Publications (11)0 Total impact
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Article: A Soft X‐ray Imager for MIRAX
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ABSTRACT: The flight spare model of the BeppoSAX Wide Field Cameras is being considered as the Soft X‐ray Imager for MIRAX. A description is provided of this instrument, the performance of its siblings on BeppoSAX, and the prospects of flying it on MIRAX. Like on BeppoSAX, the instrument on MIRAX will excel in the study of transient phenomena lasting shorter than 1 day. © 2006 American Institute of PhysicsAIP Conference Proceedings. 06/2006; 840(1):8-17. -
Chapter: Fast X-ray transients and x-ray flashes
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ABSTRACT: Not Available04/2006: pages 267-278; , ISBN: 978-0-521-82659-4; 0-521-82659-4 -
Article: Two-phase X-ray burst from GX 3+1 observed by INTEGRAL
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ABSTRACT: INTEGRAL detected on August 31, 2004, an unusual thermonuclear X-ray burst from the low-mass X-ray binary GX 3+1. Its duration was 30 min, which is between the normal burst durations for this source (<~10 s) and the superburst observed in 1998 (several hours). We see emission up to 30 keV energy during the first few seconds of the burst where the bolometric peak luminosity approaches the Eddington limit. This peculiar burst is characterized by two distinct phases: an initial short spike of ~6 s consistent with being similar to a normal type I X-ray burst, followed by a remarkable extended decay of cooling emission. We discuss three alternative schemes to explain its twofold nature: 1) unstable burning of a hydrogen/helium layer involving an unusually large amount of hydrogen, 2) pure helium ignition at an unusually large depth (unlikely in the present case), and 3) limited carbon burning at an unusually shallow depth triggered by unstable helium ignition. Though none of these provide a satisfactory description of this uncommon event, the former one seems the most probable. Comment: A&A class LateX file, 5 pages, 4 postscript figures. Accepted in Astronomy & Astrophysics Letters. One co-author added, modified abstract and improved conclusions12/2005; -
Article: A BeppoSAX-WFC viewpoint of new INTEGRAL sources, particularly IGR J17544-2619
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ABSTRACT: Of the 21 new sources that INTEGRAL discovered up to Feb. 1, 2004, five were detected with the BeppoSAX Wide Field Cameras at earlier times. IGR J16320-4751 appears to be a persistently active X-ray source which hints at a supergiant Roche-lobe overflowing companion star in this proposed high-mass X-ray binary. IGR J17091-3624 is a transient source that was detected in 1996 and 2001 with a maximum flux of 20 mCrab (2-28 keV). It is either a Be X-ray binary or a low mass X-ray binary transient. IGR J18483-0311 may be a high-mass X-ray binary, because it is located in a region rich of such objects, just like IGR J19140+098. IGR J17544-2619 appears to be a frequently active X-ray source whose hours-long flares, of which WFC detected five, are reminiscent of the stellar black hole source V4641 Sgr. We discuss this source in detail.08/2004; -
Article: BeppoSAX-WFC monitoring of the Galactic Center region
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ABSTRACT: We review the results obtained with the Galactic center campaigns of the BeppoSAX Wide Field X-ray Cameras (WFCs). This pertains to the study of luminous low-mass X-ray binaries (LMXBs). When pointed at the Galactic center, the WFC field of view contains more than half of the Galactic LMXB population. The results exemplify the excellent WFC capability to detect brief X-ray transients. Firstly, the WFCs expanded the known population of Galactic thermonuclear X-ray bursters by 50%. At least half of all LMXBs are now established to burst and, thus, to contain a neutron star as compact accretor rather than a black hole candidate. We provide a complete list of all 76 currently known bursters, including the new case 1RXS J170854.4-321857. Secondly, the WFCs have uncovered a population of weak transients with peak luminosities up to ~10^37 erg/s and durations from days to weeks. One is the first accretion-powered millisecond pulsar SAX J1808.4-3658. Thirdly, the WFCs contributed considerably towards establishing that nearly all (12 out of 13) luminous low-mass X-ray binaries in Galactic globular clusters contain neutron stars rather than black holes. Thus, the neutron star to black hole ratio in clusters differs from that in the Galactic disk at a marginal confidence level of 97%. Comment: 10 pages 6 figures, to appear in Proc. "The Restless High-Energy Universe" (2nd BeppoSAX Symposium), eds. E.P.J. van den Heuvel, J.J.M. in 't Zand & R.A.M.J. Wijers, Nucl. Instrum. Meth. B Suppl. Ser03/2004; -
Article: X-ray spectral and timing properties of the 2001 superburst of 4U 1636-536
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ABSTRACT: Preliminary results are reported on the spectral and timing properties of the spectacular 2001 superburst of 4U 1636-536 as seen by the RXTE/PCA. The (broad-band) power-spectral and hardness properties during the superburst are compared to those just before and after the superburst. Not all of the superburst emission can be fitted by pure black-body radiation. We also gathered BeppoSAX/WFC and RXTE/ASM data, as well as other RXTE/PCA data, obtained days to months before and after the superburst to investigate the normal X-ray burst behavior around the time of the superburst. The first normal X-ray burst after the 2001 superburst was detected 23 days later. During inspection of all the RXTE/ASM data we found a third superburst. This superburst took place on June 26, 1999, which is ~2.9 yrs after the 1996 superburst and ~1.75 yrs before the 2001 superburst. The above findings are the strongest constraints observed so far on the duration of the cessation of normal X-ray bursts after a superburst and the superburst recurrence times. Comment: 4 pages, 4 figures,to appear in the proceedings of "X-Ray Timing 2003: Rossi and Beyond", eds. P. Kaaret, F.K. Lamb, & J.H. Swank (Melville, NY: AIP)02/2004; -
Article: X-ray Bursts from the Accreting Millisecond Pulsar XTE J1814-338
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ABSTRACT: Since the discovery of the accreting millisecond pulsar XTE J1814-338 a total of 27 thermonuclear bursts have been observed from the source with the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE). Spectroscopy of the bursts, as well as the presence of continuous burst oscillations, suggests that all but one of the bursts are sub-Eddington. The remaining burst has the largest peak bolometric flux of 2.64 x E^-8 erg/sec/cm^2, as well as a gap in the burst oscillations, similar to that seen in Eddington limited bursts from other sources. Assuming this burst was Eddington limited we obtain a source distance of about 8 kpc. All the bursts show coherent oscillations at the 314.4 Hz spin frequency. The burst oscillations are strongly frequency and phase locked to the persistent pulsations. Only two bursts show evidence for frequency drift in the first few seconds following burst onset. In both cases the initial drift corresponds to a spin down of a few tenths of a Hz. The large oscillation amplitude during the bursts confirms that the burst flux is modulated at the spin frequency. We detect, for the first time, a significant first harmonic component in burst oscillations. The ratio of countrate in the first harmonic to that in the fundamental can be > 0.25 and is, on average, less than that of the persistent pulsations. If the pulsations result from a single bright region on the surface, the harmonic strength suggests the burst emission is beamed, perhaps due to a stronger magnetic field than in non-pulsing LMXBs. Alternatively, the harmonic content could result from a geometry with two bright regions. Comment: AASTeX, 15 pages, 4 figures. Accepted for publication in the Astrophysical Journal Letters08/2003; -
Article: X-ray Transients from X-ray Binaries to Gamma Ray Bursts
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ABSTRACT: We discuss three classes of x-ray transients to highlight three new types of transients found with the Wide Field Cameras onboard BeppoSAX. First there are the transients related to Low Mass X-ray Binaries in outburst, typically lasting weeks to months and reaching luminosities of the Eddington limit for a few solar masses. Recently another subclass of outbursts in such binaries has been discovered, which are an order of magnitude fainter and last shorter than typical hours to days. We discuss whether they constitute a separate subset of x-ray binaries. A second class of x-ray transients are the x-ray bursts. Thermonuclear explosions on a neutron star (type I x-ray bursts) usually last of order minutes or less. We discovered a second type (called super x-ray bursts) with a duration of several hours. They relate to thermonuclear detonations much deeper in the neutron star atmosphere, possibly burning on the nuclear ashes of normal x-ray bursts. The third class are the enigmatic Fast X-ray Transients occurring at all galactic latitudes. We found that the bright ones are of two types only: either nearby coronal sources (lasting hours) or the socalled x-ray flashes (lasting minutes). The new class, the X-ray flashes, may be a new type of cosmic explosion, intermediate between supernovae and gamma ray bursts, or they may be highly redshifted gamma ray bursts. It thus appears that the three classes of x-ray transients each come in two flavors: long and short.01/2002; -
Article: X-ray flashes and X-ray rich Gamma Ray Bursts
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ABSTRACT: X-ray flashes are detected in the Wide Field Cameras on BeppoSAX in the energy range 2-25 keV as bright X-ray sources lasting of the order of minutes, but remaining undetected in the Gamma Ray Bursts Monitor on BeppoSAX. They have properties very similar to the x-ray counterparts of GRBs and account for some of the Fast X-ray Transient events seen in almost every x-ray satellite. We review their X-ray properties and show that x-ray flashes are in fact very soft, x-ray rich, untriggered gamma ray bursts, in which the peak energy in 2-10 keV x-rays could be up to a factor of 100 larger than the peak energy in the 50-300 keV gamma ray range. The frequency is ~100 per year. Comment: 6 pages, 3 figures (2 in color), to appear in the proceedings of the October 2000 Rome Workshop on ``Gamma-Ray Bursts in the Afterglow Era''11/2001; -
Article: Very low luminosities from the accretion-driven millisecond X-ray pulsar SAX J1808.4-3658 during quiescence
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ABSTRACT: We have observed the millisecond X-ray pulsar SAX J1808.4-3658 on three occasions during its 2000 outburst with the BeppoSAX satellite. The source was highly variable and erratic during this outburst, and by coincidence we obtained data only during times when the source had very low luminosities. During our observations, we detected four faint sources. The source closest to the position of SAX J1808.4-3658 is still ~1.6' away. This source can only be identified with SAX J1808.4-3658 if we assume that the BeppoSAX positional reconstruction is not completely understood. We also reanalyzed a BeppoSAX observation taken in March 1999 when the source was in quiescence and during which the source was thought to have been detected (Stella et al. 2000). Based on the similarities (position and luminosity) of this source with the above mentioned source ~1.6' away from SAX J1808.4-3658, it is possible that they are the same source. If this source is not the millisecond pulsar, then during all BeppoSAX observations of SAX J1808.4-3658 (the 2000 outburst ones and the 1999 quiescent one), the millisecond pulsar was not detected. A reanalysis of the ASCA quiescent data of SAX J1808.4-3658 (Dotani, Asai, & Wijnands 2000) confirms that during this observation the source was securely detected in quiescence. We discuss our results for SAX J1808.4-3658 in the context of the quiescent properties of low-mass X-ray binary transients. Comment: Accepted for publication by ApJ Main Journal, 30 January 200205/2001; -
Article: The Corrected Log N-Log Fluence Distribution of Cosmological Gamma-Ray Bursts
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ABSTRACT: Recent analysis of relativistically expanding shells of cosmological gamma-ray bursts has shown that if the bursts are cosmological, then most likely total energy (E_0) is standard and not peak luminosity (L_0). Assuming a flat Friedmann cosmology (q_o = 1/2, Lambda = 0) and constant rate density (rho_0) of bursting sources, we fit a standard candle energy to a uniformly selected log N-log S in the BATSE 3B catalog correcting for fluence efficiency and averaging over 48 observed spectral shapes. We find the data consistent with E_0 = 7.3^{+0.7}_{-1.0} X 10^{51} ergs and discuss implications of this energy for cosmological models of gamma-ray bursts. Comment: A five page LateX file that uses the Revtex conference proceedings macro aipbook.sty, and includes three postscript figures using psfig. To Be published in the Proceedings of the Third Hunstville Symposium on Gamma-Ray Bursts, eds. C. Kouveliotou, M.S. Briggs and G.J. Fishman (New York:AIP). Postscript version availible at http://nis-www.lanl.gov/~jsbloom/LOG_S.ps04/1996;
Top co-authors
Institutions
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2006
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Netherlands Institute for Space Research, Utrecht
Utrecht, Provincie Utrecht, Netherlands
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2005
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Universiteit Utrecht
Utrecht, Provincie Utrecht, Netherlands
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