New ROTSE3 transient: ROTSE3 J015118.59-022300.1

On October 11, 2001 the ROTSE-III automated GRB followup telescope began observations in Los Alamos NM. ROTSE-III is an 0.45m telescope instrumented with an unfiltered, thinned CCD with a 1.85 degree field-of-view. When not responding to satellite GRB triggers (most of the time) the telescope automatically patrols the sky. Pairs of images are taken for each of around 100 patrol fields several times a night.

Recent analysis of the first ROTSE-III dark run has uncovered an interesting transient event which we designate ROTSE3 J015118.59-022300.1. This object is absent in images taken on 10/11/01 to limiting magnitudes of R~18.2. It is also absent from skyview images, scanned SERC plates from the USNO PMM archive, and from the USNO A2.0 catalog.

On 10/13/01 the object appears at R=13.9, after which it fades rapidly, falling by more than 2 magnitudes over a period of 13 days. The onset time is in the 1.9 days between the 10/11 and 10/13 images. Assuming a time of 1 day, the transient fades with a power law index of around -0.9. The latest ROTSE-III observation (10/26/01 at 09:10:21.97 UT) shows the transient at R=16.2. We estimate the current R magnitude (11/01/01) to be 16.5-17.5.

Thanks to Steve Shectman at Magellan, we have a quick spectrum. The object is not at high redshift, and appears to be a CV. The exact classification of the type of CV remains uncertain.

It could be a fast nova (NA) in the halo. Fast novae are intrinsically bright. For this event the scaling relations in Duerbeck (1981 PASP 93, 165) would predict a peak absolute magnitude around MV~-8.5. The observed peak brightness of 13.9 suggests a distance modulus of 22, and a distance of ~300 kpc. The high galactic latitude of this event suggests that extinction is not the explanation. If it is a fast nova, it is an unusual one.

It is also possible that it is a dwarf nova, though the increase in brightness is rather extreme. Also, its absence in the plates scanned by the USNO PMM machine (12 epochs from 1953-1997) requires a low duty cycle.

The position of the object is (J2000):
RA: 27.827476DEC: -2.3834
L: 190.62224B: -40.740092

Five figures provide additional information. They can be found at