Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · astro-ph/0510430

An ultracompact X-ray binary in the globular cluster M15 (NGC7078)

A. Dieball·C. Knigge·D. R. Zurek·M. M. Shara·K. S. Long·P. A. Charles·D. C. Hannikainen·L. van Zyl
View original source ↗Read source document ↗Export metadata ↓

Abstract

We have used the Advanced Camera for Surveys on board the Hubble Space Telescope to image the core of the globular cluster M15 in the far-ultraviolet (FUV) waveband. Based on these observations, we identify the FUV counterpart of the recently discovered low-mass X-ray binary M15 X-2. Our time-resolved FUV photometry shows a modulation with 0.062+/-0.004 mag semi-amplitude and we clearly detect a period of 22.5806+/-0.0002 min. We have carried out extensive Monte Carlo simulations which show that the signal is consistent with being coherent over the entire observational time range of more than 3000 cycles. This strongly suggests that it represents the orbital period of the binary system. M15 X-2 is FUV bright (approx. 17 mag) and is characterized by an extremely blue spectral energy distribution (F_lambda ~ lambda^{-2.0}). We also find evidence for an excess of flux between 1500 and 1600 Åand probably between 1600 and 2000 Å, which might be due to CIV 1550 and HeII 1640 emission lines. We also show that M15 X-2's X-ray luminosity can be powered by accretion at the rate expected for gravitational-wave-driven mass transfer at this binary period. The observed FUV emission appears to be dominated by an irradiated accretion disk around the neutron star primary, and the variability can be explained by irradiation of the low-mass white dwarf donor if the inclination of the system is approx. 34 degree. We conclude that all observational characteristics of M15 X-2 are consistent with it being an ultracompact X-ray binary, only the third confirmed such object in a globular cluster.

Explore related subjects

astro-ph

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

A. Dieball, C. Knigge, D. R. Zurek, M. M. Shara, K. S. Long, P. A. Charles, D. C. Hannikainen, L. van Zyl. 2005-10-14. An ultracompact X-ray binary in the globular cluster M15 (NGC7078). https://doi.org/10.1086/498712

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Frame covariance of CMBR lensing in the exact 1+3 covariant radiation hierarchy

The exact $1+3$ covariant Boltzmann hierarchy for the cosmic microwave background contains acceleration, shear and vorticity couplings whose coefficients grow linearly in $\ell$. We show that all are the multipole form of the aberration operator in the photon Liouville equation. Under a change of threading, this operator shifts by the along-ray generator of a Lorentz boost. The acceleration coupling of $\ell$ to $\ell\pm1$ and the shear coupling of $\ell$ to $\ell\pm2$ are therefore frame-covariant descriptions of the same operator, related by an algebraic, pointwise relabelling of direction. With emitter and observer frames fixed, the observed sky is independent of the intermediate threading at every $\ell$. We derive this in $1+3$ covariant and gauge-invariant variables without constructing second-order gauge-invariant variables. The $O(ε^2\ell)$ content is gravitational lensing, as known in metric variables. Linearisation about a Friedmann--Lemaître--Robertson--Walker background removes these couplings, requiring lensing to be reinstated from the geodesic equation. Keeping the threading arbitrary makes frame covariance explicit and places observer aberration in the same operator. In the Newtonian threading we compute both halves of the deflection: the equivalence-principle contribution enters through aberration, while the spatial-curvature contribution arises from free streaming on perturbed spatial sections and reduces to the same operator. The lensing efficiency follows from the direction derivative. The angular-power-spectrum contribution is quartic in the potential: for a deflection statistically independent of the source, the two fourth-order terms carrying $\ell^2$ cancel where the spectrum is smooth on the deflection scale, and lensing redistributes power without adding ensemble variance.

astro-ph↗
arXiv2026

Cosmic Conundrums with Quantum Corrections

Darh energy was discovered over 25 years ago and we do not have an explanation of it. Dark matter comprises 95% of matter in the universe and we still don't know what it is. The Webb telescope has been finding fully formed galaxies with massive black holes millions of times the mass of the sun in the early universe and we don't have any explanation. A quantum density limitation will be used to solve these and other outstanding problems.

astro-ph↗
arXiv2026

On binary pulsars and the force of gravity

The energy-momentum budget of the astrophysical systems can be studied by the exact local conservation equation derived by Landau and Lifshitz. We show that a similar equation is valid for the Einstein-Cartan gravity. We reanalyze a binary pulsar system using the Landau-Lifshitz conservation equation and show that the orbital period change rate can be completely understood as a curvature backreaction process. Taking into account the detailed theoretical and observational research of relativistic binary pulsar systems, especially the system of Hulse and Taylor, we conclude that general relativity and astrophysical observations rule out the existence of gravitational radiation. We comment upon the LIGO GW events and their alternative explanation, as well as the recent pulsar timing arrays data.

astro-ph↗