Istituto di Astrofisica Spaziale e Fisica CosmicaIstituto di Fisica dello Spazio Interplanetario...

Istituto di Astrofisica Spaziale e Fisica Cosmica Istituto di Fisica dello Spazio Interplanetario

Roma, 15-16 dicembre 2003relatore: M. Cocchi

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)



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



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



BeppoSAX-WFC image of the

Galactic bulge (1999,

February).



•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

•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

•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 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

Bursters with no detection of persistent emissionNew BeppoSAX-WFC transients

known sources discovered as bursters

•XTE 1709-267 •SLX 1735-269•GRS 1741.9-2853•4U 1745-203 •X 1803-245 •GS 1826-238 •NGC 6652

•XTE 1709-267 •SLX 1735-269•GRS 1741.9-2853•4U 1745-203 •X 1803-245 •GS 1826-238 •NGC 6652



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: >2000 X-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 17 new bursters

• 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).



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



BeppoSAX WFCdiscovery of

hour-long X-ray bursts

(superbursts)

the known superbursters

source e-folding time

4U1820-30 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

Ser X-1



WFC discovery of new NS-LMXBs via the detection of X-

ray bursts: the burst-only

sources

SAX J1752.3-3138:an Eddington-limited

burst with no observed persistent counterpart

(Cocchi et al. 2001)



SAX J1752.3-3138 9.2 +/- 0.4 Cocchi et al. (2001)

A homogeneous sample of Eddington-Limited X-ray bursts observed by the BeppoSAX-WFCs



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



SAX J1808.4-36 : pulsed emission during type-I X-ray bursts

first 20 s of MJD 50389.126 burst

_burst = _spin

qpo = _burst / 2= _spin / 2

spin origin for the HQPOs



WFC Hard X-ray Galactic Plane catalogThe 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).



Source Monitoring by the BeppoSAX-WFCs: the HMXB 4U 1700-377

countrate

countrate

hardness ratio



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 BeppoSAX observations 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.



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)

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).

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).

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.



Detections during 2003 Spring GCDE, (500 ksec exposure)

Source name 20-40 keV 40-100 keV 100-200 keV4U1636-536 yes4U1702-429 yes yes4U1705-44 yes yesSAX J1712-3739 yes yes1E1724-3045** yes yesGX 354-0 yes yesGX 17+2* yes yes4U1735-44* yes yesSLX 1735-269 yes yesKS1741-29 yes yesA1742-298 yes yesSLX1744-299** yes yesEXO1747-214 yes yesGX3+1* yes4U1812-12 yes yes yes H1820-30 yes yesGS1826-238 yes yes yes H1832-33 yes yes4U 1916-053 yesRapid 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

INTEGRAL and X-Ray Bursters

IBIS detected burst from GX354-0, in 3 different band, 15-40, 40-100 and 100-200 keV



INTEGRAL and X-Ray Bursters

GS 1826-238cutoffpl (syst 5%)1.5 +/- 0.2

cut = 69.9 +/- 0.2

blackbodykT = 2.3 keV



IDENTIFICATION of OPTICAL COUNTERPARTS of X-RAY SOURCESWe (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).

BibliographyBernabei & Polcaro V.F. 2001a, Astron. & Astrophys. , 366, 817 Bernabei S., Polcaro V.F., 2001b, Astron. & Astrophys., 371, 123Israel G.L, Covino S., Polcaro V.F., Stella L., 1999, Astron. & Astrophys., 345, L1Polcaro V.F. & Viotti R. 1997, VII ADASS Conf., ASP Conf. Ser., 145, 78Polcaro V.F., Viotti R., Bernabei S., 2003, X ADASS Conf., ASP Conf. Ser., in press

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