Optical spectroscopic follow up of the EP X-ray transient, EP240305a (EPW20240305aa), with the Southern African Large Telescope (SALT)
ATel #16529; I. M. Monageng (UCT/SAAO), P. A. Charles (Southampton, UFS), D. A.H. Buckley (SAAO, UFS), W. Yuan (NAOC/CAS), D. Y. Li (NAOC/CAS) and H. Y. Liu (NAOC/CAS)
on 14 Mar 2024; 14:58 UT
Credential Certification: Itumeleng Monageng (itu@saao.ac.za)
Subjects: Optical, X-ray, Transient
On 09 March 2024 at 21:58:30 UTC we performed follow-up observations of the possible optical counterpart of the new X-ray flare source, EP240305a (ATel #16509 and ATel #16514), with the Southern African Large Telescope (SALT) under the SALT transient follow-up programme (2021-2-LSP-001). We used the Robert Stobie Spectrograph (RSS) with the PG0700 grating (R~800) to acquire two exposures, each with an exposure time of 1500 seconds. The two exposures were combined to obtain a high signal-to-noise spectrum with a wavelength range 3500 - 7500 Angstroms. The spectrum exhibits several weak absorption features (Balmer lines, CaII H&K being the strongest), while being devoid of any helium lines. This is suggestive of a late A or early F spectral-type star.
Following on the Swift/XRT detection of EP240305a (ATel # 16514), we performed another XRT observation starting at on 09 March 2024 at 13:30:52 UTC with an exposure time of 971 seconds in the Photon Counting mode. No source was detected around the position of EP240305a. Assuming the same spectral shape as that of the XRT source, we set a flux limit of 1.7e-13 erg/s/cm2 (90% c.l.).
We thank the Neil Gehrels Swift Observatory team for making the ToO observation possible.
