ASASSN-16em: Discovery of A Supernova in GALEXASC J133213.24+844042.7
ATel #8953; I. Cruz (Cruz Observatory), J. Brimacombe (Coral Towers Observatory), J. L. Prieto (Diego Portales; MAS), J. S. Brown, T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, D. Godoy-Rivera, U. Basu (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), D. Bersier (LJMU), Subo Dong, Ping Chen (KIAA-PKU), E. Conseil (Association Francaise des Observateurs d'Etoiles Variables), S. Kiyota (Variable Star Observers League in Japan), R. A. Koff (Antelope Hills Observatory), G. Masi (Virtual Telescope Project, Ceccano, Italy)
on 15 Apr 2016; 15:43 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Jonathan Brown (brown@astronomy.ohio-state.edu)
Subjects: Optical, Supernovae, Transient
During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), 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 GALEXASC J133213.24+844042.7.
ASASSN-16em (AT 2016bmh) was discovered in images obtained on UT 2016-04-14.41 at V~17.0 mag. We also detect the object in images obtained on UT 2016-04-15.49 (V~16.8) and UT 2016-04-13.26 (V~16.8). We do not detect (V>17.5) the object in images taken on UT 2016-04-11.39 and before. Images obtained on 2016-04-15 by I. Cruz and J. Brimacombe confirm the discovery of the transient. This figure shows the archival DSS image of the host (left) and the J. Brimacombe confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the J. Brimacombe image.
The position of ASASSN-16em is approximately 0.5" South and 1.5" East from the center of the galaxy GALEXASC J133213.24+844042.7. An optical spectrum of ASASSN-16em was obtained on UT 2016-04-15.2 by T. Holoien and D. Godoy with OSMOS mounted on the MDM 2.4m telescope. The spectrum shows that this is normal Type Ia around maximum light. We detect nebular emission lines ([O III], H-alpha, [N II]) from the host galaxy at z=0.0234 (d= 97.9 Mpc, m-M=34.95, A_V=0.373). After correcting the SN spectrum by the host galaxy redshift, we measure a Si II 635.5nm expansion velocity of 11800 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-16em 13:32:14.198 +84:40:42.35 2016-04-14.41 17.0 -18.3 1.58
Obs. UT Date V mag
2016-04-11.39 >17.5
2016-04-13.26 16.8
2016-04-14.41 17.0
2016-04-15.49 16.8
Follow-up observations are encouraged.
While we are participating in the TNS system to minimize potential confusion, ASAS-SN will continue using ASASSN-16xx 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-16xx (AT2016xyz) to preserve, rather than anonymize, the origin of the transient.
We thank LCOGT and its staff for their continued support of ASAS-SN. ASAS-SN is supported by NSF grant AST-1515927, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, the Mt. Cuba Astronomical Foundation, George Skestos, and the Robert Martin Ayers Sciences Fund. For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.
