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Discovery of luminous near-infrared transient AT 2017gbl in IRAS 23436+5257

ATel #10651; E. C. Kool (Macquarie University/AAO), S. Ryder (AAO), S. Mattila (Turku), T. Reynolds (Turku), G. Cannizzaro, (SRON/RU), E. Kankare (QUB), R. McDermid (Macquarie University), M. Fraser (UCD), M. Perez-Torres (IAA-CSIC, Granada), T. Wevers (RU/SRON), P. Jonker (SRON/RU), P. Vaisanen (SAAO), S. Sweet (SUT), B. E. Tucker (ANU)
on 17 Aug 2017; 21:18 UT
Credential Certification: Seppo Mattila (seppo.mattila@utu.fi)

Subjects: Infra-Red, Optical, Transient

Referred to by ATel #: 10679, 10712

As part of a near-infrared adaptive optics assisted search for nuclear core-collapse supernovae in luminous infrared galaxies (project SUNBIRD) we report on the discovery of AT 2017gbl, a luminous transient superimposed on the northern nucleus of IRAS 23436+5257 at (RA, Dec.) = 23:46:05.53 +53:14:01.06, observed in JHKs with NIRC2 on Keck on 2017 July 8.56 UT.

Subtraction with NIRC2 reference imaging from 2016 Oct 21 yielded near-infrared magnitudes of 13.3 (0.1) in Ks, 14.5 (0.1) in H and 16.0 (0.1) in J. Assuming a host luminosity distance of 146 Mpc (NED, H0 = 70 km s-1 Mpc-1), this yields an absolute magnitude in Ks of -22.5, not corrected for extinction.

Optical follow up was obtained on 2017 July 10 with the William Herschel Telescope, including imaging in r- and i-band with ACAM and spectroscopy (300 - 970nm, R~950) with ISIS. Subtraction of reference images from the PanSTARRS-1 archive yielded a detection in i-band with a magnitude of 19.0 (0.1), but AT 2017gbl could not be recovered in r-band consistent with a large line of sight extinction. The spectrum was dominated by lines typical for luminous infrared galaxies, but no clear features associated with the transient were identified.

Further observations across multiple wavelengths are ongoing.