Swift and ATLAS observations of ASASSN-17fy/SN2017dwq
ATel #10500; K. Sokolovsky (IAASARS NOA/ASC Lebedev/SAI MSU), L. Wyrzykowski, A. Hamanowicz, M. Gromadzki (Warsaw Observatory), P. Chandra (NCRA), J. Tonry, B. Stalder, L. Denneau, A. Heinze, H. Weiland (IfA, Univ. of Hawaii), A. Rest (STScI), K. W. Smith, S. J. Smartt, D. Young (QUB)
on 16 Jun 2017; 20:25 UT
Credential Certification: Kirill Sokolovsky (firstname.lastname@example.org)
Subjects: Optical, Ultra-Violet, X-ray, Supernovae, Transient
ASASSN-17fy was discovered on 2017-05-04 near the emission-line
galaxy 6dFGS gJ090332.4-212002 (ATel #10358) that is also
associated with a faint (6.3 mJy at 1.4 GHz) radio source
NVSS 090332-212002. Spectroscopic observations with NOT
classified the object as a young Type IIn supernova at z=0.018
(ATel #10391). SALT spectroscopy on 2017-05-19 revealed spectral
features resembling SN Type Ib/c and confirming the redshift
The transient position suggested by ATLAS, SALT and Swift/UVOT
imaging is 09:03:32.49 -21:20:02.83 J2000 which is 6.2" off
the position currently reported by the Transient Name Server
(but 0.3" from the one reported in the discovery ATel #10358).
Forced photometry on ATLAS imaging shows that the transient has
been slowly rising for 40 days. It has a first detection
(o = 18.3 +/-0.2) on 2017-04-16 (JD2457859.8) and
a non-detection 4 days before (o < 19.2). The lightcurve now
looks close to peak at o = 16.3, corresponding to M_r ~ -18.6.
The ATLAS o magnitudes are measured through an r+i combined filter
and defined in the AB system.
Swift observed ASASSN-17fy for 4.3ks on 2017-05-23 (JD2457897.2).
The XRT detected no X-ray source at the position of the transient
with an upper limit of 0.0005 cts/s. Assuming power law emission
with the photon index of 2 and HI column density of 1.0x10^21 cm^-2
this translates to the unabsorbed 0.3-10 keV flux limit
of 2.3x10^-14 ergs/cm^2/s.
An ultraviolet source is detected by UVOT at the position of
the transient. The measured AB magnitudes include the host galaxy
light falling within the 5" diameter aperture. This likely explains
the discrepancy with the ATLAS photometry, which have
the host subtracted:
Band Mag. Err.
W2 18.87 0.04
M2 18.65 0.04
W1 17.92 0.04
U 16.85 0.04
B 16.05 0.03
V 15.46 0.04
Taking into account the Galactic reddening of E(B-V)=0.140
(Schlafly et al. 2011 ApJ, 737, 103) these magnitudes suggest
a black-body emission with the temperature ~ 8300 K, consistent
with the transient being a supernova.
We thank Brad Cenko and the Swift team for this ToO observation.