Del Santo, M;
Nucita, AA;
Lodato, G;
Manni, L;
De Paolis, F;
Farihi, J;
De Cesare, G;
(2014)
The puzzling source IGR J17361-4441 in NGC 6388: a possible planetary tidal disruption event.
Monthly Notices of the Royal Astronomical Society
, 444
(1)
pp. 93-101.
10.1093/mnras/stu1436.
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Abstract
On 2011 August 11, INTEGRAL discovered the hard X-ray source IGR J17361–4441 near the centre of the globular cluster NGC 6388. Follow-up observations with Chandra showed the position of the transient was inconsistent with the cluster dynamical centre, and thus not related to its possible intermediate mass black hole. The source showed a peculiar hard spectrum (Γ ≈ 0.8) and no evidence of QPOs, pulsations, type-I bursts, or radio emission. Based on its peak luminosity, IGR J17361–4441 was classified as a very faint X-ray transient, and most likely a low-mass X-ray binary. We re-analysed 200 d of Swift/XRT observations, covering the whole outburst of IGR J17361–4441 and find a t−5/3 trend evident in the light curve, and a thermal emission component that does not evolve significantly with time. We investigate whether this source could be a tidal disruption event, and for certain assumptions find an accretion efficiency ϵ ≈ 3.5 × 10−4(MCh/M) consistent with a massive white dwarf, and a disrupted minor body mass Mmb ≈ 1.9 × 1027(M/MCh) g in the terrestrial-icy planet regime. These numbers yield an inner disc temperature of the order kTin ≈ 0.04 keV, consistent with the blackbody temperature of kTin ≈ 0.08 keV estimated by spectral fitting. Although the density of white dwarfs and the number of free-floating planets are uncertain, we estimate the rate of planetary tidal disruptions in NGC 6388 to be in the range 3 × 10−6–3 × 10−4 yr−1. Averaged over the Milky Way globular clusters, the upper limit value corresponds to 0.05 yr−1, consistent with the observation of a single event by INTEGRAL and Swift.
| Type: | Article |
|---|---|
| Title: | The puzzling source IGR J17361-4441 in NGC 6388: a possible planetary tidal disruption event |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1093/mnras/stu1436 |
| Publisher version: | http://dx.doi.org/10.1093/mnras/stu1436 |
| Language: | English |
| Additional information: | This article has been accepted for publication in the Monthly Notices of the Royal Astronomical Society ©: 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. |
| Keywords: | accretion, accretion disc, white dwarfs, globular clusters: individual: NGC 6388, X-rays: individual: IGR J17361-4441 |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/1477439 |
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