Identification of the optical and near-infrared counterpart of GRS 1758-258

Abstract

Context. Understood to be a microquasar in the Galactic center region, GRS has not yet been unambiguously identified to have an optical/near-infrared counterpart, mainly because of the high absorption and the historic lack of suitable astrometric stars, which led to the use of secondary astrometric solutions. Although it is considered with 1E 1740.7-2942 as the prototypical microquasar in the Galactic center region, the Galactic origin of both sources has not yet been confirmed. Aims. We attempt to improve previous astrometry to identify a candidate counterpart to GRS 1758-258. We present observations with the Gran Telescopio de Canarias (GTC), in which we try to detect any powerful emission lines that would infer an extragalactic origin of this source. Methods. We use modern star catalogues to reanalyze archival images of the GRS 1758-258 field in the optical and near-infrared wavelengths, and compute a new astrometric solution. We also reanalyzed archival radio data of GRS 1758-258 to determine a new and more accurate radio position. Results. Our improved astrometric solution for the GRS 1758-258 field represents a significant advancement on previous works and allows us to identify a single optical/near-infrared source, which we propose as the counterpart of GRS 1758-258. The GTC spectrum of this source is however of low signal-to-noise ratio and does not rule out a Galactic origin. Hence, new spectral observations are required to confirm or discard a Galactic nature.

Accretion states of the Galactic microquasar GRS 1758−258

“…1), with an error of 0.08 arcsec in RA and 0.2 arcsec in Dec. This is still consistent with the position determined from the highest resolution VLA observations (Muñoz‐Arjonilla et al 2010, and from our direct re‐analysis of the VLA data). In the higher resolution image, the integrated core flux density, determined from an elliptical Gaussian fit with the miriad task imfit , is 0.25 ± 0.02 mJy.…”

“…Here we shall assume a distance of 8 kpc. Its BH mass and orbital period are still unknown, because optical studies of the stellar donor are hampered by high extinction (Rothstein et al 2002; Smith, Heindl & Swank 2002b; Muñoz‐Arjonilla et al 2010). The optical counterpart has a dereddened luminosity consistent with an early A‐type main‐sequence star, but unusual colours (Muñoz‐Arjonilla et al 2010); part of the optical/infrared (IR) emission may also come from the accretion disc or the jet.…”

X-ray spectral and flux variability of the microquasar GRS 1758−258 on timescales from weeks to years

“…GRS 1758−258 is a black hole binary discovered in 1990 during observations of the Galactic Center region by the Granat satellite (Mandrou, 1990;Syunyaev et al, 1991, see Heindl & Smith 2002 for the determination of the source's position). As one of only three persistent, mostly hard state, black hole binaries in our Galaxy and the Magellanic Clouds (GRS 1758(GRS −258, 1E 1740.7−2942, and Cyg X-1) 1 , GRS 1758−258 has since been observed in various energy ranges (e.g., Rodriguez et al, 1992;Cadolle Bel et al, 2006;Pottschmidt et al, 2008;Muñoz-Arjonilla et al, 2010;Soria et al, 2011;Luque-Escamilla et al, 2014, and references therein). As radio observations show a double-lobed counterpart (Rodriguez et al, 1992(Rodriguez et al, ) that et al, 1998, the companion would have to be a K giant star filling its Roche lobe (Rothstein et al, 2002).…”

Optical spectroscopy of the microquasar GRS 1758−258: a possible intermediate mass system?

“…This is because we are dealing with a very weak counterpart (R = 22.6 ± 0.3, I = 21.1 ± 0.3, Martí et al 1998) in a crowded field, thus requiring the use of sub-arcsecond angular resolution as in Luque-Escamilla et al (2014). Previous attempts by our team to secure an optical spectrum of GRS 1758−258 under average seeing conditions using a 10m-class telescope resulted in a poor quality result (Muñoz-Arjonilla et al 2010). In this paper, we report the outcome of our second attempt to acquire optical spectroscopy of this microquasar under better observing conditions.…”