EP250207b is not a collapsar fast X-ray transient. Is it due to a binary compact object merger?

P. G. Jonker; A. J. Levan; Xing Liu; Dong Xu; Yuan Liu; Xinpeng Xu; An Li; N. Sarin; N. R. Tanvir; G. P. Lamb; M. E. Ravasio; J. Sanchez-Sierras; J. A. Quirola-Vasquez; B. C. Rayson; J. N. D. Van dalen; D. B. Malesani; A. P. C. Van hoof; F. E. Bauer; J. Chacon; S. J. Smartt; A. Martin-Carrillo; G. Corcoran; L. Cotter; A. Rossi; F. Onori; M. Fraser; P. T. O'brien; R. A. J. Eyles-Ferris; J. Hjorth; T-w Chen; G. Leloudas; L. Tomasella; S. Schulze; M. De pasquale; F. Carotenuto; J. Bright; Chenwei Wang; Shaolin Xiong; Jinpeng Zhang; Wangchen Xue; Jiacong Liu; Chengkui Li; D. Mata Sanchez; M. A. P. Torres

doi:10.1093/mnras/staf2021

EP250207b is not a collapsar fast X-ray transient. Is it due to a binary compact object merger?

P. G. Jonker, A. J. Levan, Xing Liu, Dong Xu, Yuan Liu, Xinpeng Xu, An Li, N. Sarin, N. R. Tanvir, G. P. Lamb, M. E. Ravasio, J. Sanchez-Sierras, J. A. Quirola-Vasquez, B. C. Rayson, J. N. D. Van dalen, D. B. Malesani, A. P. C. Van hoof, F. E. Bauer, J. Chacon, S. J. SmarttA. Martin-Carrillo, G. Corcoran, L. Cotter, A. Rossi, F. Onori, M. Fraser, P. T. O'brien, R. A. J. Eyles-Ferris, J. Hjorth, T-w Chen, G. Leloudas, L. Tomasella, S. Schulze, M. De pasquale, F. Carotenuto, J. Bright, Chenwei Wang, Shaolin Xiong, Jinpeng Zhang, Wangchen Xue, Jiacong Liu, Chengkui Li, D. Mata Sanchez, M. A. P. Torres

Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › peer review

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Abstract

Fast X-ray transients (FXTs) are short-lived extragalactic X-ray sources. Recent progress through multiwavelength follow-up of Einstein Probe-discovered FXTs has shown that several are related to collapsars, which can also produce gamma-ray bursts (GRBs). In this paper, we investigate the nature of the FXT EP250207b. The Very Large Telescope/Multi Unit Spectroscopic Explorer spectra of a nearby (15.9 kpc in projection) lenticular galaxy reveal no signs of recent star formation. If this galaxy is indeed the host, EP250207b lies at a redshift z = 0 . 082, implying a peak observed absolute magnitude for the optical counterpart of (-)(Mr)= -14.5. At the time when supernovae (SNe) would peak, it is substantially fainter than all SN types. These results are inconsistent with a collapsar origin for EP250207b. The properties favour a binary compact object merger-driven origin. The X-ray, optical, and radio observations are compared with predictions of several types of extragalactic transients, including afterglow and kilonova models. The data can be fitted with a slightly off-axis viewing angle afterglow. However, the late-time ('30 d) optical/nearinfrared counterpart is too bright for the afterglow and also for conventional kilonova models. This could be remedied if that late emission is due to a globular cluster or the core of a (tidally disrupted) dwarf galaxy. If confirmed, this would be the first case where the multiwavelength properties of an FXT are found to be consistent with a compact object merger origin, increasing the parallels between FXTs and GRBs. We finally discuss whether the source could originate in a higher redshift host galaxy.

Originalsprog	Engelsk
Artikelnummer	staf2021
Tidsskrift	Monthly Notices of the Royal Astronomical Society
Vol/bind	545
Udgave nummer	2
Antal sider	15
ISSN	0035-8711
DOI	https://doi.org/10.1093/mnras/staf2021
Status	Udgivet - 14 nov. 2025

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Jonker, P. G., Levan, A. J., Liu, X., Xu, D., Liu, Y., Xu, X., Li, A., Sarin, N., Tanvir, N. R., Lamb, G. P., Ravasio, M. E., Sanchez-Sierras, J., Quirola-Vasquez, J. A., Rayson, B. C., Van dalen, J. N. D., Malesani, D. B., Van hoof, A. P. C., Bauer, F. E., Chacon, J., ... Torres, M. A. P. (2025). EP250207b is not a collapsar fast X-ray transient. Is it due to a binary compact object merger? Monthly Notices of the Royal Astronomical Society, 545(2), Artikel staf2021. https://doi.org/10.1093/mnras/staf2021

Jonker, PG, Levan, AJ, Liu, X, Xu, D, Liu, Y, Xu, X, Li, A, Sarin, N, Tanvir, NR, Lamb, GP, Ravasio, ME, Sanchez-Sierras, J, Quirola-Vasquez, JA, Rayson, BC, Van dalen, JND, Malesani, DB, Van hoof, APC, Bauer, FE, Chacon, J, Smartt, SJ, Martin-Carrillo, A, Corcoran, G, Cotter, L, Rossi, A, Onori, F, Fraser, M, O'brien, PT, Eyles-Ferris, RAJ, Hjorth, J, Chen, T, Leloudas, G, Tomasella, L, Schulze, S, De pasquale, M, Carotenuto, F, Bright, J, Wang, C, Xiong, S, Zhang, J, Xue, W, Liu, J, Li, C, Sanchez, DM & Torres, MAP 2025, 'EP250207b is not a collapsar fast X-ray transient. Is it due to a binary compact object merger?', Monthly Notices of the Royal Astronomical Society, bind 545, nr. 2, staf2021. https://doi.org/10.1093/mnras/staf2021

@article{c850259d3b24499b8912d322b2eac4d2,

title = "EP250207b is not a collapsar fast X-ray transient. Is it due to a binary compact object merger?",

abstract = "Fast X-ray transients (FXTs) are short-lived extragalactic X-ray sources. Recent progress through multiwavelength follow-up of Einstein Probe-discovered FXTs has shown that several are related to collapsars, which can also produce gamma-ray bursts (GRBs). In this paper, we investigate the nature of the FXT EP250207b. The Very Large Telescope/Multi Unit Spectroscopic Explorer spectra of a nearby (15.9 kpc in projection) lenticular galaxy reveal no signs of recent star formation. If this galaxy is indeed the host, EP250207b lies at a redshift z = 0 . 082, implying a peak observed absolute magnitude for the optical counterpart of (-)(Mr)= -14.5. At the time when supernovae (SNe) would peak, it is substantially fainter than all SN types. These results are inconsistent with a collapsar origin for EP250207b. The properties favour a binary compact object merger-driven origin. The X-ray, optical, and radio observations are compared with predictions of several types of extragalactic transients, including afterglow and kilonova models. The data can be fitted with a slightly off-axis viewing angle afterglow. However, the late-time ('30 d) optical/nearinfrared counterpart is too bright for the afterglow and also for conventional kilonova models. This could be remedied if that late emission is due to a globular cluster or the core of a (tidally disrupted) dwarf galaxy. If confirmed, this would be the first case where the multiwavelength properties of an FXT are found to be consistent with a compact object merger origin, increasing the parallels between FXTs and GRBs. We finally discuss whether the source could originate in a higher redshift host galaxy.",

keywords = "Stars: black holes, stars: individual: EP250207b, Supernovae: general, Transients: supernovae",

author = "Jonker, {P. G.} and Levan, {A. J.} and Xing Liu and Dong Xu and Yuan Liu and Xinpeng Xu and An Li and N. Sarin and Tanvir, {N. R.} and Lamb, {G. P.} and Ravasio, {M. E.} and J. Sanchez-Sierras and Quirola-Vasquez, {J. A.} and Rayson, {B. C.} and {Van dalen}, {J. N. D.} and Malesani, {D. B.} and {Van hoof}, {A. P. C.} and Bauer, {F. E.} and J. Chacon and Smartt, {S. J.} and A. Martin-Carrillo and G. Corcoran and L. Cotter and A. Rossi and F. Onori and M. Fraser and O'brien, {P. T.} and Eyles-Ferris, {R. A. J.} and J. Hjorth and T-w Chen and G. Leloudas and L. Tomasella and S. Schulze and {De pasquale}, M. and F. Carotenuto and J. Bright and Chenwei Wang and Shaolin Xiong and Jinpeng Zhang and Wangchen Xue and Jiacong Liu and Chengkui Li and Sanchez, {D. Mata} and Torres, {M. A. P.}",

year = "2025",

month = nov,

day = "14",

doi = "10.1093/mnras/staf2021",

language = "English",

volume = "545",

journal = "Monthly Notices of the Royal Astronomical Society",

issn = "0035-8711",