Transcript Close-by young isolated neutron stars (and black holes)

Space Cowboys Odissey:
Beyond the Gould Belt
Sergei Popov, Bettina Posselt
(co-authors: F. Haberl, R. Neuhauser, J. Truemper, R. Turolla)
astro-ph/0609275, 0710.1547 and A&A in press
The new zoo of neutron stars
During last >10 years
it became clear that neutron stars
can be born very different.
In particular, absolutely
non-similar to the Crab pulsar.
o Compact central X-ray sources
in supernova remnants.
o Anomalous X-ray pulsars
o Soft gamma repeaters
o The Magnificent Seven
o Unidentified EGRET sources
o Transient radio sources (RRATs)
o Calvera ….
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Magnificent Seven
Name
RX 1856
RX 0720
RBS 1223
RBS 1556
RX 0806
RX 0420
RBS 1774
Period, s
7.05
8.39
10.31
6.88?
11.37
3.45
9.44
Radioquiet (?)
Close-by
Thermal emission
Absorption features
Long periods
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Population of close-by young NSs
Magnificent seven
 Geminga and 3EG J1853+5918
 Four radio pulsars with thermal emission
(B0833-45; B0656+14; B1055-52; B1929+10)
 Seven older radio pulsars, without detected
thermal emission.

Where are the rest?
UNCATCHABLES
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Log of the number of sources
brighter than the given flux
Log N – Log S
calculations
-3/2 sphere:
number ~ r3
flux
~ r-2
-1 disc:
number ~ r2
flux
~ r-2
Log of flux (or number counts)
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Population synthesis: ingredients
 Birth rate of NSs
 Initial spatial distribution
 Spatial velocity (kick)
 Mass spectrum
 Thermal evolution
 Interstellar absorption
Task:
To build an artificial model
of a population of some
astrophysical sources and
to compare the results of
calculations with observations.
A brief review on population
synthesis in astrophysics can
be found in astro-ph/0411792
and in Physics-Uspekhi (2007).
 Detector properties
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Population synthesis – I.
Gould Belt : 20 NS Myr-1
Gal. Disk (3kpc) : 250 NS Myr-1
• Cooling curves by
• Blaschke et al.
• Mass spectrum
ROSAT
18°
Gould Belt
Arzoumanian et al. 2002
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The Gould Belt
Poppel (1997)
 R=300 – 500 pc
 Age 30-50 Myrs
 Center at 150 pc from the
Sun
 Inclined respect to the
galactic plane at 20 degrees
 2/3 massive stars in 600 pc
belong to the Belt

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Population synthesis – II.
recent improvements
1. Spatial distribution of progenitor stars
We use the same
normalization for
NS formation rate
inside 3 kpc: 270 per Myr.
Most of NSs are born in
OB associations.
a) Hipparcos stars up to 500 pc
[Age: spectral type & cluster age (OB ass)]
b) 49 OB associations: birth rate ~ Nstar
c) Field stars in the disc up to 3 kpc
For stars <500 pc we even
try to take into account
if they belong to OB assoc.
with known age.
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Effects of the new spatial
distribution on Log N – Log S
There are no significant
effects on the Log N – Log S
distribution due to more
clumpy initial distribution
of NSs.
But, as we’ll see below,
the effect is strong for
sky distribution.
Solid – new initial XYZ
Dashed – Rbelt = 500 pc
Dotted – Rbelt = 300 pc
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Mass spectrum of NSs



Mass spectrum of local young NSs
can be different from the general
one (in the Galaxy)
Hipparcos data on near-by
massive stars
Progenitor vs NS mass:
Timmes et al. (1996);
Woosley et al. (2002)
(masses of secondary objects in NS+NS)
astro-ph/0305599
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Population synthesis – II.
recent improvements
2. New cross sections & abundances
and new mass spectrum
Low mass progenitors for the
dotted mass spectrum are
treated following
astro-ph/0409422.
The new spectrum looks
more “natural”.
But the effect is ....
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Effects of the new mass spectrum
and abundances on the Log N – Log S
... Effect is negligible
We also introduced
new abundances, and
calculated count rate
more accurately
than before. Still,
the effect is small.
Solid – new abundances, old mass
Dotted – old abundances, old mass
Dashed – new abundances, new mass
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Population synthesis – II.
recent improvements
3. Spatial distribution of ISM (NH)
instead of :
now :
Modification of the old one
NH inside 1 kpc
(see astro-ph/0609275 for details)
Hakkila
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Effects of the new ISM distribution
Again, the effect is not
very significant for
Log N – Log S, but
it is strong for the
sky distribution
(see below).
Dot-dashed and dot-dot-dashed lines
Represent two new models of the
ISM distribution.
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First results: new maps
Popov et al. 2005
Count rate > 0.05 cts/s
b= +90°
Cep?Per?
Sco OB
Ori
b= -90°
PSRs+
Geminga+
M7
Clearly several rich
OB associations start
to dominate in the
spatial distribution
PSRs16
INSs and local surrounding
Massive star population in the Solar vicinity (up to 2 kpc)
is dominated by OB associations.
Inside 300-400 pc the Gould Belt is mostly important.
De Zeeuw et al. 1999
Motch et al. 2006
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50 000 tracks, new ISM model
Candidates:
Agueros
Chieregato
radiopulsars
Magn. 7
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Age and distance distributions
0.01 < cts/s < 0.1
0.1 < cts/s < 1
1 < cts/s < 10
Age
New cands.
Distance
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Different models: age distributions
Bars with vertical lines:
old model for Rbelt=500 pc
White bars: new initial dist
Black bars:
new ISM (analyt.) and
new initial distribution
Diagonal lines:
new ISM (Hakkila) and
new initial distribution
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Different models: distance distr.
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Where to search for more cowboys?
We do not expect to find much more candidates at fluxes >0.1 cts/s.
Most of new candidates should be at fluxes 0.01< f < 0.1 cts/s.
So, they are expected to be young NSs (<few 100 Mys) just outside the Belt.
I.e., they should be in nearby OB associations and clusters.
Most probable candidates are Cyg OB7, Cam OB1, Cep OB2 and Cep OB3.
Orion region can also be promising.
Name
l-
l+
b-
b+
Cyg OB7
84
96
-5
9
Cep OB2
96
108
-1 12
700
Cep OB3
108
113
1
700-900
7
Dist., pc 130
90
L=110
10
600-700
0
-10
Cam OB1 130
153
-3
8
800-900
(ads.gsfc.nasa.gov/mw/)
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56 EGRET sources
Recently Crawford et al. (astro-ph/0608225) presented a study
of 56 well-identified EGRET error boxes.
The idea was to find radio pulsars. Nothing was found.
Obviously, they can be geminga-like sources,
or represent some other subpopulation of cooling NSs.
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OB runaway stars
Another possibility to find new ICoNSs is
to search for (un)bound compact companions of OB runaway stars.
More than one hundred OB runaway stars are known in 1 kpc
around the Sun (astro-ph/9809227).
Unbounded NSs
Optical star
bh
Bounded NSs
Sayer et al. 1996 and Philp et al. 1996
looked for radio pulsars as companions
of runaway stars.
It is reasonable to look for M7-like
companions around young OB stars.
(for BHs done in astro-ph/0511224)
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Calvera et al.
Recently, Rutledge et al. reported the discovery of an enigmatic
NS candidated dubbed Calvera.
It can be an evolved (aged) version of Cas A source,
but also it can be a M7-like object, who’s progenitor was
a runaway (or, less probably, hypervelocity) star.
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CCO vs. M7
Gotthelf and Halpern (2007) presented evidence in favor of hypothesis
that among CCOs there is a population of NSs born with long spin
periods (few tenths of a second) and small magnetic fields (<1012 G).
These sources are hot. The M7 sources are hot, too, but they seem
to belong to different populations.
This can be explained by accreted envelopes in CCOs
(Kaminker et al. 2006).
It is necessary to make a general population synthesis,
which would include all types of isolated NSs.
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Resume





New more detailed population synthesis model for local population of
isolated NS is made
New results provide a hint to search for new coolers.
We predict that new objects can be identified at 0.01<cts/s<0.1
behind the Gould Belt in the directions of close-by rich OB
associations, in particular Cep OB2.
These objects are expected to be younger and hotter than the
Magnificent seven.
New ways to find candidates can be discussed.
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The Magnificent Seven Vs. Uncatchables
Born in the Gould Belt.
Bright. Middle-aged.
Already observed.
Born behind the Belt.
Dimmer. Younger.
Wanted.
That’s all!
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Radio detection
Malofeev et al. (2005) reported detection of
1RXS J1308.6+212708 (RBS 1223)
in the low-frequency band (60-110 MHz)
with the radio telescope in Pushchino.
In 2006 Malofeev et al. reported radio detection
of another one.
(back)
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NS+NS binaries
Pulsar
B1913+16
B2127+11C
B1534+12
J0737-3039
J1756-2251
Pulsar mass
Companion mass
1.44
1.35
1.33
1.34
1.40
1.39
1.36
1.35
1.25
1.18
(PSR+companion)/2
J1518+4904
J1811-1736
J1829+2456
1.35
1.30
1.25
(David Nice, talk at Vancouver 2005)
(Back)
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