Multiwavelength observations of KT Eri (=Nova Eri 2009) during the ongoing luminosity rise
ATel #17140; N. Masetti (INAF-OAS, Bologna), U. Munari (INAF Padova)
on 8 Apr 2025; 14:17 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)
Subjects: Optical, Ultra-Violet, X-ray, Cataclysmic Variable, Nova
Referred to by ATel #: 17141
Following the announcement in ATel #17125 of KT Eri (=Nova Eri 2009) beginning a steep rise toward record brightness and a new emission state, we observed this source in X-rays and ultraviolet (UV) with the Neil Gehrels Swift satellite, starting at 10:40 UT on 2025 Apr. 06. The source field was acquired in UV using UVOT with filters UVW1, UVW2 and UVM2 for 580 s, 720 s and 720 s, respectively; preliminary analysis shows that the source was well detected, with Vega system magnitudes UVW1=13.09+-0.04, UVM2=13.08+-0.04 and UVW2=13.10+-0.04. This corresponds to UVW1=14.60+-0.04, UVM2=14.77+-0.04 and UVW2=14.83+-0.04 in the AB system. No X-rays were instead observed from the source: a simultaneous XRT pointing of about 2000 s did not reveal any emission in the 0.3-10 keV band down to a 3-sigma limit of ~5e-3 counts/s.
Assuming a collisionally ionized plasma X-ray spectrum with kT~0.06 keV as in Pei et al. (2021, MNRAS, 507, 2073), adopting the Gaia DR3 catalog distance to the source of 5.1 kpc and considering a negligible hydrogen column density given the high Galactic latitude of KT Eri, the XRT observation implies a flux upper limit of <3e-13 erg/cm2/s and a luminosity limit of <9e32 erg/s.
The spectral energy distribution (SED) of KT Eri for the current April 2025 bright phase and the 2011-2024 quiescence following the 2009 outburst are compared in this picture. The SED for the 2011-2024 quiescence combines median UBVRI data from ATel #17125 with 2MASS JHKs values, and median NeoWISE W1 and W2 magnitudes. The SED for April 2025 is built from the UVOT observations of April 6, 2025 above described, and the UBVRI magnitudes for March 24, 2025 from ATel #17125. Integrating the SED for April 2025 over the 1800-8500 Ang covered by the UVOT-UBVRI bands, and adopting the above distance under negligible reddening, we found a radiated luminosity of 2.5e35 erg/s equivalent to 65 Solar luminosities. The source luminosity from the SED in quiescence over this range of wavelengths is a factor of 2.5 less.
We thank the Swift Team for the quick approval, scheduling and acquisition of the observation presented in this communication.
