Constraints on Relativistic Jets from the Fast X-Ray Transient 210423 Using Prompt Radio Follow-up Observations

Constraints on Relativistic Jets from the Fast X-Ray Transient 210423 Using Prompt Radio Follow-up Observations

Fast X-ray transients (FXTs) are a new observational class of phenomena with no clear physical origin. This is at least partially a consequence of limited multiwavelength follow-up of this class of transients in real time. Here we present deep optical ( g - and i -band) photometry with Keck, and pro...

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Bibliographic Details
Main Authors: Dina Ibrahimzade, R. Margutti, J. S. Bright, P. Blanchard, K. Paterson, D. Lin, H. Sears, A. Polzin, I. Andreoni, G. Schroeder, K. D. Alexander, E. Berger, D. L. Coppejans, A. Hajela, J. Irwin, T. Laskar, B. D. Metzger, J. C. Rastinejad, L. Rhodes
Format: Article
Language:English
Published: IOP Publishing 2025-01-01
Series:The Astrophysical Journal
Subjects:
X-ray transient sources
Online Access:https://doi.org/10.3847/1538-4357/ad9397
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Summary:Fast X-ray transients (FXTs) are a new observational class of phenomena with no clear physical origin. This is at least partially a consequence of limited multiwavelength follow-up of this class of transients in real time. Here we present deep optical ( g - and i -band) photometry with Keck, and prompt radio observations with the Very Large Array of FXT 210423 obtained at δ t ≈ 14–36 days since the X-ray trigger. We use these multiband observations, combined with publicly available data sets, to constrain the presence and physical properties of on-axis and off-axis relativistic jets such as those that can be launched by neutron star mergers and tidal disruption events, which are among the proposed theoretical scenarios of FXTs. Considering a wide range of possible redshifts z ≤ 3.5, circumstellar medium density n = 10 ^−6 –10 ^−1 cm ^−3 , and isotropic-equivalent jet kinetic energy E _k _,iso = 10 ^48 –10 ^55 erg, we find that we can rule out wide jets with opening angle θ _j = 15° viewed within 10° off-axis. For more collimated jets ( θ _j = 3°) we can only rule out on-axis ( θ _obs = 0°) orientations. This study highlights the constraining power of prompt multiwavelength observations of FXTs discovered in real time by current (e.g., Einstein Probe) and future facilities.
ISSN:1538-4357

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