GCN Circular 36414
Subject
EP240506a: Archival radio searching
Date
2024-05-08T10:50:46Z (12 days ago)
From
Ning Chang at Xinjiang Astronomical Observatory, CAS <changning@xao.ac.cn>
Via
Web form
Ning Chang (XAO), Lang Cui (XAO), Yongfeng Huang (NJU), Tao An (SHAO), Jie Liao (XAO, UCAS), Pengfei Jiang (XAO), Wancheng Xu (XAO) and Dongyue Li(NAOC) report:
We report an archival radio source located within the error circle of the fast X-ray transient EP240506a. EP240506a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Li et al., GCN 36405). Aryan et al., (GCN 36408) observed the field of the EP240506a using the 40cm SLT, and only found a variable star which corresponds to SDSS J141557.82-164317.2 within the error circle of 3 arcmin. Perez-Garcia et al. (GCN 36412) reported that no source was detected within the error position of the field of EP240506a using the telescopes of the Global BOOTES Network. Additionally, Tinyanont et al. (GCN 36413) observed the field of EP240506a using the 0.7-m telescope of TRT and found no uncatalogued optical transient.
We have searched for a radio counterpart using the data from the Rapid ASKAP Continuum Survey (RACS, Hale et al. 2021 PASA 38, e058). We only found one radio detection in the RACS images within the uncertainty of 3 arcmin reported in GCN 36405. We also inspected the VLA Sky Survey data (VLASS, Gordon et al. 2021 ApJS 255, 30) but found no detections.
The fluxes and position of this radio source from RACS are:
2019-04-27: 2.74 mJy (0.8875 GHz, from RACS low, with RA=14h15m56.348s, DEC=-16d41m22.947s)
2021-02-12: 2.46 mJy (1.3675 GHz, from RACS mid, with RA=14h15m56.187s, DEC=-16d41m22.673s)
2022-01-09: 1.42 mJy (1.655 GHz, from RACS high, with RA=14h15m56.12s, DEC=-16d41m23.16s)
The power-law spectral index is -1.47. This radio source is about 1.6 arcmin away from the X-ray transient EP240506a position, and about 2 arcmin away from the variable star position. We further inspected the AllWISE Source Catalog and found that WISEA J141556.28-164124.4 is close to the radio source about 2 arcsec away. We infer that the radio source could be a background galaxy.
The figures of this radio source can be accessed from https://drive.google.com/drive/folders/1Yy9nHYF9JKhmnQhD27fqg5vQkaBpl4Nr?usp=sharing
Multi-wavelength follow-up observations are strongly encouraged to help further reveal the nature of the new X-ray transient.