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 ɛ ≈ 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.

Autore Pugliese

• De Paolis Francesco , Nucita Achille

Tutti gli autori

• M. Del Santo , A. A. Nucita , G. Lodato , L. Manni , F. De Paolis , J. Farihi , G. De Cesare , A. Segreto

Titolo volume/Rivista

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Anno di pubblicazione

2014

ISSN

0035-8711

ISBN

Non Disponibile

Numero di citazioni Wos

Nessuna citazione

Ultimo Aggiornamento Citazioni

Non Disponibile

Numero di citazioni Scopus

1

Ultimo Aggiornamento Citazioni

28/04/2018

Settori ERC

Non Disponibile

Codici ASJC

Non Disponibile