MIV: "Neutron stars — Equation of State"
Physics of Neutron Stars
Neutron Star Cooling
Pulsars
Microquasars
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Neutron Stars
Also: "Neutron stars and quark matter" by Gordon Baym
[nucl-th/0612021 
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”Isolated Neutron Stars: from the Interior to the Surface” (London, April 2006).
Many presentations from this conference are available on the Web:
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Authors: S.B. Popov | |
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ref: "Dense Matter In Heavy Ion Collisions and Astrophysics" (2007) [astro-ph/0610593 ] | |
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Title: The Zoo of Neutron Stars | |
1 Introduction
As the Moscow Zoo, the Zoo of neutron stars (NSs) can be separated into old
and new parts. The old part includes classical radio pulsars and accreting NSs in
close binary systems. This territory started to be filled with ”animals” already
in 60s, and most of the ”beasts” are well known even to general public.
The new one is mostly populated by isolated NSs which belong to five main types which have been mainly recognized in the last 10 years or so. These five species are: • soft gamma repeaters (SGRs), • anomalous X-ray pulsars (AXPs), • central compact objects in supernova remnants (CCOs in SNRs), • the Magnificent seven (M7), and • rotating radio transients (RRATs). May be in near future more types will be recognized (for example, related to unidentified EGRET sources, in this respect data from the GLAST mission will be of crucial importance). In the following section I try to give an extremely brief guide for this new territory of the Zoo of NSs. As a general introduction to the Zoo of NSs one can take the short encyclopedic article by Baym and Lamb [1] and references therein. SGRs and AXPs are very well described in [2]. Theory of magnetars was reviewed many times, one can use, for example, the review by Heyl [3]. A perfect recent review on AXPs can be found in [4]. Observations of SGRs are also reviewed in [5]. To have an impression of how CCOs look like, one can take the brief paper [6]. A huge set of Chandra results on observations of SNRs (including CCOs) can be found in [7]. An extensive search for compact sources in SNRs was presented in [8]. The Magnificent seven attracted much interest in last few years. Two interesting reviewing papers were published recently by Trümper [9] and Haberl [10]. RRATs appeared in the Zoo very recently, so there are no reviews, yet. One should refer to the original paper [11]. In the last part of this note I speak about tests of theories of the thermal evolution of NSs. A very good recent review on the cooling can be found in [12]. All subjects touched in this paper have been excellently reviewed during the conference ”Isolated Neutron Stars: from the Interior to the Surface” (London, April 2006). Proceedings of the meeting will be published soon in the journal Astrophysics and Space Science, and this volume is going to be the best set of materials on the subject in the near future. In the Table 1 I give the list of sources. Mostly, data on SGRs are taken from [2], on AXPs – from [4], on CCOs – from [6], on the M7 – from [10]. However, some additions from other publications are made. In particular, I want to underline a recent determination of spin period of RX J1856-3754 [13]. References [1] Baym G., Lamb F.K. Encyclopedia of Physics, 2005. [physics/0503245 | ||
K1.1
EOS
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Neutron stars — Equation of State | ||||||||||||||||||||||||||||||||
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Observational tests of whether other neutron stars obey this constraint will be possible in the near future.
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Authors: Lattimer, J.M. & Prakash, M. |
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Journal-ref: Phys. Rep. 442 (2007) 109 [astro-ph/0612440 ] |
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Title: Neutron Star Observations: Prognosis for Equation of State Constraints |
| Abstract:
We investigate how current and proposed observations of neutron stars can
lead to an understanding of the state of their interiors and the key unknowns:
the typical neutron star radius and the neutron star maximum mass.
A theoretical analysis of neutron star structure, including general relativistic limits to mass, compactness, and spin rates is made. We consider observations made not only with photons, ranging from radio waves to X-rays, but also those involving neutrinos and gravity waves. We detail how precision determinations of structural properties would lead to significant restrictions on the poorly understood equation of state near and beyond the equilibrium density of nuclear matter. References [6] J.M. Lattimer & M. Prakash, ApJ, 550, 426 (2001) | |
Quark matter
[1998]
Cosmologists are finding evidence that the universe, lacking sufficient density of mass to reverse the process
of creation unleashed by the Big Bang, will continue to expand forever. However, according to a Berkeley Lab
physicist and his international collaborators, the creation process can be reversed in the aftermath of a
supernova and should be observable in the universe today. If their theory is true, a state of matter that
existed for about one-millionth of a second after the Big Bang has reappeared within the colossal densities
of the cosmic anomalies known as neutron stars.
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Quark matter
Pressure within the core of a neutron star is thought to be so tremendous that nucleons (protons and neutrons) burst apart like the popping of balloons. This sets free the three quarks that combine to form each nucleon. |
eutron stars
are formed out of the deaths
of massive stars (several times larger than the sun) so old they burned
up all their nuclear fuel. Such stars throw off their outer layers in
the mighty explosions known as supernovas, leaving only a core that is
generally less than 10 miles in diameter but with a density of hundreds
of millions of tons per cubic inch.
Credit: NASA / F. Walter
The isolated neutron star RX J185635-3754 is the closest known neutron star to the Sun:
distance is 117 ± 12 pc, age is 5 kyr, space velocity ~ 185 km/s, radius (inferred from thermal emission) is 15 km. |
According to Berkeley Lab's Norman Glendenning, an internationally recognized expert on compact stars, it is generally believed that quarks -- the elementary particles that combine to form hadrons such as protons and neutrons -- are liberated when matter is compressed to very high densities.
"A neutron star, because it is so dense, may be the only natural place in the universe where quark matter exists," says Glendenning. "We may have discovered a way of learning if this (the existence of free quarks) is true."
Some neutron stars spin rapidly - several hundred rotations per
second -- causing them to send out regular pulses of radio signals that
earned them the name "pulsars." Radio signals from pulsars can be heard
on Earth and could be used to confirm some of the theories about the
universe in its earliest stages. Glendenning and his colleagues have
postulated that the presence of quark matter in pulsars should be
detectable by measuring their rates of spin. As pulsars age, their
rotation slows. This "spin-down" means a loss of outward-pushing
centrifugal force, which in turn means further compression of the
pulsar's interior until nuclear matter is crushed into quark matter.
"First at the center and then in an expanding region, the relatively
incompressible nuclear matter will be converted to the highly
compressible quark matter phase," says Glendenning. "This conversion to
quark matter (which has been likened to the consistency of soup) allows
the pulsar to rapidly shrink."
The pulsar's sudden reduction in size results in a "spin-up," much
like rotating ice skaters spin faster when they tuck their arms in close
to their bodies. For example, a pulsar spinning at 200 rotations per
second might, for a time, spin at 202 rotations per second.
By deconfined phase of quarks we mean that
quarks are asymptotically free over extended regions. This phase is also
called the quark matter phase. By confined phase we mean the phase in which
quarks are confined in hadrons.
Glendenning and his colleagues estimate that converting the entire core of a pulsar
from nuclear to quark matter should take about 100,000 years. Since
there are currently 700 known pulsars, this means that about seven of
them could be undergoing this transition now. Pulsar observations are
still in their infancy, and many of the known pulsars were only recently
discovered. Still, Glendenning and his colleagues believe that spin-ups
as a result of nuclear-quark phase matter transitions are a very easy
signal to detect and should be observable. The discovery of such
spin-ups would be momentous, they say.
"It would prove that the essentially free quark state predicted for
matter at very high energy densities actually exists," says Glendenning.
"The detection of this state would give us a picture of an early phase
of the Universe that is based on observation."
K1.3
NS spins and the EOS
Zum Thema: —
— Millisecond X-Ray Pulsars —
Recycling — QPO — Tables | |
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Authors: Duncan Galloway | |||
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Journal-ref: (2007) [0711.4420 ] | |||
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Title: Accreting neutron star spins and the equation of state | |||
| Abstract:
X-ray timing of neutron stars in low-mass X-ray binaries (LMXBs) with RXTE has since
1996 revealed several distinct high-frequency phenomena.
Among these are oscillations during thermonuclear (type-I) bursts, which (in addition to persistent X-ray pulsations) are thought to trace the neutron star spin. Recent discoveries bring the total number of measured LMXB spin rates to 22. An open question is why the majority of the ~100 known neutron stars in LMXBs show neither pulsations nor burst oscillations. Recent observations suggest that persistent pulsations may be more common than previously thought, although detectable intermittently, and in some cases at very low duty cycles. For example, the 377.3 Hz pulsations in HETE J1900.1-2455 were only present in the first few months of it's outburst, and have been absent since (although X-ray activity continues). Intermittent (persistent) pulsations have since been detected in a further two sources. In two of these three systems the pulsations appear to be related to the thermonuclear burst activity, but in the third (Aql X-1) they are not. This phenomenon offers new opportunities for spin measurements in known systems. Such measurements can constrain the poorly-known neutron star equation of state, and neutron stars in LMXBs offer observational advantages over rotation-powered pulsars which make the detection of more rapidly-spinning examples more likely. Even so, spin rates of at least 50% faster than the present maximum appear necessary to give constraints stringent enough to discriminate between the various models. Although the future prospects for such rapidly-spinning objects do not appear optimistic, several additional observational approaches are possible for LMXBs. 1. Introduction
Particle accelerators probe the conditions in matter at extreme temperatures and densities (up to a factor of ten higher than nuclear). Matter within neutron stars is also expected to reach super-nuclear densities, but at comparatively “cool” temperatures (no more than 109 K!). Neutron stars thus play an important complementary role for studies of condensed matter, and measurements which may constrain the EOS are a high priority for observers. Since the EOS affects the bulk properties (mass and radius) of neutron stars, simultaneous measurement of these parameters with moderate precision in an individual object would in some cases be sufficient to identify the EOS. However, such measurements have proved surprisingly elusive. The masses of neutron stars in binary (rotation-powered) pulsars can bemeasured in some cases to a fraction of a percent (e.g. [3]) although simultaneous radius measurements are generally not available. While the maximum neutron star mass also provides a constraint on the EOS, most of the measured masses cluster around 1.4 M  , which is not useful in
distinguishing between different models.
Measurement of the spin rate in rapidly-rotating neutron stars provides a relatively model-independent way to constrain the EOS. The maximum spin rate of a neutron star (above which it will break up due to centrifugal forces) can be expressed in terms of the neutron star mass M and radius R, roughly independent of the EOS [1]:  nmax = 1045
(M/M)1/2(10 km/R)3/2,
where M and R are the neutron star mass and radius.
Constraining the possible candidates for the neutron star EOS thus requires detection of ever-more rapidly spinning neutron stars. The fastest-spinning neutron star presently known is the radio pulsar PSR J1748-2446ad, at 716 Hz [4]. Although it’s mass is unknown, assuming a value consistent with the measurements from other radio pulsars leads to an upper radius limit of 14.4 km. Without a mass measurement, this limit does not yet allow us to reject any individual EOS. Rapid spins in neutron-star LMXBs
Evidence of rapid spins in neutron-star LMXBs has been obtained exclusively via observations with the
Proportional Counter Array (PCA; [5]) aboard the Rossi X-ray Timing Explorer (RXTE). The PCA is the only
instrument to date with the sensitivity (effective area ~ 6500 cm2) and time resolution
(~ 1 ms) necessary to detect rapid variability from these systems.
With the exception of a few high-field neutron stars in LMXB systems (including Her X-1 and GX 1+4), measured spin frequencies fall in the range 45–620 Hz (Table 1), with all but one > 180 Hz. These rapid spins confirm the LMXBs as the evolutionary precursor to the “recycled” millisecond radio pulsars [6, 7]. The LMXBs for which spins have been measured represent only about 20% of the known population of more than 100 (e.g. [8]). It remains an open question as to why it is so difficult tomeasure the spin in the majority of neutron stars in LMXBs. The two conventional explanations are that either • the non-pulsing neutron stars in LMXBs have magnetic fields that are too weak to channel accretion onto polar hotspots (perhaps due to suppression by the accreted material) or • that the pulsations are scattered by a surrounding region of high optical depth. A comparison of the spectral properties of the pulsing and non-pulsing LMXBs does not support the latter explanation ([12]). Furthermore, while the sources which exhibit pulsations tend to have low time-averaged X-ray fluxes (and hence accretion rates), this condition is not sufficient for pulsations to be detectable. The contrast with the rotation-powered pulsars is even more marked when one considers that even the LMXBs which do exhibit pulsations, do not exhibit pulsations at all times. Pulsations may only be detected from the accretion-powered millisecond pulsars (AMSPs) when in outburst; similarly, burst oscillations are only detected for a few seconds at the peak of some thermonuclear bursts. This property presents an observational challenge to the measurement of rapid neutron star spins which is quite distinct from the difficulties encountered in searches for rapidly-spinning rotation-powered pulsars. In further contrast to the rotation-powered pulsars, the spin rate for neutron stars in LMXBs may be measured in two distinct ways: • burst oscillations and persistent pulsations. • In addition, intermittent (persistent) pulsations have been detected recently in three systems. Below I describe each of these phenomena in more detail. References 1. J. M. Lattimer, and M. Prakash, Phys. Rep. 442, 109–165 (2007). | ||||
K2
Isolated Neutron Stars
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Author: J. E. Trümper | |
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Journal-ref: In: A. Baykal et al. (ed.) Proceedings The Electromagnetic Spectrum of Neutron Stars,
Marmaris, Turkey, June 7-18 2004, 133-136. Springer (2006) [astro-ph/0502457 ] | |
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Title: Isolated Neutron Stars | |
neutron star,
indicating a stiff equation of state at high
densities. A comparison of the result with mass-radius relations shows that in
this case a quark star or a neutron star with a quark matter core can be ruled out with high confidence.
Fig. 1:— The P-dP/dt diagram
P—P' distribution of radio pulsars (black dots).
X-ray detected pulsars (grey filled circles); X-ray detected ms-pulsars (tringles)
Lupe: open circles: Radio Quiet Isolated Neutron Stars (INS) INTRODUCTION
One of the fundamental problems of neutron star physics is to determine the
equation of state at supra-nuclear densities. In order to get a handle on that
one must constrain the mass-radius relation and this can be done in principle
by various methods which all have their specific problems:
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| X-ray emission from Isolated Neutron Stars | |
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Authors: V. M. Kaspi, M. S. E. Roberts, A. K. Harding |
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Journal-ref: "Compact Stellar X-ray Sources", eds. W.H.G. Lewin and M. van der Klis [astro-ph/0402136
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( book: )
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Title: Isolated Neutron Stars |
| Abstract: This is a review of X-ray emission from all types of isolated neutron stars, with an emphasis on rotation-powered pulsars. Topics include magnetospheric and thermal emission, as well as pulsar wind nebulae. | |
Fig. 7.1. P– P' diagram for the 1403 currently catalogued rotation-powered pulsars.
The 66 X-ray detected sources are indicated with an “X.” Solid lines show constant E', and dotted lines show constant inferred surface di-polar magnetic field. “X-ray-detected” means pulsed, unpulsed or nebular emission, be it thermal or non-thermal. X-ray detected sources are generally those with the greatest spin-down luminosity, although the correlation is not perfect because of the wide range of source distances and observational selection effects.
The indicated sources are summarized in Table
Table 7.1, non-thermal X-ray detected sources
Table 7.2, thermally cooling X-ray detected sources
and Table 7.5 (cf. text). Note that the X-ray-detected millisecond pulsars in the globular cluster 47 Tucanae do not have observable intrinsic P' due to contamination by acceleration in the cluster potential; for those sources (numbering 15), we have used an inferred P'.
| RX J1605.3+3249 — vtrans = 68 (d/100pc) km s-1 | |
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Authors: C. Motch, K. Sekiguchi, F. Haberl, V.E. Zavlin, A. Schwope, M.W. Pakull |
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Journal-ref: A&A (2004) [astro-ph/0408356] |
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Title: The proper motion of the isolated neutron star RX J1605.3+3249 |
| Abstract:
We obtained deep optical imaging of the thermally emitting X-ray
bright and radio-quiet isolated neutron star RX J1605.3+3249 with the Subaru
telescope in 1999 and 2003. Together with archival HST images acquired in 2001 these data reveal
a proper motion of µ = 144.5 ± 13.2 mas/yr. This implies a relatively high spatial velocity (vtrans = 68 (d/100pc) km s-1) and indicates that the star is unlikely to be re-heated by accretion of matter from the interstellar medium. Assuming that RX J1605.3+3249 is a young (105-106 yr) cooling neutron star, its apparent trajectory is consistent with a birth in the nearby Sco OB2 OB association at a location close to that derived for RX J1856.5-3754 and perhaps also to that of RX J0720.4-3125. This suggests that the X-ray bright part of ROSAT-discovered isolated neutron stars is dominated by the production of the Sco OB2 complex which is the closest OB association and a part of the Gould belt. The B and R magnitudes of the faint optical counterpart did not vary from 1999 to 2003 at B = 27.22 ± 0.10. Its B-R colour index of +0.32 ± 0.17 is significantly redder than that of other isolated neutron stars and the optical flux lies a factor 11.5 above the extrapolation of the X-ray blackbody-like spectrum. The red optical colour reveals the presence of an additional emitting component in the optical regime over the main neutron star thermal emission. We also discovered a small elongated Ha nebula approximately centered on the neutron star and aligned with the direction of motion. The width of the nebula is unresolved and smaller than ~ 0.4" for a length of about 1". The shape of the Balmer emitting nebula is very different from those seen close to other neutron stars and should be confirmed by follow-up observations. We shortly discuss the possible mechanisms which could give rise to such a geometry. | |
K2.1
Neutron Stars at Optical/IR Wavelengths
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Authors: R. P. Mignani, S. Bagnulo, A. De Luca, G. L. Israel, G. Lo Curto, C. Motch, R. Perna, N. Rea, R. Turolla, S. Zane | |
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Journal-ref: Astrophysics and Space Science (2006) [astro-ph/0608025 ] | |
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Title: Studies of Neutron Stars at Optical/IR Wavelengths | |
| Abstract:
In the last years, optical studies of Isolated Neutron Stars
(INSs) have expanded from the more classical rotation-powered ones to other
categories, like the Anomalous X-ray Pulsars (AXPs) and the Soft Gamma-ray
Repeaters (SGRs), which make up the class of the magnetars, the radio-quiet
INSs with X-ray thermal emission and, more recently, the enigmatic Compact
Central Objects (CCOs) in supernova remnants. Apart from 10 rotation-powered
pulsars, so far optical/IR counterparts have been found for 5 magnetars and
for 4 INSs. In this work we present some of the latest observational results
obtained from optical/IR observations of different types of INSs.
INTRODUCTION
After the spectacular results of the 1990s, which yielded to seven of the ten present RPP identifications thanks to the ESO NTT and to the HST telescopes, only PSR J0437-4715 (Kargaltsev et al. 2004) has been added to the record, despite several attempts carried out after the advent of the ESO VLT. The optical emission properties of RPPs depend on the age, with the young ones featuring purely magnetospheric spectra and the middle-aged ones featuring composite spectra with an additional thermal component arising from the cooling neutron star surface. For older objects the situation is less clear although there is evidence for a dominant magnetospheric emission, while only the very old PSR J0437-4715 features a purely thermal emission. Multi-wavelength observations carried out in the last decades have unveiled the existence of other groups of INSs, most of them radio-quiet, which have been later studied in the optical/IR. ROSAT observations lead to the identification of seven nearby (~ 300 pc) INSs dubbed “The Magnificent Seven” (S. Popov) with purely thermal X-ray emission. Being no unanimous consensus on the acronime to use from now on I will personally refer to these objects as X-ray Thermal INSs (XTINSs). Four XTINS have optical counterparts, with the identification of three of them secured via proper motion measures. Their inferred velocities have also allowed to rule out surface heating from ISM accretion as the source of the thermal X-ray emission in favour of heating from the cooling neutron star core. The XTINS optical emission is mostly thermal and exceeds the extrapolation of the soft X-ray spectrum by a factor ~ 10, which suggests that it arises from a cooler and larger area on the neutron star surface with respect to the X-ray one. Other peculiar INSs discovered through their X-ray/g-ray emission are the AXPs and the SGRs which are bealived to be magnetars, neutron stars with hyperstrong magnetic fields (~ 1014-15 G). Out of the twelve magnetars so far identified, only four have been observed in the optical/IR. Very little is known on the optical/IR spectra of the magnetars, apart from the fact that they flatten with respect to the extrapolation of the soft X-ray spectrum. This flattening can be taken as an indication of either a turnover in the magnetar spectrum or of the presence of an additional emitting source (e.g. an X-ray irradiated fallback disk). Other very enigmatic, supposedly isolated, neutron stars are the so-called CCOs in SNRs (Pavlov et al. 2004). Out of the seven CCOs known, only two have proposed optical/IR counterparts, classified as low-mass K or M stars. This would suggest that CCOs are indeed binary rather than isolated neutron stars. Last entry in the INS family are the newly discovered Rapid Radio Transients or RRATs for which optical/IR follow ups have just started. Mignani, R.P.: Optical studies of isolated neutron stars and their environments. In: A. Baykal et al. (ed.) Proceedings The Electromagnetic Spectrum of Neutron Stars, Marmaris, Turkey, June 7-18 2004, 133-136. Springer (2006) Zane, S., De Luca, A., Mignani, R.P., Turolla, R.: The proper motion of the isolated neutron star RX J1605.3+3249. A&A, | ||
K3
High-Magnetic-Field Radio Pulsars
| Radio pulsar J1718-3718 — B = 7.4 × 1013 G | ||
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Authors: V.M. Kaspi, M.A. McLaughlin | |
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Journal-ref: ApJ 618 (2004) L41-L44 [astro-ph/0411615 ] | |
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Title: Chandra X-ray Detection of the High-Magnetic-Field Radio Pulsar PSR J1718-3718 | |
Abstract: We report on the serendipitous X-ray detection, using
the Chandra X-ray Observatory, of the radio pulsar J1718-3718.
This pulsar has one of the highest inferred surface dipole magnetic fields in the radio pulsar population, higher than that inferred for one well-known Anomalous X-ray Pulsar (AXP). The X-ray emission for J1718-3718 appears point-like and has a purely thermal spectrum, with kT = 0.145 keV and absorbed 0.5-2 keV flux of (6.3-6.9) × 10-15 erg cm-2 s-1. We show that the pulsar's 2-10 keV luminosity is several orders of magnitude smaller than those of the non-transient AXPs, and consistent with the predictions of standard models for initial cooling. The number of high-magnetic-field radio pulsars observed at X-ray energies now stands at five. All are X-ray faint, suggesting that either there is a significant physical distinction between high-magnetic-field radio pulsars and AXPs, or that high-magnetic-field radio pulsars are, in fact, quiescent AXPs. | ||
SGR 1900+14: Fast X-ray Oscillations During the 1998 Giant Flare
| SGR 1900+14 — l = 2, 4, 7, and 13 toroidal modes (QPO) | |
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Authors: T.E. Strohmayer, A.L. Watts |
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Journal-ref: ApJ 632 (2005) L111-L114 [astro-ph/0508206 ] |
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Title: Discovery of Fast X-ray Oscillations During the 1998 Giant Flare from SGR 1900+14 |
| Abstract:
We report the discovery of complex high frequency variability during the
August 27, 1998 giant flare from SGR 1900+14 using the Rossi X-ray Timing Explorer (RXTE).
We detect an 84 Hz oscillation (QPO) during a 1 s interval beginning approximately 1 min after the initial hard spike. The modulation amplitude is energy dependent, reaching a maximum of 26% (rms) for photons above 30 keV, and is not detected below 11 keV, with a 90% confidence upper limit of 14% (rms). Remarkably, additional QPOs are detected in the average power spectrum of data segments centered on the rotational phase at which the 84 Hz signal was detected. Two signals, at 53.5 and 155.1 Hz, are strongly detected, while a third feature at 28 Hz is found with lower significance. These QPOs are not detected at other rotational phases. The phenomenology seen in the SGR 1900+14 flare is similar to that of QPOs recently reported by Israel et al. from the December 27, 2004 flare from SGR 1806-20, suggesting they may have a common origin, perhaps torsional vibrations of the neutron star crust. Indeed, an association of the four frequencies (in increasing order) found in SGR 1900+14 with l = 2, 4, 7, and 13 toroidal modes appears plausible. We discuss our findings in the context of this model and show that if the stars have similar masses then the magnetic field in SGR 1806-20 must be about twice as large as in SGR 1900+14, broadly consistent with magnetic field estimates from pulse timing. | |
K4
Pulsar evolution
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Authors: P. Esposito, A. Tiengo, A. De Luca, F. Mattana |
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Journal-ref: A&A Letters (2007) [0704.0205 ] |
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Title: Discovery of X-ray emission from the young radio pulsar PSR J1357-6429 |
| Abstract:
We present the first X-ray detection of the very young pulsar PSR J1357-6429
(characteristic age of 7.3 kyr) using data from the XMM-Newton and Chandra
satellites.
We found that the spectrum is well described by a power-law plus blackbody model, with photon index G=1.4 and blackbody temperature kT=160 eV. For the estimated distance of 2.5 kpc, this corresponds to a 2-10 keV luminosity of about LX(0.5-10 keV) ~ 1.2 × 1032 erg s-1, thus the fraction of the spin-down energy channeled by PSR J1357-6429 into X-ray emission is one of the lowest observed. The Chandra data confirm the positional coincidence with the radio pulsar and allow to set un upper limit of LX(2-10 keV) < 3 × 1031 erg s-1 on the luminosity of a compact pulsar wind nebula. We do not detect any pulsed emission from the source and determine an upper limit of 30% for the modulation amplitude of the X-ray emission at the radio frequency of the pulsar. | |
| J1357-6429 — A Very Young Radio Pulsar | |||||||||||||||||
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Authors: F. Camilo, R. N. Manchester, A. G. Lyne, B. M. Gaensler, A. Possenti, N. D'Amico, I. H. Stairs, A. J. Faulkner, M. Kramer, D. R. Lorimer, M. A. McLaughlin, G. Hobbs | ||||||||||||||||
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Journal-ref: Astrophys.J. 611 (2004) L25 [astro-ph/0406528] | ||||||||||||||||
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Title: The Very Young Radio Pulsar J1357-6429 | ||||||||||||||||
We have measured a large rotational glitch in this pulsar, with DP/P = - 2.4 × 10-6, similar in magnitude to those experienced occasionally by the Vela pulsar. At a nominal distance of only ~ 2.5 kpc, based on the measured free electron column density of 127 pc/cc and the electron distribution model of Cordes & Lazio, this may be, after the Crab, the nearest very young pulsar known. The pulsar is located near the radio supernova remnant candidate G309.8-2.6.  
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| Neutron Stars — Review | |
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Authors: J.M. Lattimer, M. Prakash |
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Journal-ref: Science 304 (2004) 536-542 [astro-ph/0405262
] |
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Title: The Physics of Neutron Stars |
| Abstract: Neutron stars are some of the densest manifestations of massive objects in the universe. They are ideal astrophysical laboratories for testing theories of dense matter physics and provide connections among nuclear physics, particle physics and astrophysics. Neutron stars may exhibit conditions and phenomena not observed elsewhere, such as hyperon-dominated matter, deconfined quark matter, superfluidity and superconductivity with critical temperatures near 1010 kelvin, opaqueness to neutrinos, and magnetic fields in excess of 1013 Gauss. Here, we describe the formation, structure, internal composition and evolution of neutron stars. Observations that include studies of binary pulsars, thermal emission from isolated neutron stars, glitches from pulsars and quasi-periodic oscillations from accreting neutron stars provide information about neutron star masses, radii, temperatures, ages and internal compositions. | |
K4.1
PSR B1133+16 in X-rays
Zum Thema: Hyperfast Pulsars | |
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| PSR B1133+16 — P = 1.18 s — tc = P/2P' ~ 5 Myr — E'rot = 8.8 × 1031 erg s-1 — LX = 1.4 × 1029 erg s-1 | ||
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Authors: O. Kargaltsev, G.G. Pavlov, G.P. Garmire | |
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Journal-ref: ApJ 636 (2006) 406-410 [astro-ph/0510466 ] | |
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Title: X-ray Emission from the nearby PSR B1133+16 and Other Old Pulsars | |
We detected a nearby (d=360 pc), old (5 Myr) pulsar B1133+16 with Chandra. The observed pulsar's flux is fX = (0.8±0.2) ×10-14 erg cm-2 s-1 in the 0.5-8 keV band. Because of the small number of counts detected, the spectrum can be described by various models. A power-law fit of the spectrum gives a photon index G = 2.5 and an isotropic luminosity of LX = 1.4 × 1029 erg s-1 in the 0.5-8 keV band, which is about 1.6 ×10-3 of the spin-down power E'rot. The spectrum can also be fitted by a blackbody model with a temperature of ~ 2.8 MK and a projected emitting area of ~ 500 m2, possibly a hot polar cap. The X-ray properties of PSR B1133+16 are similar to those of other old pulsars observed in X-rays, particularly the drifting pulsar B0943+10. 1. Introduction
Models of neutron star (NS) cooling (e.g., Yakovlev & Pethick 2004) predict that at an age of
> 1 Myr at least passively cooling NSs become too cold to emit X-rays from the bulk of NS surface.
Therefore, X-ray emission from isolated radio pulsars of such old ages is expected to consist of a magnetospheric component and, possibly, a thermal component emitted from small areas (polar caps [PCs]) heated by relativistic particles created in the pulsar’s acceleration zones. Hence, studying the X-ray emission from old pulsars allows one to examine the properties and evolution of magnetospheric radiation, probe the particle acceleration mechanisms operating in the magnetospheres, and constrain the PC heating and emission models. Although most of the ~ 1600 currently known radio pulsars are older than 1 Myr (see Fig. 1), they are intrinsically faint X-ray sources because the luminosities of both the magnetospheric and PC components are fractions of the spin-down power E'rot, which decreases with pulsar’s age. So far, only seven pulsars with characteristic ages tc = P/2P' > 1 Myr have been detected in X-rays (i.e., about 10% of X-ray detected “ordinary” pulsars), all of them at distances <2 kpc (Zavlin & Pavlov 2004). In principle, the magnetospheric and PC components of X-ray radiation can be distinguished by their spectra and pulse shapes (e.g., the magnetospheric radiation is expected to have a harder spectrum and show sharper pulsations). However, even the brightest of the detected old pulsars are too faint to establish the spectral shape unambiguously. For instance, the spectrum of the relatively bright PSR B0950+08 (d = 260 pc, tc = 17 Myr, fX(0.2-10 keV) = 1.1 × 10-13 erg cm-2 s-1, observed recently with XMM-Newton, can be fitted with either a single power-law (PL) model with photon index G ~ 1.75 or a combination of a PL model (G ~ 1.35) and a thermal (hydrogen atmosphere) model, with PC temperature Tpc ~ 1 MK and radius Rpc ~ 250 m (the two-component interpretation is supported by the energy-dependent pulse shape). Therefore, it is important to observe a larger sample of old pulsars and study their properties via comparative analysis. PSR B1133+16 = J1136+1551
In this Letter, we report on first X-ray detection of one of the nearest pulsars, PSR B1133+16.
This old pulsar (tc = 5 Myr) has the largest proper motion, 375
mas/yr, among the known radio pulsars, which corresponds to the transverse velocity Vc = 630 km/s at
the distance of 360 pc inferred from the radio parallax measurement (Brisken et al. 2002). The pulsar shows
a double-peaked radio pulse, and it is known to spend ~ 15% of the time in a “null state” where it does not
emit radio pulses (Biggs 1992). From radio polarization observations, Lyne & Manchester (1988) infer the angle
α = 51.3° between the magnetic and rotation axes, and the angle ß = 3.7° of the closest approach of the
magnetic axis to the line of sight.
References Biggs, J.D. 1992, ApJ, 394, 574 Brisken, W.F., Benson, J.M., Gross, W.M., & Thorsett, S.E. 2002, ApJ, 571, 906 | ||
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Authors: S.V. Zharikov, Yu.A. Shibanov, R.E. Mennickent, V.N. Komarova | |
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Journal-ref: A&A (2007) [0712.0826 ] | |
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Title: Possible optical detection of a fast, nearby radio pulsar PSR B1133+16 | |
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• Aims: We performed deep optical observations of the field of an old, fast-moving radio pulsar PSR B1133+16 in an attempt to detect its optical counterpart and a bow shock nebula. • Methods: The observations were carried out using the direct imaging mode of FORS1 at the ESO VLT/UT1 telescope in the B, R, and H_alpha bands. We also used archival images of the same field obtained with the VLT in the B band and with the Chandra/ACIS in X-rays. • Results: In the B band we detected a faint (B=28.1+/-0.3) source that may be the optical counterpart of PSR B1133+16, as it is positionally consistent with the radio pulsar and with the X-ray counterpart candidate published earlier. Its upper limit in the R band implies a color index B-R <0.5, which is compatible with the index values for most pulsars identified in the optical range. The derived optical luminosity and its ratio to the X-ray luminosity of the candidate are consistent with expected values derived from a sample of pulsars detected in both spectral domains. No Balmer bow shock was detected, implying a low density of ambient matter around the pulsar. However, in the X-ray and H_alpha images we found the signature of a trail extending ~4"-5" behind the pulsar and coinciding with the direction of its proper motion. If confirmed by deeper studies, this is the first time such a trail has been seen in the optical and X-ray wavelengths. • Conclusions: Further observations at later epochs are necessary to confirm the identification of the pulsar by the candidate's proper motion measurements.
1. Introduction
Until now optical emission has only been detected from < 1% of > 1500 known radio pulsars
(e.g., Mignani et al. 2005).
Even such a small number of optical identifications implies that rotation-powered neutron stars (NSs) can be active in the optical, as well as in the radio range. This follows from the fact that a small group of the optical pulsars contains not only young, ~1 kyr, and energetic objects like the Crab pulsar (Percival et al. 1993), but also much older pulsars such as ~3.1 Myr PSR B1929+10, ~17.4 Myr PSR B0950+08 ( Zavlin et al. 2004), and even the very old ~1 Gyr recycled millisecond pulsar PSR J0437-4715 (Kargaltsev et al. 2004). The power-law nonthermal spectral component is dominant in the pulsar’s optical emission, presumably originating in the magnetospheres of the NSs. The non-thermal component, which also is frequently observed in a wider spectral range including X-rays, is believed to be powered by the NS rotational energy loss E', called a spindown luminosity. The parameter η = L/ E', where L is the radiative luminosity, describes the efficiency of the transformation of the rotational energy into the emission. The most striking result of the optical study of ordinary pulsars is that the two old pulsars, PSR B1929+10 and PSR B0950+08, with rather low E', have almost the same optical efficiency as young and energetic Crab-like objects with much higher spin-down luminosities (Zharikov et al. 2004). At the same time, the efficiencies of middle-aged pulsars are significantly lower. In addition, a strong correlation between the non-thermal optical and X-ray luminosities of pulsars was found, indicating a general origin of the emission in both ranges. To confirm these findings it is necessary to increase the number of optically identified pulsars. An old, ~5 Myr, nearby pulsar PSR B1133+16 has almost the same parameters as the two old objects mentioned above. It is located at a high galactic latitude, l = 242°, b = 69°, implying a low interstellar extinction E(B-V) = 0.04. The direct proper motion and annual parallax measurements in the radio range by Brisken et al. (2002) yield a high transverse velocity of 631±30 km/s and a short distance to the pulsar 350±20 pc. The pulsar is younger than PSR B0950+08, but its spin-down luminosity, E' ~ 8.8 × 1031 erg s-1, is about an order of magnitude lower than those of PSR B1929+20 and PSR B0950+08. Nevertheless, it is higher than that of the nearby old PSR J0108-1431, whose optical counterpart has been unsuccessfully searched by Mignani et al. (2003). The high transverse velocity is promising for detecting an Ha bow shock nebula expected to be produced by the supersonic motion of the pulsar in the interstellar matter, as has been found around several rapidly moving pulsars and radio-silent NSs (e.g., Gaensler & Slane 2006). Recently, the field of PSR B1133+16 has been observed in X-rays with the Chandra/ACIS and a faint X-ray counterpart candidate was found at a flux level of (8±2)×10-15 erg cm-2 s-1 in 0.5 – 8 keV range (Kargaltsev et al. 2006). Given this value and using an empirical relation between the optical and X-ray luminosities of pulsars (Zharikov et al. 2004, 2006; see also Zavlin & Pavlov 2004), one can expect to detect the pulsar in the optical range at a sensitivity level of 27–29 magnitudes. References Brisken, W.F., Benson, J.M., Goss, W.M., et al. 2002, ApJ, 571, 906 | ||
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 | H. Heintzmann | ( Eintrag vom 24.2.2008) |
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