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Clockwise evolution in the hardness–intensity diagram of the black hole X-ray binary Swift J1910.2−0546

Saikia, Payaswini, Russell, David M, Pirbhoy, Saarah F, Baglio, M C, Bramich, D M, Alabarta, Kevin, Lewis, Fraser and Charles, Phil 2023. Clockwise evolution in the hardness–intensity diagram of the black hole X-ray binary Swift J1910.2−0546. Monthly Notices of the Royal Astronomical Society 524 (3) , 4543–4553. 10.1093/mnras/stad2044

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We present a detailed study of optical data from the 2012 outburst of the candidate black hole X-ray binary Swift J1910.2−0546 using the Faulkes Telescope and Las Cumbres Observatory (LCO). We analyse the peculiar spectral state changes of Swift J1910.2−0546 in different energy bands, and characterize how the optical and UV emission correlates with the unusual spectral state evolution. Using various diagnostic tools like the optical/X-ray correlation and spectral energy distributions, we disentangle the different emission processes contributing towards the optical flux of the system. When Swift J1910.2−0546 transitions to the pure hard state, we find significant optical brightening of the source along with a dramatic change in the optical colour due to the onset of a jet during the spectral state transition. For the rest of the spectral states, the optical/UV emission is mostly dominated by an X-ray irradiated disc. From our high cadence optical study, we have discovered a putative modulation. Assuming that this modulation arises from a superhump, we suggest Swift J1910.2−0546 to have an orbital period of 2.25–2.47 h, which would make it the shortest orbital period black hole X-ray binary known to date. Finally, from the state transition luminosity of the source, we find that the distance to the source is likely to be ∼4.5–20.8 kpc, which is also supported by the comparative position of the source in the global optical/X-ray correlation of a large sample of black hole and neutron star X-ray binaries.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 23 November 2023
Date of Acceptance: 4 July 2023
Last Modified: 27 Nov 2023 14:31

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