GRB 071227: an additional case of a disguised short burst

(shortened) […] In the context of the fireshell model, […] a new family of disguised short bursts has been identified: long bursts with a protracted low instantaneous luminosity due to a low density CircumBurst Medium (CBM). In the 15-150 keV energy band GRB 071227 exhibits a short duration (about 1.8s) spike-like emission followed by a very soft extended tail up to one hundred seconds after the trigger. It is a faint (E_{iso}=5.8x10^{50}) nearby GRB (z=0.383) that does not have an associated type Ib/c bright supernova (SN). For these reasons, GRB 071227 has been classified as a short burst not fulfilling the Amati relation holding for long burst. We check the classification of GRB 071227 provided by the fireshell model. In particular, we test whether this burst is another example of a disguised short burst, after GRB 970228 and GRB 060614, and, for this reason, whether it fulfills the Amati relation. We simulate GRB 071227 light curves in the Swift BAT 15-50 keV bandpass and in the XRT (0.3-10 keV) energy band within the fireshell model. We perform simulations of the tail in the 15-50 keV bandpass, as well as of the first part of the X-ray afterglow. This infers that: E_{tot}^{e^\pm}=5.04x10^{51} erg, B=2.0x10^{-4}, E_{P-GRB}/E_{aft}~0.25, and <n_{cbm}>=3.33 particles/cm^3. These values are consistent with those of “long duration” GRBs. We interpret the observed energy of the first hard emission by identifying it with the P-GRB emission. The remaining long soft tail indeed fulfills the Amati relation. Previously classified as a short burst, GRB 071227 on the basis of our analysis performed in the context of the fireshell scenario represents another example of a disguised short burst, after GRB 970228 and GRB 060614. Further confirmation of this result is that the soft tail of GRB 071227 fulfills the Amati relation.

💡 Research Summary

This paper analyzes GRB 071227 and presents it as an additional case of a “disguised short burst,” which initially appears as a short gamma-ray burst but actually exhibits characteristics similar to long-duration bursts. The study is conducted within the context of the fireshell model, where a new family of disguised short bursts has been identified due to low-density CircumBurst Medium (CBM). GRB 071227 shows a short duration spike-like emission followed by an extended soft tail up to one hundred seconds after the trigger. It is classified as faint and nearby with no associated type Ib/c bright supernova, leading it initially to be categorized as a short burst not fulfilling the Amati relation for long bursts.

The authors simulate GRB 071227’s light curves in both Swift BAT (15-50 keV) and XRT (0.3-10 keV) energy bands within the fireshell model, testing whether this burst is another example of a disguised short burst like GRB 970228 and GRB 060614. The simulations infer values such as E_{tot}^{e^\pm}=5.04x10^{51} erg, B=2.0x10^{-4}, E_{P-GRB}/E_{aft}~0.25, and <n_{cbm}>=3.33 particles/cm^3, which are consistent with long-duration GRBs. The initial hard emission is identified as the prompt gamma-ray burst (P-GRB) emission, while the extended soft tail fulfills the Amati relation.

The analysis suggests that GRB 071227 should be reclassified as a disguised short burst based on its fulfillment of the Amati relation and characteristics similar to long-duration bursts. This classification is further supported by the fact that the soft tail of GRB 071227 fulfills the Amati relation, indicating it shares properties with other long-duration bursts despite its initial appearance as a short burst.