Comprehensive X-ray Observations of the Exceptional Ultra-long X-ray and Gamma-ray Transient GRB 250702B with Swift, NuSTAR, and Chandra: Insights from the X-ray Afterglow Properties
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2025
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| author | O'Connor, Brendan Gill, Ramandeep DeLaunay, James Hare, Jeremy Pasham, Dheeraj Coughlin, Eric R. Bandopadhyay, Ananya Anumarlapudi, Akash Beniamini, Paz Granot, Jonathan Andreoni, Igor Carney, Jonathan Moss, Michael J. Göğüş, Ersin Kennea, Jamie A. Busmann, Malte Dichiara, Simone Freeburn, James Gruen, Daniel Hall, Xander J. Palmese, Antonella Parsotan, Tyler Ronchini, Samuele Tohuvavohu, Aaron Williams, Maia A. |
| author_facet | O'Connor, Brendan Gill, Ramandeep DeLaunay, James Hare, Jeremy Pasham, Dheeraj Coughlin, Eric R. Bandopadhyay, Ananya Anumarlapudi, Akash Beniamini, Paz Granot, Jonathan Andreoni, Igor Carney, Jonathan Moss, Michael J. Göğüş, Ersin Kennea, Jamie A. Busmann, Malte Dichiara, Simone Freeburn, James Gruen, Daniel Hall, Xander J. Palmese, Antonella Parsotan, Tyler Ronchini, Samuele Tohuvavohu, Aaron Williams, Maia A. |
| contents | GRB 250702B is an exceptional transient that produced multiple episodes of luminous gamma-ray radiation lasting for $>25$ ks, placing it among the class of ultra-long gamma-ray bursts (GRBs). However, unlike any known GRB, the \textit{Einstein Probe} detected soft X-ray emission up to 24 hours before the gamma-ray triggers. We present comprehensive X-ray observations of the transient's afterglow obtained with the Neil Gehrels Swift Observatory, the Nuclear Spectroscopic Telescope Array, and the Chandra X-ray Observatory between 0.5 to 65 days (observer frame) after the initial high-energy trigger. The X-ray emission decays steeply as $\sim t^{-1.9}$, and shows short timescale X-ray variability ($ΔT/T < 0.03$) in both Swift and NuSTAR, consistent with flares superposed on an external shock continuum. Serendipitous detections by the Swift Burst Alert Telescope (BAT) out to $\sim$0.3 days and continued NuSTAR variability to $\sim$2 days imply sustained central engine activity; including the precursor, the required engine duration is $\gtrsim 3$ days. Afterglow modeling favors the combination of forward and reverse shock emission in a wind-like ($k \approx 2$) environment. These properties, especially the long-lived engine and early soft X-ray emission, are difficult to reconcile with a collapsar origin, and GRB 250702B does not fit neatly with canonical ultra-long GRBs or relativistic tidal disruption events (TDEs). A hybrid scenario in which a star is disrupted by a stellar-mass black hole (a micro-TDE) provides a plausible explanation, although a relativistic TDE from an intermediate-mass black hole remains viable. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_22787 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Comprehensive X-ray Observations of the Exceptional Ultra-long X-ray and Gamma-ray Transient GRB 250702B with Swift, NuSTAR, and Chandra: Insights from the X-ray Afterglow Properties O'Connor, Brendan Gill, Ramandeep DeLaunay, James Hare, Jeremy Pasham, Dheeraj Coughlin, Eric R. Bandopadhyay, Ananya Anumarlapudi, Akash Beniamini, Paz Granot, Jonathan Andreoni, Igor Carney, Jonathan Moss, Michael J. Göğüş, Ersin Kennea, Jamie A. Busmann, Malte Dichiara, Simone Freeburn, James Gruen, Daniel Hall, Xander J. Palmese, Antonella Parsotan, Tyler Ronchini, Samuele Tohuvavohu, Aaron Williams, Maia A. High Energy Astrophysical Phenomena GRB 250702B is an exceptional transient that produced multiple episodes of luminous gamma-ray radiation lasting for $>25$ ks, placing it among the class of ultra-long gamma-ray bursts (GRBs). However, unlike any known GRB, the \textit{Einstein Probe} detected soft X-ray emission up to 24 hours before the gamma-ray triggers. We present comprehensive X-ray observations of the transient's afterglow obtained with the Neil Gehrels Swift Observatory, the Nuclear Spectroscopic Telescope Array, and the Chandra X-ray Observatory between 0.5 to 65 days (observer frame) after the initial high-energy trigger. The X-ray emission decays steeply as $\sim t^{-1.9}$, and shows short timescale X-ray variability ($ΔT/T < 0.03$) in both Swift and NuSTAR, consistent with flares superposed on an external shock continuum. Serendipitous detections by the Swift Burst Alert Telescope (BAT) out to $\sim$0.3 days and continued NuSTAR variability to $\sim$2 days imply sustained central engine activity; including the precursor, the required engine duration is $\gtrsim 3$ days. Afterglow modeling favors the combination of forward and reverse shock emission in a wind-like ($k \approx 2$) environment. These properties, especially the long-lived engine and early soft X-ray emission, are difficult to reconcile with a collapsar origin, and GRB 250702B does not fit neatly with canonical ultra-long GRBs or relativistic tidal disruption events (TDEs). A hybrid scenario in which a star is disrupted by a stellar-mass black hole (a micro-TDE) provides a plausible explanation, although a relativistic TDE from an intermediate-mass black hole remains viable. |
| title | Comprehensive X-ray Observations of the Exceptional Ultra-long X-ray and Gamma-ray Transient GRB 250702B with Swift, NuSTAR, and Chandra: Insights from the X-ray Afterglow Properties |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2509.22787 |