Past Event

Colloquium by Columbia Postdocs

April 5, 2023
4:05 PM - 5:05 PM
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Pupin 1402

Colloquium by Jordy DavelaarTatsuya Matsumoto, and Hiromichi Tagawa, Columbia

Probing black hole shadows via electromagnetic self-lensing flares
Jordy Davelaar

Black hole binaries are thought to reside in the cores of numerous galaxies. As of today, around 250 candidates are identified based on putative Doppler-induced periodicity in their light curves. This periodicity can, however be confused with red noise produced by the accretion processes of single black holes. This ambiguity is lifted when the binary is seen close to edge on, in that case, the binary produces self-lensing flares (SLFs) when one of the black holes moves in front of the background black hole. This causes the emission to be gravitationally lensed. In my talk, I will show that these SLFs can contain additional information on the size and shape of the emission morphology of the lensed black hole, often referred to as the black hole shadow. If the viewing angle of the binary is close to edge on, a dipping feature is present in the SLF, which directly correlates with the black hole shadow size. I will argue that the upcoming time-domain surveys such as the Vera Rubin Observatories LSST might observe these dips and that they additionally could be observed in precursor emission from LISA sources.


Synchrotron modeling of AT 2022cmc: A jetted tidal disruption event?
Tatsuya Matsumoto

AT 2022cmc is a luminous optical transient accompanied by bright X-ray and radio emissions. I show the optical/radio signals are consistent with a synchrotron emission from a relativistic jet in a tidal disruption event of a star.


Observational signatures of compact objects in active galactic nuclei
Hiromichi Tagawa

Stellar-mass black holes (BHs) are predicted to be embedded in the disks of active galactic nuclei (AGN) due to gravitational drag and in-situ star formation. However, we have yet to obtain clear signatures that BHs are indeed embedded in AGN disks. As possible signatures, we have investigated the properties of gravitational wave, electromagnetic, and high-energy emission produced from the BHs. Promising findings are that breakout emission predicted to be associated with BH mergers in these environments can explain the possible associations between gravitational wave events and the optical transient ZTF19abanrhr and the proposed gamma-ray counterparts GW150914-GBM and LVT151012-GBM. Furthermore, high-energy emission, including background neutrino and gamma-ray intensities, ultrahigh energy cosmic rays, Fermi bubbles, can be explained by emission from the jets launched by the BHs. I will present these possibilities and how to test the models.

Followed by wine and cheese.

Host: Zoltan Haiman