The INTEGRAL Galactic bulge monitoring program: the first 1.5 years

Kuulkers, E.; Shaw, S. E.; Paizis, A.; Chenevez, J.; Brandt, S.; Courvoisier, T. J. L.; Domingo, A.; Ebisawa, Ken; Kretschmar, P.; Markwardt, C. B.; Mowlavï, N.; Oosterbroek, T.; Orr, A.; Rísquez, D.; Sánchez–Fernández, C.; Wijnands, Rudy

doi:10.1051/0004-6361:20066651

Cited by 100 publications

(112 citation statements)

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“…However, the observed behavior is far from being satisfactorily interpreted within the current bursting theory due to the presence of unexpected short bursts or even absence thereof, in a regime where long bursts would be expected (Kuulkers et al 2007). The reason of this could be that in the case of high accretion rates accretion is unlikely through a plain disk, and the TL configuration may have an extra effect on the bursting behavior.…”

Section: Discussionmentioning

confidence: 83%

“…Indeed a hard tail in the spectra of GX 5−1 had already been detected by previous observations (Asai et al 1994;Paizis et al 2005, P06). The second spectrum (7 < HR < 10) shows a weaker hard tail between 40 and 150 keV; the third one (10 < HR < 12) does not show a hard tail and is soft; the last spectrum is the softest (HR > 12), again with no hard tail (see also Kuulkers et al 2007;Paizis et al 2005, on the variability of GX 5−1). As required by the data, we used the two-component model for all spectra in the fitting process and obtained the following results (see Table 3):…”

Section: Gx 5-1mentioning

confidence: 95%

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Spectral evolution of bright NS LMXBs withINTEGRAL: an application of the thermal plus bulk Comptonization model

Mainardi¹,

Paizis²,

Farinelli

et al. 2010

A&A

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Aims. The aim of this work is to investigate in a physical and quantitative way the spectral evolution of bright neutron star low-mass X-ray binaries (NS LMXBs) with special regard to the transient hard X-ray tails. Methods. We analyzed INTEGRAL data for five sources (GX 5-1, GX 349+2, GX 13+1, GX 3+1, GX 9+1) and built broad-band X-ray spectra from JEM-X1 and IBIS/ISGRI data. For each source, X-ray spectra from different states were fitted with the recently proposed model compTB. Results. The spectra have been fit with a two-compTB model. In all cases the first compTB describes the dominant part of the spectrum that we interpret as thermal Comptonization of soft seed photons (<1 keV), likely from the accretion disk, by a 3−5 keV corona. In all cases, this component does not evolve much in terms of Comptonization efficiency, with the system converging to thermal equilibrium for an increasing accretion rate. The second compTB varies more dramatically, spanning from bulk plus thermal Comptonization of blackbody seed photons to the blackbody emission alone. These seed photons (R < 12 km, kT s > 1 keV), likely from the neutron star and the innermost part of the system, the transition layer, are Comptonized by matter in a converging flow. The presence and nature of this second compTB component (whether a pure blackbody or Comptonized) are related to the inner local accretion rate which can influence the transient behavior of the hard tail: high values of accretion rates correspond to an efficient bulk Comptonization process (bulk parameter δ 0), while even higher values of accretion rates suppress the Comptonization, resulting in simple blackbody emission (δ = 0). Conclusions. The spectral evolution of the sources has been successfully studied in terms of thermal and bulk Comptonization efficiency in relation to the physical conditions in the transition layer.

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Section: Discussionmentioning

confidence: 83%

Section: Gx 5-1mentioning

confidence: 95%

Spectral evolution of bright NS LMXBs withINTEGRAL: an application of the thermal plus bulk Comptonization model

Mainardi¹,

Paizis²,

Farinelli

et al. 2010

A&A

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“…Our average value found for 2003 and 2005 is 2.5 ± 0.4 × 10 −9 erg cm −2 s −1 , and our measured value for 2012 is 1.7 ± 0.1 × 10 −9 erg cm −2 s −1 , while the averaged between 2006 and 2008 value measured by Suzaku is 2.2 × 10 −9 erg cm −2 s −1 . It is noteworthy that recent monitoring by the INTEGRAL/IBIS program in the Galactic Bulge reported that 1E 1740.7−2942 is below the detection sensitivity limit (Kuulkers et al 2013).…”

Section: Discussionmentioning

confidence: 95%

Confirming the thermal Comptonization model for black hole X-ray emission in the low-hard state

Castro¹,

D'Amico²,

Braga³

et al. 2014

A&A

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Hard X-ray spectra of black hole binaries in the low/hard state are well modeled by thermal Comptonization of soft seed photons by a corona-type region with kT ∼ 50 keV and optical depth around 1. Previous spectral studies of 1E 1740.7−2942, including both the soft and the hard X-ray bands, were always limited by gaps in the spectra or by a combination of observations with imaging and non-imaging instruments. In this study, we have used three rare nearly-simultaneous observations of 1E 1740.7−1942 by both XMM-Newton and INTEGRAL satellites to combine spectra from four different imaging instruments with no data gaps, and we successfully applied the Comptonization scenario to explain the broadband X-ray spectra of this source in the low/hard state. For two of the three observations, our analysis also shows that, models including Compton reflection can adequately fit the data, in agreement with previous reports. We show that the observations can also be modeled by a more detailed Comptonization scheme. Furthermore, we find the presence of an iron K-edge absorption feature in one occasion, which confirms what had been previously observed by Suzaku. Our broadband analysis of this limited sample shows a rich spectral variability in 1E 1740.7−2942 at the low/hard state, and we address the possible causes of these variations. More simultaneous soft/hard X-ray observations of this system and other black-hole binaries would be very helpful in constraining the Comptonization scenario and shedding more light on the physics of these systems.

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“…Swift J1749.4−2807 was detected again in a high X-ray luminosity state on 2010 April 10, during the INTEGRAL Galactic bulge monitoring program (Pavan et al 2010;Kuulkers et al 2007). Swift and RXTE target of opportunity observations (ToO) were immediately requested, and these monitored the source outburst for about two weeks.…”

Section: Swift J17494−2807mentioning

confidence: 99%

INTEGRAL,Swift, andRXTEobservations of the 518 Hz accreting transient pulsar Swift J1749.4−2807

Ferrigno

Bozzo

Falanga

et al. 2010

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Context. The burst-only source Swift J1749.4−2807 was discovered in a high X-ray-active state, during an INTEGRAL observations of the Galactic bulge on 2010 April 10. Pulsations at 518 Hz were discovered in the RXTE data, confirming previous suggestions of possible associations between burst-only sources and accreting millisecond X-ray pulsars. The subsequent discovery of X-ray eclipses made Swift J1749.4−2807 the first eclipsing accreting millisecond X-ray pulsar. Aims. We obtain additional information on Swift J1749.4−2807 and other burst-only sources. Methods. We report on the results of a monitoring campaign on the source, carried out for about two weeks with the Swift, INTEGRAL, and RXTE satellites. Results. The observations showed that the X-ray spectrum (energy range 0.5-40 keV) of Swift J1749.4−2807 during the entire event was accurately modeled by an absorbed power-law model (N H 3 × 10 22 cm −2 , Γ 1.7). X-ray eclipses were also detected in the Swift data and provides a clear evidence of a dust-scattering halo located along the line of sight to the source. Only one type-I X-ray burst was observed throughout the two-weeks long monitoring. The X-ray flux of Swift J1749.4−2807 decayed below the detection threshold of Swift /XRT about 11 days after the discovery, in a exponential fashion (e-folding time of τ = 12 +7 −3 days). Conclusions. We compare the properties of the outburst observed from Swift J1749.4−2807 with those of the previously known millisecond X-ray pulsars and other transient low mass X-ray binaries.

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The INTEGRAL Galactic bulge monitoring program: the first 1.5 years

Cited by 100 publications

References 97 publications

Spectral evolution of bright NS LMXBs withINTEGRAL: an application of the thermal plus bulk Comptonization model

Spectral evolution of bright NS LMXBs withINTEGRAL: an application of the thermal plus bulk Comptonization model

Confirming the thermal Comptonization model for black hole X-ray emission in the low-hard state

INTEGRAL,Swift, andRXTEobservations of the 518 Hz accreting transient pulsar Swift J1749.4−2807

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