# Investigation of the Outburst Activity of the Black Hole Candidate GRS 1739-278

## TL;DR

This study analyzes the 2014 outburst of GRS 1739-278, revealing state transitions, QPOs, mini-outbursts, and the influence of accretion history on outburst characteristics using joint spectral and timing data.

## Contribution

It provides a detailed spectral and timing analysis of the outburst, identifying new mini-outbursts and exploring the relationship between accretion history and outburst features.

## Key findings

- Detection of type-C QPOs in 0.1-5 Hz range.
- Identification of four new mini-outbursts.
- Correlation between peak flux and inter-outburst interval.

## Abstract

We have performed a joint spectral and timing analysis of the outburst of GRS 1739-278 in 2014 based on Swift and INTEGRAL data. We show that during this outburst the system exhibited both intermediate states: hard and soft. Peaks of quasi-periodic oscillations (QPOs) in the frequency range 0.1-5 Hz classified as type-C QPOs have been detected from the system. Using Swift/BAT data we show that after the 2014 outburst the system passed to the regime of mini-outburst activity: apart from the three mini-outbursts mentioned in the literature, we have detected four more mini-outbursts with a comparable (~20 mCrab) flux in the hard energy band (15-50 keV). We have investigated the influence of the accretion history on the outburst characteristics: the dependence of the peak flux in the hard energy band in the low/hard state on the time interval between the current and previous peaks has been found (for the outbursts during which the system passed to the high/soft state).