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http://hdl.handle.net/20.500.12386/31275
Titolo: | Enhanced optical activity 12 days before X-ray activity, and a 4 day X-ray delay during outburst rise, in a low-mass X-ray binary | Autori: | Goodwin, A. J. Russell, D. M. Galloway, D. K. Baglio, M. C. Parikh, A. S. Buckley, D. A. H. Homan, J. Bramich, D. M. in 't Zand, J. J. M. Heinke, C. O. Kotze, E. J. DE MARTINO, Domitilla PAPITTO, ALESSANDRO Lewis, F. Wijnands, R. |
Data pubblicazione: | 2020 | Rivista: | MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY | Numero: | 498 | Fascicolo: | 3 | Da pagina:: | 3429 | Abstract: | X-ray transients, such as accreting neutron stars, periodically undergo outbursts, thought to be caused by a thermal-viscous instability in the accretion disk. Usually outbursts of accreting neutron stars are identified when the accretion disk has undergone an instability, and the persistent X-ray flux has risen to a threshold detectable by all sky monitors on X-ray space observatories. Here we present the earliest known combined optical, UV, and X-ray monitoring observations of the outburst onset of an accreting neutron star low mass X-ray binary system. We observed a significant, continuing increase in the optical i'-band magnitude starting on July 25, 12 days before the first X-ray detection with Swift/XRT and NICER (August 6), during the onset of the 2019 outburst of SAX J1808.4-3658. We also observed a 4 day optical to X-ray rise delay, and a 2 day UV to X-ray delay, at the onset of the outburst. We present the multiwavelength observations that were obtained, discussing the theory of outbursts in X-ray transients, including the disk instability model, and the implications of the delay. This work is an important confirmation of the delay in optical to X-ray emission during the onset of outbursts in low mass X-ray binaries, which has only previously been measured with less sensitive all sky monitors. We find observational evidence that the outburst is triggered by ionisation of hydrogen in the disk. | URI: | http://hdl.handle.net/20.500.12386/31275 | URL: | http://arxiv.org/abs/2006.02872v2 https://academic.oup.com/mnras/article/498/3/3429/5897366 |
ISSN: | 0035-8711 | DOI: | 10.1093/mnras/staa2588 | Bibcode ADS: | 2020MNRAS.498.3429G | Fulltext: | open |
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