Panchromatic study of GRB 060124: from precursor to afterglow

Abstract

We present observations of GRB 060124, the first event for which both the prompt and the afterglow emission could be observed simultaneously and in their entirety by the three Swift instruments. Indeed, Swift-BAT triggered on a precursor ∼570 s before the main burst peak, and this allowed Swift to repoint the narrow field instruments to the burst position ∼350 s before the main burst occurred. GRB 060124 also triggered Konus-Wind, which observed the prompt emission in a harder gamma-ray band (up to 2 MeV). Thanks to these exceptional circumstances, the temporal and spectral properties of the prompt emission can be studied in the optical, X-ray and gamma-ray ranges. While the X-ray emission (0.2-10 keV) clearly tracks the gamma-ray burst, the optical component follows a different pattern, likely indicating a different origin, possibly the onset of external shocks. The prompt GRB spectrum shows significant spectral evolution, with both the peak energy and the spectral index varying. As observed in several long GRBs, significant lags are measured between the hard-and low-energy components, showing that this behaviour extends over 3 decades in energy. The GRB peaks are also much broader at soft energies. This is related to the temporal evolution of the spectrum, and can be accounted for by assuming that the electron spectral index softened with time. The burst energy (E iso ∼ 5 × 10 53 erg) and average peak energy (E p ∼ 300 keV) make GRB 060124 consistent with the Amati relation. The X-ray afterglow is characterized by a decay which presents a break at t b ∼ 10 5 s.

Constraining the properties of neutron star crusts with the transient low-mass X-ray binary Aql X-1

“…For observations with count rates of >150 c s −1 (WT) and >0.6 c s −1 (PC), pile-up corrections were applied by exercising as many inner pixels as needed for the count rate to drop below these limiting values (Vaughan et al 2006;Romano et al 2006). For creating count rate light curves, corrections for losses due to pile-up and dead zones on the CCD (hot pixels and bad columns) were applied by simulating the complete (i.e., unaffected) and partial (i.e., affected) PSFs for each interval, the ratio of which gives the required correction factor (Evans et al 2007).…”

Disc reflection and a possible disc wind during a soft X-ray state in the neutron star low-mass X-ray binary 1RXS J180408.9–342058

“…In all observations considered here, the XRT count rate was >100 c s −1 and hence sufficiently high to cause pile-up. Following the recommended procedure, we therefore excised as many inner pixels as needed for the spectrum to remain unchanged after removing more pixels (e.g., Romano et al 2006). This resulted in the exclusion of the inner 2 ′′ for all five XRT observations.…”

Afterglow rebrightenings as a signature of a long-lasting central engine activity?

“…Swift started observing GRB 100814A in windowed timing mode and moved to photon counting (PC) mode 450 s after the trigger when the photon count rate was ∼4 cts/s. Before ∼6 ks the PC mode count rate exceeded 0.6 cts/s, therefore a standard pile-up correction procedure was applied (see Moretti et al 2005;Romano et al 2006;Vaughan et al 2006). The extraction used a circular region of a typical width of 25 pixels, as discussed in Evans et al (2009).…”

“…From the observational point of view, long periods of quiescence of the central engine, lasting up to thousands of seconds, have been observed in a fraction of GRBs showing the so called pre-or post-cursors in their prompt gamma-ray emission phase (Ramirez-Ruiz et al 2001;Romano et al 2006;Burlon et al 2008Burlon et al , 2009Gruber et al 2010). If these gamma-ray emission episodes are associated with the acceleration of different shells with respect to the main prompt event, these are supposed to interact with the latter ones, probably leading to an observable optical flux rebrightening if the difference in Γ is large enough.…”