Observations of AXPs and SGRs: 1E and SGR 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 14 th

Soft Gamma-ray Repeaters & Anomalous X-ray Pulsars SGRsAXPs Soft Gamma-ray Repeaters & Anomalous X-ray Pulsars SGRs AXPs Identified as subclass of: Soft burst spectrum Repetition of bursts from same position Gamma-Ray BurstsX-Ray Pulsars Period 5-12 s and spin-down No bright optical counterpart Soft spectrum and stable flux But then discovery of: SGR-like burstsAXP-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 Time observation of the Anomalous X-ray Pulsar 1E Results (Tiengo, Göhler, Staubert & Mereghetti 2002):

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

SAX ASCA XMM

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

 Same spectrum as GT observation  No narrow features in EPIC and RGS spectra Guest Observer (AO2) observation of 1E ks (43 ks with low bkg) observation in June 2003

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

SAX ASCA XMM GT XMM GO Gavriil, Kaspi & Woods (2002) reported bursts from 1E in Nov 2001

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

Pulse profiles GT observationGO observation

The new AXP XTE J  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 J is a Transient AXP  XMM ToO on Sep 8 (Tiengo & Mereghetti 2003, ATEL 193; Gotthelf et al. 2003, astro-ph/ ) : XTE J is very similar to 1E

Spectrum XTE J E (GO data) N H = 1.05  0.05 x cm –2 Γ= 3.7  0.2 kT= 0.67  0.01 keV F 2-10 keV = 3 x erg cm –2 s –1 N H = 1.14  0.01 x cm –2 Γ= 3.40  0.03 kT= 0.64  0.01 keV F 2-10 keV = erg cm –2 s –1

Pulse profiles XTE J E (GO data)

GO (AO2) observation of SGR ks observation in April 2003 but only 5 ks with low bkg Results: Powerlaw spectrum (Γ=1.6, N H =6x10 22 cm -2 ); no BB component No narrow features in EPIC spectrum

GO (AO2) observation of SGR 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  erg cm -2 )

GO (AO2) observation of SGR 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  erg cm -2 )

CONCLUSIONS: The flux of 1E is confirmed to be variable (more than a factor 2) First evidence for variation in pulsed fraction of 1E (from  90% to  50%)  AXPs are more variable than previously thought! 1E is very similar to the “transient AXP” XTE J Are these variations related to bursts, as in SGRs? AXP 1E became 1 order of magnitude brighter and changed pulse profile after bursts (Kaspi et al. 2003)