Swift J1910.2-0546/MAXI J1910-057: Optical Imaging and Spectroscopy with the Liverpool Telescope
ATel #4210; Phil Charles (Southampton/UCT), Remon Cornelisse (IAC), Jorge Casares (IAC)
on 25 Jun 2012; 16:36 UT
Credential Certification: Phil Charles (pac@saao.ac.za)
Subjects: Optical, X-ray, Binary, Black Hole, Neutron Star
Referred to by ATel #: 4347
We report on optical spectroscopy of the high-energy transient Swift J1910.2-0546 / MAXI 1910-057 (ATel #4139; #4140; #4171; #4195; #4198) using the 2m Liverpool Telescope on La Palma and the FRODOSPEC spectrograph. On 2012 June 18 (01:25 UTC) we obtained 1500s exposures simultaneously in the red (5700-8050A at 0.59A/pixel) and blue (3800-5150A at 0.35A/pixel) using the integral field unit, and giving central resolutions of 1.3 and 0.8A respectively. According to the online MAXI monitoring of the source, it was still in the high soft state.
The resulting spectra are dominated by an almost featureless continuum in the blue, with very weak (<~0.2A EW), broad He II 4686 emission, diffuse interstellar absorption at 4430A (EW 0.2A, consistent with the low X-ray column density given in ATel #4149), but no evidence for Balmer or He I lines. The red spectrum does contain somewhat stronger (EW 1.5A) H alpha emission, but is still dominated by the continuum. Given the absence of a star at that position prior to outburst implying a large outburst amplitude (ATel #4144), these spectra are typical of an LMXB, thereby confirming the optical identification, and indicating that it is comparable with other neutron star/black hole soft X-ray transients. We suggest that the optical spectrum is similar to that of the short-period black hole system, Swift J1753.5-0127 (ATel #566).
Observers should note that the coordinates given in ATel #4144 are incorrect, in that the declination is wrong by 10 arcsecs. The correct coordinates are as given in ATel #4146, i.e. RA: 19:10:22.80; Dec: -05:47:55.9 (J2000). A 10s r-band image was obtained by the Liverpool Telescope's imaging camera RATCam and is available at http://www.astro.soton.ac.uk/Swift1910.2_r.jpg.
We would like to thank the LJMU team that operate the Liverpool Telescope (particularly Iain Steele) for their assistance in performing these observations.
