The Astrophysical Journal Letters (Jan 2025)
Characterization of a Peculiar Einstein Probe Transient EP240408a: An Exotic Gamma-Ray Burst or an Abnormal Jetted Tidal Disruption Event?
- Brendan O’Connor,
- Dheeraj Pasham,
- Igor Andreoni,
- Jeremy Hare,
- Paz Beniamini,
- Eleonora Troja,
- Roberto Ricci,
- Dougal Dobie,
- Joheen Chakraborty,
- Mason Ng,
- Noel Klingler,
- Viraj Karambelkar,
- Sam Rose,
- Steve Schulze,
- Geoffrey Ryan,
- Simone Dichiara,
- Itumeleng Monageng,
- David Buckley,
- Lei Hu,
- Gokul P. Srinivasaragavan,
- Gabriele Bruni,
- Tomás Cabrera,
- S. Bradley Cenko,
- Hendrik van Eerten,
- James Freeburn,
- Erica Hammerstein,
- Mansi Kasliwal,
- Chryssa Kouveliotou,
- Keerthi Kunnumkai,
- James K. Leung,
- Amy Lien,
- Antonella Palmese,
- Takanori Sakamoto
Affiliations
- Brendan O’Connor
- ORCiD
- McWilliams Center for Cosmology and Astrophysics, Department of Physics, Carnegie Mellon University , Pittsburgh, PA 15213, USA ; [email protected]
- Dheeraj Pasham
- ORCiD
- MIT Kavli Institute for Astrophysics and Space Research , Cambridge, MA 02139, USA
- Igor Andreoni
- ORCiD
- Joint Space-Science Institute, University of Maryland , College Park, MD 20742, USA; Department of Astronomy, University of Maryland , College Park, MD 20742, USA; Astrophysics Science Division, NASA Goddard Space Flight Center , Mail Code 661, Greenbelt, MD 20771, USA; University of North Carolina at Chapel Hill , 120 E. Cameron Ave., Chapel Hill, NC 27514, USA
- Jeremy Hare
- ORCiD
- Astrophysics Science Division, NASA Goddard Space Flight Center , 8800 Greenbelt Rd, Greenbelt, MD 20771, USA; Center for Research and Exploration in Space Science and Technology, NASA/GSFC , Greenbelt, MD 20771, USA; The Catholic University of America , 620 Michigan Ave., N.E. Washington, DC 20064, USA
- Paz Beniamini
- ORCiD
- Department of Natural Sciences, The Open University of Israel , P.O Box 808, Ra’anana 4353701, Israel; Astrophysics Research Center of the Open University (ARCO), The Open University of Israel , P.O Box 808, Ra’anana 4353701, Israel; Department of Physics, The George Washington University , Washington, DC 20052, USA
- Eleonora Troja
- ORCiD
- Department of Physics, University of Rome “Tor Vergata” , via della Ricerca Scientifica 1, I-00133 Rome, Italy
- Roberto Ricci
- ORCiD
- Department of Physics, University of Rome “Tor Vergata” , via della Ricerca Scientifica 1, I-00133 Rome, Italy; INAF-Istituto di Radioastronomia , Via Gobetti 101, I-40129 Bologna, Italy
- Dougal Dobie
- ORCiD
- Sydney Institute for Astronomy, School of Physics, The University of Sydney , New South Wales 2006, Australia; ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) , Hawthorn, Victoria, Australia
- Joheen Chakraborty
- ORCiD
- MIT Kavli Institute for Astrophysics and Space Research , Cambridge, MA 02139, USA
- Mason Ng
- ORCiD
- Department of Physics, McGill University , 3600 rue University, Montréal, QC H3A 2T8, Canada; Trottier Space Institute, McGill University , 3550 rue University, Montréal, QC H3A 2A7, Canada
- Noel Klingler
- ORCiD
- Astrophysics Science Division, NASA Goddard Space Flight Center , 8800 Greenbelt Rd, Greenbelt, MD 20771, USA; Center for Research and Exploration in Space Science and Technology, NASA/GSFC , Greenbelt, MD 20771, USA; Center for Space Sciences and Technology, University of Maryland , Baltimore County, Baltimore, MD 21250, USA
- Viraj Karambelkar
- ORCiD
- Division of Physics, Mathematics and Astronomy, California Institute of Technology , Pasadena, CA 91125, USA
- Sam Rose
- ORCiD
- Division of Physics, Mathematics and Astronomy, California Institute of Technology , Pasadena, CA 91125, USA
- Steve Schulze
- ORCiD
- Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) , Northwestern University, 1800 Sherman Ave, Evanston, IL 60201, USA
- Geoffrey Ryan
- ORCiD
- Perimeter Institute for Theoretical Physics , Waterloo, Ontario N2L 2Y5, Canada
- Simone Dichiara
- ORCiD
- Department of Astronomy and Astrophysics, The Pennsylvania State University , 525 Davey Lab, University Park, PA 16802, USA
- Itumeleng Monageng
- ORCiD
- South African Astronomical Observatory , P.O. Box 9, Observatory 7935, Cape Town, South Africa; Department of Astronomy, University of Cape Town , Private Bag X3, Rondebosch 7701, South Africa
- David Buckley
- ORCiD
- South African Astronomical Observatory , P.O. Box 9, Observatory 7935, Cape Town, South Africa; Department of Astronomy, University of Cape Town , Private Bag X3, Rondebosch 7701, South Africa; Southern African Large Telescope , P.O. Box 9, Observatory 7935, Cape Town, South Africa; Department of Physics, University of the Free State , P.O. Box 339, Bloemfonein 9300, South Africa
- Lei Hu
- ORCiD
- McWilliams Center for Cosmology and Astrophysics, Department of Physics, Carnegie Mellon University , Pittsburgh, PA 15213, USA ; [email protected]
- Gokul P. Srinivasaragavan
- ORCiD
- Joint Space-Science Institute, University of Maryland , College Park, MD 20742, USA; Department of Astronomy, University of Maryland , College Park, MD 20742, USA; Astrophysics Science Division, NASA Goddard Space Flight Center , 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
- Gabriele Bruni
- ORCiD
- INAF – Istituto di Astrofisica e Planetologia Spaziali , via del Fosso del Cavaliere 100, Roma, 00133, Italy
- Tomás Cabrera
- ORCiD
- McWilliams Center for Cosmology and Astrophysics, Department of Physics, Carnegie Mellon University , Pittsburgh, PA 15213, USA ; [email protected]
- S. Bradley Cenko
- ORCiD
- Joint Space-Science Institute, University of Maryland , College Park, MD 20742, USA; Astrophysics Science Division, NASA Goddard Space Flight Center , 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
- Hendrik van Eerten
- ORCiD
- Department of Physics, University of Bath , Claverton Down, Bath, BA2 7AY, UK
- James Freeburn
- ORCiD
- Centre for Astrophysics and Supercomputing, Swinburne University of Technology , John St, Hawthorn, VIC 3122, Australia; ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) , John St, Hawthorn, VIC 3122, Australia
- Erica Hammerstein
- ORCiD
- Department of Astronomy, University of California , Berkeley, CA 94720-3411, USA
- Mansi Kasliwal
- ORCiD
- Division of Physics, Mathematics and Astronomy, California Institute of Technology , Pasadena, CA 91125, USA
- Chryssa Kouveliotou
- ORCiD
- Department of Physics, The George Washington University , Washington, DC 20052, USA
- Keerthi Kunnumkai
- ORCiD
- McWilliams Center for Cosmology and Astrophysics, Department of Physics, Carnegie Mellon University , Pittsburgh, PA 15213, USA ; [email protected]
- James K. Leung
- ORCiD
- David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4, Canada; Dunlap Institute for Astronomy and Astrophysics, University of Toronto , 50 St. George Street, Toronto, ON M5S 3H4, Canada; Racah Institute of Physics, The Hebrew University of Jerusalem , Jerusalem 91904, Israel
- Amy Lien
- ORCiD
- University of Tampa , Department of Physics and Astronomy, 401 W. Kennedy Blvd, Tampa, FL 33606, USA
- Antonella Palmese
- ORCiD
- McWilliams Center for Cosmology and Astrophysics, Department of Physics, Carnegie Mellon University , Pittsburgh, PA 15213, USA ; [email protected]
- Takanori Sakamoto
- ORCiD
- Department of Physics and Mathematics, Aoyama Gakuin University , 5-10-1 Fuchinobe, Chuo-ku, Sagamihara-shi Kanagawa 252-5258, Japan
- DOI
- https://doi.org/10.3847/2041-8213/ada7f5
- Journal volume & issue
-
Vol. 979,
no. 2
p. L30
Abstract
We present the results of our multiwavelength (X-ray to radio) follow-up campaign of the Einstein Probe transient EP240408a. The initial 10 s trigger displayed bright soft X-ray (0.5–4 keV) radiation with peak luminosity L _X ≳ 10 ^49 (10 ^50 ) erg s ^−1 for an assumed redshift z ≳ 0.5 (2.0). The Neil Gehrels Swift Observatory and Neutron star Interior Composition ExploreR discovered a fading X-ray counterpart lasting for ∼5 days (observer frame), which showed a long-lived (∼4 days) plateau-like emission ( t ^−0.5 ) before a sharp power-law decline ( t ^−7 ). The plateau emission was in excess of L _X ≳ 10 ^46 (10 ^47 ) erg s ^−1 at z ≳ 0.5 (2.0). Deep optical and radio observations resulted in nondetections of the transient. Our observations with Gemini South revealed a faint potential host galaxy ( r ≈ 24 AB mag) near the edge of the X-ray localization. The faint candidate host, and lack of other potential hosts ( r ≳ 26 AB mag; J ≳ 23 AB mag), imply a higher redshift origin ( z ≳ 0.5), which produces extreme X-ray properties that are inconsistent with many known extragalactic transient classes. In particular, the lack of a bright gamma-ray counterpart, with the isotropic-equivalent energy (10–10,000 keV) constrained by GECam and Konus-Wind to E _γ _,iso ≲ 4 × 10 ^50 (6 × 10 ^51 ) erg at z ≈ 0.5 (2.0), conflicts with known gamma-ray bursts of similar X-ray luminosities. We therefore favor a jetted tidal disruption event as the progenitor of EP240408a at z ≳ 1.0, possibly caused by the disruption of a white dwarf by an intermediate-mass black hole. The alternative is that EP240408a may represent a new, previously unknown class of transient.
Keywords
