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COMPACT OBJECTS in the X and γ -Ray bands

COMPACT OBJECTS in the X and γ -Ray bands. The Topic includes: Neutron Stars in Low Mass Binary Systems (X-ray Bursters, Atoll and Z sources) and in High Mass Binary Systems (high B NSs) Black Holes (persistent & transient) in LMXB and HMXB Isolated Neutron Stars (SGRs).

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COMPACT OBJECTS in the X and γ -Ray bands

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  1. COMPACT OBJECTS in the X and γ-Ray bands • The Topic includes: • Neutron Stars in Low Mass Binary Systems (X-ray Bursters, Atoll and Z sources) and in High Mass Binary Systems (high B NSs) • Black Holes (persistent & transient) in LMXB and HMXB • Isolated Neutron Stars(SGRs)

  2. This topic has been firstly exploited with observations by balloon borne experiments developed at IAS in 1977-1989. IASF/Roma was deeply involved in the SAX programme (1996-2002), participating as hardware team and to the mission CORE PROGRAMME definition and exploiting for the WFCs and PDS, with particular emphasis on Galactic Bulge source monitoring. The involvement in INTEGRAL as IBIS hardware team. IBIS Core Programme: Galactic Plane Scan and Galactic Centre Deep Exposure. Search for optical counterparts of X-ray sources

  3. Monitoring the Galactic bulge by the BeppoSAX-WFCs: overview of the main results • Until April 2002, WFC has been exposed to the Galactic centre region for > 5 Ms (i.e. about 8% of the BeppoSAX observing programme), directly comparable both for coverage and exposure to the Galactic Centre Deep Exposure of the INTEGRAL Core Programme we are part of. • NS `weak` transients (a new class of objects?), and the BH/NS ratio • type-I X-ray bursts: • superbursts • quasi-periodic bursters (GS 1826-238) • burst-only sources • Eddington-limited bursts as standard candles • NS-LMXB as hard X-ray emitters? Yes, thanks! (e.g. SAX J1810.8-2609) • BH-like source states in NS-LMXB (SAX J1747.0-2853) • the long-awaited accreting millisecond pulsar SAX J1808.4-3658: evidence for pulsed emission during X-ray bursts

  4. BeppoSAX-WFC image of the Galactic bulge (1999, February).

  5. New BeppoSAX-WFC transients Bursters with no detection of persistent emission • SAX J0104.5+583 • SAX J0835.9+5118 • SAX J0840.7+2248 • SAX J1603.9-775 • 1RXS J1708-402 • GRS 1741.9-2853 • SAX J1752.4-3138 • SAX J1753.5-2349 • SAX J1806.5-2215 • SAX J1709.0-3623 • SAX J1711.6-3808 • SAX J1712.6-3739, Burster (*) • SAX J1747.0-2853, Burster (*) • SAX J1748.9-2021, Burster (*) • SAX J1750.8-2900, Burster (*) • SAX J1805.5-2031 • SAX J1806.8-2435, Burster • SAX J1808.4-3658, ms Pulsating Burster • SAX J1810.8-2609, Burster (*) • SAX J1818.6-1703, Fast Transient • SAX J1819.2-2525, Black Hole (*) • SAX J2103.5+4545, 6 min pulsar • SAX J2239.3+6116, possibly Be XRB • (*) NFI TOO in the WFC GC monitoring program known sources discovered as bursters • XTE1709-267 • SLX 1735-269 • GRS 1741.9-2853 • 4U1745-203 • X 1803-245 • GS 1826-238 • NGC 6652

  6. The Galactic bulge monitoring program • Source monitoring: A total of 55 sources monitored, including: the transient BHCs GRO 1655-40, XTE 1755-324, GRS1737-31 and GRS 1739-278; the persistent BHCs 1E1740.7-2942 & GRS 1758-25; the X-ray pulsar GX1+4; all the bright persistent GX atoll and Z sources in the f.o.v. • WFC Transients in the Bulge: this almost unbiased sample indicates the ratio BH/NS in such objects is lower than previously (<1996) thought. The updated value is 0.16 < BH/NS < 0.24. • X-ray bursts: >2000X-ray bursts from 39 LMXBs including Rapid Burster (>500 bursts) and Bursting pulsar (>200). Population of LMXB bursters increased by 30%through the discovery of 17newbursters • Soft X-ray Transients: 9 objects have been discovered by the WFCs. Their main characteristics are: rather faint outbursts (L x< 3x 1037 erg/s); short e-folding time (~2-6 days); 90% are type I X-ray bursters (i.e. the accretor is a Neutron Star). Heise et al. (1999) proposed these sources as a new class of (weak and fast) transient NS binaries. A simple irradiated-disc picture (King 2000) gives consistent fit to the properties of this class, probably consisting of LMXB with short orbital periods (<2 h) possibly recurrent. • WFC-related TOO programs are BeppoSAX-NFI wide-band Observation of new WFC Transients and new WFC Bursts sources. Performed TOOs: SAX J1712.6-3739, SAX J 1747.0-2853, SAX J1748.9-2021, SAX J 1810.8-2609, SAX J1750.8-2900 (5, new WFC bursters); SAX J 1819.3-2525(transient BHC); GRS 1747-313 (recurrent transient in Terzan 6, the only non-bursting Globular Cluster source left).

  7. Quasi-periodic thermonuclear flashes on a NS: GS 1826-238

  8. BeppoSAX WFCdiscovery of hour-long X-ray bursts(superbursts) Ser X-1 the known superbursters source e-folding time 4U1820-30 1 h Ser X-1 1.2 +/- 0.1 4U1735-44 1.4 +/- 0.1 4U1636-53 1.5 +/- 0.1 GX 3+1 1.6 +/- 0.2 KS 1731-26 2.7 +/- 0.1

  9. WFC discovery of new NS-LMXBs via the detection of X-ray bursts: the burst-only sourcesSAX J1752.3-3138:an Eddington-limited burst with no observed persistent counterpart(Cocchi et al. 2001)

  10. A homogeneous sample of Eddington-Limited X-ray bursts observed by the BeppoSAX-WFCs SAX J1752.3-3138 9.2 +/- 0.4 Cocchi et al. (2001)

  11. Location of the WFC-observed Eddington-luminosity bursters in the Galaxy

  12. SAX J1808.4-36 : pulsed emission during type-I X-ray bursts n_burst = n_spinDn_qpo = n_burst / 2= n_spin / 2=> spin origin for the HQPOs first 20 s of MJD 50389.126 burst

  13. WFC Hard X-ray Galactic Plane catalog The map shows all detected sources as filled circle with radius representing the average flux corresponding to different detections in all the sampled observing period. We selected the 18-28 keV band for direct comparison with the IBIS low energy sky images. This set of data is used to both predict persistent, though variable, source detection with IBIS along the Galactic Plane survey and also to perform archival searches of newly discovered INTEGRAL sources (Capitanio et al. 2003).

  14. Source Monitoring by the BeppoSAX-WFCs: the HMXB 4U 1700-377 countrate countrate hardness ratio

  15. NFI follow-ups: Spectral properties of X-ray bursters HIGH ENERGY TAILS. High energy tail in these source have been firstly suggested from the SIGMA/GRANAT observation. The BeppoSAXobservations of transient and persistent X-ray bursters mainly by our team have confirmed the picture of these sources being hard X-ray emitters when in low/hard state (Lx~1036-1037 erg/s). The high energy emission mechanism is found to be thermal comptonization by a hot, optically thin plasma with temperatures kTe~ 15-20 keV. This shows up as an exponential cutoff at energies E~3kTe There are, however, few relevant exceptions: one is SAX J1810.8-2609, showing a very hard spectrum with no evidence of cutoff (Natalucci et al., ApJ 2000, 536, 891). Low state spectra of two transient NS detected by BeppoSAX in spring of 1998.

  16. An interesting and peculiar source: SAX J1747.0-2853 Discovered in March 1998 as X-ray burster, is a recurrent transient ~ 0.5° off the GC. Two X-ray outbursts have been studied in detail by BeppoSAX: in March 1998, a low luminosity event with a slowly rising light curve, and ~1 month duration (from Natalucci et al. 2000, ApJ 543,L73) Spectrum during the 2000 event, short after the maximum of the 1st peak, compared to the low state of 1998 (from Natalucci et al. 2003, A&A in press). in March 2000, a high luminosity event with a fast rising light curve, multiple peaks and several months duration (from in ’t Zand 2001, Proc. 4th INTEGRAL Workshop, ESA-SP 459, p.463). This long duration outburst is rather exceptional for a NS transient. After this event, SAX J1747.0-2853 remained active at a low intensity level (~1035 erg/s) for more than one year.

  17. INTEGRAL and X-Ray Bursters Detections during 2003 Spring GCDE, (500 ksec exposure) Source name 20-40 keV 40-100 keV 100-200 keV 4U1636-536 yes 4U1702-429 yes yes 4U1705-44 yes yes SAX J1712-3739 yes yes 1E1724-3045** yes yes GX 354-0 yes yes GX 17+2* yes yes 4U1735-44* yes yes SLX 1735-269 yes yes KS1741-29 yes yes A1742-298 yes yes SLX1744-299** yes yes EXO1747-214 yes yes GX3+1*yes 4U1812-12 yes yes yes H1820-30 yes yes GS1826-238yes yes yes H1832-33 yes yes 4U 1916-053yes Rapid Burster** yes yes - The Topic has been allocated to IBIS, Responsible Scientist A. Bazzano (*) sources allocated to others => collaboration (**) sources allocated to other ISWT member IBIS detected burst from GX354-0, in 3 different band, 15-40, 40-100 and 100-200 keV

  18. INTEGRAL and X-Ray Bursters • GS 1826-238 • cutoffpl (syst 5%) • = 1.5 +/- 0.2 Ecut = 69.9 +/- 0.2 blackbody kT = 2.3 keV

  19. IDENTIFICATION of OPTICAL COUNTERPARTS of X-RAY SOURCES We (Polcaro & Viotti, 1997) have developed a technique, that allows the simultaneous spectroscopy of all the objects included in a squared field of view with ~10' side, using of the widely diffused FOSC-type optical spectrometer and camera focal-plane instruments. The technique is based on the use of a slitless low dispersion grism coupled with a broad-band filter, which perform an "objective prism like" spectrogram of ~200nm centered on H, without a serious overlap of adjacent spectra, where emission line and peculiar spectrum objects are easily identified. We tuned this technique on the BFOSC instrument, mounted at the Cassegrain focus of the Bologna Astronomical Observatory "G.B. Cassini" 1.52 m telescope. This method was effectively employed in the identification of optical counterparts of galactic X-Ray sources , as well as in the search of very high mass stars (see, e.g. Bernabei & Polcaro, 2002a,b; Israel et al., 1999). We have recently developed a new, more effective slitless procedure based on a wavelength window centred on H (Polcaro, Viotti & Bernabei, 2003 - see figure).   Bibliography Bernabei & Polcaro V.F. 2001a, Astron. & Astrophys. , 366, 817 Bernabei S., Polcaro V.F., 2001b, Astron. & Astrophys., 371, 123 Israel G.L, Covino S., Polcaro V.F., Stella L., 1999, Astron. & Astrophys., 345, L1 Polcaro V.F. & Viotti R. 1997, VII ADASS Conf., ASP Conf. Ser., 145, 78 Polcaro V.F., Viotti R., Bernabei S., 2003, X ADASS Conf., ASP Conf. Ser., in press

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