Showing papers by "A. P. Beardmore published in 2007"
TL;DR: In this paper, the authors present a suite of programs which automatically generate Swift /XRT light curves of GRBs, which can be used to provide the community with an online repository of X-ray light curves obtained with Swift.
Abstract: Context. Swift data are revolutionising our understanding of Gamma Ray Bursts. Since bursts fade rapidly, it is desirable to create and disseminate accurate light curves rapidly.Aims. To provide the community with an online repository of X-ray light curves obtained with Swift . The light curves should be of the quality expected of published data, but automatically created and updated so as to be self-consistent and rapidly available.Methods. We have produced a suite of programs which automatically generates Swift /XRT light curves of GRBs. Effects of the damage to the CCD, automatic readout-mode switching and pile-up are appropriately handled, and the data are binned with variable bin durations, as necessary for a fading source. Results. The light curve repository website (http://www.swift.ac.uk/xrt_curves) contains light curves, hardness ratios and deep images for every GRB which Swift 's XRT has observed. When new GRBs are detected, light curves are created and updated within minutes of the data arriving at the UK Swift Science Data Centre.
746 citations
TL;DR: In this article, the authors report the results of the Swift and XMM-Newton observations of the discovered GRB 060729 (T90 = 115 s) and show that the afterglow of this burst was exceptionally bright in X-rays as well as at UV/optical wavelengths, showing an unusually long slow decay phase (? = 0.14? 0.02), suggesting a larger energy injection phase at early times than in other bursts.
Abstract: We report the results of the Swift and XMM-Newton observations of the Swift -discovered GRB 060729 (T90 = 115 s). The afterglow of this burst was exceptionally bright in X-rays as well as at UV/optical wavelengths, showing an unusually long slow decay phase (? = 0.14 ? 0.02), suggesting a larger energy injection phase at early times than in other bursts. The X-ray light curve displays a break at about 60 ks after the burst. The X-ray decay slope after the break is ? = 1.29 ? 0.03. Up to 125 days after the burst we do not detect a jet break, suggesting that the jet opening angle is larger than 28?. We find that the X-ray spectra of the early phase change dramatically and can all be fitted by an absorbed single-power-law models or alternatively by a blackbody plus power-law model. The power-law fits show that the X-ray spectrum becomes steeper while the absorption column density decreases. In the blackbody model the temperature decreases from kT = 0.6 to 0.1 keV between 85 and 160 s after the burst in the rest frame. The afterglow was clearly detected up to 9 days after the burst in all six UVOT filters and in UVW1 even for 31 days. A break at about 50 ks is clearly detected in all six UVOT filters from a shallow decay slope of about 0.3 and a steeper decay slope of 1.3.The XMM-Newton observations started about 12 hr after the burst and show a typical afterglow X-ray spectrum with ?X = 1.1 and absorption column density of 1 ? 1021 cm-2.
103 citations
10 Aug 2007
TL;DR: The bound-free absorption by neutral elements in the line of sight, resonance absorption lines plus self-absorbed emission-line components, collisionally excited emission lines from the shock, He-like intersystem lines, and spectral changes during an episode of high-amplitude variability are discussed.
Abstract: The phase of supersoft source (SSS) emission of the sixth recorded outburst of the recurrent nova RS Oph was observed on days 39.7 and 66.9 after outburst with Chandra and on day 54.0 with XMM-Newton. A ~35 s period on day 54.0 originates from the SSS emission and not from the shock. We discuss the bound-free absorption by neutral elements in the line of sight, resonance absorption lines plus self-absorbed emission-line components, collisionally excited emission lines from the shock, He-like intersystem lines, and spectral changes during an episode of high-amplitude variability. We find a decrease of the oxygen K-shell absorption edge that can be explained by photoionization of oxygen. The absorption component has average velocities of -1286 ± 267 km s-1 on day 39.7 and of -771 ± 65 km s-1 on day 66.9. The wavelengths of the emission-line components are at rest wavelengths, as confirmed by measurements of non-self-absorbed He-like intersystem lines. We found collisionally excited emission lines from the radiatively cooling shock at wavelengths shorter than 15 A that are systematically blueshifted by -526 ± 114 km s-1 on day 39.7 and are fading. We found anomalous He-like f/i ratios, which indicates either high densities or significant UV radiation near the plasma where the emission lines are formed. During the phase of strong variability the spectral hardness light curve overlies the total light curve when shifted by 1000 s. This can be explained by photoionization of neutral oxygen in the line of sight if the densities are of order 1010-1011 cm-3.
82 citations
TL;DR: In this article, bound-free absorption by neutral elements in the line of sight, resonance absorption lines plus self-absorbed emission line components, collisionally excited emission lines from the shock, He-like intersystem lines, and spectral changes during an episode of high-amplitude variability.
Abstract: The phase of Super-Soft-Source (SSS) emission of the sixth recorded outburst of the recurrent nova RS Oph was observed twice with Chandra and once with XMM-Newton. The observations were taken on days 39.7, 54.0, and 66.9 after outburst. We confirm a 35-sec period on day 54.0 and found that it originates from the SSS emission and not from the shock. We discus the bound-free absorption by neutral elements in the line of sight, resonance absorption lines plus self-absorbed emission line components, collisionally excited emission lines from the shock, He-like intersystem lines, and spectral changes during an episode of high-amplitude variability. We find a decrease of the oxygen K-shell absorption edge that can be explained by photoionization of oxygen. The absorption component has average velocities of -1286+-267 km/s on day 39.7 and of -771+-65 km/s on day 66.9. The wavelengths of the emission line components are consistent with their rest wavelengths as confirmed by measurements of non-self absorbed He-like intersystem lines. We have evidence that these lines originate from the shock rather than the outer layers of the outflow and may be photoexcited in addition to collisional excitations. We found collisionally excited emission lines that are fading at wavelengths shorter than 15A that originate from the radiatively cooling shock. On day 39.5 we find a systematic blue shift of -526+-114 km/s from these lines. We found anomalous He-like f/i ratios which indicates either high densities or significant UV radiation near the plasma where the emission lines are formed. During the phase of strong variability the spectral hardness light curve overlies the total light curve when shifted by 1000sec. This can be explained by photoionization of neutral oxygen in the line of sight if the densities of order 10^{10}-10^{11} cm^{-3}.
70 citations
TL;DR: The light curve observed by the XRT is characterized by the presence of a long flaring activity lasting up to 1-2 h after the burst onset in the burst rest frame, with no evidence of a smooth power-law decay following the prompt emission as seen in other GRBs.
Abstract: Context Swift discovered the high redshift (z = 629) GRB 050904 with the Burst Alert Telescope (BAT) and began observing with its narrow field instruments 161 s after the burst onset This gamma-ray burst is the most distant cosmic explosion ever observed Because of its high redshift, the X-ray Telescope (XRT) and BAT simultaneous observations provide 4 orders of magnitude of spectral coverage (02-150 keV; 14-1090 keV in the source rest frame) at a very early source-frame time (22 s) The X-ray emission was monitored by the XRT up to 10 days after the burst Aims We present the analysis of BAT and XRT observations of GRB 050904 and a complete description of its high energy phenomenology Methods We performed time resolved spectral analysis and light curve modeling Results GRB 050904 was a long, multi-peaked, bright GRB with strong variability during its entire evolution, The light curve observed by the XRT is characterized by the presence of a long flaring activity lasting up to 1-2 h after the burst onset in the burst rest frame, with no evidence of a smooth power-law decay following the prompt emission as seen in other GRBs However, the BAT tail extrapolated to the XRT band joins the XRT early light curve and the overall behavior resembles that of a very long GRB prompt The spectral energy distribution softens with time, with the photon index decreasing from -12 during the BAT observation to -19 at the end of the XRT observation The dips of the late X-ray flares may be consistent with an underlying X-ray emission arising from the forward shock and with the properties of the optical afterglow reported by Tagliaferri et al (2005b, AA very low metallicities of the progenitor at these epochs may provide an explanation © ESO 2007
33 citations
TL;DR: In this paper, the authors report on the temporal and spectral characteristics of the early X-ray emission from the Gamma Ray Burst 051117A as observed by Swift, and place stringent limits on the detection of lines.
Abstract: We report on the temporal and spectral characteristics of the early X-ray emission from the Gamma Ray Burst 051117A as observed by Swift . The superb quality of the early X-ray light-curve and spectra of this source, one of the brightest seen by the X-ray Telescope at such early times, allows an unprecedented look at the spectral and temporal evolution of the prompt and early afterglow emission for this GRB and allows us to place stringent limits on the detection of lines. GRB 051117A displays a highly complex light-curve, with an apparent initial slow decline of slope $\alpha=0.77\pm0.07$ ($f(t)\propto t^{-\alpha}$) dominated by numerous superposed flares of varying amplitude and duration. Between orbits 2 and 3, the X-ray light-curve drops abruptly, highlighting the dominance of flaring activity at early times, and indicating that the central engine for this burst remains active for several kiloseconds after the initial explosion. The late time slope ($t>10^{4}$ s) also decays relatively slowly with a powerlaw index of $\alpha=0.66$, breaking to a steeper slope of 1.1, 170 ks after the BAT trigger. The X-ray light-curve at early times is characteristic of a noise process, consisting of random shots superposed on an underlying powerlaw decay, with individual shots well-modelled by a fast-rise and exponential decay spanning a broad range in rise-times and decay rates. A temporal spectral analysis of the early light-curve shows that the photon index and source intensity are highly correlated with the spectrum being significantly harder when brighter, consistent with the movement of the peak of the Band function to lower energies following individual flares. The high quality spectrum obtained from the first orbit of WT mode data, enables us to place a $3\sigma$ upper limit on the strength of any emission line features of ${\it EW}< 15$ eV, assuming a narrow emission-line of 100 eV at the peak of the effective area.
25 citations
TL;DR: In this paper, the authors exploit the Swift X-ray Telescope (XRT) deep GRB follow-up observations to study the cosmic X-Ray Background (XRB) population in the 0.2-10 keV energy band.
Abstract: We are exploiting the Swift X-ray Telescope (XRT) deepest GRB follow-up observations to study the cosmic X-Ray Background (XRB) population in the 0.2-10 keV energy band. We present some preliminary results of a serendipitous survey performed on 221 fields observed with exposure longer than 10 ks. We show that the XRT is a profitable instrument for surveys and that it is particularly suitable for the search and observation of extended objects like clusters of galaxies. We used the brightest serendipitous sources and the longest observations to test the XRT optics performance and the background characteristics all over the field of view, in different energy bands during the first 2.5 years of fully operational mission.
20 citations
10 Jun 2007
15 citations
TL;DR: In this article, the authors reported on the K-W detection of the prompt gamma-ray emission from GRB 050713A and an upper limiting GeV measurement of the afterglow made by the MAGIC imaging atmospheric Cerenkov telescope.
Abstract: Swift discovered GRB 050713A and slewed promptly to begin observing with its narrow-field instruments 72.6 s after the burst onset, while the prompt gamma-ray emission was still detectable in the BAT. Simultaneous emission from two flares is detected in the BAT and XRT. This burst marks just the second time that the BAT and XRT have simultaneously detected emission from a burst and the first time that both instruments have produced a well-sampled, simultaneous data set covering multiple X-ray flares. The temporal rise and decay parameters of the flares are consistent with the internal-shock mechanism. In addition to the Swift coverage of GRB 050713A, we report on the Konus-Wind (K-W) detection of the prompt emission, an upper limiting GeV measurement of the prompt emission made by the MAGIC imaging atmospheric Cerenkov telescope, and XMM-Newton observations of the afterglow. Simultaneous observations with Swift XRT and XMM-Newton produce consistent results, showing a break in the light curve at T0+ ~ 15 ks. Together, these four observatories provide unusually broad spectral coverage of the prompt emission and detailed X-ray follow-up of the afterglow for 2 weeks after the burst trigger. Simultaneous spectral fits of K-W with BAT and BAT with XRT data indicate that an absorbed broken power law is often a better fit to GRB flares than a simple absorbed power law. These spectral results together with the rapid temporal rise and decay of the flares suggest that flares are produced in internal shocks due to late-time central-engine activity.
14 citations
TL;DR: The Swift X-ray Telescope focal plane camera is a front-illuminated MOS CCD, providing a spectral response kernel of 135 eV FWHM at 5.9 keV as measured before launch as discussed by the authors.
Abstract: The Swift X-ray Telescope focal plane camera is a front-illuminated MOS CCD, providing a spectral response kernel of 135 eV FWHM at 5.9 keV as measured before launch. We describe the CCD calibration program based on celestial and on-board calibration sources, relevant in-flight experiences, and developments in the CCD response model. We illustrate how the revised response model describes the calibration sources well. Comparison of observed spectra with models folded through the instrument response produces negative residuals around and below the Oxygen edge. We discuss several possible causes for such residuals. Traps created by proton damage on the CCD increase the charge transfer inefficiency (CTI) over time. We describe the evolution of the CTI since the launch and its effect on the CCD spectral resolution and the gain.
10 citations
TL;DR: In this paper, the authors investigated the properties of the instrumental background, focusing on its dynamic behavior on both long and short timescales, and determined the fraction of the detector background that is due to the internal, instrumental background and the part that are due to unresolved astrophysical sources (the cosmic X-ray background).
Abstract: The X-ray telescope (XRT) on board the Swift Gamma Ray Burst Explorer has successfully operated since the spacecraft launch on 20 November 2004, automatically locating GRB afterglows, measuring their spectra and lightcurves and performing observations of high-energy sources. In this work we investigate the properties of the instrumental background, focusing on its dynamic behavior on both long and short timescales. The operational temperature of the CCD is the main factor that influences the XRT background level. After the failure of the Swift active on-board temperature control system, the XRT detector now operates at a temperature range between -75C and -45C thanks to a passive cooling Heat Rejection System. We report on the long-term effects on the background caused by radiation, consisting mainly of proton irradiation in Swift's low Earth orbit and on the short-term effects of transits through the South Atlantic Anomaly (SAA), which expose the detector to periods of intense proton flux. We have determined the fraction of the detector background that is due to the internal, instrumental background and the part that is due to unresolved astrophysical sources (the cosmic X-ray background) by investigating the degree of vignetting of the measured background and comparing it to the expected value from calibration data.
TL;DR: The Swift X-ray Telescope focal plane camera is a front-illuminated MOS CCD, providing a spectral response kernel of 135 eV FWHM at 5.9 keV as measured before launch as discussed by the authors.
Abstract: The Swift X-ray Telescope focal plane camera is a front-illuminated MOS CCD, providing a spectral response kernel of 135 eV FWHM at 5.9 keV as measured before launch. We describe the CCD calibration program based on celestial and on-board calibration sources, relevant in-flight experiences, and developments in the CCD response model. We illustrate how the revised response model describes the calibration sources well. Comparison of observed spectra with models folded through the instrument response produces negative residuals around and below the Oxygen edge. We discuss several possible causes for such residuals. Traps created by proton damage on the CCD increase the charge transfer inefficiency (CTI) over time. We describe the evolution of the CTI since the launch and its effect on the CCD spectral resolution and the gain.
TL;DR: In this article, the authors describe observations of GRB 050422, a Swift-discovered gamma-ray burst, and describe the X-ray light curve, which shows a steep early decline, with an initial decay slope of α 1 ∼ 5.0, a break time tb ∼ 270 s and a post-break decay slope α 2 ∼ 0.9.
Abstract: We describe observations of GRB 050422, a Swift-discovered gamma-ray burst. The prompt gamma-ray emission had a T90 duration of 59 s and was multipeaked, with the main peak occurring at T + 53 s. Swift was able to follow the X-ray afterglow within 100 s of the burst trigger. The X-ray light curve, which shows a steep early decline, can be described by a broken power law with an initial decay slope of α1 ∼ 5.0, a break time tb ∼ 270 s and a post-break decay slope of α2 ∼ 0.9, when the zero time of the X-ray emission is taken to be the burst trigger time. However, if the zero time is shifted to coincide with the onset of main peak in the gamma-ray light curve then the initial decay slope is shallower with α1 ∼ 3.2. The initial gamma-ray spectrum can be modelled by a power law with a spectral index of β B = 0.50 ± 0.19. However, the early time X-ray spectrum is significantly steeper than this and requires a spectral index of βX = 2.33 +0.58 −0.55. In comparison with other Swift bursts, GRB 050422 was unusually X-ray faint, had a soft X-ray spectrum, and had an unusually steep early X-ray decline. Even so, its behaviour can be accommodated by standard models. The combined BAT/XRT light curve indicates that the initial, steeply declining, X-ray emission is related to the tail of the prompt gamma-ray emission. The shallower decay seen after the break is consistent with the standard afterglow model.
TL;DR: The Swift X-ray Telescope (XRT) is a CCD-based Xray telescope designed for localization, spectroscopy and long-term light curve monitoring of Gamma-Ray Bursts and their afterglows as mentioned in this paper.
Abstract: The Swift X-ray Telescope (XRT) is a CCD based X-ray telescope designed for localization, spectroscopy and long term light curve monitoring of Gamma-Ray Bursts and their X-ray afterglows. Since the launch of Swift in November 2004, the XRT has undergone significant evolution in the way it is operated. Shortly after launch there was a failure of the CCD thermo-electric cooling system, which led to the XRT team being required to devise a method of keeping the CCD temperature below −50C utilizing only passive cooling by minimizing the exposure of the XRT radiator to the Earth. We present in this paper an update on how the modeling of this passive cooling method has improved in first ~1000 days since the method was devised, and the success rate of this method in day-to-day planning. We also discuss the changes to the operational modes and onboard software of the XRT. These changes include improved rapid data product generation in order to improve speed of rapid Gamma-Ray Burst response and localization to the community; changes to the way XRT observation modes are chosen in order to better fine tune data acquisition to a particular science goal; reduction of “mode switching” caused by the contamination of the CCD by Earth light or high temperature effects.
22 Nov 2007