ASASSN-17er: Discovery of A Supernova in NGC 3546

ATel #10279; G. Bock (Runaway Bay Observatory, Australia), R. S. Post (Post Astronomy), J. Brimacombe (Coral Towers Observatory), J. Klusmeyer (MDM Observatory), J. L. Prieto (Diego Portales; MAS), J. S. Brown, K. Z. Stanek, T. W.-S. Holoien, C. S. Kochanek, J. Shields, T. A. Thompson (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), D. Bersier (LJMU), Subo Dong, S. Bose, Ping Chen (KIAA-PKU), P. Cacella (DogsHeaven Observatory), I. Cruz (Cruz Observatory), S. Kiyota (Variable Star Observers League in Japan), G. Stone (Sierra Remote Observatories)
on 18 Apr 2017; 16:09 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Jonathan Brown (

Subjects: Optical, Supernovae, Transient

During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014), using data from the quadruple 14-cm "Brutus" telescope in Haleakala, Hawaii, we discovered a new transient source, most likely a supernova, in the galaxy NGC 3546.

ASASSN-17er (AT 2017cze) was discovered in images obtained on UT 2017-04-11.29 at V~15.8 mag. We do not detect (V>18.2) the object in images taken on UT 2017-04-02.25 and before. Follow-up images obtained on 2017-04-11 confirm the discovery of the transient. This figure shows the archival Pan-STARRS (Chambers et al. 2016, arXiv:1612.05560) g-band image of the host (left) and the G. Bock confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the G. Bock image.

The position of ASASSN-17er is approximately 0.7" North and 0.1" East from the center of the galaxy NGC 3546 (z=0.014860, d=66.9 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.4 (m-M=34.09, A_V=0.145). We obtained a spectrum of ASASSN-17er on UT 2017-04-16.20 with OSMOS mounted on the MDM 2.4m telescope at KPNO. The spectrum is characteristic of a normal SN Ia past peak with strong host galaxy contamination. Using SNID to fit the spectrum, the best fitting template is the normal SN Ia 2005hf at +9 days. After correcting the spectrum for the redshift of the host, we measure a Si II 6355 velocity of 8000 km/s Properties of the new source and photometry are summarized in the tables below:

Object       RA (J2000)     DEC (J2000)      Disc. UT Date   Disc. V mag  Approx. Abs. Mag   Offset from Host (") 
ASASSN-17er  11:09:46.795   -13:22:50.36     2017-04-11.29      15.8          -18.4               0.71 
Obs. UT Date         V mag 
2017-04-02.25        >18.2 
2017-04-05.28         17.2 
2017-04-11.29         15.8 
2017-04-13.11         15.9 
2017-04-15.02         16.1 

Follow-up observations are encouraged.

While we are participating in the TNS system to minimize potential confusion, ASAS-SN will continue using ASASSN-17xx transient names as our primary nomenclature (including supernovae, but also other classes of transients), and we encourage others to do the same. We prefer merging the names as ASASSN-17xx (AT 2017xyz) to preserve, rather than anonymize, the origin of the transient.

We thank Las Cumbres Observatory and its staff for their continued support of ASAS-SN. ASAS-SN is funded in part by the Gordon and Betty Moore Foundation through grant GBMF5490 to the Ohio State University, NSF grant AST-1515927, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, the Chinese Academy of Sciences South America Center for Astronomy (CASSACA), and the Mt. Cuba Astronomical Foundation. For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.