Swift/XRT observations of the X-ray transient EP240408a
ATel #16585; Amar Deo Chandra (Aryabhatta Research Institute of Observational Sciences (ARIES))
on 12 Apr 2024; 16:30 UT
Credential Certification: Amar Deo Chandra (amar.deo.chandra@gmail.com)
Subjects: X-ray, Transient
The fast X-ray transient EP240408a was detected on April 8, 2024 at 17:56:30 UTC by the Einstein Probe (GCN #36053). The location of the source was inferred to be R.A.=158.840 deg, DEC=-35.749 deg (J2000) having an uncertainty of 3 arcmin (90% C.L., GCN #36053). Swift/XRT ToO observations of the source were carried out for about 1.8 ks in the Photon Counting (PC) mode on April 10, 2024 (MJD 60410) beginning at 02:54:18 UTC. We detected an X-ray source at the location RA/Dec(J2000)=158.851, -35.747 which is equivalent to:
RA(J2000) = 10h 35m 24.28s, Dec(J2000) = -35d 44m 49.9s,
with an error radius of 3.5 arc-seconds (90% confidence). The location of this source is consistent with the reported location of EP240408a (GCN #36053,GCN #36057). The estimated average count rate during this observation was about 0.54 cts/s in the 0.3-10 keV energy band. The PC mode spectrum is well described by an absorbed power-law with photon index = 2.12 +/- 0.17, with absorption N_H = 1.4 +/- 0.5 x 10^21 cm^-2. The estimated unabsorbed flux in the 0.3-10 keV band is 2.48 +/- 0.21 x 10^-11 erg/s/cm^2. The estimated unabsorbed flux in the 0.5-4 keV band using Swift/XRT observations is about 1.64 x 10^-11 erg/s/cm^2 which suggests a decrease in the flux by about 240 times compared to the flux during its detection by the Einstein Probe (GCN #36053).
Follow-up multi-wavelength observations are encouraged. We thank the Swift Team and Observatory Duty Scientists who made these observations possible.
