Alert Notice 522: V404 Cyg HST multiwavelength observations scheduled

Correction: In the text below, the date of the detection by the Swift satellite was incorrectly given as 2015 June 16.77197 UT. The correct date is 2015 June 15.77197 UT.

Our sincere apologies for this error!

July 1, 2015:

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 16.77197 UT (Barthelmy et al., GCN Circular 17929). It was announced in 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).

C. Knigge (University of Southampton) et al. announce (ATel #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).

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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