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

Palermo, 2003 October 14 th. 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. Gamma-Ray Bursts. X-Ray Pulsars.

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

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  1. Palermo, 2003 October 14th 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

  2. Gamma-Ray Bursts X-Ray Pulsars • Soft burst spectrum • Repetition of bursts from same position • Period 5-12 s and spin-down • No bright optical counterpart • Soft spectrum and stable flux Soft Gamma-ray Repeaters& Anomalous X-ray Pulsars SGRsAXPs Identified as subclass of: But then discovery of: • AXP-like counterparts • SGR-like bursts SGRs and AXPs are the same class of objects! Interpretations: Magnetar or NS accreting from fall-back disc

  3. Guaranteed Time observation of the Anomalous X-ray Pulsar 1E 1048.1-5937 5 ks observation performed on 28 Dec 2000 Results(Tiengo, Göhler, Staubert & Mereghetti 2002): • Power-law (=3) + Blackbody (kT=0.65 keV) • No narrow features in EPIC spectrum

  4. Guaranteed Time observation of the Anomalous X-ray Pulsar 1E 1048.1-5937 5 ks observation performed on 28 Dec 2000 Results(Tiengo, Göhler, Staubert & Mereghetti 2002): • Power-law (=3) + Blackbody (kT=0.65 keV) • No narrow features in EPIC spectrum • Flux within 50% from previous observations (SAX, ASCA)

  5. SAX ASCA XMM

  6. Guaranteed Time observation of the Anomalous X-ray Pulsar 1E 1048.1-5937 5 ks observation performed on 28 Dec 2000 Results(Tiengo, Göhler, Staubert & Mereghetti 2002): • Power-law (=3) + Blackbody (kT=0.65 keV) • No narrow features in EPIC spectrum • Flux within 50% from previous observations (SAX, ASCA) • Energy dependent pulse profile: pulsed fraction 75% for E<1.5 keV and 100% for E>1.5keV

  7. Guest Observer (AO2)observation of 1E 1048-593 70 ks (43 ks with low bkg) observation in June 2003 • Same spectrum as GT observation • No narrow features in EPIC and RGS spectra

  8. Guest Observer observation of 1E 1048-593 70 ks (43 ks with low bkg) observation in June 2003 • Same spectrum as GT observation • No narrow features in EPIC and RGS spectra BUT: • Flux a factor 2 higher than in GT observation

  9. XMM GO SAX ASCA XMM GT Gavriil, Kaspi & Woods (2002) reported bursts from 1E1048.1-5937 in Nov 2001

  10. Guest Observer observation of 1E 1048-593 70 ks (43 ks with low bkg) observation in June 2003 • Same spectrum as GT observation • No narrow features in EPIC and RGS spectra BUT • Flux a factor 2 higher than in GT observation • Lower pulsed fraction: 50%

  11. Pulse profiles GT observation GO observation

  12. The 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

  13. Spectrum XTE J1810-297 1E 1048.1-5937 (GO data) NH= 1.05  0.05 x 1022 cm–2 Γ= 3.7  0.2 kT= 0.67  0.01 keV F2-10 keV = 3 x 10-11 erg cm–2 s–1 NH= 1.14  0.01 x 1022 cm–2 Γ= 3.40  0.03 kT= 0.64  0.01 keV F2-10 keV = 10-11 erg cm–2 s–1

  14. Pulse profiles XTE J1810-297 1E 1048.1-5937 (GO data)

  15. GO (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

  16. GO (AO2) observation of SGR 1806-20 30 ks observation but only 5 ks with low bkg Results: • Powerlaw spectrum (no BB component) • No narrow features in EPIC spectrum • 1 burst detected (2-10 keV fluence 10-9 erg cm-2)

  17. GO (AO2) observation of SGR 1806-20 30 ks observation but only 5 ks with low bkg Results: • Powerlaw spectrum (no BB component) • No narrow features in EPIC spectrum • 1 burst detected (2-10 keV fluence 10-9 erg cm-2) 20 ks obs. performed on 7 Oct and 50 ks accepted in AO-3

  18. 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%) • 1E 1048.1-5937 is very similar to the “transient AXP” XTE J1810-297 • AXPs are more variable than previously thought! 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)

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