Title: PowerPoint-Pr
1Anomalous X-ray Pulsars and Soft Gamma-ray
Repeaters Sandro Mereghetti INAF - IASF Milano
2OUTLINE
Short review of AXP and SGR properties AXP /
SGR relationship 2 recent results XMM-Newton
gt Variability in AXP 1E1048 INTEGRAL
gt Spectral evolution in bursts from SGR 1806
3NORMAL x-ray pulsars are rotating magnetized
neutron stars
1) In binary systems powered by accretion from a
companion star e.g. Vela X-1, Cen X-3
Periods from 60 ms to a few 1000 s
2) rotation powered radio pulsars e.g. Crab
, Geminga, PSR 195720 Periods from 1.5 ms -
a few seconds
4AXP in the context Accreting pulsars
Most accreting pulsars are in massive binaries
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6AXP PROPERTIES
No evidence for massive companion stars
limits on ax sin i from timing limits on
Fx/Fopt from optical/IR observations Period of
a few seconds (6-12 s) Almost steady spin
down Very soft X-ray spectrum kTBB lt 0.5
keV ? ph gt 3-4
7AXP have very soft X-ray spectra
AXP
8AXP PROPERTIES
2 ( or 3 ? ) are in SNRs X-ray
luminosity Lx 1034 - 1036 erg s-1 Lx
gt rotational energy loss for a neutron star
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10Operational definition of AXP
a spinning down pulsar, with a soft X-ray
spectrum, apparently not powered by accretion
from a (massive) companion star, and with
luminosity larger than the rotational energy loss
(assuming a neutron star)
11 AXP census
P dP/dt (s) (10-11 s/s) 4U
014261 8.7 0.2 - 1E 2259586 7 0.05 CTB
109 1E 1048-5937 6.4 2-3 - 1E
1841-045 11.8 4 Kes 73 AX J1845-03 7 - G296
0.1, Var. RXS 1708-40 11 2 - CXO
J0110-72 8 2 in SMC XTE J1810-197 5.5 1.8 -
Var.
12- MAGNETIC ENERGY - field decay
- enhanced thermal emission
13Isolated NS accretion disk Thorne-Zytkow
object (Van Paradijs et al.
1995, Ghosh et al. 1997) fall back after SN
explosion (Chatterjiee et al. 2000, Alpar 2001)
capture of SNR ejecta by fast moving
NS (Marsden et al. 2000, 2001)
14Magnetar model (Thompson and Duncan)
Emission powered by magnetic field decay and/or
enhanced cooling
15Soft Gamma-ray Repeaters
- Initially discovered as a peculiar class of
Gamma-Ray Bursts - soft
- repeating
- About 5 currently known (1 in the LMC)
- Not always active (long quiescent periods)
16SGRs vs. GRBs
Durations
Spectra
Courtesy K. Hurley
17Energetics of SGRs
- Short Bursts
- Peak Luminosity 1038-1042 erg s-1
- Total Energy 1039-1042 erg
- Giant Flares
- Peak Luminosity 4 x 1044 erg s-1
- Total Energy 0.7-2 x 1044 erg
-
18Giant Flares
1998 August 27 from SGR 190014
1979 March 5 from SGR 0526-66
Feroci et al. 1999
Mazets et al. 1979, Cline et al. 1980
19Persistent X-ray emission from SGRs
- Lx 1035 -1036 erg /s (1-10 keV)
- Pulsations with periods 5 - 10 s
- secular spin-down at 10-11 s/s
- power law ( blackbody) spectra
VERY SIMILAR TO AXPs !!
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21(Kaspi et al. 2003)
SGR-like activity in the AXP 1E2259586
22bursts have Lpeak 1036-4 1038 erg/s Change in
pulse morphology Glitch ???? 4
10-6 (Kaspi et al. 2003)
23AXPSGR ?
Only observational selection effects introduced a
distinction between these sources belonging to
the same class of objects in AXP the quiescent,
pulsating emission was discovered first SGR
were discovered through their bursts
24OUTLINE
Short review of AXP and SGR properties AXP /
SGR relationship 2 recent results XMM-Newton
gt Variability in AXP 1E1048 INTEGRAL
gt Spectral evolution in bursts from SGR 1806
25First evidence for significant variability in 1E
1048-59
26The pulsed fraction decreased while the flux
increased
Spectrum did not vary BBPL kT0.6 keV ? 3
274U 014261 SAX (Israel et al 1999)
Power law photon index 3.9
Blackbody kT 0.4 keV
28Most AXP require 2 component model PL BB
Phot.index kTBB RBB NH 1022 1E
1048-59 2.9 0.63 keV 0.4 d3 km
1.0 4U014261 3.9 0.40 keV 1.8 d1 km
1.1 1E 225958 3.6 0.41 keV 2.6 d4 km
0.9 RXS1708-40 2.6 0.46 keV 7.9 d8 km
1.4 AXJ1845-00 - 0.64 keV 3.9 d15 km
6 1E 1841-0045 3.0 - - 2
29Are the two spectral components related to
distinct emitting regions and/or physical
processes ?
30small energy dependence of pulsed fraction
requires ad hoc tuning of the BB and PL components
31Despite the large flux variation the spectral
shape did not vary BBPL in both observations
kT 0.6 keV phot. Index 3 ... these are
the typical parameters seen in this source
32The pulsed fraction decreased while the flux
increased
33OUTLINE
Short review of AXP and SGR properties AXP /
SGR relationship 2 recent results XMM-Newton
gt Variability in AXP 1E1048 INTEGRAL
gt Spectral evolution in bursts from SGR 1806
34 - SGR1806-20 entered a new period of activity in
July 2003 - An INTEGRAL ToO observation started on 3
September 2003, while the source was still active
-
- INTEGRAL continued to observe SGR 1806-20 (l
9.99 deg, b -0.24 deg) during the Galactic
Center Deep Exposre (GCDE) until mid October - 24 bursts were detected by IBIS in real time by
the INTEGRAL Burst Alert System (IBAS) and
confirmed later by off-line analysis
3524 bursts from SGR 1806-20 have been detected
with the INTEGRAL Burst Alert System.
36GCDE Bursts
373-20 keV
JEM-X
Yoff -0.97º Zoff -2.22º
15-40 keV
40-100 keV
IBIS/ISGRI
Fluence (15-100 keV) 2.510-8 erg cm-2
100-200 keV
38Spectral Analysis
- 15-100 keV IBIS/ISGRI spectra of the bursts with
more than 500 net counts - Optically Thin Thermal Bremsstrahlung model
provides good fits (power-law, blackbody, Band
GRB model are ruled out) - kT 32-42 keV
- Conversion factor (15-100 keV, ltkTgt 38 keV) 1
count s-1 1.5x10-10 erg cm-2 s-1
39INTEGRAL Log N- Log P (Peak Flux distribution)
INTEGRAL Log N- Log S (Fluence distribution)
40THE SGR BURSTS OBSERVED BY IBIS ARE NORMAL IN
MOST RESPECTS
- Durations, energy spectra are typical
- However, the fluences are very low,1.5x10-8
erg/cm2 , 25-100 keV - These are the among the weakest bursts seen from
this SGR thanks to imaging, we are certain that
the source is indeed SGR1806-20
41IBIS (20-40 keV)
(INTEGRAL CP data 1 Msec, courtesy Ada Paizis)
42The MAGNETAR model predictions
- Highly magnetized (B1015 G), slowly rotating
(P 5-8 s) neutron stars - Bursts are triggered by a sudden shift in the
magnetospheric footpoints driven by a fracture in
the neutron star crust - The radiation originates from the cooling of an
optically thick pair-photon plasma
ee- plasma
Thompson Duncan (1995)
43- For typical (0.1 s long) bursts
- No signifcant spectral evolution predicted and in
general NOT observed up to now (e.g. Fenimore et
al. 1994, Kouveliotou et al. 1987)
SGR 190014 an exception Two peculiar bursts of
intermediate duration (1 s) and and with hard
(kT100 keV) spectra
Woods et al. (1999)
44Spectral Evolution of weak bursts with INTEGRAL
15-40 keV
40-100 keV
Götz et al., 2004, AA submitted
45Hardness-Intensity Anticorrelation with
INTEGRAL (bursts with more than 200 net counts)
Götz et al., 2004, AA submitted
46Conclusions
- 1) XMM / EPIC detected the first significant
variation in the flux and pulsed fraction of the
AXP 1048the spectral invariance is a further
evidence that the PLBB spectral decomposition
does not have a physical meaning - 2) INTEGRAL / IBIS detected the first evidence
for spectral evolution of fain SGR bursts as well
as a hardness intensity anticorrelationthese
properties are not (yet) foreseen in the
magnetar model