Observations of AXPs and SGRs: 1E 1048.1-5937 and SGR 1806-20

Observations of AXPs and SGRs:1E 1048.1-5937 and SGR 1806-20

Andrea Tiengo (IASF-MI, Univ. Milano)

S. Mereghetti, G. L. Israel, L. Stella, S. Zane, A. Treves, G. Ramsay,

M. Feroci, R. Turolla, M. Cropper

Palermo, 2003 October 14th

SSoft oft GGamma-ray amma-ray RRepeatersepeaters & & AAnomalous nomalous XX-ray -ray PPulsars ulsars

SGRsSGRs AXPsAXPs

Identified as subclass of:

• Soft burst spectrum• Repetition of bursts from

same position

Gamma-Ray Bursts X-Ray Pulsars

• Period 5-12 s and spin-down• No bright optical counterpart• Soft spectrum and stable flux

But then discovery of:• SGR-like bursts• AXP-like counterparts

SGRs and AXPs are the same class of objects!

Interpretations: Magnetar or NS accreting from fall-back disc

No narrow features in EPIC spectrum

Power-law (=3) + Blackbody (kT=0.65 keV)

5 ks observation performed on 28 Dec 2000

Guaranteed TimeGuaranteed Time observation of the observation of the Anomalous X-ray Pulsar 1E 1048.1-5937Anomalous X-ray Pulsar 1E 1048.1-5937

Results (Tiengo, Göhler, Staubert & Mereghetti 2002):

Flux within 50% from previous observations (SAX, ASCA)






SAXASCA

XMM

Energy dependent pulse profile: pulsed fraction 75% for E<1.5 keV and 100% for E>1.5keV

Flux within 50% from previous observations (SAX, ASCA)






Same spectrum as GT observation No narrow features in EPIC and RGS spectra

Guest Observer (AO2)Guest Observer (AO2) observation of 1E 1048-593observation of 1E 1048-593

70 ks (43 ks with low bkg) observation in June 2003


Flux a factor 2 higher than in GT observation

Guest ObserverGuest Observer observation of 1E 1048-593 observation of 1E 1048-593


BUT:

SAXASCA

XMM GT

XMM GO

Gavriil, Kaspi & Woods (2002) reported bursts from 1E1048.1-5937 in Nov 2001


BUT

Guest ObserverGuest Observer observation of 1E 1048-593 observation of 1E 1048-593


Lower pulsed fraction: 50%

Flux a factor 2 higher than in GT observation

Pulse profilesPulse profiles

GT observation GO observation

The new AXP XTE J1810-297The new AXP XTE J1810-297

New AXP (P = 5.54 s) discovered by RXTE in Aug 03 (Ibrahim et al. 2003)

From Einstein, ROSAT and ASCA archival data: it was ~100 times fainter! (Gotthelf et al. 2003)

XTE J1810-297 is a Transient AXP

XMM ToO on Sep 8 (Tiengo & Mereghetti 2003, ATEL 193; Gotthelf et al. 2003, astro-ph/0309745):

XTE J1810-297 is very similar to 1E 1048.1-5937

SpectrumSpectrum

XTE J1810-297 1E 1048.1-5937 (GO data)NH= 1.05 0.05 x 1022 cm–2 Γ= 3.7 0.2kT= 0.67 0.01 keVF2-10 keV = 3 x 10-11 erg cm–2 s–1

NH= 1.14 0.01 x 1022 cm–2 Γ= 3.40 0.03kT= 0.64 0.01 keVF2-10 keV = 10-11 erg cm–2 s–1

Pulse profilesPulse profiles

XTE J1810-297 1E 1048.1-5937 (GO data)

GO (AO2) observation of SGR 1806-20GO (AO2) observation of SGR 1806-20

30 ks observation in April 2003 but only 5 ks with low bkg

Results:

• Powerlaw spectrum (Γ=1.6, NH=6x1022 cm-2); no BB component

• No narrow features in EPIC spectrum


30 ks observation but only 5 ks with low bkg

Results:

• No narrow features in EPIC spectrum• Powerlaw spectrum (no BB component)

• 1 burst detected (2-10 keV fluence 10-9 erg cm-2)


30 ks observation but only 5 ks with low bkg

Results:

• No narrow features in EPIC spectrum• Powerlaw spectrum (no BB component)

20 ks obs. performed on 7 Oct and 50 ks accepted in AO-3

•1 burst detected (2-10 keV fluence 10-9 erg cm-2)

CONCLUSIONS:CONCLUSIONS:

• The flux of 1E 1048.1+5937 is confirmed to be variable (more than a factor 2)

• First evidence for variation in pulsed fraction of

1E 1048.1-5937 (from 90% to 50%)

AXPs are more variable than previously thought!

• 1E 1048.1-5937 is very similar to the “transient AXP” XTE J1810-297

Are these variations related to bursts, as in SGRs?

AXP 1E 2259+586 became 1 order of magnitude brighter and changed pulse profile after bursts (Kaspi et al. 2003)

Observations of AXPs and SGRs: 1E 1048.1-5937 and SGR 1806-20

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