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THE ASTRONOMER Electronic Circular No 3717      2022 Jun 27 09.53UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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POSSIBLE NOVA: TCP J15244460-6059200

Andrew Pearce (TA member) and others relay on ATEL 15473;

They report on spectroscopic follow up of the optical transient TCP
J15244460-6059200 which was discovered by Andrew Pearce, Nedlands, Western
Australia, on UT 2022-06-25.48 at an unfiltered magnitude of 10.7. The
discoverer reports that the transient was not visible on three frames taken
on 2022-06-22.52 and 2022-06-24.47, meaning that the transient is less than
a day old. The latest data from the All-Sky Automated Survey for SNe show
that the transient peaked at g-magnitude = 10.9 and has declined by 1.4 mag
in one day.

The transient matches a Gaia source (ID #5875610751015084544), with a mean
G-magnitude = 13.75, implying an outburst magnitude of less than 3
magnitudes. Archival data from the SkyMapper Southern Sky Survey of the
candidate match reports the following photometry: g = 13.9, r = 13.7, and i
= 13.6.  

On 2022-06-26.21 they obtained a low-resolution spectrum using the Goodman
spectrograph on the 4.1 m SOAR telescope, covering a wavelength range of
4000-7800 A. The spectrum shows a red continuum with broad and strong
emission lines of H I, He I, and O I. The lines show a broad emission base
with a narrower emission core. Halpha has a FWZI larger than 10,000 km/s. 

The spectrum resembles that of a very fast classical nova after optical
peak. The low amplitude of the transient raises questions about its nature
and the possible progenitor match. TCP J15244460-6059200 could be an
unusually low-amplitude, ultra-fast nova or a more exotic phenomenon.

There is a slight chance that the actual progenitor system is much fainter
and coincides with the bright (~14 mag) match, which would explain the
unusually low-amplitude of the transient. Follow-up observations are
encouraged in all bands.   

They used SOAR images to measure the position of the nova with respect to
UCAC3 stars in the field:  

RA 15:24:47.63 DEC -60:59:47.3 +/-0.2" J2000 

Preliminary photometry using an ensemble of APASS stars results in the
following values:  

2459756.74489 g=11.8; 2459756.74480 r=10.8; 2459756.74549 i=10.4 

Guy M Hurst

