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Title: THE PECULIAR EVOLUTIONARY HISTORY OF IGR J17480-2446 IN TERZAN 5

Abstract

The low-mass X-ray binary (LMXB) IGR J17480-2446 in the globular cluster Terzan 5 harbors an 11 Hz accreting pulsar. This is the first object discovered in a globular cluster with a pulsar spinning at such low rate. The accreting pulsar is anomalous because its characteristics are very different from the other five known slow accreting pulsars in galactic LMXBs. Many features of the 11 Hz pulsar are instead very similar to those of accreting millisecond pulsars, spinning at frequencies >100 Hz. Understanding this anomaly is valuable because IGR J17480-2446 could be the only accreting pulsar discovered so far which is in the process of becoming an accreting millisecond pulsar. We first verify that the neutron star (NS) in IGR J17480-2446 is indeed spinning up by carefully analyzing X-ray data with coherent timing techniques that account for the presence of timing noise. We then study the present Roche lobe overflow epoch and the two previous spin-down epochs dominated by magneto-dipole radiation and stellar wind accretion. We find that IGR J17480-2446 is very likely a mildly recycled pulsar and suggest that it has started a spin-up phase in an exceptionally recent time, which has lasted less than a few 10{sup 7} yr.more » We also find that the total age of the binary is surprisingly low ({approx}< 10{sup 8} yr) when considering typical parameters for the newborn NS and propose different scenarios to explain this anomaly.« less

Authors:
; ; ;  [1]
  1. Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Science Park 904, 1098 SJ Amsterdam (Netherlands)
Publication Date:
OSTI Identifier:
22037098
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 752; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; BINARY STARS; DIPOLES; GAMMA ASTRONOMY; MASS; NEUTRON STARS; NOISE; PULSARS; ROCHE EQUIPOTENTIALS; SPIN; STAR CLUSTERS; STELLAR WINDS; X RADIATION

Citation Formats

Patruno, Alessandro, Alpar, M. Ali, Van der Klis, Michiel, and Van den Heuvel, Ed P. J., E-mail: a.patruno@uva.nl. THE PECULIAR EVOLUTIONARY HISTORY OF IGR J17480-2446 IN TERZAN 5. United States: N. p., 2012. Web. doi:10.1088/0004-637X/752/1/33.
Patruno, Alessandro, Alpar, M. Ali, Van der Klis, Michiel, & Van den Heuvel, Ed P. J., E-mail: a.patruno@uva.nl. THE PECULIAR EVOLUTIONARY HISTORY OF IGR J17480-2446 IN TERZAN 5. United States. doi:10.1088/0004-637X/752/1/33.
Patruno, Alessandro, Alpar, M. Ali, Van der Klis, Michiel, and Van den Heuvel, Ed P. J., E-mail: a.patruno@uva.nl. Sun . "THE PECULIAR EVOLUTIONARY HISTORY OF IGR J17480-2446 IN TERZAN 5". United States. doi:10.1088/0004-637X/752/1/33.
@article{osti_22037098,
title = {THE PECULIAR EVOLUTIONARY HISTORY OF IGR J17480-2446 IN TERZAN 5},
author = {Patruno, Alessandro and Alpar, M. Ali and Van der Klis, Michiel and Van den Heuvel, Ed P. J., E-mail: a.patruno@uva.nl},
abstractNote = {The low-mass X-ray binary (LMXB) IGR J17480-2446 in the globular cluster Terzan 5 harbors an 11 Hz accreting pulsar. This is the first object discovered in a globular cluster with a pulsar spinning at such low rate. The accreting pulsar is anomalous because its characteristics are very different from the other five known slow accreting pulsars in galactic LMXBs. Many features of the 11 Hz pulsar are instead very similar to those of accreting millisecond pulsars, spinning at frequencies >100 Hz. Understanding this anomaly is valuable because IGR J17480-2446 could be the only accreting pulsar discovered so far which is in the process of becoming an accreting millisecond pulsar. We first verify that the neutron star (NS) in IGR J17480-2446 is indeed spinning up by carefully analyzing X-ray data with coherent timing techniques that account for the presence of timing noise. We then study the present Roche lobe overflow epoch and the two previous spin-down epochs dominated by magneto-dipole radiation and stellar wind accretion. We find that IGR J17480-2446 is very likely a mildly recycled pulsar and suggest that it has started a spin-up phase in an exceptionally recent time, which has lasted less than a few 10{sup 7} yr. We also find that the total age of the binary is surprisingly low ({approx}< 10{sup 8} yr) when considering typical parameters for the newborn NS and propose different scenarios to explain this anomaly.},
doi = {10.1088/0004-637X/752/1/33},
journal = {Astrophysical Journal},
number = 1,
volume = 752,
place = {United States},
year = {Sun Jun 10 00:00:00 EDT 2012},
month = {Sun Jun 10 00:00:00 EDT 2012}
}
  • IGR J17480-2446 is an accreting X-ray pulsar in a low-mass X-ray binary harbored in the Galactic globular cluster Terzan 5. Compared with other accreting millisecond pulsars, IGR J17480-2446 is peculiar for its low spin frequency (11 Hz), which suggests that it might be a mildly recycled neutron star at the very early phase of mass transfer. However, this model seems to be in contrast with the low field strength deduced from the kilo-Hertz quasi-periodic oscillations observed in IGR J17480-2446. Here, we suggest an alternative interpretation, assuming that the current binary system was formed during an exchange encounter either between amore » binary (which contains a recycled neutron star) and the current donor, or between a binary and an isolated, recycled neutron star. In the resulting binary, the spin axis of the neutron star could be parallel or anti-parallel with the orbital axis. In the latter case, the abnormally low frequency of IGR J17480-2446 may result from the spin-down to spin-up evolution of the neutron star. We also briefly discuss the possible observational implications of the pulsar in this scenario.« less
  • The 2010 outburst of the transient neutron star low-mass X-ray binary IGR J17480-2446 has exhibited a series of unique X-ray bursts as well as millihertz (mHz) quasi-periodic oscillations (QPOs) related to these bursts. It has been recently proposed that these are type-II bursts, powered by the gravitational energy. This implies that the current nuclear-burning-based model of mHz QPOs is not correct, and this timing feature cannot be used as a tool to measure the neutron star parameters. We report the analysis of the Rossi X-Ray Timing Explorer data of IGR J17480-2446 to show that the burst properties of this sourcemore » are quite different from the properties of the type-II bursts observed from the rapid burster and GRO J1744-28. For example, the inferred ratio ({approx}50-90) of the non-burst fluence to burst fluence is consistent with the thermonuclear origin of IGR J17480-2446 bursts and is significantly different from this ratio ({approx}<4) for type-II bursts. Our results suggest that the bursts and the mHz QPOs from IGR J17480-2446 are powered by the nuclear energy.« less
  • Accretion disk winds are revealed in Chandra gratings spectra of black holes. The winds are hot and highly ionized (typically composed of He-like and H-like charge states) and show modest blueshifts. Similar line spectra are sometimes seen in 'dipping' low-mass X-ray binaries (LMXBs), which are likely viewed edge-on; however, that absorption is tied to structures in the outer disk, and blueshifts are not typically observed. Here, we report the detection of blueshifted He-like Fe XXV (3100 {+-} 400 km s{sup -1}) and H-like Fe XXVI (1000 {+-} 200 km s{sup -1}) absorption lines in a Chandra/HETG spectrum of the transientmore » pulsar and LMXB IGR J17480-2446 in Terzan 5. These features indicate a disk wind with at least superficial similarities to those observed in stellar-mass black holes. The wind does not vary strongly with numerous weak X-ray bursts or flares. A broad Fe K emission line is detected in the spectrum, and fits with different line models suggest that the inner accretion disk in this system may be truncated. If the stellar magnetic field truncates the disk, a field strength of B= (0.7-4.0)x10{sup 9} G is implied, which is in line with estimates based on X-ray timing techniques. We discuss our findings in the context of accretion flows onto neutron stars and stellar-mass black holes.« less
  • The recently discovered accreting X-ray pulsar IGR J17480-2446 spins at a frequency of {approx}11 Hz. We show that Type I X-ray bursts from this source display oscillations at the same frequency as the stellar spin. IGR J17480-2446 is the first secure case of a slowly rotating neutron star (NS) which shows Type I burst oscillations (BOs), all other sources featuring such oscillations spin at hundreds of Hertz. This means that we can test BO models in a completely different regime. We explore the origin of Type I BOs in IGR J17480-2446 and conclude that they are not caused by globalmore » modes in the NS ocean. We also show that the Coriolis force is not able to confine an oscillation-producing hot spot on the stellar surface. The most likely scenario is that the BOs are produced by a hot spot confined by hydromagnetic stresses.« less
  • EXO1745-248 is a transient neutron star low-mass X-ray binary located in the globular cluster Terzan 5. It was in outburst in 2000 and displayed during one Rossi X-ray Timing Explorer observation a highly coherent quasi-periodic oscillation (QPO) at frequencies between 670 and 715 Hz. Applying a maximum likelihood method to fit the X-ray power density spectrum, we show that the QPO can be detected on segments as short as T = 48 s. We find that its width is consistent with being constant, while previous analysis based on longer segment duration (200 s) found it variable. If the QPO frequencymore » variations in EXO1745-248 follow a random walk (i.e., the contribution of the drift to the measured width increases like {radical}T), we derive an intrinsic width of {approx}2.3 Hz. This corresponds to an intrinsic quality factor of Q {approx} 297 {+-} 50 at 691 Hz. We also show that Q is consistent with being constant between 2.5 and 25 keV. IGR J17480-2446 is another X-ray transient located in Terzan 5. It is a very interesting object showing accretion-powered pulsations and burst oscillations at 11 Hz. We report on the properties of its kHz QPOs detected between October 18 and October 23, soon after the source had moved from the so-called Atoll state to the Z state. Its QPOs are typical of persistent Z sources; in the sense that they have low Q factors ({approx}30) and low rms amplitudes ({approx}5%). The highest frequency (at 870 Hz), if orbital, sets a lower limit on the inner disk radius of {approx}18.5 km and an upper limit to the dipole moment of the magnetic field {mu} {<=} 5 Multiplication-Sign 10{sup 26} G cm{sup 3}.« less