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Investigating peculiar prompt emission properties of the multi-Peaked GRB 250129A

Ankur Ghosh, Tamador K. M. Aldowma, Soebur Razzaque

Abstract

We present a high-energy spectral analysis of GRB 250129A, which was triggered by the Swift-BAT. The burst exhibits a complex, multi-peaked temporal structure characterized by two distinct emission episodes, with the main peak occurring approximately 180 seconds after the BAT trigger. The time-integrated spectral analysis in the 15 - 150 keV energy range indicates that a broken power-law (BPL) model provides the best fit, signifying a non thermal origin of the prompt emission. A time resolved spectral analysis, performed using the Bayesian block technique, shows that the intervals around the main emission peak are well described by the BPL model, while the fits for low count intervals remain less constrained. An evident intensity tracking behavior is observed between the flux and the spectral peak energy (Ep). Furthermore, both the Amati relation and hardness - intensity correlation suggest that GRB~250129A occupies an intermediate regime, acting as a bridge between long and ultra long GRBs.

Investigating peculiar prompt emission properties of the multi-Peaked GRB 250129A

Abstract

We present a high-energy spectral analysis of GRB 250129A, which was triggered by the Swift-BAT. The burst exhibits a complex, multi-peaked temporal structure characterized by two distinct emission episodes, with the main peak occurring approximately 180 seconds after the BAT trigger. The time-integrated spectral analysis in the 15 - 150 keV energy range indicates that a broken power-law (BPL) model provides the best fit, signifying a non thermal origin of the prompt emission. A time resolved spectral analysis, performed using the Bayesian block technique, shows that the intervals around the main emission peak are well described by the BPL model, while the fits for low count intervals remain less constrained. An evident intensity tracking behavior is observed between the flux and the spectral peak energy (Ep). Furthermore, both the Amati relation and hardness - intensity correlation suggest that GRB~250129A occupies an intermediate regime, acting as a bridge between long and ultra long GRBs.
Paper Structure (7 sections, 3 figures, 2 tables)

This paper contains 7 sections, 3 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Swift-BAT data reduction and analysis
  3. Time resolved spectral analysis
  4. GRB correlations
  5. Amati correlation
  6. Ep--T90 Correlation
  7. Summary and conclusion

Figures (3)

  • Figure 1: Evolution of spectral parameters obtained for GRB 250129A from the time-resolved spectral analysis: (first row) The background subtracted mask weighted light curve with time binning of 4 s where the blue dash dotted line represents the background level, (second row) The evolution of the peak energy (the crimson circles), (third row) The evolution of the low-energy spectral index (the indigo circles) using the Swift-BAT data. Grey solid and dashed line indicate lines of death for synchrotron fast cooling ($\alpha$ = $-3/2$) and slow cooling ($\alpha$ = $-2/3$), respectively, and (fourth row) the evolution of high-energy spectral index.
  • Figure 2: Time-integrated Swift/BAT spectrum (15-150 keV) of GRB 250129A was best fitted with a broken power-law model. The bottom panel presents the residuals between the data and the model. (b) Posterior distributions of the broken power-law model parameters obtained from the fitting and optimisation using dynasty-nested.
  • Figure 3: The $E_{\rm p,i}$--$E_{\rm iso}$ and $E_{\rm p}$--$T_{90}$ correlation for the sample of long (golden circles) and short (purple circles) GRBs. In the $E_{\rm p,i}$--$E_{\rm iso}$ plot, the dashed line in the same color corresponds to the 3-$\sigma$ scatter of the correlation. The light-green diamond symbol represents the position of GRB 250129A in these plots. Black dashed line in Fig. 3(b) indicates the boundary between short and long GRBs at $T_{\rm 90}$ = 2 s.