# First hard X-ray detection and broad band X-ray study of the unidentified transient AX J1949.8+2534

## TL;DR

This study reports the first detection of hard X-ray outbursts from the transient AX J1949.8+2534, identifying its likely nature as a high mass X-ray binary, and providing detailed spectral and positional analysis.

## Contribution

The paper presents the first hard X-ray detection and broad band spectral study of AX J1949.8+2534, improving its positional accuracy and identifying probable stellar counterparts.

## Key findings

- First hard X-ray outburst detection above 20 keV.
- Duty cycle of approximately 4% and dynamic range over 630.
- Identification of likely high mass X-ray binary counterparts.

## Abstract

We present the results from INTEGRAL and Swift/XRT observations of the hitherto poorly studied unidentified X-ray transient AX J1949.8+2534, and on archival multiwavelength observations of field objects. Bright hard X-ray outbursts have been discovered above 20 keV for the first time, the measured duty cycle and dynamic range are of the order of 4% and >630, respectively. The source was also detected during a low soft X-ray state (2x10E-12 erg cmE-2 sE-1) thanks to a Swift/XRT followup, which allowed for the first time to perform a soft X-ray spectral analysis as well as significantly improve the source positional uncertainty from arcminute to arcsecond size. From archival near-infrared data, we pinpointed two bright objects as most likely counterparts whose photometric properties are compatible with an early type spectral nature. This strongly supports a High Mass X-ray Binary (HMXB) scenario for AX J1949.8+2534, specifically a Supergiant Fast X-ray Transient (more likely) or alternatively a Be HMXB.