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Register a new userGamma-Ray Bursts observed by XMM-Newton
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P.T. OBrien
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Analysis of observations with XMM-Newton have made a significant contribution to the study of Gamma-ray Burst (GRB) X-ray afterglows. The effective area, bandpass and resolution of the EPIC instrument permit the study of a wide variety of spectral features. In particular, strong, time-dependent, soft X-ray emission lines have been discovered in some bursts. The emission mechanism and energy source for these lines pose major problems for the current generation of GRB models. Other GRBs have intrinsic absorption, possibly related to the environment around the progenitor, or possible iron emission lines similar to those seen in GRBs observed with BeppoSAX. Further XMM-Newton observations of GRBs discovered by the Swift satellite should help unlock the origin of the GRB phenomenon over the next few years.
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In A0-1 we proposed an ambitious long-term survey of selected regions of our Galaxy (the XGPS survey) using the EPIC CCD cameras on XMM-Newton. The first phase of the programme, which aims to survey a strip of the Galactic Plane in the Scutum region, is currently underway. Here we report on the preliminary results from the first 15 survey pointings. We show that the XGPS survey strategy of fairly shallow (5-10 ks) exposures but wide-angle coverage is well tuned to the goal of providing a large catalogue of predominantly Galactic sources at relatively faint X-ray fluxes in the hard 2-6 keV band.
We have carried out a study of the X-ray properties of the supernova remnant (SNR) population in M33 with XMM-Newton, comprising deep observations of 8 fields in M33 covering all of the area within the D$_{25}$ contours, and with a typical luminosity of 7.1$times$10$^{34}$ erg s$^{-1}$ (0.2-2.0 keV) . Here we report our work to characterize the X-ray properties of the previously identified SNRs in M33, as well as our search for new X-ray detected SNRs. With our deep observations and large field of view we have detected 105 SNRs at the 3$sigma$ level, of which 54 SNRs are newly detected in X-rays, and three are newly discovered SNRs. Combining XMM-Newton data with deep Chandra survey data allows detailed spectral fitting of 15 SNRs, for which we have measured temperatures, ionization timescales, and individual abundances. This large sample of SNRs allows us to construct an X-ray luminosity function, and compare its shape to luminosity functions from host galaxies of differing metallicities and star formation rates to look for environmental effects on SNR properties. We conclude that while metallicity may play a role in SNR population characteristics, differing star formation histories on short timescales, and small-scale environmental effects appear to cause more significant differences between X-ray luminosity distributions. In addition, we analyze the X-ray detectability of SNRs, and find that in M33 SNRs with higher [SII]/H$alpha$ ratios, as well as those with smaller galactocentric distances, are more detectable in X-rays.
We study the time-resolved spectra of eight GRBs observed by Fermi GBM in its first five years of mission, with 1 keV - 1 MeV fluence $f>1.0times10^{-4}$ erg cm$^{-2}$ and signal-to-noise level $text{S/N}geq10.0$ above 900 keV. We aim to constrain in detail the spectral properties of GRB prompt emission on a time-resolved basis and to discuss the theoretical implications of the fitting results in the context of various prompt emission models. We perform time-resolved spectral analysis using a variable temporal binning technique according to optimal S/N criteria, resulting in a total of 299 time-resolved spectra. We fit the Band function to all spectra and obtain the distributions for the low-energy power-law index $alpha$, the high-energy power-law index $beta$, the peak energy in the observed $ u F_ u$ spectrum $E_text{p}$, and the difference between the low- and high-energy power-law indices $Delta s=alpha-beta$. Using the distributions of $Delta s$ and $beta$, the electron population index $p$ is found to be consistent with the moderately fast scenario which fast- and slow-cooling scenarios cannot be distinguished. We also apply a physically motivated synchrotron model, which is a triple power-law with constrained power-law indices and a blackbody component, to test for consistency with a synchrotron origin for the prompt emission and obtain the distributions for the two break energies $E_text{b,1}$ and $E_text{b,2}$, the middle segment power-law index $beta$, and the Planck function temperature $kT$. A synchrotron model is found consistent with the majority of time-resolved spectra for these eight energetic Fermi GBM bursts with good high-energy photon statistics, as long as both the cooling and injection break are included and the leftmost spectral slope is lifted either by inclusion of a thermal component or when an evolving magnetic field is accounted for.
We present a catalog of XMM-Newton and Chandra observations of gamma-ray burst (GRB) afterglows, reduced in a common way using the most up-to-date calibration files and software. We focus on the continuum properties of the afterglows. We derive the spectral and temporal decay indices for 16 bursts. We place constraints on the burst environment and geometry. A comparison of the fast XMM-Newton follow-up and the late Chandra observations shows a significant difference in those parameters, likely produced by a transition from jet expansion taking place between two and ten days after the burst. We do not observe a significant shrinking of the luminosity distribution when we correct for beaming; more burst observations are needed to confirm this result. We also compare our results with those obtained by BeppoSAX and SWIFT; there is no strong discrepancy between the afterglow fluxes observed with these satellites when we carefully take into account the different median observation time of each observatory.
The detection of flares with the Swift satellite triggered a lot of bservational and theoretical interest in these phenomena. As a consequence a large analysis effort started within the community to characterize the phenomenon and at the same time a variety of theoretical speculations have been proposed to explain it. In this presentation we discuss part of the results we obtained analyzing a first statistical sample of GRBs observed with Swift. The first goal of this research is very simple: derive those observational properties that could distinguish between internal and external shock and between an ever active central engine and delayed shocks (refreshing) related to a very small initial Lorentz bulk factor. We discuss first the method of analysis and the morphology evidencing the similarities such flares have with the prompt emission pulses. We conclude that GRB flares are due to internal shocks and leave still open the question of whether or not the central engine is active for a time of the order of 105 seconds after the prompt emission.
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