PTF 10fqs: A Luminous Red Nova in the Spiral Galaxy Messier 99


The Palomar Transient Factory (PTF) is systematically charting the optical transient and variable sky. A primary science driver of PTF is building a complete inventory of transients in the local universe (distance less than 200 Mpc). Here, we report the discovery of PTF 10fqs, a transient in the luminosity ``gap’’ between novae and supernovae. Located on a spiral arm of Messier 99, PTF 10fqs has a peak luminosity of M$_r$ = -12.3, red color (g - r = 1.0), and is slowly evolving (decayed by 1 mag in 68 days). It has a spectrum dominated by intermediate-width Hα (≈930 km s$^-1$) and narrow calcium emission lines. The explosion signature (the light curve and spectra) is overall similar to that of M85 OT2006-1, SN 2008S, and NGC 300 OT. The origin of these events is shrouded in mystery and controversy (and in some cases, in dust). PTF 10fqs shows some evidence of a broad feature (around 8600 ̊A) that may suggest very large velocities (≈10,000 km s$^-1$) in this explosion. Ongoing surveys can be expected to find a few such events per year. Sensitive spectroscopy, infrared monitoring, and statistics (e.g., disk versus bulge) will eventually make it possible for astronomers to unravel the nature of these mysterious explosions.

Astrophysical Journal