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V404 Cyg optical spectroscopic evolution with BOOTES-2/TELMA (+COLORES)

ATel #7772; M. D. Caballero-Garcia (CTU-FEL, Prague), A. J. Castro-Tirado (IAA-CSIC, Spain), M. Jelinek (ASU-CAS, Ondrejov), R. Cunniffe (IAA-CSIC, Spain), S. Oates (IAA-CSIC, Spain), P. Galindo (IAA-CSIC, Spain), J. C. Tello (IAA-CSIC, Spain), on behalf of a larger collaboration.
on 8 Jul 2015; 09:32 UT
Credential Certification: Maria D. Caballero-Garcia (mcaballe@brera.inaf.it)

Subjects: Black Hole, Transient

Referred to by ATel #: 7959

In light of the recent extreme outburst of V404 Cyg (GCN#17929) and follow-up by SWIFT, MAXI, INTEGRAL and many other ground-based observatories (ATELs from #7646 to #7763) the 0.6m TELMA robotic telescope at the BOOTES-2 astronomical station in Malaga (Spain), obtained 6 optical 4000-9000 A spectra using the COLORES spectrograph during the nights 2015-06-17 (22:35:11 UT), 2015-06-26 (03:45:13 UT), 2015-06-28 (23:54:16 UT) and 2015-06-29 (00:03:26, 00:12:33, 00:21:36 UT).

The most prominent feature of the spectra is the variable H alpha line. The equivalent width varies between the values EW=-93.12 A (2015-06-17) and -152.3,-282.5,-131.4 A (2015-06-28/29). The negative sign indicates that the lines are in emission. During 2015-06-26 we obtained the highest S/N spectrum, that resembles (in shape) the one obtained on 2015-06-16 with GTC (+OSIRIS) in the same wavelength range (ATEL #7699).

During 2015-06-26 we observe strong and single peaked H-alpha line in emission (H-beta is weaker but significant). HeI (5876 A and 6678 A) lines are also observed plus an emission line at 7100 A approx. that might be a 300 A shifted H alpha Pfund line (7460 A). The latter is similar to the one detected in SS 433 during its outburst on 2014 (ATEL #6385). All these features are the same as the ones observed in the 2015-06-16 GTC (+OSIRIS) spectrum.

Optical photometry at BOOTES-2/TELMA is also available for most of the outburst.