Swift observations of ASASSN-15ni
ATel #7859; S. Campana (INAF-OA Brera)
on 30 Jul 2015; 16:14 UT
Credential Certification: Sergio Campana (campana@merate.mi.astro.it)
Subjects: Ultra-Violet, X-ray, Cataclysmic Variable
Referred to by ATel #: 7875
Swift observed ASASSN-15ni (Dong et al. 2015, Atel #7850) starting on 2015-07-29 01:13:07.00 UT for 2.0 ks.
The XRT detected one source coincident with the optical position of ASASSN-15ni at a rate of (1.4+/-0.3) x 10^-2 counts s^-1. The number of photons is however too small to prevent an accurate spectral analysis. Assuming a Crab-like spectrum and the Galactic column density (1.2x10^21 cm^-2) we estimate an unabsorbed 0.3-10 keV flux of 7x10^-13 erg cm^-2 s^-1.
The UVOT observed ASASSN-15ni with all its filters. The following magnitudes (AB system not corrected for absorption) are:
V=13.15+/-0.04 (79 s),
B=12.92+/-0.05 (79 s),
U<12.93 (79 s, due to coincidence losses),
UVW1=12.91+/-0.02 (157 s),
UVM2=12.99+/-0.02 (1231 s),
UVW2=12.81+/-0.02 (315 s).
The source is clearly blue, with a bright UV emission supporting the dwarf nova interpretation, based on spectroscopic data (Berardi 2015, Atel #7854).
Further observations can lead to a detection of an X-ray brightening as the optical flux declines, as observed in other dwarf novae.