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Swift triggers on V404 Cyg (ATel #8455)

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SPK's picture
Swift triggers on V404 Cyg (ATel #8455)

Swift triggers on V404 Cyg

ATel #8455; A. P. Beardmore (U. Leicester), K. L. Page (U. Leicester), E. Kuulkers (ESAC/ESA)
on 23 Dec 2015; 17:00 UT

On 2015-Dec-23 at 05:19:52 UT, the Swift Burst Alert Telescope (BAT) triggered and located a source consistent with V404 Cyg (trigger=668097; GCN Circ. 18716). As is typical with BAT image triggers, the real-time light curve did not show anything significant. However, this is the first automatic detection of V404 Cyg by BAT since the on-board trigger threshold level was reset back to the pre-2015 June outburst value for the source on 2015-Aug-03.


The Swift UV and Optical Telescope (UVOT) obtained white and v-band images of the field which showed the source at magnitudes of 17.79+/-0.06 and 16.23+/-0.25, respectively. The latter is consistent with the MASTER-Tunka observations taken 3.5 hours later (GCN Circ. 18718).

Further Swift observations have been approved in an attempt to determine whether the source is entering another active phase.


Complete text:


Merry Christmas and clear skies!



stellakafka's picture
Possible target!

Thanks for posting this, Patrick. The source seems to be borderline active, but there is something in x-rays that makes it suspicious. I would like to encourage optical observations; it would be very interesting (and rare!) for this object to go through a second flaring phase in a year!


During the June optical flare, we issued the following alert, which has more information on the source and can assist with new observations:

Sequences for the star and finding charts can be created through VSP. Let's see what the object is doing this time...


Best wishes - clear skies,


stellakafka's picture
Observations needed!

I would like to encourage anyone who can observe this target to acquire data and send them to the AAVSO. It seems that V404 Cyg is doing something "interesting" in x-rays!

Best wishes - clear skies,


BPO's picture
V0404 Cyg

V0404 Cyg brightened to around mag 12.5 in the I band as of JD2457388.26100


FRF's picture
Optical spectra

Optical spectra by Peter Somogyi (HAA/VSS) of the recent rebrightening:


More details:

Observations by Tamás Tordai (HAA/VSS) show it peaked around 13.7V in the evening 31 December:

Clear skies,



stellakafka's picture

Lots of activity in the optical and in x-rays:

Cygnus is getting low in the horizon, but more observations are strongly encouraged for as long as possible!


Best wishes - clear skies,



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