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Spectroscopy of the optical counterpart of MAXI J1957+032 (=IGR J19566+0326)

ATel #8197; E. J. Marchesini (UNLP, Argentina), G. L. Israel (INAF-OA Roma, Italy), N. Masetti (INAF/IASF-Bologna, Italy) and G. Rodriguez (INAF-OA Roma, Italy)
on 20 Oct 2015; 17:41 UT
Credential Certification: Nicola Masetti (masetti@iasfbo.inaf.it)

Subjects: Optical, X-ray, Star, Transient, Variables

Referred to by ATel #: 8529, 9565, 9591, 9649

We observed the optical counterpart (ATels #7524, #8149) of MAXI J1957+032 (=IGR J19566+0326; ATels #7504, #7506) in the aftermath of its latest outburst occurred on 6 October 2015 (ATel #8143).

Two 20-min spectra were acquired on 12 October 2015, starting at 21:43 UT, in Canary Islands (Spain) with the Nordic Optical Telescope plus ALFOSC using Grism #4 and a slit width of 1.0 arcsec: this setup afforded a dispersion of 3.1 Angstroms/pixel.
To the best of our knowledge, this is the first spectroscopic observation acquired from this optical source.

The overall spectral continuum of the source resembles that of an intermediate-type star, with Halpha and Hbeta lines in absorption (with equivalent widths of ~3.0 and ~3.3 Angstroms, respectively), G-band, MgI band and Na doublet, all at a redshift consistent with zero.
No emission features are apparent.

This indicates that the outburst, which started about 6 days before our observations, already exhausted its effects on the optical emission of this Galactic object at the time of the acquisition of the spectra presented here.

Based on observations made with the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias.