V404 Cyg going into outburst!?

It's about 1.5 mags brighter than quiescence Eddy, so something is happening.  

Fingers crossed for a major outburst as 1989!

Gary

V404 Cyg was detected by the Swift satellite in X-rays at 18:31:38UT June 15.  A subsequent GCN notice by Gazeas and Spapountzis (Univ. Athens) indicated that it was about R=12.6 20 minutes after the trigger and faded rapidly.  The report by Eddie about 8 hours later, showing it to have faded to mag 16, indicates that it has continued to fade but is still above quiescent levels.  I expect it to continue to fade over the next day or two.  Monitoring of it until it has returned to quiescence is recommended!

Arne

Hi All, 

Half a magnitude ellipsoidal variations near min and a V-Rc about 1.9 in VSX. Unfiltered detectors might pick up on this longer wavelength 'excess' as well. See Otero note2 in VSX. Eddy, have you ever seen it in the 17s with the same equipment setup ?

Certainly bears close watching. Not all LMXBs/XNe have lightning fast outbursts. BW Cir (ATel 7367) seems to be undergoing a more protracted one as we speak.

Steve

Most unfiltered BRT measures are in the mid 17's - my own included.

Gary

Hi all,

Just measured V0404 Cyg at 13.1V

Douglas.

Since my last post, less than half an hour ago, V0404 Cyg has faded to around mag 15!

Douglas.

V0404 continued to fade and has now recovered to 15, (I'm estimating off my obsy laptop)

I should be able to image 'til dawn. Coffee's brewing..

Douglas.

Minor correction:  V404 Cyg  V=14.98  (0.06) at JD 190.52653  /  June 17.02653 UT.

Steve

I'm observing with 5-second exposures using an Ic filter. V404 Cyg is flickering on timescales of seconds by up to several tenths of a mag, and it has already fluctuated by nearly half a mag in just several minutes. If anything, 5 seconds is too long an exposure to capture the fast variation! I definitely recommend short exposures.

Colin

I observed V404 Cyg visually at 13.8 mag on 2015 June 16.978 UT with my 203-mm SCT.

And still no Alert Notice...?

Eddy

An Alert will be issued today (Thursday June 18).  V404 continues to trigger a number of X-ray alerts via GCN, so the star remains very active.

In the meantime please continue observing, and if you have already observed, please submit your observations to the AID as soon as possible.

Last nights run in I band:

AAVSO Alert Notice 520 reports on the 2015 outburst of the X-ray nova and LMXB with black hole V404 Cyg. Please see the Alert Notice for observing recommendations.

Good observing,

Elizabeth Waagen, AAVSO HQ

Last night, I used 2-second exposures on a 60-cm telescope. There were numerous fluctuations of several tenths of a magnitude on timescales shorter than 2 seconds. My uncertainties were ~0.02 mag, far less than the observed variations.

Out of curiosity, I tried binning my data into 30-second bins, and with the longer effective integration time, you'd never guess that there are such strong, rapid variations.

Colin

Hallo Klaus,

From your BAV Forum report, you indicated a rise to a maximum and then a decline over a period of about a half hour.  I think visual observers have a key role in monitoring V404 Cyg because of the indications from the CCD observers of very rapid brightness changes.  Flickering in the one-second regime is difficult to follow with a CCD, but easy to notice visually.  Did you see any fast flickering during your observations, or was the change relatively smooth?

For other observers, V404 Cyg continues to flare in the X-rays; it has been observed now at sub-mm wavelengths as well.  It would be a great object to observe with a spectrograph, or even a diffraction grating, with the highest cadence possible.  There is some indication of possible color changes during the V-band variations.  I think either V or Ic is fine for monitoring this LMXB.  Be sure to have accurate UT for your observations, so bandpass overlaps between observers can be used to look for color changes.

Arne

Hello Arne,

in my opinion, the decline was relativeley smooth, but  I can not exclude that fast flickerings are possible.

Klaus

Hello, all,

this is the first time I post in the AAVSO forums.

Last night (June 18th-19th) I monitored V404 Cyg in the V-band with a 20 cm (8") telescope for 6 hours, taking exposures of 300". I have strong light pollution and I need long time exposures in order to increase the S/N relationship. I was shocked for the very strong brigthness variations: up to 2 magnitudes in less than half an hour!

I have already uploaded my observations. This night I will continue monitoring the star. This time I will use a 30 cm (12") telescope and also a V-filter (but I could use also the Rc or Ic filter).

Very iinteresting star!

Clear skies

Fran

Hynes, Robinson and Morales in ATEL 7677 report on high time cadence photometry using the ARGOS instrument on the UT 2.1m telescope.  Rob gave me permission to post the r' light curve, taken on June 18 with 2 second exposures.  As you can see, flickering is very prevalent, below the 2-second exposure limit.  Surprisingly, the curve is smooth through the one flare they observed, which corroborates what Klaus saw visually on another flare.  Basically, feel free to use whatever cadence your system can obtain, as there is information at all scales.

Arne

I've been watching the star for several nights, but last night, it absolutely went crazy: in V-band, it dropped by 3.5 mag (not a misprint) in about 90 minutes, then recovered by 2 magnitudes in the next 60 minutes.

You can see a light curve at

http://spiff.rit.edu/richmond/ritobs/jun23_2015/jun23_2015.html

or just look it up in the AAVSO light curve generator.

Crazy.

p.s. I've made a little animated GIF movie of my 3-hour observing run. See if you can figure out which star is V404 Cyg.

http://spiff.rit.edu/richmond/ritobs/jun23_2015/v404cyg_anim.gif

Dear colleagues,

I am at an international professional astronomy conference, and during today's sessions, people were discussing first results on x-Ray and radio variability of V404 Cyg. Everybody is really excited (and puzzled) by the various behaviors of the object, and they call it their 'poster child' -- they are observing it with new instruments to demonstrate both the efficiency of their new toys and the great science they can do with them. And everyone is relying on the optical light curves AAVSO observers will provide. It is amazing how professional astronomers really rely on us for optical data. So, please keep observing it. Your work is essential for great science to happen.

Best wishes - clear skies,

Stella

Now that V404 Cyg is getting faint, you need to be aware of nearby contaminating stars.  I'm attaching an I-band finding chart of V404 Cyg, taken by Mark Wagner with the USNO 1.0m telescope in 1993, when the target was near quiescence.  Note that this is a closeup view - the star to the south of V404 Cyg, about the same brightness, is about 6.5arcsec distant.  Therefore, for most of you, it will get included in the aperture.

Arne

Colleagues,

Here's the latest ATel with Swift (x-ray) data: http://www.astronomerstelegram.org/?read=7736 Seems there is a dust scattering halo around the system!

Please keep observing it! Lots of interesting science is already coming out from this system!

Best wishes - clear skies,

Stella.

Please see image below:

http://www.swift.ac.uk/V404Cyg_XRT_halos.png

AAVSO Alert Notice 522 reports on the upcoming observations of V404 Cyg by HST. Please see the notice for details and observing instructions.

AAVSO Alert Notice 523 reports an error in the date of detection of the V404 Cyg outburst by Swift. There are no corrections to the HST observations times or observing instructions

Good observing,

Elizabeth Waagen, AAVSO HQ

Just a note that results from this summer's observational campaign -- including measurements made by 4 AAVSO members -- have been published.   See the announcement at

https://www.aavso.org/aavso-observers-contribute-understanding-black-ho…

There's a good summary of the paper at

http://www.nature.com/nature/journal/v529/n7584/full/529028a.html

There are additional materials describing the project at varying levels at

http://www.kusastro.kyoto-u.ac.jp/~mkimura/welcome-cygv404-eng.html

and

http://www.kusastro.kyoto-u.ac.jp/~mkimura/v404cyg-eng.html

And, in a shameless plug for my own little contribution, here's a movie you can watch to see the strong variations in brightness over the course of just 5 hours:

http://spiff.rit.edu/richmond/ritobs/jun23_2015/v404cyg_anim.gif