Transcript Soft gamma repeaters outside the Local group

Origin of magnetars and
observability of
soft gamma repeaters outside the
Local group
S.B. Popov
(Sternberg Astronomical Institute)
Co-authors:
M.E. Prokhorov, B.E. Stern
(astro-ph/0502391; astro-ph/0503532; astro-ph/0505406)
Plan of the talk
• Introduction: magnetars (Woods, Thompson 2004)
• Origin of magnetars (astro-ph/0505406)
• Search for extragalactic magnetars
(astro-ph/0502391; astro-ph/0503532)
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Introduction: magnetars
Magnetars are neutron stars
powered by their magnetic fields
(i.e. not by rotation, thermal evolution, etc.)
Usually they have high magnetic fields.
There are two main types of magnetars:
Soft gamma repeaters (SGRs) and
Anomalous X-ray pulsars (AXPs).
Magnetic field measurements
Large fields:
1014 – 1015 G
• Direct measurement
of the magnetic field
of the SGR
• Spin-down
• Long periods
Ibrahim et al. 2002
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Alternative theory
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Fossil disk
Mereghetti, Stella 1995
Van Paradijs et al.1995
Alpar 2001
Marsden et al. 2001
Problems …..
How to generate strong
bursts?
(recent result by Zhongxiang Wang et al.
indicates presence of passive discs)
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Magnetars in the Galaxy
• 4 SGRs, 8 AXPs, plus candidates, plus radio
pulsars with high magnetic fields …
Note a recent discovery
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• Young objects (about 10 yrs).
by McLaughlin,
Lyne et al.
• Probably about 10% of all NSs.
(submited to Nature)
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Historical notes
• 05 March 1979. Cone experiment.
Venera-11,12 (Mazets et al.)
• Event in LMC. SGR 0520-66.
• Fluence: about 10-3 erg/cm2
Mazets et al. 1979
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SGRs: periods and giant flares
• 0526-66
• 1627-41
• 1806-20
• 1900+14
+candidates
P, sec
Giant flare
8.0
5 March 1979
6.4
18 June 1998 (?)
7.5
24 Dec 2004
5.2
27 Aug 1998
See a review in
Woods, Thompson
astro-ph/0406133
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Main types of activity of SGRs
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Weak burst. L<1041 erg/s
Intermediate bursts. L=1041–1043 erg/s
Giant bursts. L<1045 erg/s
Hyperflares. L>1046 erg/s
See a review in
Woods, Thompson
astro-ph/0406133
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Common (weak) bursts from
SGRS and AXPs
• Typical burst from
SGR 1806-20, SGR
1900+14 and from
AXP 1E 2259+586
observed by RXTE
(from Woods,
Thompson, 2004,
astro-ph/0406133)
from Woods, Thompson 2004
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Intermediate SGR bursts
• Four intermediate
bursts. However, the
forth is sometimes
considered as a
giant one
from Woods, Thompson 2004
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Giant flare from SGR 1900+14
(27 Aug 1998)
• Data from Ulysses
(figure from Hurley
et al. 1999a)
• Spike 0.35 sec
• P=5.16 sec
• L>3 1044 erg/s
• ETOTAL>1044 erg
• Influenced the Earth
ionosphere
Hurley et al. 1999
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27 Dec 2004 giant outburst of
SGR 1806-20
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Spike 0.2 sec
Fluence 1 erg/cm2
E(spike)3.5 1046 erg
L(spike)1.8 1047 erg/s
Long tail (400 s)
P=7.65 s
E(tail) 1.6 1044 erg
Distance 15 kpc
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The greatest flare of a Soft
Gamma Repeater
• On December 27 2004
the greatest flare from
SGR 1806-20 was
detected by many
satellites: Swift,
RHESSI, Konus-Wind,
Coronas-F, Integral,
HEND, …
• 100 times brighter than
ever!
Palmer et al.
astro-ph/0503030
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Konus-Wind data on SGR 180620 27 Dec 2004 flare
Mazets et al. 2005
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Medusa
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AXP: anomalous X-ray pulsars
These sources were recognized as a
separate class in 1995
They are characterized by:
• Continuous spin down
• Period about 5-10 sec
• Small and stable X-ray luminosities
about 1035 erg/s
• Soft spectra
• Absence of secondary companions
Recently bursts (similar to weak bursts of SGRs)
were discovered.
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Known AXPs and candidates
Name
CXO 010043.1-72
4U 0142+61
1E 1048.1-5937
1RXS J170749-40
XTE J1841-197
1E 1841-045
AX J1844-0258
1E 2259+586
Period, s
8.0
8.7
6.4
11.0
5.5
11.8
7.0
7.0
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Are SGRs and AXPs relatives?
• SGR-like bursts
from AXPs
• Spectral properties
• Quiet periods of
SGRs (0525-66
since 1983)
Gavriil et al. 2002
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I. Origin of magnetars: abstract
• We present population synthesis calculations of binary systems.
• Our goal is to estimate the number of neutron stars originated
from progenitors with enhanced rotation, as such compact
objects can be expected to have large magnetic fields,
i.e. they can be magnetars.
• The fraction of such neutron stars in our calculations
is about 8-14 %.
• Most of these objects are isolated due to coalescences
of components prior to a neutron star formation,
or due to a system disruption after a supernova explosion.
• The fraction of such neutron stars in survived binaries is about
1% or lower, i.e. magnetars are expected to be isolated objects.
Their most numerous companions are black holes.
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A question:
Why do all magnetars are isolated?
• 5-10 % of NSs are
expected to be binary
(for moderate and small
kicks)
• All known magnetars (or
candidates) are single
objects.
• At the moment from the
statistical point of view it
is not a miracle,
however, it’s time to ask
this question.
Two possible explanations
• Large kick velocities
• Particular evolutionary path
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Theory of magnetars
• Thompson, Duncan
ApJ 408, 194 (1993)
• Entropy-driven convection
in young NSs generate
strong magnetic field
• Twist of magnetic field
lines
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Magnetars origin
Probably, magnetars are
isolated due to their origin
• Fast rotation is necessary
(Thompson, Duncan)
• Two possibilities to spin-up
during evolution in a binary
1) Spin-up of a progenitor
star in a binary via
accretion or synchronization
2) Coalescence
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The code
We use the “Scenario Machine” code.
Developed in SAI (Moscow) since 1983
by Lipunov, Postnov, Prokhorov et al.
(http://xray.sai.msu.ru/~mystery/articles/review/ )
We run the population synthesis of binaries
to estimate the fraction of NS progenitors
with enhanced rotation.
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The model
Among all possible evolutionary paths that
result in formation of NSs we select those that
lead to angular momentum increase of
progenitors.
• Coalescence prior to a NS formation.
• Roche lobe overflow by a primary without a
common envelope.
• Roche lobe overflow by a primary with a
common envelope.
• Roche lobe overflow by a secondary without a
common envelope.
• Roche lobe overflow by a secondary with a 25
common envelope.
Parameters
We run the code for two values of the parameter
αq which characterizes the mass ratio distribution of
components, f(q), where q is the mass ratio.
At first, the mass of a primary is taken from the
Salpeter distribution, and then the q distribution is
applied.
f(q)~q αq , q=M2/M1<1
We use αq=0 (flat distribution, i.e. all variants of mass
ratio are equally probable) and αq=2 (close masses are
more probable, so numbers of NS and BH
progenitors are increased in comparison with αq=0).
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Results of calculations-1
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Results of calculations-2
Most of “magnetars” appear after coalescences or
from secondary companions after RLO by primaries.
They are mostly isolated.
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II. Extragalactic SGRs: abstract
• We propose that the best sites to search for
SGRs outside the Local group are galaxies
with active massive star formation.
• We searched for giant flares from near-by
star forming galaxies (M82, M83, NGC 253,
NGC 4945), from the Virgo cluster and from
“supernova factories” (Arp 299 and NGC
3256) in the BATSE catalogue. No good
candidates are found.
We discuss this result.
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SGR flares vs. GRBs
Woods et al.
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SGRs and starformation
• Possibility of a SGR detection outside the
Local group of galaxies
• Star forming galaxies are the best sites to
search for extragalactic SGRs
• <5 Mpc. M82, M83, NGC 253, NGC 4945
• About 40 Mpc. Arp 299, NGC 3256
• Possible candidates in the BATSE catalogue
of short GRBs
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Assumed time profiles of the initial
spike of the 05 March 1979 event
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The probability of detection by
BATSE of a giant flare
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BATSE GRBs associated with near-by starbursts
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The probability of detection by
BATSE of a hyperflare
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BATSE GRBs associated with
“supernova factories”
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Virgo cluster analysis
We also searched for GFs and HFs from
the Virgo cluster direction in BATSE data.
Nothing was found (see astro-ph/0503352).
Renormalizing this result to our Galaxy
we obtain that HFs (>5 1045 erg in spike)
should be as rare as one in 1000 years.
This estimate is in correspondence with
results obtained by other authors
(Palmer et al. 2005, Ghirlanda et al. 2005).
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Other ideas about relations
between SGR and SF galaxies
Eichler (2005) discussed a possible connection
between SGRs and high energy cosmic rays.
In this sense it is interesting to remember that
several groups (for example, Giller et al.)
reported the discovery of associations
between UHECR and star forming galaxies.
In particular, Giller et al. discussed Arp 299
and NGC 3256.
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Evolution of SGR activity
Usually the rate of GFs is assumed to be constant.
However, all types of activity of NSs normally decay with time
For example, the rate of starquakes is expected to evolve as t5/2
If the rate of GFs evolves proportionally to time or faster then:
1. The probability to detect a SGR is higher for younger objects
2. We can face “an energy crisis”, i.e. there is not enough energy
to support strong burst in SGRs youth.
All these items can be important in estimation of the
probability of detection of extragalactic SGRs.
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Conclusions.I.
• We made population synthesis of binary systems to
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derive the relative number of NSs originated from
progenitors with enhanced rotation -``magnetars''.
With an inclusion of single stars (with the total
number equal to the total number of binaries) the
fraction of ``magnetars'‘ is ~8-14%.
Most of these NSs are isolated due to
coalescences of components prior to NS
formation, or due to a system disruption after a SN
explosion.
The fraction of ``magnetars'' in survived binaries is
about 1% or lower.
The most numerous companions of ``magnetars''
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are BHs.
Conclusions. II.
• Close galaxies with enhanced star formation
rate are the best sites to search for extragalactic
SGRs
• Our search in the BATSE catalogue did not provide
good candidates
• Reasons for the non-detection
- overestimates of the peak flux
- uncertainties in spectrum
- naïve scaling of the SGRs number is not valid
- ??????
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THAT’S ALL. THANK YOU!
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Discovery of radio transients
by Lyne et al.
Lyne et al. reported transient dim radio sources with possible periods
about seconds in the galactic plane discovered in the Parkes survey
(talk by A. Lyne in Amsterdam, august 2005; subm. to Nature).
These radio transients can be relatives of the However, it is not clear
Magnificent seven
if they are young or old.
They can be propellers…
Shall we expect also similar objects from the Belt????
YES!!! And they even have to be brighter (as they are closer).
The problem – low dispersion.
It is important to monitor the Magnificent Seven to find
transient radio activity.
Malofeev et al already reported detection of one of the M7.
It can be connected with symmetric X-ray curve:
two nearly identical pulses during the period.
(back)
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P-Pdot for new transient sources
Lyne et al. 2005
Submitted to Nature
(I’m thankful to
Prof. Lyne for giving
me an opportunity
to have a picture
in advance)
Estimates show that
there should be about
400 000
sources of this type
in the Galaxy
(back)
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Magnificent Seven
Name
Period, s
RX 1856
-
RX 0720
8.39
RBS 1223
10.31
RBS 1556
-
RX 0806
11.37
RX 0420
3.45
RBS 1774
9.44
Radioquiet (?)
Close-by
Thermal emission
Long periods
(back)
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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.
(back)
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