M. Ehle

GRB 061121: Broadband Spectral Evolution through the Prompt and Afterglow Phases of a Bright Burst

Swift triggered on a precursor to the main burst of GRB 061121 (z = 1.314), allowing observations to be made from the optical to gamma-ray bands. Many other telescopes, including Konus-Wind, XMM-Newton, ROTSE, and the Faulkes Telescope North, also observed the burst. The gamma-ray, X-ray, and UV/optical emission all showed a peak ~75 s after the trigger, although the optical and X-ray afterglow components also appear early on, before or during the main peak. Spectral evolution was seen throughout the burst, with the prompt emission showing a clear positive correlation between brightness and hardness. The SED of the prompt emission, stretching from 1 eV up to 1 MeV, is very flat, with a peak in the flux density at ~ 1 keV. The optical to X-ray spectra at this time are better fitted by a broken, rather than single, power law, similar to previous results for X-ray flares. The SED shows spectral hardening as the afterglow evolves with time. This behavior might be a symptom of self-Comptonization, although circumstellar densities similar to those found in the cores of molecular clouds would be required. The afterglow also decays too slowly to be accounted for by the standard models. Although the precursor and main emission show different spectral lags, both are consistent with the lag-luminosity correlation for long bursts. GRB 061121 is the instantaneously brightest long burst yet detected by Swift. Using a combination of Swift and Konus-Wind data, we estimate an isotropic energy of 2.8 × 1053 ergs over 1 keV-10 MeV in the GRB rest frame. A probable jet break is detected at ~2 × 105 s, leading to an estimate of ~10 51 ergs for the beaming-corrected gamma-ray energy.

Magnetic field as a tracer of sheared gas flow in barred galaxies

Many spiral galaxies have stellar bars—an elongated region near the centre from which spiral arms emerge. Gas and stars in barred galaxies move on highly non-circular orbits. Models predict that the gas streamlines are strongly deflected along shock fronts in the bar region, and that the gas behind the shock is compressed. Dust lanes form in dense gas regions and it is believed that gas flows inward along these lanes to fuel bursts of star formation in a ring of dense molecular gas near the centre of the galaxy,. This inflow is difficult to measure observationally. Magnetic fields are known to pervade the interstellar gas in all spiral galaxies, but the relationship between such fields and the gas flow in barred galaxies has not hitherto been investigated. Here we report high-resolution radio observations of the magnetic fields in the barred galaxy NGC1097. We find a regular magnetic field in the bar and in the circumnuclear ring. The field in the bar is well aligned with the theoretical gas streamlines, and so appears to be a good tracer of the gas flow. The magnetic stress in the ring can drive mass inward at the rate needed to fuel the active nucleus of this galaxy.

XMM-Newton survey of the Local Group galaxy M 33 ,

In an XMM-Newton raster observation of the bright Local Group spiral galaxy M 33 we study the population of X-ray sources (X-ray binaries, supernova remnants) down to a 0.2-4.5 keV luminosity of 10 35 erg s −1 - more than a factor of 10 deeper than earlier ROSAT observations. EPIC hardness ratios and optical and radio information are used to distinguish between different source classes. The survey detects 408 sources in an area of 0.80 square degree. We correlate these newly detected sources with earlier M 33 X-ray catalogues and information from optical, infra-red and radio wavelengths. As M 33 sources we detect 21 supernova remnants (SNR) and 23 SNR candidates, 5 super-soft sources and 2 X-ray binaries (XRBs). There are 267 sources classified as hard, which may either be XRBs or Crab-like SNRs in M 33 or background AGN. The 44 confirmed and candidate SNRs more than double the number of X-ray detected SNRs in M 33. 16 of these are proposed as SNR candidates from the X-ray data for the first time. On the other hand, there are several sources not connected to M 33: five foreground stars, 30 foreground star candidates, 12 active galactic nucleus candidates, one background galaxy and one background galaxy candidate. Extrapolating from deep field observations we would expect 175 to 210 background sources in this field. This indicates that about half of the sources detected are within M 33.

The XMM-Newton survey of the Small Magellanic Cloud ,,

Context. Although numerous archival XMM-Newton observations existed towards the Small Magellanic Cloud (SMC) before 2009, only a fraction of the whole galaxy had been covered. Aims. Between May 2009 and March 2010, we carried out an XMM-Newton survey of the SMC, to ensure a complete coverage of both its bar and wing. Thirty-three observations of 30 different fields with a total exposure of about one Ms filled the previously missing parts. Methods. We systematically processed all available SMC data from the European Photon Imaging Camera. After rejecting observations with very high background, we included 53 archival and the 33 survey observations. We produced images in five different energy bands. We applied astrometric boresight corrections using secure identifications of X-ray sources and combined all the images to produce a mosaic covering the main body of the SMC. Results. We present an overview of the XMM-Newton observations, describe their analysis, and summarise our first results, which will be presented in detail in follow-up papers. Here, we mainly focus on extended X-ray sources, such as supernova remnants (SNRs) and clusters of galaxies, that are seen in our X-ray images. Conclusions. Our XMM-Newton survey represents the deepest complete survey of the SMC in the 0.15−12.0 keV X-ray band. We propose three new SNRs that have low surface brightnesses of a few 10 −14 erg cm −2 s −1 arcmin −2 and large extents. In addition, several known remnants appear larger than previously measured at either X-rays or other wavelengths extending the size distribution of SMC SNRs to larger values.

A 33 hour period for the Wolf-Rayet/black hole X-ray binary candidate NGC 300 X-1

Context. NGC 300 X-1 is the second extragalactic candidate, after IC 10 X-1, in the rare class of Wolf-Rayet/compact object X-ray binary systems exemplified in the Galaxy by Cyg X-3. From a the oretical point of view, accretion onto a black hole in a detac hed system is possible for large orbital periods only if the mass of the relativistic object is high or the velocity of the accr eted wind is low. Aims. We analysed a 2 week SWIFT XRT light curve of NGC 300 X-1 and searched for periodicities. Methods. Period searches were made using Lomb-Scargle periodogram analysis. We evaluated the confidence level using Monte Carlo simulations. Results. A period of 32.8±0.4 h (3� error) was found for NGC 300 X-1 with a confidence level >99%. Furthermore, we confirm the high irregular variability during the high flux level, as alr eady observed in the XMM-Newton observations of the source. A folded XMM-Newton light curve is shown, with a profile that is in agreement with SWIFT. The mean absorbed X-ray luminosity in the SWIFT observations was 1.5× 10 38 erg s −1 , close to the value derived from the XMM-Newton data. Conclusions. While Cyg X-3 has a short period of 4.8 h, the period of NGC 300 X-1 is very close to that of IC 10 X-1 (34.8±0.9 h). These are likely orbital periods. Possibility of formation of accretion disk for such high orbital periods strongly dep ends on the terminal velocity of the Wolf-Rayet star wind and black-hole mass. While low masses are possible for wind velocities. 1000 km s −1 , these increase to several tens of solar masses for velociti es > 1600 km s −1 and no accretion disk may form for terminal velocities larger than 1900 km s −1 .

An XMM-newton survey of the local group galaxy M 33 : variability of the detected sources

We present an analysis of the individual observations of a deep XMM-Newton survey of the Local Group spiral galaxy M 33. We detected a total of 350 sources with fluxes (in the 0.2–4.5 keV energy band) in the range 6.7

The population of X-ray supernova remnants in the Large Magellanic Cloud

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IKT 16: a composite supernova remnant in the Small Magellanic Cloud

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