# A Tidal Capture Formation Scenario for the Accreting Pulsar IGR J17480-2446 in Terzan 5

## TL;DR

This paper proposes a tidal capture formation scenario for the accreting pulsar IGR J17480-2446 in Terzan 5, supported by numerical simulations indicating recent binary formation through close encounters in a dense globular cluster environment.

## Contribution

The study introduces a new formation mechanism for the pulsar via tidal capture, explaining its recent mass transfer initiation despite the old age of its environment.

## Key findings

- Binary likely formed through tidal capture during close encounters.
- Primordial binaries are significantly affected by encounters, influencing their evolution.
- Such systems can only form in dense environments like globular clusters.

## Abstract

The low mass X-ray binary (LMXB) IGR J17480-2446 is an 11 Hz accreting pulsar located in the core of the globular cluster Terzan 5. This is a mildly recycled accreting pulsar with a peculiar evolutionary history since its total age has been suggested to be less than a few hundred Myr, despite the very old age of Terzan 5 (~12 Gyr). Solving the origin of this age discrepancy might be very valuable because it can reveal why systems like IGR J17480-2446 are so rare in our Galaxy. We have performed numerical simulations (dynamical and binary evolution) to constrain the evolutionary history of IGR J17480-2446 . We find that the binary has a high probability to be the result of close encounters, with a formation mechanism compatible with the tidal capture of the donor star. The result reinforces the hypothesis that IGR J17480-2446 is a binary that started mass transfer in an exceptionally recent time. We also show that primordial interacting binaries in the core of Terzan 5 are strongly affected by a few hundred close encounters (fly-by) during their lifetime. This effect might delay, accelerate or even interrupt the Roche lobe overflow (RLOF) phase. Our calculations show that systems of this kind can form exclusively in dense environments like globular clusters.