Astrophys. J., 871, 231-231 (2019/February-1)
Searching for the donor stars of ULX pulsars.
HEIDA M., HARRISON F.A., BRIGHTMAN M., FURST F., STERN D. and WALTON D.J.
Abstract (from CDS):
We report on our search for the optical counterparts of two ultraluminous X-ray pulsars with known orbital periods, M82 X-2 and NGC 5907 X-1, in new and archival Hubble Space Telescope observations, in an effort to characterize the donor stars in these systems. We detect five near-infrared sources consistent with the position of M82 X-2 that are too bright to be single stars. We also detect seven sources in the WFC3/UVIS F336W image whose photometry matches that of 10-15 M☉ stars turning off the main sequence. Such stars have densities consistent with the properties of the donor star of M82 X-2 as inferred from X-ray timing analysis, although it is also possible that the donor is a lower-mass star below our detection limit or that there is a significant contribution from the accretion disk to the optical emission. We detect three candidate counterparts to NGC 5907 X-1 in the near-infrared. All of these are too bright to be the donor star of the ultraluminous X-ray source (ULX), which, based on its orbital period, is a red giant. The high background at the location of NGC 5907 X-1 precludes us from detecting this expected donor star. The recently discovered NGC 5907 ULX-2 also falls within the field of view of the near-infrared imaging; we detect four sources in the error circle, with photometry that matches asymptotic giant branch stars. The star suggested to be the counterpart of NGC 5907 ULX-2 by Pintore et al. falls outside our 2σ error circle.
© 2019. The American Astronomical Society. All rights reserved.
infrared: stars - stars: neutron - X-rays: individual: (M82 X-2, NGC 5907 X-1, NGC 5907 ULX-2)
Table 5/Fig. 2: Sources 1-12 are not in SIMBAD.
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