Nature 355, 614 - 617 (13 February 1992); doi:10.1038/355614a0

A 6.5-day periodicity in the recurrent nova V404 Cygni implying the presence of a black hole

J. Casares^*, P. A. Charles^†‡ & T. Naylor^§

^*Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
^†Royal Greenwich Observatory, Apartado 321, 38780 Santa Cruz de La Palma, Tenerife, Canary Islands.
^‡Department of Astrophysics, Nuclear Physics Building, Keble Road, Oxford 0X1 3RH, UK.
^§Institute of Astronomy, Madingley Road, Cambridge CB3 OHA, UK.
Present address: Department of Physics, Keele University, Keele, Staffordshire ST5 5BG, UK.

THE X-ray transient source GS2023 + 338 was discovered in out-burst by the Ginga satellite in 1989 (ref. 1) and has since been identified with the previously known recurrent nova V404 Cygni². This system is recognized to be a low-mass X-ray binary³, with X-ray behaviour similar to black hole systems⁴, but attempts to deduce an orbital period from photometry^5–9 and spectroscopy^10,11 have yielded modulations with periods from 10 minutes to 6 hours. Two years after the outburst, we have used the William Herschel Telescope to find absorption features in V404 Cyg characteristic of a late G or early K star with a radial velocity curve of amplitude 211 4km s^-1 and period 6.473 0.001 days. The deduced mass function of 6.260.31 M is a firm lower limit to the mass of the compact object, which for reasonable assumptions of orbital inclination and companion star mass must be a black hole with probable mass in the range 8–15.5 M. We consider this the most persuasive case yet for the existence of a black hole.

References

1.	Makino, F. et al. IAUC 4782 (1989).
2.	Marsden, B. G. IAUC 4783 (1989).
3.	Charles, P. A. et al. IAUC 4794 (1989).
4.	Tanaka, Y. in Proc. 23rd ESLAB Symp. on Two Topics in X-Ray Astronomy (ed. Hunt, J. & Battrick, B.) 3 (ESA Publications, 1989).
5.	Wagner, R. M. et al. in Proc. North American Workshop on CVs and LMXRBs (ed. Mauche, C.W.) 29 (Cambridge University Press, 1990). | ChemPort |
6.	Haswell, C. A. & Shafter, A. W. IAUC 5074 (1990).
7.	Udalsky, A. & Kaluzny, J. Publs astr. Soc. Pacific 103, 198−204 (1991).
8.	Gotthelf, E., Patterson, J. & Stover, R. S. Astrophys. J. 374, 340−343 (1991). | Article |
9.	Leibowitz, E. M., Ney, A., Drissen, L., Grandchamps, A. & Moffat, A. F. J. Mon. Not. R. astr. Soc. 250, 385−391 (1991).
10.	Casares, J., Charles, P. A., Jones, D. H. P., Rutten, R. G. M. & Callanan, P. J. Mon. Not. R. astr. Soc. 250, 712−725 (1991). | ChemPort |
11.	Casares, J. & Charles, P. A. Mon. Not. R. astr. Soc. (in the press).
12.	McClintock, J. E. in The Physics of Accretion onto Compact Objects (eds Mason, K. O., Watson, M. G. & White, N. E.) 211 (Springer, Berlin, 1986).
13.	McClintock, J. E. & Remillard, R. A. Astrophys. J. 308, 110−122 (1986). | Article | ChemPort |
14.	Della Valle, M., Jarvis, B. J. & West, R. M. Nature 353, 50−52 (1991). | Article |
15.	Watson, M. G. Mon Not. R. astr. Soc. 176, 19−23p (1976).
16.	Matilsky, T. et al. Astrophys. J. 210, L127−131 (1976). | Article |
17.	Horne, K., Wade, R. A. & Szkody, P. Mon. Not. R. astr. Soc. 219, 791−808 (1986). | ChemPort |
18.	Echevarria, F. D. et al. Mon. Not. R. astr. Soc. 240, 975−990 (1989).
19.	Roberts, D. H., Lehar, J. & Dreher, J. W. Astr. J. 93, 968−989 (1987). | Article | ChemPort |
20.	Bahcall, S., Lynn, B. W. & Selipsky, S. B. Astrophys. J. 362, 251−255 (1990). | Article | ChemPort |
21.	Bahcall, J. N. Ann. Rev. Astr. Astrophys. 16, 241−264 (1978). | Article |
22.	Nagase, F. Publs astr. Soc. Japan 41, 1−79 (1989). | ChemPort |
23.	van Paradijs, J. in Accretion-driven Stellar X-ray Sources (eds Lewin, W. H. G. & van den Heuvel, E. P. J.) 189 (Cambridge University Press 1983).
24.	Cowley, A. P., Crampton, D. & Hutchings, J. B. Astrophys, J. 231, 539−550 (1979). | Article | ISI | ChemPort |
25.	Paczynski, B. Ann. Rev. Astr. Astrophys. 9, 183−208 (1971). | Article | ChemPort |
26.	Allen, C. W. Astrophysical Quantities, 3rd edn (Athlone, London, 1973).
27.	Eggleton, P. P., Bailyn, C. D. & Tout, C. A. Astrophys. J. 345, 489−491 (1989). | Article |
28.	Chevalier, C., Ilovaisky, S. A., Motch, C., Pakull, M. & Mouchet, M. Astr. Astrophys. 217, 108−114 (1989). | ChemPort |
29.	Garcia, M. R., Bailyn, C. D., Grindlay, J. E. & Molnar, L. A. Astrophys, J. 341, L75−78 (1989). | Article | ChemPort |
30.	Bailyn, C. D. & Grindlay, J. E. Astrophys. J. 312, 748−754 (1987). | Article | ChemPort |
31.	Beavers, W. I. & Eitter, J. J. Astrophys. J. Suppl. 62, 147−228 (1986). | Article | ChemPort |