Kavli Affiliate: Michael Fausnaugh
| First 5 Authors: Daniel A. Perley, Anna Y. Q. Ho, Michael Fausnaugh, Gavin P. Lamb, Mansi M. Kasliwal
| Summary:
Classical gamma-ray bursts (GRBs) have two distinct emission episodes: prompt
emission from ultrarelativistic ejecta and afterglow from shocked circumstellar
material. While both components are extremely luminous in known GRBs, a variety
of scenarios predict the existence of luminous afterglow emission with little
or no associated high-energy prompt emission. We present AT2019pim, the first
spectroscopically confirmed afterglow with no observed high-energy emission to
be identified. Serendipitously discovered during follow-up observations of a
gravitational-wave trigger and located in a contemporaneous TESS sector, it is
hallmarked by a fast-rising (t ~ 2 hr), luminous (M_UV,peak ~ -24.4 mag)
optical transient with accompanying luminous X-ray and radio emission. No
gamma-ray emission consistent with the time and location of the transient was
detected by Fermi-GBM or by Konus, placing constraining limits on an
accompanying GRB. We investigate several independent observational aspects of
the afterglow in the context of constraints on relativistic motion and find all
of them are consistent with an initial Lorentz factor of Gamma_0 ~ 10-30 for
the on-axis material, significantly lower than in any well-observed GRB and
consistent with the theoretically predicted "dirty fireball" scenario in which
the high-energy prompt emission is stifled by pair production. However, we
cannot rule out a structured jet model in which only the line-of-sight material
was ejected at low-Gamma, off-axis from a classical high-Gamma jet core, and an
on-axis GRB with below-average gamma-ray efficiency also remains a possibility.
This event represents a milestone in orphan afterglow searches, demonstrating
that luminous optical afterglows lacking detected GRB counterparts can be
identified and spectroscopically confirmed in real time.
| Search Query: ArXiv Query: search_query=au:”Michael Fausnaugh”&id_list=&start=0&max_results=3