Download SGR 1900+14

Magnetars are
magnetically powered,
rotating neutron stars
RADIO PULSARS
2000 discovered to date
Radiate covering most of the electromagnetic spectrum
Rotate with periods that span five decades
(ms to a few hours).
Are powered by their own rotational energy,
residual surface heat or accretion
Live tens of millions of years
MAGNETARS (11 discovered to date)
Radiate almost entirely in X-rays, with luminosities
ranging between 1033 to 1036 erg/s
Emit typically brief (1-100 ms) bursts that may exceed
Eddington Luminosities and very rarely, Giant Flares
Rotate in a very narrow period interval (5-11 s) and
slow down faster than any other object (~10-10-10-11 s/s)
Are powered by magnetic field energy, which heats the
neutron star interior so that the surface glows
persistently in X-rays, and fractures the crust
inducing short, repeated bursts at random intervals.
Die rather young; typical ages are ~10000 yrs
Radio pulsars
Magnetars
MAGNETARS
AGE:
Ordinary
Star
(8-10 Msun)
0-10 s
0-10,000 years
above 10,000 years
0-10 million years
above 10 million yrs
Newborn
Neutron
star
AGE:
0-10 s
RADIO PULSARS
Several neutron star populations may belong
to the Magnetar class:
Soft Gamma Repeaters (SGRs)
Anomalous X-ray Pulsars (AXPs)
Dim Isolated Neutron Stars (DINs)
Compact Central X-ray Objects (CCOs)
How were SGRs discovered?
ApJ 1987
ApJ 1995
AIP Conference Proceedings 366, 1995
~180000 lys
N49 and the March 5th error box
0.09 arcminsq
Chandra observation of SGR 1627-41
SGR 1627- 41
1.4”
SGR burst time history
Outburst of AXP 1E 2259+586 in 2002
0
5000
Time (sec)
10000
15000
Kaspi et al 2003
Persistent Emission
SGR 1806-20
Woods et al 2001
AXP 1E 1048.1-5937
Kaspi et al. 2001
SGR Timing Properties
• SGR 1806–20:
P. = 7.48 s
P = 8.3 x 10–11 s s–1
. 1/2
19
B = 3.2 x 10 (P P ) G
B ~ 8 x 10
• SGR 1900+14:
P. = 5.16 s
–11
–1
P = 6.1 x 10 s s
14
G
(Kouveliotou et al. 1998)
B ~ 5.6 x 10
14
G
(Hurley et al. 1999; Kouveliotou et al. 1999)
Object
B-field (Gauss)
Galactic nuclei
Our Galaxy
Planets:
Jupiter
Earth
Sun (general field)
(sunspots)
Common iron magnet
Common MRI field
Strongest SUSTAINED
Lab fields
Strongest man-made B
Radio Pulsars
10-2-10-3
2x10-6
Magnetars
1014-1015
4
0.6
1
4,000
100
10,000
4.5x105
107
1012-1013
What is the magnetar energy source? LX = 1035 erg/s
Ė rot = 1033 erg/s
Accretion: several arguments why it
does not work
i) No companions detected
ii) Bursts cannot be explained
iii) ISM:extremely dense and cold
medium + extremely slow SGR
iv) fossil disc: detection of persistent
emission immediately after giant flare
argues against it
Magnetar model (Duncan and Thompson 92)
Decay of a super-strong magnetic field
SGR 1900+14
1996
May 98
Aug 98
Sep-Oct 98
1999
2000
Gogus et al. 2002
BURSTS
Typical SGR Bursts
• Brief
• Soft
-2
3
• L ~ 10 – 10 LEdd
• E ~ 10
36
– 10
41
erg
Gogus et al. 1999
Intermediate SGR Bursts
E ~ 6 x 10
42
erg
Two more events
August 29, 1998 &
April 28, 2001 had
41–42
E ~ 10
erg
Continuum of
burst energies
Kouveliotou et al 2001
Giant SGR Flares
• Hard initial spike
+ spin modulated
soft tail
March 5, 1979
(Mazets et al. 1979)
August 27, 1998
6
7
• L ~ 10 – 10 LEdd
44
• E ~ 10
Time (s)
(Feroci et al. 1999)
45
– 10 erg
SGR 1900+14
Woods et al. 2001
SGR 1627-41
SGR 1900+14
Woods et al. 2001
Kouveliotou et al. 2003
Self-Organized Criticality
• It states that composite systems self-organize to a
CRITICAL STATE where a slight perturbation can
cause a chain reaction of any size.
• SOC is the evolution of a system into an organized
form in the absence of any external constraints.
• Systems evolve from non- or slight correlation to a
high degree of correlation (critical state)
Simple models: Sand piles, Earthquakes, stock market
SOC Systems
Solar Flares
Solar Flares
Earthquakes
Earthquakes
(Lay & Wallace 1995)
(Aschwanden et al. 2000)
SOC Systems: Earthquakes
Recurrence Times of Micro
Earthquakes
(adopted from Nadeau & McEvilly 1999)
Duration – Magnitude
Correlation of Earthquakes
(adopted from Lay & Wallace 1995)
Burst Duration-Fluence Correlation
SGR 1806-20
SGR 1900+14
Gogus et al. 2001
SGR 1806-20
DECEMBER 27, 2004 GIANT FLARE (SWIFT)
Palmer et al, Nature, 2005
SGR 1806-20 December 27, 2004 GIANT FLARE (RHESSI)
Hurley et al, Nature 2005
Palmer et al, 2005
Palmer et al, 2005
X-ray Flare Properties
• Main Peak duration ~ 0. 5 s
• Rise time ~ 1.5 msec
• Tail Duration ~ 380 s (50 cycles@ 7.56s)
• Peak Flux >5 ergs/cm2 s
• Total (isotropic) energy release>1046 erg (Peak)
and 5x1043 erg (tail)
Some comparisons:
GRB prompt emission peak fluxes: 10-8-10-3 ergs/cm2 s
X-ray afterglows of long bursts: ~10-11 – 10-13 ergs/cm2 s
Previous giant flares: ~10-3 ergs/cm2 s
Typical SGR bursts: 10-9 – 10-6 ergs/cm2 s
Giant Flares and short GRBs
The two previous giant flares could have been detected
Up to 8 Mpc; the recent one up to 40 Mpc
Taking into account the SFR in our Galaxy, we would
expect 80 such events per year to be compared with the
150 BATSE detected
The isotropic distribution of short GRBs, the lack of
excess from Virgo cluster indicates that at most 5%
of short GRBs are SGR GFs or
The distance to SGR 1806-20 is less than 15 kpc
The SGR GF rate is less than assumed, the GF rate is
less than 1/30-40 years, or there are more luminous GFs.
Detection of an expanding Radio
Nebula associated with the
December 27, 2004 Giant Flare
SGR 1900+14
Frail et al Nature 1998
VLA image (330 MHz) of the area around SGR 1806-20
Crystal Brogan, NRAO/UoHawaii
VLA J180839-202439
Gaensler et al Nature 2005
At a distance of D = 15 d15, the 1.4 GHz
flux of VLA J180839-202439, at first
detection, implies an isotropic spectral
luminosity of 5D2x1015 W/Hz, which is
~ 700 times larger than the radio
afterglow seen from SGR 1900+14 !
International campaign monitoring over
0.35-16 GHz the AG from days 6-19 after
the GF: VLA, ATCA, WSRT, MOST here
(MERLIN, VLBA, GBT pending)
The nebula shape is resolved at 8.5 GHz: except
for day 16.8, the source is elliptical with axial
ratio ~0.6 and major axis oriented ~60º W to N
Constant isotropic expansion at 0.27(10)c until
day 19.7
SGR 1900+14
Frail et al Nature 1998
Gaensler et al Nature 2005
The light curve exhibits an achromatic break at
8.8 days: e.g. at 4.8 GHz the decay index
transitioning from 1.5 to 2.84
Significant linear polarization indicating
synchrotron radiation. The early PA indicated B
field alignment with the nebular axis
Spectral steepening at high freg. From day 11.2
single PL (0.84-8.5 GHz) with index -0.75(2)->
electron index p= 2.50(4) [p=1-2a]
Gaensler et al, Nature 2005
RADIO Flare Properties
• the radio emission was 500 times more luminous than the
1900+14 flare (at 15 kpc)
• the radio emission lasted over 45 days and counting
• the light curve exhibits a VERY STEEP achromatic break
• the spectrum is consistent with a power law index of –0.75(2)
from 0.84 – 8.5 GHz
•VARIABLE linear polarization
• the radio nebula expands with 0.3c (~ 4mas per day)
• Emin > 4x1043 ergs
OPEN QUESTIONS
What is the association between bursts and spin changes?
Is there a thermal component in the persistent emission
in all magnetars? When does it emerge?
Are there lines in the X-ray spectra of magnetars?
Is there an association of magnetars with Supernovae
Remnants and clusters of very massive stars? Which are
the magnetar progenitors? What is the magnetar formation
Rate?