Threshold for Extended Emission in Short Gamma-Ray Bursts

• Main Authors: Norris, Jay P, Gehrels, Neil, Scargle, Jeffrey D
• Format: Journal Article
• Language: English
• Published: 04-05-2010
• Subjects: Physics - High Energy Astrophysical Phenomena
• DOI: 10.48550/arxiv.0910.2456

Astrophys.J.717:411-419,2010 The initial pulse complex (IPC) in short gamma-ray bursts is sometimes
accompanied by a softer, low-intensity extended emission (EE) component. In
cases where such a component is not observed, it is not clear if it is present
but below the detection threshold. Using Bayesian Block (BB) methods, we
measure the EE component and show that it is present in one quarter of a
Swift/BAT sample of 51 short bursts, as was found for the Compton/BATSE sample.
We simulate bursts with EE to calibrate the BAT threshold for EE detection and
show that this component would have been detected in nearly half of BAT short
bursts if it were present, to intensities ~ 10^-2 counts cm^-2 s^-1, a factor
of five lower than actually observed in short bursts. In the BAT sample the
ratio of average EE intensity to IPC peak intensity, Rint, ranges over a factor
of 25, Rint ~ 3 x 10^-3 to 8 x 10^-2. In comparison, for the average of the 39
bursts without an EE component, the 2-sigma upper limit is Rint < 8 x 10^-4.
These results suggest that a physical threshold effect operates near Rint ~ few
x 10^-3, below which the EE component is not manifest.