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  • 1
    Electronic Resource
    Electronic Resource
    An optical supernova associated with the X-ray flash XRF 060218 (2006)
    [s.l.] : Nature Publishing Group
    Nature 442 (2006), S. 1011-1013 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Long-duration γ-ray bursts (GRBs) are associated with type Ic supernovae that are more luminous than average and that eject material at very high velocities. Less-luminous supernovae were not hitherto known to be associated with GRBs, and therefore GRB–supernovae were thought to be ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature05082
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    Paper (German National Licenses)
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  • 2
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    Symbiotic stars in OGLE data - I. Large Magellanic Cloud systems (2014)
    Oxford University Press
    Details
    Publication Date: 2014-01-16
    Description: Symbiotic stars are long-orbital-period interacting binaries characterized by extended emission over the whole electromagnetic range and by complex photometric and spectroscopic variability. In this paper, the first of a series, we present Optical Gravitational Lensing Experiment (OGLE) light curves of all the confirmed symbiotic stars in the Large Magellanic Cloud, with one exception. By careful visual inspection and combined time series analysis techniques, we investigate for the first time in a systematic way the photometric properties of these astrophysical objects, trying in particular to distinguish the nature of the cool component (e.g. semiregular Variable versus OGLE small-amplitude red giant), to provide its first-order pulsational ephemerides and to link all this information with the physical parameters of the binary system as a whole. Among the most interesting results, there is the discovery of a 20 yr-long steady fading of Sanduleak's star, a peculiar symbiotic star known to produce the largest stellar jet ever discovered. We discuss by means of direct examples the crucial need for long-term multi-band observations to get a real understanding of symbiotic and other interacting binary stars. We eventually introduce BOMBOLO, a multi-band simultaneous imager for the Southern Astrophysical Research 4 m Telescope, whose design and construction we are currently leading.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    On the nature of the hard X-ray sources SWIFT J1907.3-2050, IGR J12123-5802 and IGR J19552+0044 (2013)
    Oxford University Press
    Details
    Publication Date: 2013-10-12
    Description: The INTEGRAL and Swift hard X-ray surveys have identified a large number of new sources, among which many are proposed as Cataclysmic Variables (CVs). Here, we present the first detailed study of three X-ray-selected CVs, Swift J1907.3–2050, IGR J12123–5802 and IGR J19552+0044 based on XMM–Newton , Suzaku , Swift observations and ground-based optical and archival (near-IR) nIR/IR data. Swift J1907.3–2050 is highly variable from hours to months–years at all wavelengths. No coherent X-ray pulses are detected but rather transient features. The X-ray spectrum reveals a multitemperature optically thin plasma absorbed by complex neutral material and a soft blackbody component arising from a small area. These characteristics are remarkably similar to those observed in magnetic CVs. A supra-solar abundance of nitrogen could arise from nuclear processed material from the donor star. Swift J1907.3–2050 could be a peculiar magnetic CV with the second longest (20.82 h) binary period. IGR J12123–5802 is variable in the X-rays on a time-scale of 7.6 h. No coherent pulsations are detected, but its spectral characteristics suggest that it could be a magnetic CV of the Intermediate Polar (IP) type. IGR J19552+0044 shows two X-ray periods, ~1.38 h and ~1.69 h and an X-ray spectrum characterized by a multitemperature plasma with little absorption. We derive a low accretion rate, consistent with a CV below the orbital period gap. Its peculiar nIR/IR spectrum suggests a contribution from cyclotron emission. It could either be a pre-polar or an IP with the lowest degree of asynchronism.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Orbital period of Swift J1816.7-1613 revealed by the Swift Burst Alert Telescope (2014)
    Oxford University Press
    Details
    Publication Date: 2014-10-17
    Description: We have analysed the Swift data relevant to the high-mass X-ray binary Swift J1816.7–1613. The timing analysis of the Burst Alert Telescope survey data unveiled a modulation at a period of P 0  = 118.5 ± 0.8 d, which we interpret as the orbital period of the X-ray binary system. The modulation is the result of a sequence of bright flares, lasting ~30 d, separated by long quiescence intervals. This behaviour is suggestive of a Be binary system, where periodic or quasi-periodic outbursts are the consequence of an enhancement of the accretion flow from the companion star at the periastron passage. The position of Swift J1816.7–1613 on the Corbet diagram strengthens this hypothesis. The broad-band 0.2–150 keV spectrum is well modelled with a strongly absorbed power law with a flat photon index  ~ 0.2 and a cut-off at ~10 keV.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    A Swift view on IGR J19149+1036 (2014)
    Oxford University Press
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    Publication Date: 2014-11-16
    Description: IGR J19149+1036 is a high-mass X-ray binary detected by INTEGRAL in 2011 in the hard X-ray domain. We have analysed the Burst Alert Telescope (BAT) survey data of the first 103 months of the Swift mission detecting this source at a significance level of ~30 standard deviations. The timing analysis on the long-term BAT light curve reveals the presence of a strong sinusoidal intensity modulation of 22.25 ± 0.05 d, that we interpret as the orbital period of this binary system. A broad-band (0.3–150 keV) spectral analysis was performed combining the BAT spectrum and the X-Ray Telescope (XRT) spectra from the pointed follow-up observations. The spectrum is adequately modelled with an absorbed power law with a high-energy cutoff at ~24 keV and an absorption cyclotron feature at ~31 keV. Correcting for the gravitational redshift, the inferred magnetic field at the neutron star surface is B surf ~ 3.6 x 10 12 G.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Engulfing a radio pulsar: the case of PSR J1023+0038 (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-01
    Description: The binary millisecond radio pulsar PSR J1023+0038 has been recently the subject of multiwavelength monitoring campaigns which revealed that an accretion disc has formed around the neutron star (since 2013 June). We present here the results of X-ray and UV observations carried out by the Swift satellite between 2013 October and 2014 May, and of optical and NIR observations performed with the REM telescope, the Liverpool Telescope, the 2.1-m telescope at the San Pedro Mártir Observatory and the 1.52-m telescope at the Loiano observing station. The X-ray spectrum is well described by an absorbed power law, which is softer than the previous quiescent epoch (up to 2013 June). The strong correlation between the X-ray and the UV emissions indicates that the same mechanism should be responsible for part of the emission in these bands. Optical and infrared photometric observations show that the companion star is strongly irradiated. Double-peaked emission lines in the optical spectra provide compelling evidence for the presence of an outer accretion disc too. The spectral energy distribution from IR to X-rays is well modelled if the contributions from the companion, the disc and the intrabinary shock emission are all considered. Our extensive data set can be interpreted in terms of an engulfed radio pulsar: the radio pulsar is still active, but undetectable in the radio band due to a large amount of ionized material surrounding the compact object. X-rays and gamma-rays are produced in an intrabinary shock front between the relativistic pulsar wind and matter from the companion and an outer accretion disc. The intense spin-down power irradiates the disc and the companion star, accounting for the UV and optical emissions.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Finding a 61.0 d orbital period for the HMXB 4U 1036-56 with the Swift-BAT monitoring (2013)
    Oxford University Press
    Details
    Publication Date: 2013-11-23
    Description: Since 2004 November, the Burst Alert Telescope on board Swift is producing a monitoring of the entire sky in the 15–150 keV band, recording the timing and spectral behaviour of the detected sources. Here, we study the properties of the High mass X-ray binary (HMXB) 4U 1036–56 using both the BAT survey data and those from a Swift -X-ray Telescope (XRT) observation. A folding analysis performed on the BAT light curve of the first 100 months of survey unveils a periodic modulation with a period of ~61.0 d, tied to the presence in the BAT light curve of several intensity enhancements lasting ~1/4 of P 0 . We explain this modulation as the orbital period of the binary system. The position of 4U 1036–56 on the Corbet diagram, the derived semimajor orbit axis (~=180 R ) and the bulk of the source emission observed in a limited portion of the orbit are consistent with a Be companion star. The broad-band 0.2–150 keV spectrum is well modelled with a flat absorbed power law with a cutoff at ~16 keV. Finally, we explore the possible association of 4U 1036–56 with the -ray source AGL J1037–5808, finding that the BAT light curve does not show any correlation with the -ray outburst observed in 2012 November.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    BAT AGN Spectroscopic Survey - III. An observed link between AGN Eddington ratio and narrow-emission-line ratios (2016)
    Oxford University Press
    Details
    Publication Date: 2016-10-27
    Description: We investigate the observed relationship between black hole mass ( M BH ), bolometric luminosity ( L bol ) and Eddington ratio ( Edd ) with optical emission-line ratios ([N  ii ] 6583/Hα, [S  ii ] 6716, 6731/Hα, [O  i ] 6300/Hα, [O  iii ] 5007/Hβ, [Ne  iii ] 3869/Hβ and He  ii 4686/Hβ) of hard X-ray-selected active galactic nuclei (AGN) from the BAT AGN Spectroscopic Survey. We show that the [N  ii ] 6583/Hα ratio exhibits a significant correlation with Edd ( R Pear = –0.44, p -value = 3 x 10 –13 , = 0.28 dex), and the correlation is not solely driven by M BH or L bol . The observed correlation between [N  ii ] 6583/Hα ratio and M BH is stronger than the correlation with L bol , but both are weaker than the Edd correlation. This implies that the large-scale narrow lines of AGN host galaxies carry information about the accretion state of the AGN central engine. We propose that [N  ii ] 6583/Hα is a useful indicator of Eddington ratio with 0.6 dex of rms scatter, and that it can be used to measure Edd and thus M BH from the measured L bol , even for high-redshift obscured AGN. We briefly discuss possible physical mechanisms behind this correlation, such as the mass–metallicity relation, X-ray heating, and radiatively driven outflows.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Spectral evolution of the X-ray nova XTE J1859+226 during its outburst observed by BeppoSAX and RXTE (2013)
    Oxford University Press
    Details
    Publication Date: 2013-01-03
    Description: We report results of an extensive analysis of the X-ray nova XTE J1859+226 observed with BeppoSAX and the Rossi X-ray Timing Explorer during the 1999 source outburst. We modelled the source spectrum with a multicolour blackbody-like feature plus the generic Comptonization model bmc which has the advantage of providing spectral description of the emitted-radiation properties without assumptions on the underlying physical process. The multicolour component is attributed to the geometrically thin accretion disc, while the Comptonization spectrum is claimed to originate in the innermost sub-Keplerian region of the system (transition layer). We find that XTE J1859+226 covers all the spectral states typical of black hole sources during its evolution across the outburst; however, during the very high state, when the disc contribution to the total luminosity is more than 70 per cent and the root mean square variability 5 per cent, the high-energy photon index is closer to a hard state value ( ~ 1.8). The bmc normalization and photon index well correlate with the radio emission, and we also observed a possible saturation effect of at the brightest radio emission levels. A strong positive correlation was found between the fractions of Comptonized seed photons and the integrated root mean square variability, which strengthens the idea that most of the fast variability in these systems is attributable to the innermost Compton cloud, which may be also identified as a jet.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    CXOU J005047.9-731817: a 292-s X-ray binary pulsar in the Small Magellanic Cloud (2013)
    Oxford University Press
    Details
    Publication Date: 2013-07-26
    Description: We report on the discovery of a transient X-ray pulsar, located in the Small Magellanic Cloud, with a pulse period of 292 s. A series of Chandra pointings fortuitously recorded in 2010 April–May the occurrence of a two-weeks-long outburst, during which the source luminosity increased by a factor of about 100, reaching a peak of ~10 36 erg s –1 (for a distance of 61 kpc). Complex-shape and energy-dependent pulsations were detected close to the outburst peak and during the very first part of its decay phase. During the outburst, the phase-averaged spectrum of the pulsar was well described by an absorbed power law with photon index  ~ 0.6, but large variations as a function of phase were present. The source was also detected by Chandra several times (during 2002, 2003, 2006 and 2010) at a quiescent level of ~10 34 erg s –1 . In 2012, we performed an infrared photometric follow-up of the R  ~ 15 mag optical counterpart with the European Southern Observatory/Very Large Telescope and a spectroscopic observation by means of the CTIO telescope. The optical spectra suggest a late-Oe or early Be V–III luminosity-class star, though a more evolved companion cannot be ruled out by our data (we can exclude a luminosity class I and a spectral type later than B2). Finally, we show that the outburst's main parameters (duration and peak luminosity) can be accounted for by interpreting the source transient activity as a type I outburst in a Be X-ray binary.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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