The near-infrared counterpart of 4U 1636-53
Abstract
Context. The optical counterpart of the neutron star X-ray binary and well known X-ray burster, 4U 1636-53 (=4U 1636-536 = V801 Ara) has been studied for three decades. However, no infrared studies have been reported to date.
Aims: Our aims are to identify and investigate the near-infrared (NIR) counterpart of 4U 1636-53.
Methods: We present deep, KS-band (2.2 μm) imaging of the region of 4U 1636-53 taken with the Infrared Spectrometer And Array Camera (ISAAC) on the Very Large Telescope. Archival optical and UV data were used to infer the 0.2-2.2 μm spectral energy distribution (SED).
Results: One star is located at coordinates α = 16:40:55.57, δ = -53:45:05.2 (J2000; 1σ positional uncertainty of ~0.3 arcsec), which is consistent with the known optical position of 4U 1636-53; its magnitude is KS = 16.14 ± 0.12. This star is also detected in the 2MASS survey in the J-band and has a magnitude of J = 16.65 ± 0.22. Assuming that the persistent emission is quite steady, the 0.4-2.2 μm de-reddened SED can be described by a power law Fν ∝ ν1.5 ± 0.3, with some possible curvature (Fν ∝ ν ≲ 1.5) at 0.2-0.4 μm. The SED can be approximated by a blackbody of temperature ~27 000 K. This is typical for an active low-mass X-ray binary, and the emission can be explained by the outer regions of a (likely irradiated) accretion disc. We therefore interpret this KS-band star as the NIR counterpart.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- March 2012
- DOI:
- 10.1051/0004-6361/201118033
- arXiv:
- arXiv:1109.1839
- Bibcode:
- 2012A&A...539A..53R
- Keywords:
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- stars: neutron;
- X-rays: binaries;
- infrared: stars;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- Accepted in A&