<i>Chandra</i>Observation of the Globular Cluster NGC 6440 and the Nature of Cluster X‐Ray Luminosity Functions

Pooley, David; Lewin, W. H. G.; Verbunt, F.; Homer, Lee; Margon, B.; Gaensler, B. M.; Kaspi, V. M.; Miller, J. M.; Fox, D. B.; Klis, M. van der

doi:10.1086/340498

Cited by 90 publications

(143 citation statements)

References 21 publications

Supporting

Mentioning

134

Contrasting

Order By: Relevance

“…If globular cluster quiescent neutron star binaries behave similarly to those in the disk, then our observation should provide a complete census of the content of such objects in ω Cen (a similar conclusion was derived by , from the Chandra observations). Some of these objects have also been found in other clusters (Edmonds 2002;Grindlay et al 2001;Pooley et al 2002b). In globular clusters, these systems are certainly formed from a close encounter between a neutron star with a single star or with a binary (see Verbunt 2002b, for a recent review).…”

Section: Discussionmentioning

confidence: 65%

An XMM-Newton observation of the globular cluster Omega Centauri

Gendre

Barret

Webb

2003

A&A

View full text Add to dashboard Cite

Abstract. We report on a deep XMM-Newton EPIC observation of the globular cluster Omega Cen performed on August 13th, 2001. We have detected 11 and 27 faint X-ray sources in the core and half mass radii, searching down to a luminosity of 1.3 × 10 31 ergs s −1 in the 0.5-5 keV range. Most sources have bolometric X-ray luminosities between ∼10 31 −10 32 ergs s −1 . We present the color-color and hardness-intensity diagrams of the source sample, as well as high-quality EPIC spectra of the brightest objects of the field, including the two candidate Cataclysmic Variables (CVs) in the core and the quiescent neutron star low-mass X-ray binary candidate. The spectra of the latter objects fully support their previous classification. We show that the bulk of sources are hard and spectrally similar to CVs. The lack of soft faint sources might be related to the absence of millisecond pulsars in the cluster. The XMM-Newton observations reveal the presence of an excess of sources well outside the core of the cluster where several RS CVn binaries have already been found. We have also analyzed a publicly available Chandra ACIS-I observation performed on January 24-25th, 2000, to improve the XMM-Newton source positions and to search for source intensity variations between the two data sets. 63 XMM-Newton sources have a Chandra counterpart, and 15 sources within the half-mass radius have shown time variability. Overall, the general properties of the faint X-ray sources in ω Cen suggest that they are predominantly CVs and active binaries (RS CVn or BY Dra).

show abstract

Section: Discussionmentioning

confidence: 65%

An XMM-Newton observation of the globular cluster Omega Centauri

Gendre

Barret

Webb

2003

A&A

View full text Add to dashboard Cite

show abstract

“…We study the four brightest identified qLMXB candidates in or near the core of this cluster, CX 1, CX 2 (not to be confused with the AMXP denoted as NGC 6440 X-2, which is not detected in deep quiescence, e.g. Heinke et al 2010), CX 3, and CX 5, which were identified as likely qLMXBs by Pooley et al (2002).…”

Section: Ngc 6440mentioning

confidence: 99%

Limits on thermal variations in a dozen quiescent neutron stars over a decade

Bahramian¹,

Heinke²,

Degenaar³

et al. 2015

Mon. Not. R. Astron. Soc.

Self Cite

View full text Add to dashboard Cite

In quiescent low-mass X-ray binaries (qLMXBs) containing neutron stars, the origin of the thermal X-ray component may be either release of heat from the core of the neutron star, or continuing low-level accretion. In general, heat from the core should be stable on timescales < 10 4 years, while continuing accretion may produce variations on a range of timescales. While some quiescent neutron stars (e.g. Cen X-4, Aql X-1) have shown variations in their thermal components on a range of timescales, several others, particularly those in globular clusters with no detectable nonthermal hard X-rays (fit with a powerlaw), have shown no measurable variations. Here, we constrain the spectral variations of 12 low mass X-ray binaries in 3 globular clusters over ∼ 10 years. We find no evidence of variations in 10 cases, with limits on temperature variations below 11% for the 7 qLMXBs without powerlaw components, and limits on variations below 20% for 3 other qLMXBs that do show non-thermal emission. However, in 2 qLMXBs showing powerlaw components in their spectra (NGC 6440 CX 1 & Terzan 5 CX 12) we find marginal evidence for a 10% decline in temperature, suggesting the presence of continuing low-level accretion. This work adds to the evidence that the thermal X-ray component in quiescent neutron stars without powerlaw components can be explained by heat deposited in the core during outbursts. Finally, we also investigate the correlation between hydrogen column density (N H ) and optical extinction (A V ) using our sample and current models of interstellar X-ray absorption, finding N H (cm −2 ) = (2.81 ± 0.13) × 10 21 A V .

show abstract

“…The 1998 and 2001 outbursts are from the same object (in 't Zand et al 2001), identified with the optical star referred to as V2 in (Verbunt et al 2000). Whether the 1971 outburst is from the same object or one of the other, currently quiescent LMXBs in NGC 6440 (Pooley et al 2002) The RXTE All-Sky Monitor (ASM) light curve of the 2001 outburst is shown in Figure 1. The outburst started around MJD 52129 (2001 August 8), as reported by the MIT ASM team.…”

Section: Observations Of Ngc 6440mentioning

confidence: 99%

“…We fitted the resulting spectra in the 3-20 keV band with an absorbed blackbody model with the column density fixed to 5:9 Â 10 21 cm À2 , the value equivalent to the optical reddening (Pooley et al 2002). The results are shown in Table 1.…”

Section: X-ray Burstsmentioning

confidence: 99%

Discovery of X‐Ray Burst Oscillations from a Neutron Star X‐Ray Transient in the Globular Cluster NGC 6440

Kaaret

Zand

Heise

et al. 2003

ApJ

View full text Add to dashboard Cite

We report the discovery of millisecond oscillations in an X-ray burst from the X-ray transient SAX J1748.9À2021 in the globular cluster NGC 6440. Oscillations at a frequency of 409:7 AE 0:3 Hz were present in one of 15 X-ray bursts observed with the Proportional Counter Array on the Rossi X-Ray Timing Explorer during the outburst that occurred in 2001. The burst was relatively dim and had the second longest duration and decay time. The average peak luminosity of two bursts showing radius expansion is ð3:6 AE 0:4Þ Â 10 38 ergs s À1 , consistent with the Eddington luminosity for a 1:4 M and 10 km radius neutron star burning hydrogen-poor matter. We speculate that the dichotomy observed between sources with burst oscillations at once versus twice the frequency difference of kHz quasiperiodic oscillations in the persistent emission may be related to the magnetic field geometry of the neutron stars.

show abstract

ChandraObservation of the Globular Cluster NGC 6440 and the Nature of Cluster X‐Ray Luminosity Functions

Cited by 90 publications

References 21 publications

An XMM-Newton observation of the globular cluster Omega Centauri

An XMM-Newton observation of the globular cluster Omega Centauri

Limits on thermal variations in a dozen quiescent neutron stars over a decade

Discovery of X‐Ray Burst Oscillations from a Neutron Star X‐Ray Transient in the Globular Cluster NGC 6440

Contact Info

Product

Resources

About