IGR J17480-2446

• Swift XRT spectral analysis =>fit with an absorbed (N_H = 0.50x10²² cm-2) blackbody of temperature kT~1.27 keV.

• Type I X-ray burst seen with JEM X

• Pulsation at 11.0452 Hz (P = 0.090535 s) and an eclipse lasting 512s detected with RXTE

• Burst oscillations at frequency compatible with that of the spin

• RXTE => QPO at 690 Hz

• Refinement of Swift position
• SOurce is at 6.8" from Chandra position of EXO 1745-248. Sources are not associated

• Orbital solution of the source with orbital period = 21.327 hr
• Projected semi-major axis of asin(i) = 2.46(12) lt-s,
• T0 (MJD)=55481.783
• Consitent with the eclipse interpretation

• Further analysis of RXTE obs. => 202 X-ray bursts
• Time resolved spectro of bursts => well fitted by an absorbed black body
• After October 13 burst likely type-II bursts due to episodic accretion
• Relatively wide orbit, slow pulsations, and type-II bursts are characteristics shared by the bursting pulsar, GRO J1744-28 => second such source ever discovered, and first to show a type-I (thermonuclear) burst

• significant cooling during decay of the bursts observed on 2010 November 13, 14, 15, 18
• Might indicate return of thermonuclear bursts as the persistent intensity
• Suggest other scenario for apparent disappearance of bursts during the high intensity state of the source

• Analyse whole RXTE/PCA data set
• Total of ~400 X-ray bursts
• Studied spectral properties of the source during the bursts
• All the bursts from the source originate from the same mechanism : thermonuclear origin
• Clear cooling may not always be present during a thermonuclear burst decay

• Archival Chandra data of the field around IGR J17480-2446 during inactivity of the source
• Quiescent spectra of the source: no difference between the 2 observations; soft spectra with most photons detected below 2 keV.
• Absorbed NS atmosphere yields a good chi square with N_H = 2.1X 10²² /cm2 and kT= 72.7 eV
• Comparison of the spectral properties of this source during quiescence with 5 other accreting ms pulsars
• Estimating duty cycle of the source => > 100 years in quiescence
• Scenario for low quiescent luminosity presented

• Study of the morphological, spectral and temporal properties of the bursts as observed by RXTE
• Recurrence time and fluence of bursts anticorrelate with increase of persistent X-ray flux
• Helium ignited in a Hydrogen rich layer
• All the bursts of this source = Type-I X-Ray bursts
• Pulsations detected in all brightest bursts with no drifts of the frequency within 0.25 Hz of the spin frequency

• Chandra/HETG spectra=> blue-shifted absorption lines from helium-like Fe XXV and hydrogen-like Fe XXVI
• Suggest presence of accretion disk wind which does show strong variations with X-ray bursts or flares.
• Clearest detection yet of such a wind in a neutron star system.
• Fits to the broad Fe K emission line => inner accretion disk radially-truncated =>Stellar magnetic field strength of ~(1-4)x10⁹ G
• Results discussed in context of accretion onto compact objects, and difference with disk winds in stellar-mass black holes

• Chandra observations seven weeks after the end of 2010 outburst
• Thermal emission (~100 eV) from the neutron star elevated compared to the quiescent value (~70 eV)
• Interpret as evidence for crustal heating during the outburst

• Extensive analysis of all (373) X-ray bursts observed with RXTE
• All bursts have a thermonuclear origin (type I burst), even those without a cooling tail.

• VLT observations => two possible IR source within 0.3" of the Chandra position
• Favor the one located at RA=17:48:04.829, DEC=-24:46:49.10 (+/-0.3"), with Ks = 16.6 as the candidate counterpart due to its absence in previous catalogues.

• RXTE spectral analysis => large hysteresis in the C-like HID during the Atoll state
• Nature of spectral evolution does not depend on the peak luminosity
• Spectra: two components (+iron line in emission): black body and power law
• Components probably connected and somehow linked to cause the spectral evolution
• A possible analogue to the clock burster GS 1826-238

• Properties of the all bursts from this source as seen with RXTE
• Typical duration of 100-200 s
• Type I burst when persistent luminosity is <15% Ledd
• No classification due to the lack of evidence for cooling for burst occurring when L=15-35% Ledd
• Burst oscillations detected in all bursts
• In this source: burst oscillations probably due to magnetic confinement of the burning material.

• Possible identification of the optical Counterpart in HST archival observations
• Resolve a close-by red giant object and the optical counterpart to the previously suggested faint IR candidate counterpart, therefore identified as one candidate optical counterpart
• Magnitudes F606W = 22.46 and F814W=19.14
• Finding chart at http://www.astro.uva.nl/~apatruno/17480.html

• Analysis of all the RXTE, INTEGRAL and Swift observations of IGR J17480-2446 during October-November 2010 outburst
• NS average spin up rate ~1.48e-12Hz/s over this period
• Compatible with spin up due to disc accretion => disc inner radius of 47-93 km estimated at the peak luminosity
• Spectral analysis => spectrum due to thermal comptonisation of 1 keV photons probably emitted by NS surface
• Coptonising medium evolves from kt~20 keV plasma to kt~3 keV with larger optical depth
• In the mean time pulse fraction decreases significantly =>a part of the accreted matter is not channeled to the pole but accreted evenly by the NS

• Timing analysis of RXTE observations => discovery of HF QPOs at frequencies between ~803 and ~875Hz
• Does not confirm the marginal detection previously reported from another study.
• As usually observed in Z sources, the QPO have low RMS amplitudes and coherences
• Highest frequency + assuming it is orbital frequency at the inner disc radius => lower limit of 18.5 km for a neutron star of 1.4 Msun.

• Source indeed is spun up at 1.4e-12 Hz/s
• Discuss the history of the evolution of this system.
• 3 distinct evolutionary epochs: a dipole dominated spin down one, a wind one, a the current roche lobe overflow epoch
• Source has not yet reached spin equilibrium; it has been spun up in the current phase for a few 1e7 years, and that it is in a exceptionnaly early Roche lobe overflow phase.
• Further discuss the apparent discrepancy between the age of this system and that of the globular cluster.

• Near IR observations with VLT, plus archival HST
• Identification of likely counterpart in the Ks band
• Source visible in quiescence both in the NIR and optical
• Study of the properties during outburst, and discussion of the original population of the companion

• sub arsec localisation of IGR J17480-2446 with RXTE and and lunar occultation of the source

• Timing analysis of 6 RXTE observations
• Power spectra resemble those of Z sources with QPO in the 35-50 Hz range and a kHz QPO at 815 Hz
• 35-50 Hz QPO not due to Lense-Thirring precession

• Study of the formation of the source
• Discuss the validity of source being a mildly recycled NS at very early phases of mass transfer
• Instead of previous scenario suggest binary formed during an exchange encounter either between a binary and the current donor or between a binary and an isolated NS
• Observational implications of this scenario are discussed

• Chandra observation extending the monitoring into 2.2 year in quiescence
• Thermal flux has continued to decrease but remains still higher than pre-outburst values =>Crust has not thermally relaxed

• Spin period and accretion rate should imply B~1e10G (instead of 1-4e-9) => accreting pulsar with clear departure from spin up line
• Numerical study of magnetothermal evolution => long period, low B pulsars expected, and IGR source is a member of this class of objects