GRB 090618: Detection of thermal X-ray emission from a bright gamma-ray burst

GRB 090618 was an extremely bright burst, detected across the electromagnetic spectrum. It has a redshift of 0.54 and a supernova (SN) was identified in ground-based photometry. We present a thorough analysis of the prompt and early afterglow emission using data from Swift, Fermi Gamma-ray Burst Monitor and ROTSE, in which we track the evolution of the synchrotron spectral peak during the prompt emission and through the steep decay phase. We find evidence of a thermal X-ray component alongside the expected non-thermal power-law continuum. Such a component is rare among gamma-ray bursts (GRBs), with firm data for only GRBs 060218 and 100316D so far, and could potentially originate from an SN shock breakout, although there remains doubt regarding this explanation for any of the bursts. However, in contrast to these other Swift GRB–SNe with similar thermal signatures, GRB 090618 is a much more ‘typical’ burst: GRB–SNe 060218 and 100316D were both low-luminosity events, with long durations and low peak energies, while GRB 090618 was more representative of the wider population of long GRBs in all of these areas. It has been argued, based both on theory and observations, that most long GRBs should be accompanied by SNe. If this thermal X-ray component is related to the SN, its detection in GRB 090618, a fairly typical burst in many ways, may prove an important development in the study of the GRB–SN connection

The Swift Burst Analyser I. BAT and XRT spectral and flux evolution of gamma ray bursts

Context: Gamma ray burst models predict the broadband spectral evolution and the temporal evolution of the energy flux. In contrast, standard data analysis tools and data repositories provide count-rate data, or use single flux conversion factors for all of the data, neglecting spectral evolution. Aims: We produce Swift BAT and XRT light curves in flux units, where the spectral evolution is accounted for. Methods: We have developed software to use the hardness ratio information to track spectral evolution of GRBs, and thus to convert the count-rate light curves from the BAT and XRT instruments on Swift into accurate, evolution-aware flux light curves. Results: The Swift Burst Analyser website (http://www.swift.ac.uk/burst_analyser) contains BAT, XRT and combined BAT-XRT flux light curves in three energy regimes for all GRBs observed by the Swift satellite. These light curves are automatically built and updated when data become available, are presented in graphical and plain-text format, and are available for download and use in research

The late peaking afterglow of GRB 100418A

GRB 100418A is a long gamma-ray burst (GRB) at redshift z = 0.6235 discovered with the Swift Gamma-ray Burst Explorer with unusual optical and X-ray light curves. After an initial short-lived, rapid decline in X-rays, the optical and X-ray light curves observed with Swift are approximately flat or rising slightly out to at least ~7 × 10[superscript: 3] s after the trigger, peak at ~5 × 10[superscript: 4] s, and then follow an approximately power-law decay. Such a long optical plateau and late peaking is rarely seen in GRB afterglows. Observations with Rapid Eye Mount during a gap in the Swift coverage indicate a bright optical flare at ~2.5 × 10[superscript: 4] s. The long plateau phase of the afterglow is interpreted using either a model with continuous injection of energy into the forward shock of the burst or a model in which the jet of the burst is viewed off-axis. In both models the isotropic kinetic energy in the late afterglow after the plateau phase is ≥10[superscript: 2] times the 10[superscript: 51] erg of the prompt isotropic gamma-ray energy release. The energy injection model is favored because the off-axis jet model would require the intrinsic T [subscript: 90] for the GRB jet viewed on-axis to be very short, ~10 ms, and the intrinsic isotropic gamma-ray energy release and the true jet energy to be much higher than the typical values of known short GRBs. The non-detection of a jet break up to t ~ 2 × 10[superscript: 6] s indicates a jet half-opening angle of at least ~14°, and a relatively high-collimation-corrected jet energy of E [subscript: jet] ≥ 10[superscript: 52] erg

Multiwavelength observations of the energetic GRB 080810 : detailed mapping of the broad-band spectral evolution

GRB 080810 was one of the first bursts to trigger both Swift and the Fermi Gamma-ray Space Telescope. It was subsequently monitored over the X-ray and UV/optical bands by Swift, in the optical by Robotic Optical Transient Search Experiment (ROTSE) and a host of other telescopes, and was detected in the radio by the Very Large Array. The redshift of z = 3.355 ± 0.005 was determined by Keck/High Resolution Echelle Spectrometer (HIRES) and confirmed by RTT150 and NOT. The prompt gamma/X-ray emission, detected over 0.3–10³ keV, systematically softens over time, with E[subscript peak] moving from ∼600 keV at the start to ∼40 keV around 100 s after the trigger; alternatively, this spectral evolution could be identified with the blackbody temperature of a quasi-thermal model shifting from ∼60 to ∼3 keV over the same time interval. The first optical detection was made at 38 s, but the smooth, featureless profile of the full optical coverage implies that this is originated from the afterglow component, not from the pulsed/flaring prompt emission

Gaia Data Release 1

Context: This paper presents an overview of the photometric data that are part of the first Gaia data release. Aims: The principles of the processing and the main characteristics of the Gaia photometric data are presented. Methods: The calibration strategy is outlined briefly and the main properties of the resulting photometry are presented. Results: Relations with other broadband photometric systems are provided. The overall precision for the Gaia photometry is shown to be at the milli-magnitude level and has a clear potential to improve further in future releases