J/A+A/670/A130 Multi-epoch variability of AT 2000ch (Mueller+, 2023)
Multi-epoch variability of AT 2000ch (SN 2000ch) in NGC 3432.
A radio continuum and optical study.
Mueller A., Frohn V., Dirks L., Stein M., Adebahr B., Bomans D., Weis K.,
Dettmar R.J.
<Astron. Astrophys. 670, A130 (2023)>
=2023A&A...670A.130M 2023A&A...670A.130M (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, variable ; Photometry, SDSS
Keywords: stars: individual: SN 2000ch - stars: mass-loss -
radiation mechanisms: thermal - radio continuum: stars
Abstract:
AT 2000ch is a highly variable massive star and supernova imposter in
NGC 3432 first detected in 2000, similar and often compared to SN
2009ip. Because of this, AT 2000ch is suspected to undergo a
core-collapse supernova - a supernova impostor of similar brightness -
in the near future.
We characterize the long-term variability of AT 2000ch in the radio
and optical regimes with archival data reaching back to the year 1984.
These newly reduced observations, as well as those of previously
published literature, are used to restrict the mass loss rates of AT
2000ch at multiple epochs based on different approaches, and to infer
general properties of its circumstellar nebula with respect to the
detected radio brightness.
We extend the known optical lightcurve of AT 2000ch up to the
beginning of 2022 by performing Point Spread Function photometry on
archival data from the Palomar Transient Factory and Zwicky Transient
Facility. Archival radio continuum observations with the Very Large
Array were reduced using standard calibration and imaging methods and
is complemented by pre-reduced Continuum Halos in Nearby Galaxies - an
Expanded Very Large Array Survey observations as well as the
Westerbork Synthesis Radio Telescope and Low Frequency Array
observations. For the analysis of AT 2000ch we consider the optical
lightcurve and color evolution, its radio continuum brightness at
different frequencies and times, and the corresponding spectral
indices. Mass loss rates and optical depths are estimated based on
radio continuum brightnesses and Hα fluxes.
We report two newly detected outbursts of AT 2000ch similar to those
found in the 2000s and 13 re-brightening events of which at least four
are not conclusively detected because of insufficient sampling of the
lightcurve. The dates of all outbursts and significant, well-sampled
re-brightening events are consistent with a period of ∼201±12 days
over a total timespan of two decades. Such a behavior has never been
found for any supernova imposter, especially not for candidate SN
2009ip-analogues before. During 2010 to 2012 and 2014 to 2018 we only
have a few detections insufficient to make conclusive remarks about a
possible less eruptive phase of the transient. We find steady dimming
after the most recent re-brightening events and hint at porosity in
the circumstellar envelope suggesting AT 2000ch may currently be in
transition to a state of relative calm. We identified a second,
unrelated source at a projected distance of ∼23pc (∼0.5") that has
contaminated the optical measurements of AT 2000ch on its minimum
luminosity over the last two decades probably on a 5-10% level but
don't affect the overall findings and is negligible during
re-brightening. We are able to restrict the mass loss rate of AT
2000ch to range between several 10-6M☉/yr to several
10-5M☉/yr. The fresh ejecta appear to be optically thick to
radio continuum emission at least within the first ∼25 days after
significant re-brightening.
We suggest that other supernova imposter and probably also candidate
SN 2009ip-analogues at comparable distances emit radio continuum
fluxes on the order of a few to several tens of µJy at 6GHz. Deep
and frequent continuum surveys in the radio range are needed to study
these kind of objects in a broader context.
Description:
We investigate a continuation of the optical light curve of AT 2000ch
presented in Pastorello et al. (2010MNRAS.408..181P 2010MNRAS.408..181P, Cat.
J/MNRAS/408/181). The resulting optical light curve of AT 2000ch shown
in table A1 is made up of published observations from Wagner et al.
(2004PASP..116..326W 2004PASP..116..326W) and Pastorello et al. (2010MNRAS.408..181P 2010MNRAS.408..181P, Cat.
J/MNRAS/408/181) as well as re-measured archival data points from the
Palomar Transient Factory (PTF) and Zwicky Transient Facility (ZTF).
The archival data in the different filters of both surveys were
already reduced and we only re-investigated the photometry to ensure
the best possible detection rate for AT 2000ch (see below). We
complemented these observations with reported detections of amateur
astronomers.
Objects:
------------------------------------------------
RA (2000) DE Designation(s)
------------------------------------------------
10 52 41.40 +36 40 09.5 AT 2000ch = SN 2000ch
------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 70 575 Compiled data points for AT 2000ch
--------------------------------------------------------------------------------
See also:
J/MNRAS/408/181 : CN2002ch UBVRI and ugriz light curves (Pastorello+, 2010)
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 F13.7 d MJD Modified Julian Day
17- 26 A10 "date" Obs.date Observation date
28- 39 A12 "h:m:s" Obs.time Observation time
43- 45 A3 --- Observ Observatory (Ama, PTF or ZTF)
49- 53 F5.2 mag mag Observed magnitude in Band
57- 60 F4.2 mag e_mag ? Uncertainty of magnitude
64- 67 A4 --- Band Band of magnitude (1)
69- 70 I2 --- Amateur ? Name of observing amateur (2)
--------------------------------------------------------------------------------
Note (1): 4 different kinds of bands were observed, as follows:
r = r-band magnitude
g = g-band magnitude
i = i-band magnitude
UCNC = unfiltered/clear filter/not corrected magnitudes
Note (2): We took observational data from 15 amateur observers, as follows:
1 = Rick Johnson
2 = V. Nevski E. Romas and I. Molotov
3 = Giancarlo Cortini
4 = L. Elenin and I. Molotov
5 = Joseph Brimacombe
6 = Federica Luppi and Luca Buzz
7 = S. Foglia and G. Galli
8 = Thomas Langhans
9 = Koichi Itagaki
10 = Masakatsu Aoki
11 = Lars Hermansson
12 = Paolo Campaner
13 = Andrea Mantero
14 = Jordi Camarasa
15 = G. Wells and D. Bamberger
--------------------------------------------------------------------------------
Acknowledgements:
Ancla Mueller, amueller(at)astro.rub.de
(End) Ancla Mueller [RUB, Germany], Patricia Vannier CDS 09-Nov-2022