1. ESTREMO meeting, IASF-BO 05/05/2006 M. Cocchi, J.J.M. In ‘t Zand X-ray Bursters with ESTREMO Looking for burst lines: investigating the NS EOS Superbursts as peculiar thermonuclear flashes XrB population study (not a main driver) XrB spectroscopy (not a main driver) -> requirements for advanced XrB studies

2. ESTREMO meeting, IASF-BO 05/05/2006 M. Cocchi, J.J.M. In ‘t Zand Cottam, Paerels & Mendez: absorption lines in the burst spectra of EXO 0748-676 (28 events average, XMM/RGS)

3. ESTREMO meeting, IASF-BO 05/05/2006 M. Cocchi, J.J.M. In ‘t Zand Lines -> redshift -> determination of M/R ratio -> guess on the NS EOS Fe XXV, XXVI (n=2-3) and O VIII (n=1-2) with redshift z=0.35 -> in agreement with normal nuclear matter (some exotic models excluded) M = 1.4-1.8 M sun, R = 9-12 km Better / updated NS atmosphere models (taking into account also burst effects) are expected

4. ESTREMO meeting, IASF-BO 05/05/2006 M. Cocchi, J.J.M. In ‘t Zand Looking for Bursts lines: 1) normal bursts: look at the longer bursts (eg GS 1826-238, KS 1731-2609, H 1608-52, 4U 1812-12 - the latter 2 being Eddington-limited bursters ) GS1826-238 is the best candidate + easy trigger + most frequent bursts (1/3h) + pretty long events (~120 s) + GS 1826 shows quasi-periodic bursts (other pointings possible between consecutive events) - need for fast slew (<20 s not to miss the first phase) - need for low energy sensitivity in WFGC (~4 keV)

5. ESTREMO meeting, IASF-BO 05/05/2006 M. Cocchi, J.J.M. In ‘t Zand Looking for Bursts lines: 2) superbursts: + very long bursts (hours, excellent statistics) + no real need for quick repointing (a few minutes is ok) + WFGC low energy threshold can be higher (5 keV) as more statistics available and integrating on larger timebins + less WFGC sensitivity needed - tricky trigger, possibly manual (high persistent intensity sources) - rare events (1-2 per year for 5-10% Edd sources) - LEO gaps interfering with the burst light curve and affecting count statistics

6. ESTREMO meeting, IASF-BO 05/05/2006 M. Cocchi, J.J.M. In ‘t Zand Requirements on the WFGC low energy threshold for burst detection For bursts with BB kT 99% of photon flux is below 20 keV For kT>2.0 keV, you get >85% of photons with LET=2 keV, >50% for LET=5 keV and >10% for LET=10 keV (so going down to 2 keV from 5 keV leads to an improvement of 35% only) For a 1 Crab (2-10 keV) 2.0 keV burst I 5-20 keV = 0.9 c/s/cm 2 For a 1 Crab (2-10 keV) 2.5 keV burst I 5-20 keV = 2.3 c/s/cm 2 In general, A eff = 5 x sqrt(bkg) / sqrt(tri x delta-T) x I 5-20 keV. => For a 2.5 keV burst, A eff =70 cm 2 ; for tri=0.5 A eff = 100 cm 2 Detect triggers  monitor sensitivity should be able to detect 2 keV black body spectrum with bolometric flux of 10 -8 erg s -1 cm -2 within 1 s, e.g. 100 cm 2 at 40 x 40 sq deg monitor sensitivity should be able to detect 2 keV black body spectrum with bolometric flux of 10 -8 erg s -1 cm -2 within 1 s, e.g. 100 cm 2 at 40 x 40 sq deg Have X-ray bursters in field of view, for instance through considerable exposure on Galactic center Have X-ray bursters in field of view, for instance through considerable exposure on Galactic center

7. ESTREMO meeting, IASF-BO 05/05/2006 M. Cocchi, J.J.M. In ‘t Zand fallout science (depending on the pointing strategy): 1) XrB population study by WFGC: burst recurrence time vs bolometric luminosity, burning regimes big FOV, best sensitivity and energy response for a 40x40 ever. => Improving the nice results of BeppoSAX-WFC. Nothing like that since BeppoSAX! 2) Spectroscopy of bursters: refinement of spectral models (e.g. Compton tails & breaks, double Compton – see Thompson et al.)

8. ESTREMO meeting, IASF-BO 05/05/2006 M. Cocchi, J.J.M. In ‘t Zand Burst Spectroscopy: 3 main spectral stases with INTEGRAL Simple Comptonized emission fits quite well the 20-200 keV spectra of INTEGRAL bursters Fitted electron kT’s range from ~3 to ~20 keV, possibly clustered in 2-3 ranges of values, likely related to the source state: –kT e ~ 3 keV, bursters in soft state, no evidence for hard tail, emission drops at < 50 keV (4U 1735-444, 4U 1820-303, possibly H 1702-429) –kT e ~ 6-10 keV, bursters in a sort of intermediate state, emergence of a hard Compton tail at 50-100 keV (GX 3+1, SLX 1744-300, GX 354-0, H 1705-440) –kT e > 15 keV, bursters in very hard state, Compton hard tail extended well above 100 keV, up to 200 keV (GS 1826-238, 4U 1812-12)

9. ESTREMO meeting, IASF-BO 05/05/2006 M. Cocchi, J.J.M. In ‘t Zand kT = 3.0 ± 0.1 keV  = 17 ± 10  2  (dof) = 1.0 (18)  = 2.15  10 -10 erg cm -2 s -1 kT = 12.1 ± 1.4 keV  = 4.6 ± 0.6  2  (dof) = 1.0 (21)  = 8.7  10 -10 erg cm -2 s -1 kT = 28 ± 5 keV  = 1.1 ± 0.2  2 (dof) = 1.3 (17)  = 11.5  10 -10 erg cm -2 s -1

10. ESTREMO meeting, IASF-BO 05/05/2006 M. Cocchi, J.J.M. In ‘t Zand What XrB community wants (requirements for ESTREMO): WFGC: - bandpass: Emin = 3-4 keV, ok if Emin < 5 keV Emax up to 200 keV for bolometric studies - spectral resolution 15-20% FWHM - detector area: a few hundred cm 2 - timing: 1 ms - field of view: at least 40 deg fwzr (to trade off with the X-ray BGD) - source.location.accuracy. 1 arcmin - sensitivity: 500 mCrab in 1 s (normal burst trigger) much less for superbursts - slew speed: 1-2 deg/s, if combined with dedicated observation programs (e.g. Galactic Bulge) NF telescope: - bandpass: 0.3-10 keV - spectral resolution: 3 eV @ 1 keV, even less for fast rotators - area: as large as possible.. - timing 0.1 ms (ms oscillations in bursts) - maximum countrate: 10,000 (pile up?) - field of view: none - angular resolution: none