Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where M. J. Coe is active.

Publication


Featured researches published by M. J. Coe.


Monthly Notices of the Royal Astronomical Society | 2005

Optical properties of small magellanic cloud X-ray binaries

M. J. Coe; W. R. T. Edge; J. L. Galache; V. A. McBride

This work represent the first major study of the optical and IR characteristics of the mass donor companions to the X-ray pulsars in the Small Magellanic Cloud (SMC). In this work several new counterparts have been identified, and possible ones confirmed, as companions to X-ray pulsars in the SMC giving a total of 34 such objects now identified. In addition this work presents three new binary periods and confirms two X-ray periods using optical data for objects in this group. This homogeneous sample has been studied as a group to determine important general characteristics that may offer insight into the evolution of such systems. In particular, the spectral class distribution shows a much greater agreement with those of isolated Be stars, and appears to be in some disagreement with the galactic population of Be stars in Be/X-ray binaries. Studies of the long term optical modulation of the Be star companions reveal an extremely variable group of objects, a fact which will almost certainly make a major contribution to the pronounced X-ray variability. The spatial distribution of these systems within the SMC is investigated and strongly suggests a link between massive star formation and the HI density distribution. Finally, studies of the circumstellar disk characteristics reveal a strong link with optical variability offering important clues into the long-term stability of such disks.


The Astrophysical Journal | 2002

A Decade in the Life of EXO 2030+375: A Multiwavelength Study of an Accreting X-Ray Pulsar

Colleen A. Wilson; Mark H. Finger; M. J. Coe; S. Laycock; J. Fabregat

Using BATSE and RXTE observations from 1991 April to 2001 August, we have detected 71 outbursts from 82 periastron passages of EXO 2030+375, a 42 s transient X-ray pulsar with a Be star companion, including several outbursts from 1993 August to 1996 April, when the source was previously believed to be quiescent. Combining BATSE, RXTE, and EXOSAT data, we have derived an improved orbital solution. Applying this solution results in a smooth profile for the spin-up rate during the giant outburst and results in evidence for a correlation between the spin-up rate and observed flux in the brighter BATSE outbursts. Infrared and H? measurements show a decline in the density of the circumstellar disk around the Be star. This decline is followed by a sudden drop in the X-ray flux and a turnover from a spin-up trend to spin-down in the frequency history. This is the first Be/X-ray binary that shows an extended interval, about 2.5 yr, in which the global trend is spin-down, but the outbursts continue. In 1995 the orbital phase of EXO 2030+375s outbursts shifted from peaking about 6 days after periastron to peaking before periastron. The outburst phase slowly recovered to peaking at about 2.5 days after periastron. We interpret this shift in orbital phase followed by a slow recovery as evidence of a global one-armed oscillation propagating in the Be disk. This is further supported by changes in the shape of the H? profile, which are commonly believed to be produced by a reconfiguration of the Be disk. The truncated viscous decretion disk model provides an explanation for the long series of normal outbursts and the evidence of an accretion disk in the brighter normal outbursts. Long-term multiwavelength observations such as these clearly add considerably to our knowledge of Be/X-ray binaries and the relationship among optical, infrared, and X-ray observations.


Nature | 2011

Two populations of X-ray pulsars produced by two types of supernova

Christian Knigge; M. J. Coe; Philipp Podsiadlowski

Two types of supernova are thought to produce the overwhelming majority of neutron stars in the Universe. The first type, iron-core-collapse supernovae, occurs when a high-mass star develops a degenerate iron core that exceeds the Chandrasekhar limit. The second type, electron-capture supernovae, is associated with the collapse of a lower-mass oxygen–neon–magnesium core as it loses pressure support owing to the sudden capture of electrons by neon and/or magnesium nuclei. It has hitherto been impossible to identify the two distinct families of neutron stars produced in these formation channels. Here we report that a large, well-known class of neutron-star-hosting X-ray pulsars is actually composed of two distinct subpopulations with different characteristic spin periods, orbital periods and orbital eccentricities. This class, the Be/X-ray binaries, contains neutron stars that accrete material from a more massive companion star. The two subpopulations are most probably associated with the two distinct types of neutron-star-forming supernova, with electron-capture supernovae preferentially producing systems with short spin periods, short orbital periods and low eccentricities. Intriguingly, the split between the two subpopulations is clearest in the distribution of the logarithm of spin period, a result that had not been predicted and which still remains to be explained.


Monthly Notices of the Royal Astronomical Society | 2008

Spectral distribution of Be/X-ray binaries in the Small Magellanic Cloud*

V. A. McBride; M. J. Coe; I. Negueruela; M. P. E. Schurch; K. E. McGowan

The spectral distributions of Be/X-ray binaries in the Large Magellanic Cloud and Galaxy have been shown to differ significantly from the distribution of isolated Be stars in the Galaxy. Population synthesis models can explain this difference in spectral distributions through substantial angular momentum loss from the binary system. In this work, we explore the spectral distribution of Be/X-ray binaries in the Small Magellanic Cloud (SMC) using high signal-to-noise ratio spectroscopy of a sample of 37 optical counterparts to known X-ray pulsars. Our results show that the spectral distribution of Be/X-ray binaries in the SMC is consistent with that of the Galaxy, despite the lower metallicity environment of the SMC. This may indicate that, although the metallicity of the SMC is conducive to the formation of a large number of high-mass X-ray binaries, the spectral distribution of these systems is likely to be most strongly influenced by angular momentum losses during binary evolution, which are not particularly dependent on the local metallicity.


Monthly Notices of the Royal Astronomical Society | 2003

Long-term properties of accretion discs in X-ray binaries — I. The variable third period in SMC X-1

W. I. Clarkson; P. A. Charles; M. J. Coe; S. Laycock; M. D. Tout; Colleen A. Wilson

Long-term X-ray monitoring data from the Rossi X-Ray Timing Explorer (RXTE) All-Sky Monitor (ASM) and the Compton Gamma Ray Observatory (CGRO) Burst And Transient Source Experiment (BATSE) reveal that the third (superorbital) period in SMC X-1 is not constant, but varies between 40 and 60 d. A dynamic power spectrum analysis indicates that the third period has been present continuously throughout the five years of ASM observations. This period changed smoothly from 60 to 45 d and then returned to its former value, on a time-scale of approximately 1600 d. During the nearly 4 yr of overlap between the CGRO and RXTE missions, the simultaneous BATSE hard X-ray data confirm and extend this variation in SMC X-1. Our discovery of such an instability in the superorbital period of SMC X-1 is interpreted in the context of recent theoretical studies of warped, precessing accretion discs. We find that the behaviour of SMC X-1 is consistent with a radiation-driven warping model.


Astrophysical Journal Supplement Series | 2008

A Long Look at the Be/X-Ray Binaries of the Small Magellanic Cloud

Jose Luis Galache; R. H. D. Corbet; M. J. Coe; S. Laycock; M. P. E. Schurch; Craig B. Markwardt; F. E. Marshall; J. Lochner

We have monitored 41 Be/X-ray binary systems in the Small Magellanic Cloud over ~9 yr using PCA RXTE data from a weekly survey program. The resulting light curves were analyzed in search of orbital modulations with the result that 10 known orbital ephemerides were confirmed and refined, while 10 new ones where determined. A large number of X-ray orbital profiles are presented for the first time, showing similar characteristics over a wide range of orbital periods. Lastly, three pulsars, SXP 46.4, SXP 89.0, and SXP 165, were found to be misidentifications of SXP 46.6, SXP 91.1, and SXP 169, respectively.


Monthly Notices of the Royal Astronomical Society | 2014

Spin period change and the magnetic fields of neutron stars in Be X-ray binaries in the Small Magellanic Cloud

Helen Klus; Wynn C. G. Ho; M. J. Coe; R. H. D. Corbet; L. J. Townsend

We report on the long term average spin period, rate of change of spin period and X-ray luminosity during outbursts for 42 Be X-ray binary systems in the Small Magellanic Cloud. We also collect and calculate parameters of each system and use this data to determine that all systems contain a neutron star which is accreting via a disc, rather than a wind, and that if these neutron stars are near spin equilibrium, then over half of them, including all with spin periods over about 100 seconds, have magnetic fields over the quantum critical level of 4.4x10^13 G. If these neutron stars are not close to spin equilibrium, then their magnetic fields are inferred to be much lower, on the order of 10^6-10^10 G, comparable to the fields of neutron stars in low mass X-ray binaries. Both results are unexpected and have implications for the rate of magnetic field decay and the isolated neutron star population.


The Astrophysical Journal | 2003

XTE J1946+274 = GRO J1944+26: An Enigmatic Be/X-Ray Binary

Colleen A. Wilson; Mark H. Finger; M. J. Coe; I. Negueruela

XTE J1946+274 = GRO J1944+26 is a 15.8 s Be/X-ray pulsar discovered simultaneously in 1998 September with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) and the All-Sky Monitor (ASM) on the Rossi X-Ray Timing Explorer (RXTE). Here we present new results from BATSE and RXTE including a pulse timing analysis, spectral analysis, and evidence for an accretion disk. Our pulse timing analysis yielded an orbital period of 169.2 days, a moderate eccentricity of 0.33, and implied a mass function of 9.7 M☉. We observed evidence for an accretion disk, a correlation between measured spin-up rate and flux, which was fitted to obtain a distance estimate of 9.5 ± 2.9 kpc. XTE J1946+274 remained active from 1998 September to 2001 July, undergoing 13 outbursts that were not locked in orbital phase. Comparing RXTE Proportional Counter Array observations from the initial bright outburst in 1998 and the last pair of outbursts in 2001, we found energy and intensity-dependent pulse profile variations in both outbursts and hardening spectra with increasing intensity during the fainter 2001 outbursts. In 2001 July, optical Hα observations indicated that a density perturbation appeared in the Be disk as the X-ray outbursts ceased. We propose that the equatorial plane of the Be star is inclined with respect to the orbital plane in this system and that this inclination may be a factor in the unusual outburst behavior of the system.


Astronomy and Astrophysics | 2002

The population of massive X-ray binaries - I. The Large Magellanic Cloud

I. Negueruela; M. J. Coe

We present high resolution blue spectroscopy of an almost complete sample of optical counterparts to massive X-ray binaries in the Large Magellanic Cloud (LMC) and derive their spectral classication. We nd an spectral type B0II for the optical counterpart to RX J0532.5 6551, conrming it as the rst wind-fed massive X-ray binary in the LMC. We also conrm the Be nature of the proposed counterpart to RX J0535.0 6700. The proposed optical counterpart to RX J0531.5 6518 is a B2V star with signs of emission in the Balmer lines. In total, we give accurate spectral types for 14 counterparts. We nd that the overall observed population of massive X-ray binaries in the LMC has a distribution not very dierent from the observed Galactic population and we discuss dierent selection eects aecting our knowledge of this population. The spectral distribution of the Be/X-ray binary population is also rather similar to the Galactic one. This distribution implies that Be/X-ray binaries must have preferentially formed from moderately massive binaries undergoing semi-conservative evolution. The observation of several Be/X-ray binaries with large eccentricities implies then the existence of supernova kicks.


Astronomy and Astrophysics | 2001

On the radio emitting high mass X-ray binary LS 5039

J. S. Clark; P. Reig; S. P. Goodwin; V. M. Larionov; P. Blay; M. J. Coe; J. Fabregat; I. Negueruela; I. E. Papadakis; Iain A. Steele

We present new optical { near{IR spectroscopic and photometric observations of the newly discovered galactic microquasar LS 5039, which indicate a classication for the mass donor in the system of O6.5V((f)). Optical spectroscopy and photometry shows no variability over a timescale of years, and we nd no evidence of modulation by, or emission from the compact companion in these data. However signicant photometric variability (0:4 mag) is present in the H and K bands between 1995{2000. Such variability has been observed in other radio bright X-ray binaries where it has been attributed to synchrotron emission from the jet. However, given the non{thermal spectral index of the radio emission in LS 5039 this explanation appears unlikely, predicting a near{IR flux3 orders of magnitude too small to contribute signicantly at such wavelengths. Nightly optical photometry over a 21 day period between 2000 May{June reveals variability at a level of a few hundredths of a magnitude, with no periodicity or long term trend visible. Likewise, while the radio lightcurves show moderate variability (20 per cent of the mean flux density) we nd no evidence of periodic modulation { Monte Carlo simulations constrain any such periodic variability to <4 per cent modulation at 2.25 GHz. The dierences in behaviour between LS 5039 and Cygnus X-1 { the most closely related radio emitting High Mass X-ray Binary { are likely to be a result of the weaker stellar wind and probable greater orbital separation of LS 5039 compared to Cyg X-1.

Collaboration


Dive into the M. J. Coe's collaboration.

Top Co-Authors

Avatar
Top Co-Authors

Avatar

Robin H. D. Corbet

Goddard Space Flight Center

View shared research outputs
Top Co-Authors

Avatar

J. Fabregat

University of Valencia

View shared research outputs
Top Co-Authors

Avatar

S. Laycock

University of Massachusetts Lowell

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar

P. Roche

University of South Wales

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar

R. H. D. Corbet

Universities Space Research Association

View shared research outputs
Top Co-Authors

Avatar

Mark H. Finger

Universities Space Research Association

View shared research outputs
Top Co-Authors

Avatar

I. Negueruela

Liverpool John Moores University

View shared research outputs
Researchain Logo
Decentralizing Knowledge