AAVSO Alert Notice 520
June 18, 2015

X-ray nova and LMXB V404 Cyg in rare outburst

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, http::www.aavso.org/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.

V-band Time Series June 18 2015  Roger Pickard
Outburst image. Martin Mobberley
Time Series VR&Ic band.  Nick James
Visual short term variations June 20-21  G. Poyner
BAAVSS data.  Click on thumbnail for larger image
Time Series Ic band.  Ian Miller
AAVSO Alert Notice 522
July 1, 2015

V404 Cyg HST multiwavelength observations scheduled

The dramatic outburst of the black hole X-ray transient LMXB V404 Cyg continues. It was detected 2015 June 16.1688 UT at 16.18 CV +/-0.035 by E. Muyllaert (MUY, Oostende, Belgium); the first satellite detection was by Swift on June 15.77197 UT (Barthelmy et al., GCN Circular 17929, http://gcn.gsfc.nasa.gov/gcn3/17929.gcn3).
It was announced in AAVSO Alert Notice 520 (http://www.aavso.org/aavso-alert-notice-520).

V404 Cyg has been observed by the professional community across the spectrum from X-ray to radio wavelengths, and by the amateur community in all bands available to it. Large- and small-scale variations have been seen occurring at timescales ranging from seconds to hours, with changes of 2-3 magnitudes seen over the
course of a few hours. Most recently Swift has detected a dust halo around V404 Cyg (Beardmore et al., ATel #7736, http://www.astronomerstelegram.org/?read=7736).

C. Knigge (University of Southampton) et al. announce (ATel #7735, http://www.astronomerstelegram.org/?read=7735) that Far-ultraviolet (FUV) and near-ultraviolet (NUV) spectroscopic observations of V404 Cyg with the Hubble Space Telescope have been scheduled for 2015 July 10, 11, and 12 according to the schedule below:

FUV: 10 Jul 2015 12:12:19 - 19:23:20 UTC
NUV: 11 Jul 2015 13:37:07 - 16:08:55 UTC
FUV: 12 Jul 2015 11:56:15 - 19:08:08 UTC

The HST observations were scheduled for the satellite's earliest availability, and the timing is best for ground-based locations from the western US and eastern Asia.

Regardless of location, all observers are requested to continue to observe V404 Cyg. Time-series observations are requested during as much of the HST observation intervals as possible, in as many bands as possible. A high cadence is recommended in order to detect the very short-period variations that have been seen.

Observations in the AAVSO International Database show that most recently V404 Cyg was V magnitude 17.352 (June 30.9727 UT, I. Miller (MIW), Swansea, UK), R=15.795 on July 1.0486 (MJOD, J. L. Martin, Madrid, Spain), and  I=14.469 on July 1.0501 (Martin), but it has been as bright as V=10.868 (June 26.4959, J. Foster (FJQ),
Los Angeles, CA) and I=9.102 (June 26.4854 (J. Jones (JJI), Aurora, CA) and could brighten again. To date, 59 AAVSO observers worldwide have contributed 63,478 V, B, R, I, CV, CR, and visual observations of this outburst of V404 Cyg.

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

Charts for V404 Cyg with a comparison star sequence and a photometry table may be created using the AAVSO Variable Star Plotter (VSP, http:// www.aavso.org/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.