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The Neil Gehrels Swift Observatory followed up 18 gravitational wave (GW) triggers from the LIGO/Virgo collaboration during the O3 observing run in 2019/2020, performing approximately 6500 pointings in total. Of these events, four were finally classified (if real) as binary black hole (BH) triggers, six as binary neutron star (NS) events, two each of NSBH and Mass Gap triggers, one an unmodelled (Burst) trigger, and the remaining three were subsequently retracted. Thus far, four of these O3 triggers have been formally confirmed as real gravitational wave events. While no likely electromagnetic counterparts to any of these GW events have been identified in the X-ray data (to an average upper limit of 3.60 x 10^{-12} erg cm^{-2} s^{-1} over 0.3-10 keV), or at other wavelengths, we present a summary of all the Swift-XRT observations performed during O3, together with typical upper limits for each trigger observed. The majority of X-ray sources detected during O3 were previously uncatalogued; while some of these will be new (transient) sources, others are simply too faint to have been detected by earlier survey missions such as ROSAT. The all-sky survey currently being performed by eROSITA will be a very useful comparison for future observing runs, reducing the number of apparent candidate X-ray counterparts by up to 95 per cent., Comment: 23 pages (including 4 pages of references, and a 4 page table in the appendix), 5 figures (4 in colour), accepted for publication in MNRAS. (Replaced due to annoying spelling typo in the abstract.)

The analysis of the third INTEGRAL/IBIS survey has revealed several new cataclysmic variables, most of which turned out to be intermediate polars, thus confirming that these objects are strong emitters in hard X-rays. Here we present high energy spectra of all 22 cataclysmic variables detected in the 3rd IBIS survey and provide the first average spectrum over the 20-100 keV band for this class. Our analysis indicates that the best-fit model is a thermal bremsstrahlung with an average temperature of ~22 keV. Recently, eleven (ten intermediate polars and one polar) of these systems have been followed-up by Swift/XRT (operating in the 0.3-10 keV energy band), thus allowing us to investigate their spectral behaviour over the range ~0.3-100 keV. Thanks to this wide energy coverage, it was possible for these sources to simultaneously measure the soft and hard components and estimate their temperatures. The soft emission, thought to originate in the irradiated poles of the white dwarf atmosphere, is well described by a blackbody model with temperatures in the range ~60-120 eV. The hard emission, which is supposed to be originated from optically thin plasma in the post-shock region above the magnetic poles, is indeed well modelled with a bremsstrahlung model with temperatures in the range ~16-33 keV, similar to the values obtained from the INTEGRAL data alone. In several cases we also find the presence of a complex absorber: one totally (with NH ~(0.4-28) x 10^{21} cm^{-2}) and one partially (with NH ~(0.7-9) x 10^{23} cm^{-2}) covering the source. Only in four cases (V709 Cas, GK Per, IGR J06253+7334 and IGR J17303-0601), we find evidence for the presence of an iron line at 6.4 keV. We discuss our findings in the light of the systems parameters and cataclysmic variables/intermediate polars modelling scenario., Comment: 16 pages, including 6 figures and 5 tables. Accepted for publication in MNRAS

We report time-resolved imaging UV photometry of Comet 9P/Tempel 1 during the interval 2005 June 29–2005 July 21, including intensive coverage of the collision with the Deep Impact probe and its immediate aftermath. The nuclear flux of the comet begins to rise within minutes of the collision, and peaks about 3 h after impact. There is no evidence for a prompt flash at the time of impact. The comet exhibits a significant re-brightening about 40 h after the initial outburst, consistent with the rotation period of the comet, with evidence for further periodic re-brightenings on subsequent rotations. Modelling of the brightness profile of the coma as a function of time suggests two distinct velocity systems in the ejecta, at de-projected expansion speeds of 190 and 550 m/s, which we suggest are due to dust and gas, respectively. There is a distinct asymmetry in the slower-moving (dust) component as a function of position angle on the sky. This is confirmed by direct imaging analysis, which reveals an expanding plume of material concentrated in the impact hemisphere. The projected expansion velocity of the leading edge of this plume, measured directly from the imaging data, is 190 m/s, consistent with the velocity of the dust component determined from the photometric analysis. From our data we determine that a total of ( 1.4 ± 0.2 ) × 10 32 water molecules were ejected in the impact, together with a total scattering area of dust at 300 nm of 190 ± 20 km 2 .

Over the past decade, long-duration gamma-ray bursts (GRBs)--including the subclass of X-ray flashes (XRFs)--have been revealed to be a rare variety of type Ibc supernova. Although all these events result from the death of massive stars, the electromagnetic luminosities of GRBs and XRFs exceed those of ordinary type Ibc supernovae by many orders of magnitude. The essential physical process that causes a dying star to produce a GRB or XRF, and not just a supernova, is still unknown. Here we report radio and X-ray observations of XRF 060218 (associated with supernova SN 2006aj), the second-nearest GRB identified until now. We show that this event is a hundred times less energetic but ten times more common than cosmological GRBs. Moreover, it is distinguished from ordinary type Ibc supernovae by the presence of 10(48) erg coupled to mildly relativistic ejecta, along with a central engine (an accretion-fed, rapidly rotating compact source) that produces X-rays for weeks after the explosion. This suggests that the production of relativistic ejecta is the key physical distinction between GRBs or XRFs and ordinary supernovae, while the nature of the central engine (black hole or magnetar) may distinguish typical bursts from low-luminosity, spherical events like XRF 060218.

We present the results of X-ray and optical observations of GRB050712 performed by Swift. The X-ray lightcurve of this burst exhibits episodes of flares in the first 1000s, the same epoch at which the UVOT detected an optical counterpart. A shallow X-ray decay, with a decay slope of -0.73, followed and lasted ~70ks. This behaviour can be explained in terms of activity of GRB 'inner engine', with the possibility of that the last flare is caused by the interaction of the ejecta with the surrounding medium. We also find interesting spectral parameters for the X-ray emission. In particular, data suggest the presence of an intrinsic absorption in the first 1000s, which can be explained if circumbust medium clouds lie along the line of sight.

The power-law decay of the X-ray emission of gamma-ray burst (GRB) afterglows 050319, 050401, 050607, 050713A, 050802 and 050922C exhibits a steepening at about 1-4 h after the burst which, surprisingly, is not accompanied by a break in the optical emission. If it is assumed that both the optical and X-ray afterglows arise from the same outflow then, in the framework of the standard forward shock model, the chromaticity of the X-ray light-curve breaks indicates that they do not arise solely from a mechanism related to the outflow dynamics (e.g. energy injection) or the angular distribution of the blast-wave kinetic energy (structured outflows or jets). The lack of a spectral evolution accompanying the X-ray light-curve break shows that these breaks do not arise from the passage of a spectral break (e.g. the cooling frequency) either. Under these circumstances, the decoupling of the X-ray and optical decays requires that the microphysical parameters for the electron and magnetic energies in the forward shock evolve in time, whether the X-ray afterglow is synchrotron or inverse-Compton emission. For a steady evolution of these parameters with the Lorentz factor of the forward shock and an X-ray light curve arising cessation of energy injection into the blast wave, the optical and X-ray properties of the above six Swift afterglows require a circumburst medium with a r -2 radial stratification, as expected for a massive star origin for long GRBs. Alternatively, the chromatic X-ray light-curve breaks may indicate that the optical and X-ray emissions arise from different outflows. Neither feature (evolution of microphysical parameters or the different origin of the optical and X-ray emissions) was clearly required by pre-Swift afterglows.

Supernova remnant N49 in the Large Magellanic Cloud has been observed with the Chandra X-ray Observatory . The superb angular resolution of the Chandra images resolves the diffuse filaments and knots across the remnant as well as the point source, the X-ray counterpart of soft γ-ray repeater SGR 0526-66. We detect metal-rich ejecta beyond the main shock boundary in the southwest of the remnant, which appear to be the supernova explosion fragments ejected from the progenitor star. The X-ray spectral features of N49 suggest that the post-shock regions in the east might have been reheated by the reverse shock off the dense clouds, while the blast wave shock front has decelerated as it propagates into the clouds. The X-ray spectrum of the detected point source can be described with a power law ( Γ ∼3), This confirms the conclusive detection of the X-ray counterpart of SGR 0526-66 in the quiescent state.

NASA's MIDEX program provides frequent flight opportunities for scientific investigations from space for missions of cost up to $140M (FY1998), including launch, spacecraft, instruments, ground systems, operations and data analysis. The launch rate is approximately one per year, with selection of two missions occurring every two years. The program covers all areas of space science, excluding interplanetary probes. Mission selections to date include MAP (microwave background), IMAGE (magnetospheric imager), Swift (gamma-ray bursts) and FAME (astrometric survey).