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Alert Notice 520: X-ray nova and LMXB V404 Cyg in rare outburst

Campaign extended until further notice: As V404 Cyg's behavior following outbursts is clearly unpredictable, AAVSO observers are asked to continue obtaining multicolor photometry as well as visual observations. - April 2017

June 18, 2015: V404 Cyg, an X-ray nova and a low mass X-ray binary (LMXB) with black hole component, is undergoing its first reported X-ray and optical outburst since 1989. Large scale, rapid variations are being reported in wavelengths from X-ray to radio by professional and amateur astronomers worldwide.

Satellite and ground-based observations have been and are continuing to be made by the professional community, including: S. D. Barthelmy et al. (GCN Circular 17929, 15 June 2015, Swift BAT initial detection); H. Negoro et al. (ATel #7646, 17 Jun 2015); E. Kuulkers et al. (ATel #7647, 17 June 2015, Swift observations); K. Gazeas et al. (ATel #7650, 17 June 2015, optical photometry); R. M. Wagner et al. (ATel #7655, 18 June, optical spectroscopy); K. Mooley et al. (ATel #7658, 18 June, radio observations); T. Munoz-Darias et al. (ATel #7659, 18 Jun 2015, P Cyg profiles seen). They note that P-Cyg profiles were also observed during the 1989 outburst (Casares et al. 1991, MNRAS, 250, 712), and that V404 Cyg is so far the only black hole X-ray transient that has shown this phenomenology.

Observations in all bands are requested. Filtered observations are preferred. Please use a cadence as high as possible while obtaining a suitable s/n. If spectroscopy is possible with your equipment, it is requested.

In the AAVSO International Database (AID), V-band data from D. Barrett (St. Leger Bridereix, France) on June 16.91-17.12 (JD 2457190.416111-.617176) show increasingly fainter variations V=12.95-16.308. Rc-band data from C. Littlefield (Middletown, CT) on June 17.13-.31 (JD 2457190.62715-.81017) show rapid variations Rc=13.534-15.705. Ic-band data from Barrett on June 17.92-18.12 (JD 2457191.420822-.623507) show rapid variations Ic=11.702-14.418.

Other AID data include:
June 15.94787 UT, <14.1 visual (E. Muyllaert, Oostende, Belgium);
16.16875 UT, 16.18 V +/-0.035 (Muyllaert, CCD);
16.978 UT, 13.8 visual (P. Schmeer, Bischmisheim, Germany);
17.02653, 14.98 V +/-0.06 (S. O'Connor, St. George, Bermuda).

In the 1989 outburst, which was detected by Ginga on May 22 (F. Makino et al. IAUC 4782), V404 Cyg remained brighter than visual magnitude 15.3 for at least 37 days. The AID shows a maximum visual magnitude of 14.0 on 1989 June 3.021 UT (JD 2447680.521; S. Korth, Germany); the last positive observation was 15.3 on 1989 July 10.2 (2447717.7; C. Scovil, Stamford, CT).

Coordinates: 20 24 03.83 +33 52 02.2  (J2000.0)

Charts with comparison star sequence for V404 Cyg may be created using the AAVSO Variable Star Plotter (VSP). A photometry table containing multicolor magnitudes of comparison stars may also be obtained via VSP.

Please report observations to the AAVSO International Database using the name V404 CYG. Be sure to include error values and comparison star information.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.


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