The Optical Counterpart to the Accreting Millisecond X-ray Pulsar SAX J1748.9-2021 in the Globular Cluster NGC 6440

Abstract

We used a combination of deep optical and Halpha images of the Galactic globular cluster NGC 6440, acquired with the Hubble Space Telescope, to identify the optical counterpart to the accreting millisecond X-ray pulsar SAX J1748.9-2021during quiescence. A strong Halpha emission has been detected from a main sequence star (hereafter COM-SAX J1748.9-2021) located at only 0.15" from the nominal position of the X-ray source. The position of the star also agrees with the optical counterpart found by Verbunt et al. (2000) during an outburst. We propose this star as the most likely optical counterpart to the binary system. By direct comparison with isochrones, we estimated that COM-SAX J1748.9-2021 has a mass of 0.70 Msun - 0.83 Msun, a radius of 0.88 pm 0.02 Rsun and a superficial temperature of 5250pm80 K. These parameters combined with the orbital characteristics of the binary suggest that the system is observed at a very low inclination angle (~8 deg -14 deg) and that the star is filling or even overflowing its Roche Lobe. This, together with the equivalent width of the Halpha emission (~20 Ang), suggest possible on-going mass transfer. The possibile presence of such a on-going mass transfer during a quiescence state also suggests that the radio pulsar is not active yet and thus this system, despite its similarity with the class of redback millisecond pulsars, is not a transitional millisecond pulsar.

arXiv comment8 pages, 6 figures. Accepted for publication in ApJ

References in corpus (53)

• Evolutionary tracks and isochrones for low- and intermediate-mass stars: from 0.15 to 7 M_sun, and from Z=0.0004 to 0.03
• The Dartmouth Stellar Evolution Database
• A large stellar evolution database for population synthesis studies. I. Scaled solar models and isochrones
• The Fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)
• A Radio Pulsar/X-ray Binary Link
• Swings between rotation and accretion power in a millisecond binary pulsar
• A state change in the low-mass X-ray binary XSS J12270-4859
• The long-term evolution of the spin, pulse shape, and orbit of the accretion-powered millisecond pulsar SAX J1808.4-3658
• Eight New Millisecond Pulsars in NGC 6440 and NGC 6441
• Astrometry and photometry with HST WFC3. II. Improved geometric-distortion corrections for 10 filters of the UVIS channel
• Near-IR properties of 24 Globular Clusters in the Galactic Bulge
• A New Accretion Disk Around the Missing Link Binary System PSR J1023+0038
• Improved Mass and Radius Constraints for Quiescent Neutron Stars in Omega Cen and NGC 6397
• Discovery of PSR J1227-4853: A transition from a low-mass X-ray binary to a redback millisecond pulsar
• Discovery of the Optical Counterparts to Four Energetic Fermi Millisecond Pulsars
• Intermittent millisecond X-ray pulsations from the neutron-star X-ray transient SAX J1748.9-2021 in the globular cluster NGC 6440
• The Red Giant Branch in the Near-Infrared Colour-Magnitude Diagrams. I: The calibration of photometric indices
• The bright optical companion to the eclipsing millisecond pulsar in NGC 6397
• Multi-wavelength emissions from the millisecond pulsar binary PSR J1023+0038 during an accretion active state
• The peculiar Horizontal Branch of NGC 2808
• Chandra Observation of the Globular Cluster NGC 6440 and the Nature of Cluster X-ray Luminosity Functions
• Photometric determination of the mass accretion rates of pre-main sequence stars. I. Method and application to the SN1987A field
• Accelerated Orbital Expansion And Secular Spin Down of the Accreting Millisecond Pulsar SAX J1808.4-3658
• High resolution infrared spectra of NGC 6440 and NGC 6441: two massive Bulge Globular Clusters
• Identification of the optical and quiescent counterparts to the bright X-ray transient in NGC 6440
• Discovery of a 205.89 Hz accreting-millisecond X-ray pulsar in the globular cluster NGC 6440
• Properties and Evolution of the Redback Millisecond Pulsar Binary PSR J2129-0429
• Gamma-ray Timing of Redback PSR J2339-0533: Hints for Gravitational Quadrupole Moment Changes
• The optical counterpart to SAX J1808.4-3658: observations in quiescence
• A Millisecond Pulsar Optical Counterpart with Large-Amplitude Variability in the Globular Cluster 47 Tucanae
• The Helium White Dwarf orbiting the Millisecond Pulsar in the halo of the Globular Cluster NGC 6752
• Phase-coherent timing of the accreting millisecond pulsar SAX J1748.9-2021
• Multi-wavelength observations of the transitional millisecond pulsar binary XSSJ12270-4859
• High resolution reddening map in the direction of the stellar system Terzan 5
• The optical counterpart to the X-ray transient IGR J18245-2452 in the globular cluster M28
• The optical companion to the binary millisecond pulsar J1824-2452H in the globular cluster M28
• Timing of the accreting millisecond pulsar SAX J1748.9-2021 during its 2015 outburst
• Discovery of a new accreting millisecond X-ray pulsar in the globular cluster NGC 2808
• Radio timing and optical photometry of the black widow system PSR J1518+0204C in the globular cluster M5
• Observations of the 599 Hz Accreting X-ray Pulsar IGR J00291+5934 during the 2004 Outburst and in Quiescence
• Radio pulse search and X-Ray monitoring of SAX J1808.4-3658: What Causes its Orbital Evolution?
• Optical Identification of He White Dwarfs Orbiting Four Millisecond Pulsars in the Globular Cluster 47 Tucanae
• The complex Halpha line profile of the bright companion to PSR J1740-5340 in NGC 6397
• Discovery of 442-Hz Pulsations from an X-ray Source in the Globular Cluster NGC 6440
• Identification of twenty-three accreting binaries in the Galactic Bulge Survey
• The optical counterparts of Accreting Millisecond X-Ray Pulsars during quiescence
• New clues on the nature of the companion to PSR~J1740-5340 in NGC6397 from XSHOOTER spectroscopy
• IGR J17062-6143 is an Accreting Millisecond X-ray Pulsar
• Radio Timing and Optical Photometry of the Black Widow System PSR J1953+1846A in the Globular Cluster M71
• Hα photometry of low mass stars in 47 Tucanae: chromospheric activity and exotica
• Constraining the true nature of an exotic binary in the core of NGC 6624
• Probing the Galactic Bulge with deep Adaptive Optics imaging: the age of NGC 6440
• Very Large Telescope Observations of the peculiar globular cluster NGC6712. Discovery of a UV, H-alpha excess star in the core

Cited by in corpus (25)

• The Multi-INstrument Burst ARchive (MINBAR)
• Accreting pulsars: mixing-up accretion phases in transitional systems
• The "dynamical clock": dating the internal dynamical evolution of star clusters with Blue Straggler Stars
• An extremely low-mass He white dwarf orbiting the millisecond pulsar J1342+2822B in the globular cluster M3
• Digging for relics of the past: the ancient and obscured bulge globular cluster NGC6256
• PSR J1641+3627F: a low-mass He white dwarf orbiting a possible high-mass neutron star in the globular cluster M13
• A new identity card for the bulge globular cluster NGC 6440 from resolved star counts
• Digging into the Galactic Bulge: stellar population and structure of the poorly studied cluster NGC 6316
• A broadband look of the Accreting Millisecond X-ray Pulsar SAX J1748.9-2021 using AstroSat and XMM-Newton
• High-resolution extinction map in the direction of the bulge globular cluster NGC 6440
• Empirical measurement of the dynamical ages of three globular clusters and some considerations on the use of the dynamical clock
• Mixed H/He bursts in SAX J1748.9-2021 during the spectral change of its 2015 outburst
• Internal kinematics and structure of the bulge globular cluster NGC 6569
• The ESO-VLT MIKiS survey reloaded: exploring the internal kinematics of NGC 6440
• A young white dwarf orbiting PSR J1835-3259B in the bulge globular cluster NGC 6652
• A Photometric in-depth look at the core-collapsed globular cluster NGC 6284
• X-ray sources in Galactic globular clusters and old open clusters
• Study of the reflection spectra of SAX J1748.9-2021
• The "canonical" White Dwarf Cooling Sequence of M5
• Identification and characterization of optical companions to the population of millisecond pulsars in the globular cluster M3
• Structural parameters, chronological age and dynamical age of the LMC globular cluster NGC 1754
• The X-ray bursts within the 2010 outburst of the accreting millisecond X-ray pulsar SAX J1748.9-2021
• The ESO-VLT MIKiS survey reloaded: velocity dispersion profile and rotation curve of NGC 1904
• A candidate to the long sought optical counterpart to the Rapid Burster in the bulge fossil fragment Liller 1
• Revealing the stellar population of the ultra-obscured Galactic globular cluster Glimpse-C02