude 2-h modulation of its flux is revealed. This has the same phasing and approximately sinusoidal modulation as seen during outburst, and with photometric minimum when the pulsar is behind the companion. The lack of a double-humped morphology rules out an ellipsoidal origin, implying that the bulk of the optical flux does not arise from the companion. Moreover, applying crude modelling to the disc and X-ray irradiated face of the donor shows that the internal energy release of a remnant disc (with mass transfer driven by gravitational radiation) is sufficient to explain most of the optical emission, and with the modulation because of the varying contribution of the heated face of the star. We note that this model is also consistent with the much lower X-ray to optical flux ratio in quiescence versus outburst, and with the phasing of the optical modulation.