ASASSN-17dh and ASASSN-17dk: Discovery of Two Probable Supernovae in NGC 6321 and SDSS J152927.45+565558.3
ATel #10156; G. Stone (Sierra Remote Observatories), I. Cruz (Cruz Observatory), J. Brimacombe (Coral Towers Observatory), R. S. Post (Post Astronomy), T. W.-S. Holoien, K. Z. Stanek, C. S. Kochanek, J. S. Brown, J. Shields, T. A. Thompson (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), D. Bersier (LJMU), Subo Dong, S. Bose, Ping Chen (KIAA-PKU), J. M. Fernandez (Observatory Inmaculada del Molino), S. Kiyota (Variable Star Observers League in Japan), R. A. Koff (Antelope Hills Observatory)
on 9 Mar 2017; 17:27 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Thomas Holoien (firstname.lastname@example.org)
Subjects: Optical, Supernovae, Transient
During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014), we discovered two new transient sources, most likely supernovae, in the galaxies NGC 6321 and SDSS J152927.45+565558.3.
ASASSN-17dh (AT 2017cal) was discovered in images obtained on UT 2017-03-07.53 at V~15.9 mag. We also detect the object in images obtained on UT 2017-03-06.54 (V~15.9), UT 2017-03-05.54 (V~15.8), UT 2017-03-04.54 (V~15.8), and UT 2017-02-25.56 (V~16.4). We do not detect (V>17.2) the object in images taken on UT 2017-02-21.62 and before. An image obtained on UT 2017-03-09 by R. S. Post confirms the discovery of the transient. This figure shows the archival SDSS g-band image of the host (left) and the R. S. Post confirmation image (right). The red circle has a radius of 5" and is centered on the position of the transient in the R. S. Post image.
The position of ASASSN-17dh is approximately 0.3" North and 0.3" East from the center of the galaxy NGC 6321 (z=0.020764, d=86.4 Mpc, via NED), giving an absolute V-band magnitude of approximately -18.9 (m-M=34.68, A_V=0.141).
ASASSN-17dk (AT 2017cax) was discovered in images obtained on UT 2017-03-07.53 at V~17.5 mag. We do not detect (V>18.0) the object in images taken on UT 2017-03-06.410 and before. An image obtained on UT 2017-03-09 by J. Brimacombe confirms the discovery of the transient. This figure shows the archival SDSS g-band image of the host (left) and the J. Brimacombe confirmation image (right). The red circle has a radius of 4" and is centered on the position of the transient in the J. Brimacombe image.
The position of ASASSN-17dk is approximately 2.1" South and 4.7" West from the center of the galaxy SDSS J152927.45+565558.3 (z=0.050551, d=217 Mpc, via NED), giving an absolute V-band magnitude of approximately -19.2 (m-M=36.68, A_V=0.030).
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-17dh 17:14:24.24 +20:18:50.38 2017-03-07.53 15.9 -18.9 0.42
ASASSN-17dk 15:29:26.88 +56:55:56.30 2017-03-07.53 17.5 -19.2 5.15
Obs. UT Date V mag
Obs. UT Date V mag
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.