Archival VLBA Observations of the Cygnus A Nuclear Radio Transient (Cyg A-2) Strengthen the Tidal Disruption Event Interpretation
We have analyzed archival Very Long Baseline Array (VLBA) data for Cygnus A between 2002 and 2013, to search for radio emission from the transient discovered in 2015 by Perley et al. approximately 0.″4 from the nucleus of Cygnus A (Cyg A-2). Perley et al. use Very Large Array and VLBA archival data...
| Main Authors: | , , |
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| Format: | Journal Article |
| Language: | English |
| Published: |
IOP PUBLISHING LTD
2020
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.3847/2041-8213/abb60d http://hdl.handle.net/20.500.11937/90031 |
| Summary: | We have analyzed archival Very Long Baseline Array (VLBA) data for Cygnus A between 2002 and 2013, to search for radio emission from the transient discovered in 2015 by Perley et al. approximately 0.″4 from the nucleus of Cygnus A (Cyg A-2). Perley et al. use Very Large Array and VLBA archival data (between 1989 and 1997) to show that the transient rises in flux density by a factor of at least 5 in less than approximately 20 yr. With the additional data presented here, we revise the rise time to between approximately 4 and 6 yr, based on a new detection of the source at 15.4 GHz from 2011 October. Our results strengthen the interpretation of Cyg A-2 as the result of a tidal disruption event (TDE), as we can identify the location of the compact object responsible for the TDE and can estimate the angular expansion speed of the resulting radio-emitting structures, equivalent to an apparent expansion speed of <0.9c. While our results are consistent with recent X-ray analyses, we can rule out a previously suggested date of early 2013 for the timing of the TDE. We favor a timing between early 2009 and late 2011. Applying the model of Nakar Piran, we suggest a TDE causing a mildly relativistic outflow with a (density-dependent) total energy >1049 erg. Due to the improved temporal coverage of our archival measurements, we find that it is unlikely that Cyg A-2 has previously been in a high luminosity radio state over the last 30 yr. |
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