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| Format: | Preprint |
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2024
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2410.21622 |
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| _version_ | 1866912183925866496 |
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| author | O'Connor, B. Pasham, D. Andreoni, I. Hare, J. Beniamini, P. Troja, E. Ricci, R. Dobie, D. Chakraborty, J. Ng, M. Klingler, N. Karambelkar, V. Rose, S. Schulze, S. Ryan, G. Dichiara, S. Monageng, I. Buckley, D. Hu, L. Srinivasaragavan, G. Bruni, G. Cabrera, T. Cenko, S. B. van Eerten, H. Freeburn, J. Hammerstein, E. Kasliwal, M. Kouveliotou, C. Kunnumkai, K. Leung, J. K. Lien, A. Palmese, A. Sakamoto, T. |
| author_facet | O'Connor, B. Pasham, D. Andreoni, I. Hare, J. Beniamini, P. Troja, E. Ricci, R. Dobie, D. Chakraborty, J. Ng, M. Klingler, N. Karambelkar, V. Rose, S. Schulze, S. Ryan, G. Dichiara, S. Monageng, I. Buckley, D. Hu, L. Srinivasaragavan, G. Bruni, G. Cabrera, T. Cenko, S. B. van Eerten, H. Freeburn, J. Hammerstein, E. Kasliwal, M. Kouveliotou, C. Kunnumkai, K. Leung, J. K. Lien, A. Palmese, A. Sakamoto, T. |
| contents | We present the results of our multi-wavelength (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 $L_\textrm{X} \gtrsim 10^{49}$ ($10^{50}$) 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 $\sim$5 d (observer frame), which showed a long-lived (~4 d) plateau-like emission ($t^{-0.5}$) before a sharp powerlaw decline ($t^{-7}$). The plateau emission was in excess of $L_\textrm{X} \gtrsim 10^{46}$ ($10^{47}$) erg s$^{-1}$ at z>0.5 (2.0). Deep optical and radio observations resulted in non-detections of the transient. Our observations with Gemini South revealed a faint potential host galaxy ($r \approx 24$ AB mag) near the edge of the X-ray localization. The faint candidate host, and lack of other potential hosts ($r \gtrsim 26$ AB mag; $J \gtrsim 23$ AB mag), implies 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 $E_{γ,\textrm{iso}} \lesssim 4\times10^{51}$ ($6\times10^{52}$) erg at z>0.5 (2.0), conflicts with known gamma-ray bursts (GRBs) of similar X-ray luminosities. We therefore favor a jetted tidal disruption event (TDE) 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2410_21622 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Characterization of a peculiar Einstein Probe transient EP240408a: an exotic gamma-ray burst or an abnormal jetted tidal disruption event? O'Connor, B. Pasham, D. Andreoni, I. Hare, J. Beniamini, P. Troja, E. Ricci, R. Dobie, D. Chakraborty, J. Ng, M. Klingler, N. Karambelkar, V. Rose, S. Schulze, S. Ryan, G. Dichiara, S. Monageng, I. Buckley, D. Hu, L. Srinivasaragavan, G. Bruni, G. Cabrera, T. Cenko, S. B. van Eerten, H. Freeburn, J. Hammerstein, E. Kasliwal, M. Kouveliotou, C. Kunnumkai, K. Leung, J. K. Lien, A. Palmese, A. Sakamoto, T. High Energy Astrophysical Phenomena We present the results of our multi-wavelength (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 $L_\textrm{X} \gtrsim 10^{49}$ ($10^{50}$) 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 $\sim$5 d (observer frame), which showed a long-lived (~4 d) plateau-like emission ($t^{-0.5}$) before a sharp powerlaw decline ($t^{-7}$). The plateau emission was in excess of $L_\textrm{X} \gtrsim 10^{46}$ ($10^{47}$) erg s$^{-1}$ at z>0.5 (2.0). Deep optical and radio observations resulted in non-detections of the transient. Our observations with Gemini South revealed a faint potential host galaxy ($r \approx 24$ AB mag) near the edge of the X-ray localization. The faint candidate host, and lack of other potential hosts ($r \gtrsim 26$ AB mag; $J \gtrsim 23$ AB mag), implies 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 $E_{γ,\textrm{iso}} \lesssim 4\times10^{51}$ ($6\times10^{52}$) erg at z>0.5 (2.0), conflicts with known gamma-ray bursts (GRBs) of similar X-ray luminosities. We therefore favor a jetted tidal disruption event (TDE) 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. |
| title | Characterization of a peculiar Einstein Probe transient EP240408a: an exotic gamma-ray burst or an abnormal jetted tidal disruption event? |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2410.21622 |