Apparent Outburst of Comet 12P/Pons-Brooks

ATel #16254; Michael S. P. Kelley (Univ. Maryland), Helen Usher (Open University, Cardiff University, Faulkes Telescope Project), Tim Lister (Las Cumbres Observatory), Richard Miles (British Astronomical Association), Pieter-Jan Dekelver (Belgium), Nicolas Biver (Obs. Paris, LESIA), Thomas Lehmann (Germany), Jean-Francois Soulier (France), Cai Stoddard-Jones (Cardiff University), on behalf of the Zwicky Transient Facility Collaboration, the Comet Chasers Project, and the LCO Outbursting Objects Key Project
on 26 Sep 2023; 21:14 UT
Credential Certification: Tim Lister (tlister@lco.global)

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We report an apparent outburst of comet 12P/Pons-Brooks, identified in Zwicky Transient Facility (ZTF; Bellm et al. 2019, PASP 131, a8002) images taken with the 1.2-m Oschin Schmidt telescope at Palomar Observatory. In ZTF data taken on 2023 Sep 22.15, 22.18, and 22.24 UTC, the comet's brightness was g = 16.52 ± 0.04, r = 16.08 ± 0.03, and 15.85 ± 0.04 mag, respectively (all photometry measured with a 5" radius aperture using the PS1 magnitude system). The comet was also observed with LCO's Faulkes Telescope North 2-m telescope at Haleakala Observatory (cf. ATel #16229) on 2023 Sep 22.34 UTC with r = 16.02 ± 0.02 mag. However, the comet had brightened in data taken Sep 25.14, 25.16, and 25.20 UTC, with i = 15.01 ± 0.03, r = 15.17 ± 0.02, and g = 15.66 ± 0.04 mag, respectively. The mean brightening over all filters was -0.87 ± 0.03 mag.

Independent measurements of the comet shared on the Groups.io Comets Mailing List provide further confirmation of the event and significant information on the timing onset, which appears to have occurred between Sep 23.83 and 23.93 UTC. Observer, site, effective bandpass, aperture radius, day, and photometric measurements (and uncertainty, if available) are as follows:

 
Dekelver, 0.3-m, Observatory Grömme (M09), PS1 r, 6.1" 
22.96  16.02  (0.01) 
23.93  14.99  (0.01) 
24.85  15.13  (0.01) 
 
Lehman, 0.28-m, Weimar (Germany, D15), G, 5.5" 
20.83  16.23 
24.82  15.38 
 
Durig, 0.4-m, Cewanee Observatory (V21), G, 5" 
23.20  16.2 
24.16  15.2 
 
Soulier, 0.3-m, Maisoncelles Observatory (C10), R, 6.5" 
23.83  15.8 
 
Nicolas, 0.41-m, Chante-Perdrix Observatory (A77), R, 5.6" 
24.83  15.0 
 
Biver, 0.41-m, Boulonville (France), V, 6.0" 
14.95  16.1 (0.1) 
24.03  15.2 (0.1) 

A manual inspection of the post-outburst ZTF data after removal of the ambient coma reveals a small arc or parabolic-shaped morphology, extending up to 12" from the nucleus in 1.7" seeing conditions. This distance corresponds to a plane-of-sky maximum expansion speed of 240 to 260 m/s. The total apparent magnitude of the ejecta was r = 15.63 ± 0.02 mag. Following the approach of Kelley et al. (2021, PSJ 2, 131), the total dust mass is of order magnitude 10**7 kg.

Based on observations obtained with the Samuel Oschin Telescope 48-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, Weizmann Institute for Science, Oskar Klein Center at Stockholm University, University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, TANGO Consortium of Taiwan, University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW.

The UK-based Comet Chasers project works with students and educators across the world, engaging and supporting them in making scientific observations (with the Las Cumbres Observatory global telescope network) of comets and other small bodies for researchers. The project is grateful for support from the Faulkes Telescope Project, the Open University, Cardiff University, the Royal Astronomical Society and the Science and Technology Facilities Council in the UK.

This work makes use of observations from the Las Cumbres Observatory global telescope network. This work is based on observations made with the MuSCAT3 instrument, developed by Astrobiology Center and under financial supports by JSPS KAKENHI (JP18H05439) and JST PRESTO (JPMJPR1775), at Faulkes Telescope North on Maui, HI, operated by the Las Cumbres Observatory.