A. J. Blustin

University of Cambridge, Cambridge, ENG, United Kingdom

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Publications (158)382.28 Total impact

  • Source
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    ABSTRACT: We observed Mrk 509 during the fall of 2009 during a multiwavelength campaign using XMM-Newton, Chandra, HST/COS, SWIFT, and Integral. The 600-ks XMM/RGS spectrum finds two kinematic components and a discrete distribution of ionized absorbers. Our high S/N COS spectrum detects additional complexity in the known UV absorption troughs from a variety of sources in Mrk 509, including the outflow from the active nucleus, the ISM and halo of the host galaxy, and infalling clouds or stripped gas from a merger that are illuminated by the AGN. The UV absorption only partially covers the emission from the AGN nucleus with covering fractions lower than those previously seen with STIS, and are comparable to those seen with FUSE. Given the larger apertures of COS and FUSE compared to STIS, we favor scattered light from an extended region near the AGN as the explanation for the partial covering. As observed in prior X-ray and UV spectra, the UV absorption has velocities comparable to the X-ray absorption, but the bulk of the ultraviolet absorption is in a lower ionization state with lower total column density than the gas responsible for the X-ray absorption. Variability compared to prior UV spectra lets us set limits on the location, density, mass flux, and kinetic energy of the outflowing gas. For component 1 at $-400 \rm km s^{-1}$, the kinetic energy flux of both the UV and the X-ray outflow is insufficient to have a significant impact on further evolution of the host galaxy.
    01/2012;
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    ABSTRACT: There exists a significant population of broad line, z∼ 2 quasi-stellar objects (QSOs) which have heavily absorbed X-ray spectra. Follow-up observations in the submillimetre show that these QSOs are embedded in ultraluminous starburst galaxies, unlike most unabsorbed QSOs at the same redshifts and luminosities. Here we present X-ray spectra from XMM–Newton for a sample of five such X-ray-absorbed QSOs that have been detected at submillimetre wavelengths. We also present spectra in the rest-frame ultraviolet from ground-based telescopes. All the five QSOs are found to exhibit strong C iv absorption lines in their ultraviolet spectra with equivalent width >5 Å. The X-ray spectra are inconsistent with the hypothesis that these objects show normal QSO continua absorbed by low-ionization gas. Instead, the spectra can be modelled successfully with ionized absorbers, or with cold absorbers if they possess unusually flat X-ray continuum shapes and unusual optical to X-ray spectral energy distributions. We show that the ionized absorber model provides the simplest, most self-consistent explanation for their observed properties. We estimate that the fraction of radiated power that is converted into kinetic luminosity of the outflowing winds is typically ∼4 per cent, in agreement with recent estimates for the kinetic feedback from QSOs required to produce the M–σ relation, and consistent with the hypothesis that the X-ray-absorbed QSOs represent the transition phase between obscured accretion and the luminous QSO phase in the evolution of massive galaxies.
    Monthly Notices of the Royal Astronomical Society 08/2011; 416(4):2792 - 2801. · 5.52 Impact Factor
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    ABSTRACT: We present the analysis of XMM-Newton and Swift optical-UV and X-ray observations of the Seyfert-1/QSO Mrk 509, part of an unprecedented multi-wavelength campaign, investigating the nuclear environment of this AGN. The XMM-Newton data are from a series of 10 observations of about 60 ks each, spaced from each other by about 4 days, taken in Oct-Nov 2009. During our campaign, Mrk 509 was also observed with Swift for a period of about 100 days, monitoring the behaviour of the source before and after the XMM-Newton observations. With these data we have established the continuum spectrum in the optical-UV and X-ray bands and investigated its variability on the timescale of our campaign with a resolution time of a few days. In order to measure and model the continuum as far as possible into the UV, we also made use of Hubble Space Telescope (HST) Cosmic Origin Spectrograph (COS) observations of Mrk 509 (part of our coordinated campaign) and of an archival Far Ultraviolet Spectroscopic Explorer (FUSE) observation. We have found that in addition to an X-ray power-law, the spectrum displays soft X-ray excess emission below 2 keV, which interestingly varies in association with the thermal optical-UV emission from the accretion disc. The change in the X-ray power-law component flux (albeit smaller than that of the soft excess), on the other hand, is uncorrelated to the flux variability of the soft X-ray excess and the disc component on the probed timescale. The results of our simultaneous broad-band spectral and timing analysis suggest that, on a resolution time of a few days, the soft X-ray excess of Mrk 509 is produced by the Comptonisation of the thermal optical-UV photons from the accretion disc by a warm (0.2 keV) optically thick (τ ∼ 17) corona surrounding the inner regions of the disc. This makes Mrk 509, with a black hole mass of about 1–3 ×10 8 M ⊙ , the highest mass known system to display such behaviour and origin for the soft X-ray excess.
    Astronomy and Astrophysics 08/2011; 534. · 5.08 Impact Factor
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    ABSTRACT: (Abridged) Active galactic nuclei show a wealth of interesting physical processes, some of which are poorly understood. We want to address a number of open questions, including the location and physics of the outflow from AGN, the nature of the continuum emission, the geometry and physical state of the X-ray broad emission line region, the Fe-K line complex, the metal abundances of the nucleus and finally the interstellar medium of our own Galaxy. We study one of the best targets for these aims, the Seyfert 1 galaxy Mrk 509 with a multiwavelength campaign using five satellites (XMM-Newton, INTEGRAL, Chandra, HST and Swift) and two ground-based facilities (WHT and PAIRITEL). Our observations cover more than five decades in frequency, from 2 um to 200 keV. The combination of high-resolution spectroscopy and time variability allows us to disentangle and study the different components. Our campaign covers 100 days from September to December 2009, and is centred on a simultaneous set of deep XMM-Newton and INTEGRAL observations with regular time intervals, spanning seven weeks. We obtain a continuous light curve in the X-ray and UV band, showing a strong, up to 60% flux increase in the soft X-ray band during the three weeks in the middle of our deepest monitoring campaign, and which is correlated with an enhancement of the UV flux. This allows us to study the time evolution of the continuum and the outflow. By stacking the observations, we have also obtained one of the best X-ray and UV spectra of a Seyfert galaxy ever obtained. In this paper we also study the effects of the spectral energy distribution (SED) that we obtained on the photo-ionisation equilibrium. Thanks to our broad-band coverage, uncertainties on the SED do not strongly affect the determination of this equilibrium.
    Astronomy and Astrophysics 07/2011; 534. · 5.08 Impact Factor
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    ABSTRACT: We present medium resolution (R~20,000) HST/COS ultraviolet spectra covering 1155-1760 A of the Seyfert 1 Mrk 509 obtained simultaneously with a Chandra/LETGS spectrum as part of a multiwavelength campaign in 2009 that included observations with XMM-Newton, SWIFT, and Integral. Our high S/N spectrum detects additional complexity in the absorption troughs from a variety of sources in Mrk 509, including the outflow from the active nucleus, the ISM and halo of the host galaxy, and infalling clouds or stripped gas from a merger that are illuminated by the AGN. Variability between the STIS and COS observation of the -400 km/s component allows us to set an upper limit on its distance of < 250 pc. Similarly, variability of a component at +150 km/s between two prior FUSE observations limits its distance to < 1.5 kpc. The UV absorption only partially covers the emission from the AGN nucleus. Covering fractions are lower than those previously seen with STIS, and are comparable to those seen with FUSE. Given the larger apertures of COS and FUSE compared to STIS, we favor scattered light from an extended region near the AGN as the explanation for the partial covering. As observed in prior X-ray and UV spectra, the UV absorption has velocities comparable to the X-ray absorption, but the bulk of the ultraviolet absorption is in a lower ionization state with lower total column density than the gas responsible for the X-ray absorption. We conclude that the outflow from the active nucleus is a multiphase wind.
    Astronomy and Astrophysics 07/2011; 534. · 5.08 Impact Factor
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    ABSTRACT: There exists a significant population of broad line, z~2 QSOs which have heavily absorbed X-ray spectra. Follow up observations in the submillimetre show that these QSOs are embedded in ultraluminous starburst galaxies, unlike most unabsorbed QSOs at the same redshifts and luminosities. Here we present X-ray spectra from XMM-Newton for a sample of 5 such X-ray absorbed QSOs that have been detected at submillimetre wavelengths. We also present spectra in the restframe ultraviolet from ground based telescopes. All 5 QSOs are found to exhibit strong C IV absorption lines in their ultraviolet spectra with equivalent width > 5 Angstroms. The X-ray spectra are inconsistent with the hypothesis that these objects show normal QSO continua absorbed by low-ionization gas. Instead, the spectra can be modelled successfully with ionized absorbers, or with cold absorbers if they posess unusually flat X-ray continuum shapes and unusual optical to X-ray spectral energy distributions. We show that the ionized absorber model provides the simplest, most self-consistent explanation for their observed properties. We estimate that the fraction of radiated power that is converted into kinetic luminosity of the outflowing winds is typically ~4 per cent, in agreement with recent estimates for the kinetic feedback from QSOs required to produce the M - sigma relation, and consistent with the hypothesis that the X-ray absorbed QSOs represent the transition phase between obscured accretion and the luminous QSO phase in the evolution of massive galaxies.
    06/2011;
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    ABSTRACT: The Ultraviolet/Optical Telescope (UVOT) is one of three instruments onboard the Swift observatory. The photometric calibration has been published, and this paper follows up with details on other aspects of the calibration including a measurement of the point spread function with an assessment of the orbital variation and the effect on photometry. A correction for large-scale variations in sensitivity over the field of view is described, as well as a model of the coincidence loss which is used to assess the coincidence correction in extended regions. We have provided a correction for the detector distortion and measured the resulting internal astrometric accuracy of the UVOT, also giving the absolute accuracy with respect to the International Celestial Reference System. We have compiled statistics on the background count rates, and discuss the sources of the background, including instrumental scattered light. In each case, we describe any impact on UVOT measurements, whether any correction is applied in the standard pipeline data processing or whether further steps are recommended.
    Monthly Notices of the Royal Astronomical Society 06/2010; 406(3):1687 - 1700. · 5.52 Impact Factor
  • 01/2010;
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    ABSTRACT: The origin of the extremely soft (low temperature) X-rays produced in the supersoft X-ray sources (or SSS) has been a subject of debate for much of the 25 years since their discovery. The currently accepted paradigm is that they are Eddington-limited accreting white dwarfs in which the accreted material is undergoing steady nuclear burning, thereby achieving the high luminosities recorded from the brightest SSS in the Magellanic Clouds. Such a model requires an extremely high mass transfer rate from the donor, only achievable via thermally unstable mass transfer from a massive (>1 M⊙) donor. An ideal SSS to probe this model in detail is the (only) recurrent, transient SSS, RX J0513.9-6951 which outbursts in X-rays every 100–150 days for a month or so, but is accompanied by a substantial (∼1 mag) optical decline. Using XMM we have obtained simultaneous soft X-ray, UV and optical observations through such an event, showing that as the X-ray flux declines the temperature declines as well (moving the peak emission into the UV) whereas the optical flux and (implied) white dwarf radius increase. Such an expansion of the white dwarf is evidenced by highly ionised outflowing gas in the high resolution X-ray spectra.
    New Astronomy Reviews 01/2010; · 1.82 Impact Factor
  • G. Branduardi-Raymont, A. Blustin
    09/2009;
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    A. J. Blustin, A. C. Fabian
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    ABSTRACT: We use a 380 ks XMM-Newton high-resolution RGS spectrum to look for narrow spectral features from the nuclear environment of 1H0707-495. We do not find any evidence of a line-of-sight ionized wind (warm absorber). We do, however, detect broad emission lines, of width ~5000 km s^-1, consistent with O VIII Ly-alpha, N VII Ly-alpha, C VI Ly-alpha and a Fe XIX/Fe XX/Ne IX He-alpha blend. Intriguingly, these lines have both blueshifted and redshifted components, whose velocity shifts are consistent with an origin in an accretion disc at ~1600 R_g from the black hole. The features can be interpreted as the narrow line cores of the disc reflection spectrum, thus providing independent support for the discline interpretation of the X-ray spectrum of 1H0707-495. We discuss the relevance of our findings for the `X-ray broad line region' in other Seyferts, and for the origins of the optical broad line region itself. Comment: 5 pages, 4 figures, accepted by MNRAS Letters
    Monthly Notices of the Royal Astronomical Society 08/2009; · 5.52 Impact Factor
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    ABSTRACT: Since the 1995 discovery of the broad iron K-line emission from the Seyfert galaxy MCG-6-30-15 (ref. 1), broad iron K lines have been found in emission from several other Seyfert galaxies, from accreting stellar-mass black holes and even from accreting neutron stars. The iron K line is prominent in the reflection spectrum created by the hard-X-ray continuum irradiating dense accreting matter. Relativistic distortion of the line makes it sensitive to the strong gravity and spin of the black hole. The accompanying iron L-line emission should be detectable when the iron abundance is high. Here we report the presence of both iron K and iron L emission in the spectrum of the narrow-line Seyfert 1 galaxy 1H 0707-495. The bright iron L emission has enabled us to detect a reverberation lag of about 30 s between the direct X-ray continuum and its reflection from matter falling into the black hole. The observed reverberation timescale is comparable to the light-crossing time of the innermost radii around a supermassive black hole. The combination of spectral and timing data on 1H 0707-495 provides strong evidence that we are witnessing emission from matter within a gravitational radius, or a fraction of a light minute, from the event horizon of a rapidly spinning, massive black hole.
    Nature 06/2009; 459(7246):540-2. · 38.60 Impact Factor
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    ABSTRACT: Since the discovery of the first broad iron-K line in 1995 from the Seyfert Galaxy MCG--6-30-15, broad iron-K lines have been found in several other Seyfert galaxies, from accreting stellar mass black holes and even from accreting neutron stars. The iron-K line is prominent in the reflection spectrum created by the hard X-ray continuum irradiating dense accreting matter. Relativistic distortion of the line makes it sensitive to the strong gravity and spin of the black hole. The accompanying iron-L line emission should be detectable when the iron abundance is high. Here we report the first discovery of both iron-K and L emission, using XMM-Newton observations of the Narrow-Line Seyfert 1 Galaxy 1H0707-495. The bright Fe-L emission has enabled us, for the first time, to detect a reverberation lag of 30 s between the direct X-ray continuum and its reflection from matter falling into the hole. The observed reverberation timescale is comparable to the light-crossing time of the innermost radii around a supermassive black hole. The combination of spectral and timing data on 1H0707-495 provides strong evidence that we are witnessing emission from matter within a gravitational radius, or a fraction of a light-minute, from the event horizon of a rapidly-spinning, massive black hole. Comment: To appear in Nature May 28 2009, 12 pages with 11 figures
    05/2009;
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    A. J. Blustin, A. C. Fabian
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    ABSTRACT: The calculation of mass outflow rates of AGN winds is of great importance in understanding the role that such winds play in AGN-galaxy feedback processes. The mass outflow rates are, however, difficult to estimate since the volume filling factors of the winds are unknown. In this paper, we use constraints imposed by the observed radio emission to obtain upper limits to the volume filling factors of wind components in certain nearby AGN. We do this by predicting the 1.4 GHz radio flux densities emitted by those components, assuming a uniform wind, and then comparing these with the observed flux densities for each AGN at this frequency. We find that the upper limits to the volume filling factors are in the range 10^{-4}-0.5.
    Monthly Notices of the Royal Astronomical Society 05/2009; · 5.52 Impact Factor
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    ABSTRACT: We present observations of GRB 050318 by the Ultraviolet/Optical Telescope (UVOT) on board the Swift observatory. The data are the first detections of a gamma-ray burst (GRB) afterglow decay by the UVOT instrument, launched specifically to open a new window on these transient sources. We showcase UVOT's ability to provide multicolor photometry and the advantages of combining UVOT data with simultaneous and contemporaneous observations from the high-energy detectors on the Swift spacecraft. Multiple filters covering 1800-6000 Å reveal a red source with a spectral slope steeper than the simultaneous X-ray continuum. Spectral fits indicate that the UVOT colors are consistent with dust extinction by systems at z = 1.2037 and 1.4436, redshifts where absorption systems have been preidentified. However, the data can be most easily reproduced with models containing a foreground system of neutral gas redshifted by z = 2.8 ± 0.3. For both of the above scenarios, spectral and decay slopes are, for the most part, consistent with fireball expansion into a uniform medium, provided a cooling break occurs between the energy ranges of the UVOT and Swift's X-ray instrumentation.
    The Astrophysical Journal 12/2008; 635(2):1187. · 6.73 Impact Factor
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    ABSTRACT: A long 280 ks observation of the Seyfert 1 galaxy NGC 3783 with XMM-Newton is reported. We focus on the oxygen line complex between 17 and 24 Å as measured with the Reflection Grating Spectrometer. Accurate absorption column densities and emission-line fluxes are obtained. We explore several options for the geometry and physical form of the emitting and absorbing gas. The lack of change in ionization in the absorber despite an increase in continuum flux during the observation restricts the high-ionization (O-K) and the low-ionization (Fe-M) gas to distances of at least 0.5 and 2.8 pc, respectively, away from the central source. Given the P Cygni type profiles in the resonance spectral lines and the similar velocity widths, column densities, and ionization structure inferred separately from the emission and absorption lines, it is tempting to relate the X-ray narrow-line emitting plasma with the X-ray-absorbing gas. Under this assumption, the scenario of dense clumped clouds can be ruled out. Conversely, extended ionization cones (r 10 pc) are consistent with the observation independent of this assumption. These findings are in stark contrast to the picture of numerous clumpy (ne 109 cm-3) clouds drawn recently from UV spectra, but they are consistent with the extended X-ray emission cones observed directly in Seyfert 2 galaxies.
    The Astrophysical Journal 12/2008; 598(1):232. · 6.73 Impact Factor
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    ABSTRACT: The UVOT telescope on the Swift observatory has detected optical afterglow emission from GRB 050319. The flux declined with a power-law slope of α = -0.57 between the start of observations some 230 s after the burst onset (90 s after the burst trigger) until it faded below the sensitivity threshold of the instrument after ~5 × 104 s. There is no evidence for the rapidly declining component in the early light curve that is seen at the same time in the X-ray band. The afterglow is not detected in UVOT shortward of the B band, suggesting a redshift of about 3.5. The optical V-band emission lies on the extension of the X-ray spectrum, with an optical-to-X-ray slope of β = -0.8. The relatively flat decay rate of the burst suggests that the central engine continues to inject energy into the fireball for as long as a few × 104 s after the burst.
    The Astrophysical Journal 12/2008; 639(1):311. · 6.73 Impact Factor
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    ABSTRACT: In 2006 March the soft gamma-ray repeater SGR 1900+14 resumed its bursting activity after ~2 yr of quiescence. The Swift mission observed the source several times. We report on the intense burst "forest" recorded on March 29, which lasted for ~30 s, when Swift was pointing at the source with the narrow field of view instruments. More than 40 bursts were detected by BAT and XRT, 7 of which were rare intermediate flares (IFs). The BAT data were used to carry out time-resolved spectroscopy in the 14-100 keV range down to 8 ms timescales. BAT and XRT simultaneous data were used to characterize the broadband energy spectra of IFs and verify the results obtained from the BAT-only spectral fits. This unique data set allowed us to test the magnetar model predictions, such as the magnetically trapped fireball and twisted magnetosphere, over an unprecedented range of fluxes and with large statistics. We confirmed that a two-blackbody component adequately fits the time-resolved and integrated spectra of IFs. However, Comptonization models give comparably good reduced χ2. Moreover, we found a change of behavior, around ~1041 erg s−1, above which the softer blackbody shows a sort of saturation, while the harder one still grows to a few times 1041 erg s−1, and a rather sharp correlation between temperature and radii of the blackbodies (R2 kT−3), which holds for the most luminous parts of the flares (~Ltot ≥ 1041 erg s−1). Within the magnetar model, the majority of these findings are accounted for in terms of thermalized emission from the E-mode and O-mode photospheres. Interestingly, the maximum observed luminosity coming from a region of ~15 km matches the magnetic Eddington luminosity at the same radius, for a surface dipole field of ~8 × 1014 G (virtually equal to that deduced from the spin-down of SGR 1900+14).
    The Astrophysical Journal 12/2008; 685(2):1114. · 6.73 Impact Factor
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    ABSTRACT: We present ultraviolet and optical light curves in six broadband filters and grism spectra obtained by Swift's Ultraviolet/Optical Telescope for the Type Ia supernova SN 2005am. The data were collected beginning about 4 days before the B-band maximum, with excellent coverage of the rapid decline phase and later observations extending out to 69 days after the peak. The optical and near-UV light curve match well those of SN 1992A. The other UV observations constitute the first set of light curves shorter than 2500 Å and allow us to compare the light curve evolution in three UV bands. One interesting feature is that the decay in the intermediate UVM2 band is shallower than in the filters on either side and may result from the bump in the interstellar extinction curve. The UV behavior of this and other low-redshift supernovae can be used to constrain theories of progenitor evolution or to interpret optical light curves of high-redshift supernovae. Using Swift's X-Ray Telescope, we also report the upper limit to SN 2005am's X-ray luminosity to be 6 × 1039 ergs s-1 in the 0.3-10 keV. This result is derived from 58 ks of exposure time spread out over 7 weeks beginning 4 days before the B-band maximum.
    The Astrophysical Journal 12/2008; 635(2):1192. · 6.73 Impact Factor
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    ABSTRACT: We report early photospheric-phase observations of the Type IIP supernova (SN) 2005cs obtained by the Swift ultraviolet-optical and X-ray telescopes. Observations started within 2 days of discovery and continued on a regular basis for 3 weeks. During this time the V-band magnitude remained essentially constant, while the UV was initially bright, but steadily faded until below the brightness of an underlying UV-bright H II region. This UV decay is similar to SNe II observed by the International Ultraviolet Explorer. UV grism spectra show the P Cygni absorption of Mg II 2798 Å, indicating a photospheric origin of the UV flux. Based on non-LTE model atmosphere calculations with the CMFGEN code, we associate the rapid evolution of the UV flux with the cooling of the ejecta, the peak of the spectral energy distribution (SED) shifting from ~700 Å on June 30 to ~1200 Å on July 5. Furthermore, the corresponding recombination of the ejecta, e.g., the transition from Fe III to Fe II, induces a considerable strengthening of metal line-blanketing at and above the photosphere, blocking more and more effectively this fading UV flux. SN 2005cs was not detected in the X-ray band, and the upper limit to the X-ray luminosity yields a limit to the mass-loss rate of the progenitor of 1 × 10-5 yr-1 (vw/10 km s-1). Overall, Swift represents a unique opportunity to capture the early and fast evolution of Type II SNe in the UV, providing additional constraints on the reddening, the SED shortward of 4000 Å, and the ionization state and temperature of the photon-decoupling regions.
    The Astrophysical Journal 12/2008; 659(2):1488. · 6.73 Impact Factor

Publication Stats

907 Citations
382.28 Total Impact Points

Institutions

  • 2011–2012
    • University of Cambridge
      • Institute of Astronomy
      Cambridge, ENG, United Kingdom
  • 2004–2011
    • University College London
      • Department of Space and Climate Physics
      London, ENG, United Kingdom
  • 2007
    • UCL Eastman Dental Institute
      Londinium, England, United Kingdom
  • 2006
    • South African Astronomical Observatory
      Kaapstad, Western Cape, South Africa
    • Aarhus University
      • Department of Physics and Astronomy
      Aarhus, Central Jutland, Denmark
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
  • 2005
    • University of Southampton
      • Department of Physics and Astronomy
      Southampton, England, United Kingdom
    • University of Leicester
      • Department of Physics and Astronomy
      Leiscester, England, United Kingdom