Browsing by Author "Littlefair, S. P."

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    Probing for the host galaxies of the fast X-ray transients XRT 000519 and XRT 110103
    (2022) Eappachen, D.; Jonker, P. G.; Fraser, M.; Torres, M. A. P.; Dhillon, V. S.; Marsh, T.; Littlefair, S. P.; Quirola-Vasquez, J.; Maguire, K.; Mata Sanchez, D.; Cannizzaro, G.; Kostrzewa-Rutkowska, Z.; Wevers, T.; Onori, F.; Inkenhaag, Anne; Brennan, S. J.
    Over the past few years, similar to 30 extragalactic fast X-ray transients (FXRTs) have been discovered, mainly in Chandra and XMM-Newton data. Their nature remains unclear, with proposed origins, including a double neutron star merger, a tidal disruption event involving an intermediate-mass black hole and a white dwarf, or a supernova shock breakout. A decisive differentiation between these three promising mechanisms for their origin requires an understanding of the FXRT energetics, environments, and/or host properties. We present optical observations obtained with the Very Large Telescope for the FXRTs XRT 000519 and XRT 110103 and Gran Telescopio Canarias observations for XRT 000519 designed to search for host galaxies of these FXRTs. In the g(s), r(s), and R-band images, we detect an extended source on the north-west side of the similar to 1 '' (68 per cent confidence) error circle of the X-ray position of XRT 000519 with a Kron magnitude of g(s) = 26.29 +/- 0.09 (AB magnitude). We discuss the XRT 000519 association with the probable host candidate for various possible distances, and we conclude that if XRT 000519 is associated with the host candidate a supernova shock breakout scenario is likely excluded. No host galaxy is found near XRT 110103 down to a limiting magnitude of R > 25.8.
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    Rotation periods and astrometric motions of the Luhman 16AB brown dwarfs by high-resolution lucky-imaging monitoring
    (2015) Mancini, L.; Giacobbe, P.; Littlefair, S. P.; Southworth, J.; Bozza, V.; Damasso, M.; Dominik, M.; Hundertmark, M.; Jorgensen, U. G.; Rabus, Markus
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    The Fast X-Ray Transient XRT 210423 and Its Host Galaxy
    (2023) Eappachen, D.; Jonker, P. G.; Levan, A. J.; Quirola-Vasquez, J.; Torres, M. A. P.; Bauer, F. E.; Dhillon, V. S.; Marsh, T.; Littlefair, S. P.; Ravasio, M. E.; Fraser, M.
    Fast X-ray Transients (FXTs) are X-ray flares with durations ranging from a few hundred seconds to a few hours. Possible origins include the tidal disruption of a white dwarf by an intermediate-mass black hole, a supernova shock breakout, or a binary neutron star merger. We present the X-ray light curve and spectrum as well as deep optical imaging of the FXT XRT 210423, which has been suggested to be powered by a magnetar produced in a binary neutron star merger. Our Very Large Telescope and Gran Telescopio Canarias (GTC) observations began on 2021 May 6, thirteen days after the onset of the flare. No transient optical counterpart is found in the 1 (3s) X-ray uncertainty region of the source to a depth g(s) = 27.0 AB mag. (We use the word "counterpart" for any transient light in a wave band other than the original X-ray detection wave band, whereas the word "host" refers to the host galaxy.) A candidate host lies within the 1 X-ray uncertainty region with a magnitude of 25.9 +/- 0.1 in the GTC/ HiPERCAM g(s) filter. Due to its faintness, it was not detected in other bands, precluding a photometric redshift determination. We detect two additional candidate host galaxies: one with zspec = 1.5082 +/- 0.0001 and an offset of 4 2 +/- 1 (37 +/- 9 kpc) from the FXT, and another one with = z 1.04+ (+0.22)(-0.14) and an offset of 3."6 +/- 1." (30 +/- 8 kpc). Based on the properties of all the prospective hosts, we favor a binary neutron star merger, as previously suggested in the literature, as the explanation for XRT 210423.