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We report on the temporal and spectral characteristics of the early X-ray emission from the bright flaring Gamma-Ray Burst GRB051117A as observed by Swift. The superb quality of the early X-ray data allows us to study the evolution of the prompt and early afterglow emission for this GRB in unprecedented detail. A temporal spectral analysis of the early X-ray data shows that the photon index, Γ, and source intensity are highly correlated with the spectrum being significantly harder when brighter. The simplest explanation for the observed temporal behaviour is an abrupt movement of the peak of the Band-function to higher energies at the onset of each flare, followed by a slower decline to lower energies as the flare fades. We find no evidence for the presence of lines in the early X-ray spectra, with a 3σ upper limit of < 15 eV for an assumed narrow line of width of 100eV at the peak of the effective area. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

GRBs 050223 and 050911 are examples of Swift bursts with two of the faintest X-ray afterglows at (relatively) early times. While a faint, fading X-ray afterglow was located for GRB 050223, GRB 050911 was not detected, making any X-ray afterglow extremely faint. The faintness of the afterglow of GRB 050223 could be explained by a large opening or viewing angle, or by the burst being at high redshift. The non-detection of GRB 050911 may indicate the burst occurred in a low-density environment, or, alternatively, was due to a compact object merger, in spite of the apparent long duration of the burst. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

An XMM-Newton observation of the bright QSO PG1211+143 was previously reported to show evidence for a massive, energetic outflow, with a velocity of v∼0.09c based on the identification of blue-shifted absorption lines detected in both EPIC and RGS spectra. Subsequently, an order-of-magnitude lower velocity has been claimed from an ion-by-ion model fit to the RGS data. We show here, from a re-analysis of the higher signal-to-noise EPIC data, that the high velocity is confirmed, with the resolution of additional absorption lines yielding a revised outflow velocity in the range ∼0.13–0.15c. Confirmation of a massive and energetic outflow in a non-BAL AGN has important implications for metal enrichment of the IGM and for the feedback mechanism implied by the correlation of black hole and galactic bulge masses. We note the near-Eddington luminosity of PG1211+143 may be the critical factor in driving such an energetic outflow, a situation likely to be common in AGN at higher redshift. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Swift very fast follow up observations of Gamma-Ray Bursts have allowed us to discover a new feature of GRB afterglows: a phase of shallow decay, usually attributed to energy injection in the burst ejecta, which can last for several thousands of seconds both in the X-ray and optical bands. Here I shall discuss this phase in the cases of Swift GRBs 050401, 050801 and 050802. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present observations of GRB 060108, the 100th burst detected by Swift. The optical afterglow was found to be below UVOT detection limits within the first 100 s, and the ratio of X-ray and R band measurements at ∼ 1000 s after the trigger gives a spectral index βOX = 0.45, which makes this burst “dark” according to the Jakobbson classification. We derive a maximum photometric redshift of z<3.2, which excludes a high redshift as a possible cause of the observed darkness, and we find that the most likely explanation is a combination of intrinsic faintness, a hard optical to X-ray spectrum and dust extinction. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present Swift observations of the faint burst GRB 050421. The X-ray light-curve shows two flares: the first peaking at ∼ 110 s after the BAT trigger (T0) and the second one peaking at ∼ 154 s. We argue that the mechanism producing these flares is probably late internal shocks. The X-ray light-curve is consistent with a power-law with a temporal index α1 ∼ 3.1. The X-ray flux decays from ∼ 10-9 erg cm-2 s-1 at T0 + 100 s to < 7 × 10-13 erg cm-2 s-1 at T0 + 1000 s. An X-ray spectral softening is also observed with time from β ∼ 0.1 to ∼ 1.2, where β is the spectral index such as Fv ∝ v-βt-α. A good joint fit to the BAT and XRT spectra indicates that the early X-ray and Gamma-ray emissions are produced by the same mechanism. The X-ray spectral softening is likely due to a shift down to lower energies of the peak of the prompt emission, and the rapid decline of the X-ray emission is probably the tail of the prompt emission. This suggests that the X-ray emission is completely dominated by high latitude radiation and the external shock, if any, is extremely faint and below the detection threshold. GRB 050421 is likely the first “naked burst” detected by Swift. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

GRBs 050223 and 050911 were discovered by the Swift Burst Alert Telescope (BAT) on 23rd February and 11th September 2005 respectively. The observation of GRB 050223 showed a faint, fading X-ray source, which was identified as the afterglow; GRB 050911, however, was not detected, making any X-ray afterglow extremely faint. The faintness of the afterglow of GRB 050223 could be explained by a large opening or viewing angle, or by the burst being at high redshift. The non-detection of GRB 050911 may indicate the burst occurred in a low-density environment, or, alternatively, was due to a compact object merger, in spite of the apparent long duration of the burst. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The Swift X-ray Telescope (XRT) focal plane camera houses a front-illuminated MOS CCD, providing a spectral response of 145 eV FWHM at 5.9 keV. We describe the status of the CCD X-ray spectral redistribution matrices, which are made using a Monte-Carlo simulation technique based on physical models of the CCD response. We emphasize how the model has been refined following in-flight experience with celestial and on-board calibration sources. Residuals less than 10% are typically observed for astrophysical sources. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have analysed BAT and XRT data for 40 gamma-ray bursts (GRBs) observed using the Swift satellite. The earliest X-ray light curve can be well described by an exponential which relaxes into a power law, often with flares superimposed. The transition time between the exponential and the power law gives a physically defined timescale for the burst duration. In most GRBs the power law decay changes to a shallower decay within the first hour. The resultant “late emission hump” can last for several tens of ks. In other bursts the late hump is weak or absent. The observed variety in light curve shape can be explained as a combination of three components: prompt emission from the central engine; afterglow; and the late hump, which may also be due to the central engine. GRBs with stronger afterglow components are more likely to have brighter early optical emission. The late emission hump can have a total fluence equivalent to that of the prompt phase. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The Swift Gamma Ray Burst Explorer is providing exciting new insights into the nature of the prompt and early afterglow emission of GRBs, filling in the 8 hr observing gap immediately following the initial explosion. Here we report on the XRT 0.3–10 keV prompt and early afterglow spectra of those GRBs for which we have early (< few minutes) XRT data and which exhibit a common behaviour in their temporal decay. We also report on GRB 051117A, a source which is bright enough in XRT to allow the most detailed temporal spectral analysis to date. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

XRF 050416A was discovered by the Swift Burst Alert Telescope and re-pointed with the Swift narrow field instruments only 64.5 s after the burst onset. The 15 – 150 keV BAT average spectrum has a photon index of Γ ∼ 3.0 which classifies the bursts as an X-ray flash. The afterglow X-ray emission was monitored by the Swift X-Ray Telescope up to 74 days after the burst. The X-ray light curve shows a decay with three different phases: an initial steep decay with a decay slope of ∼ 2.4 (phase A), then, starting at ∼172 s from the burst onset, a second phase with a flat decay slope of ∼ 0.44 (phase B), and finally, after ∼1450 s from the burst onset, a third long-lasting phase with a decay slope of ∼ 0.88 (phase C). We find evidence of spectral evolution from a softer emission in the phase A of the afterglow decay, with Γ ∼ 3.0, to a harder emission with Γ ∼ 2.0 in the phases B and C. A redshift of 0.6535 was measured for the source. The spectra show intrinsic absorption in the host galaxy of ∼ 6.8 × 1021 cm-2. The consistency of the phase A photon index with the BAT photon index suggests that the initial fast decaying phase of the XRT afterglow might be the low energy tail of the prompt emission. The lack of jet break signatures in the X-ray afterglow light curve suggests very low collimation of the expanding fireball. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]