PoS(SWIFT 10)048 http://pos.sissa.it/ 1 [email protected] mode. Swift has shown to be the effectively both bestthings for brightsuited ULXs. After a shortX-ray summary on facilitythe properties of forULXs and this purpose, recentthe advances made in this Ifield, will focus on the contribution by given Swift, reviewing capable to do by this obtained mission. successful mainthe results extraordinarily In the coming years a significant improvement in ourSources understanding(ULXs) isof expectedUltraluminous toX-ray come from the study offrom theirthe discoverylong and termfollow upX-ray of variabilitythe stilland largely unknown population of transient sources. This requires a flexible and fast scheduling strategy to monitor ULXs and observe them in 'ToO' Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. Attribution-NonCommercial-ShareAlike author(s) of the owned under by the terms CommonsCopyright the Creative
Speaker 1 2-5 December 2014 Rome, Italy La University, Sapienza Swift: 10 Years of Discovery Swift: 10 Years E-mail: Ultraluminous X-ray Ultraluminous Sources Luca Zampieri Observatory of Padova INAF-Astronomical 5, 35122, Padova, dell'Osservatorio Italy Vicolo Swift contribution to our understanding of to ourunderstandingSwift of contribution PoS(SWIFT 10)048 solar recently physical L. Zampieri L. hat hat may form through ∼ [13]), t [17]) or more massive (20-80 solar solar masses elics of the collapse of Population III stars erg/s). Hundreds of sources are reported in But the majority of them probably contain in the local Universe. Some of them may 39 2 solar masses or from the dynamical collapse of astar supermassive
M82 X-2 X-2 [12]). M82 solar masses [14] ∼ . They may also be the r ∼ irst measurements of the mass function of two ULXs have been noticed in EINSTEIN data, it was only XMM-Newton withand ROSAT, Chandra that [5,18,19]). In the latter case, the accretion rate needed to sustain the observed In a few cases a periodic modulation has been detected in the X-ray or optical light curve Although the first very luminous X-ray sources in the field of nearby galaxies were ULXs: questions, interpretations and and implications questions, ULXs: interpretations The ‘manifold population’ of Ultraluminous X-rayof Ultraluminous Sources population’ ‘manifold The masses luminosity most likely requires accretion to proceed conditionsat in ULXs could then be similar to those occurring in the super-Eddingtonfirst generation of Quasars at rates. The redshift. highvery contain the long sought massintermediate (>100BHs of stellar mass repeatedBHs mergers in dense stellar clusters [15] and the seeds of the first supermassive BHs [16]. BHs of stellar origin, either stellar-mass (<20 still challenge our interpretation of ULXs. What are the masses and origin of(BHs) the hostedblack inholes ULXs? How can a neutron star (NS) BHs?aboutintermediate extreme is accretion their environment? How mass power them? What may ULXs tell us Our present understanding suggestsdistribution of that BH masses ULXsabove 10 are the key to exploring the unknown know of a ULX that shows ~1 s X-ray pulsations modulated with a very short orbital period of ( neutron and star daysa2.5 thus contains 1.1 Despite the significant advances made in this field in the last years, many important questions (although in a couple of cases the statistical significance may not be very large) and interpreted as the orbital period of the system. Observed periods range from ~6 hr to ~60 days [7,8,9]. Most important, the f published (M 101 ULX-1 [10]; ULX P13 in NGCThey demonstrate 7793 both[11]). the binary nature of these sources and that at least some of them host stellar black holes. In fact, we now interacting with the circumstellar medium. This conclusion comes from several observational evidences, including the X-ray emission properties, the frequent association with young stellar environments, the detection of stellar optical counterparts, the relation with the properties (such [5,6]). (seee.g. galaxiestheir function)of luminosity host rate X-ray star asandformation luminosity exceeds (although not necessarily all the time)accretion onto a the Eddington limit for spherical 10 solar mass black hole (L>10 various surveys/catalogues (ROSAT, e.g. [1,2]; Chandrasignificant fraction of [3];ULXs ( XMM-Newton [4]). While 20%) are background AGNs , a the believedmajority of the population is to be accreting binaries, with a modest contamination ( 5%) from supernovae 1. already an entire population of intrinsically powerful, but faint, point-like off-nuclearnowadays X-ray calledsources, Ultraluminous X-ray sources (ULXs), has been largely uncovered. Their Swift contribution to our understandingof contributionSwift ULXs to PoS(SWIFT 10)048 L. Zampieri L. 3 [20]). The validity of these two-component thermal [34]. Other methods to estimate masses from timing include the non- ultraluminous state solar masses Short-term X-ray X-ray variabilityShort-term X-ray spectral evolution: Super-Eddington accretion? Super-Eddington evolution:X-ray spectral X-ray X-ray spectra ULXs in the X-rays ULXs the in ~400 detection of variability power [39] [40]. AGNs binaries and or the “variability plane” of both Galactic BH The detection of QPOs has prompted attempts to compare them toGalactic similar features BHin binaries and tofrequencies or by estimate extrapolating correlations the known to BH exist for mass[33,35,38]). For Galactic M82 X-1 the frequencies of the two QPOs above 1 Hz appear to be in a binaries by(e.g. scaling their characteristic ratio 3:2. An inverse-mass scaling of their frequencies with those of the high frequency (100-450 Hz) QPOs with a similar 3:2 ratio in Galactic BH binaries yields a mass of 10 s) is often absent [31]. However, some spectrumULXs (PDS) havein featuresthe formin ofthe low-frequency powerbroad-band density noise and/or oscillationsquasi (QPOs). periodic The frequencies of the QPOs are in the range fewfrom Hz: ~154-166 mHz,mHz 3.32 Hzto and a 5.07 Hz in M82 X-1 ([32,33,34]), 20 mHz in NGC X42.3+595408 X-1 in in [36], 3-4 mHz [35], 642 mHz [37]. M82 IC 342 X-1 blueshifted absorption lines may be consistent with the soft residuals seen in the X-ray spectra of two sources [30]. 2.3 on short time scalesThe timing(below behaviour of ULXs is heterogeneous. Variability conditions, likely associated Eddington limit. The to corona/wind along the line of sight causes increased thevariability in accretion the ratehigh energy beingpart of significantly the existence of such windsstrong is challenged However, by the lack of detection theof X- spectrum above on the a timescale rayof hundreds absorption of featuresseconds [28]. [29], although it has been suggested that broadened and 2.2 Spectral variability is frequently [23,24,25]). detected The and observed appears spectral tochanges in be evolutionan optically thick ratherthermal may component (corona/wind) complexand be an accretion (e.g. energetically disc, satisfactorilycoupled to it [26,27]. reproduced Both components appear by to be in unusual physical below 1 keV ( models has been recently confirmed by broadband XMM+NuSTAR observations (e.g. [21]). Spectra in the ultraluminous state are interpreted in corona covering or replacingterms the disc, or a modified accretion disc (like aof slim disc) that an optically thick is launching a [22]). wind (e.g. 2.1 The significant amount of high quality NewtonX-ray in spectrathe lastof 10 ULXsyears turnedcollected out byto differences with respect to the spectra of Galactic BHbe X-ray XMM- binaries. Many ULXs show essential to clarify subtle but important either curved X-ray spectra or a turnover at ~3-5 keV, sometimes with a soft excess Swift contribution to our understandingof contributionSwift ULXs to 2. PoS(SWIFT 10)048 mediate L. Zampieri L. was the follow-up wed by active flaring The Swift erg/s. spectrum 38 Short drops in the count rate, but no 4 NGC 1313 X-2. A very extended observing erg/s and for at least 40 days the luminosity remained fairly 39 Follow-up of transients ULXs Follow-up transients of Characterization of X-ray X-ray offlux variabilityCharacterization Search for X-ray periodicities X-ray for Search Swift contributionSwift was well described by a multi-colour disc duringblackbody model, the progressively decaysoftening (from kT ~0.9 keV to ~0.4 keV). Assuming that at maximum of the second brigthest ULX in M312012 (M31 thanksULX-2 hereafter)to discoveredthe in XMM-Newton/ChandraJanuary ThanksM31 to itsnova fast monitoringand flexible programmescheduling, after [50]. discovery follow-up observingSwift programmeto targeted this source [51]. The source reached a peak started an im luminosity of ~10 constant. Then, in the following 200 days, it faded below 10 timescales flux of these et in transitions al., (Grise' preparation). 3.3 Another area in which the Swift contribution transienthas ULXs (e.g. the ULXbeen in M 83 [49]). relevantParticularly successfull is the monitoring of although the uncertainties the to due low counting statistics are large. Another ULX well monitored by Swift campaign isof this source, started in June 2013identification and still ofongoing, has led flux-dependentto the quality ofclear activitythe data attained is (high-flaring/low-quiescientsuch that we may be phases). able to constrain also The the possible phases. High-low flux 'states' are also seen in NGC 55 ULX-1, accompanied by spectral changes similar to those observed in brighter ULXs [47]. This low-luminosity ULX is rather peculiar because in two XMM-Newton observations it showed energy-dependent dips, not commonly observed in these sources [48]. clear evidence of dips on timescales longer than 300s were detected in Swift data, term variability in ULXs, with typical flux variations up to 5-10. Crucial to this end is the unprecedented temporal coverage cadence and made possible by Swift. Extended periods of pronounced flaring activity were observed in IIHolmberg X-1, that do not appear to be associated to significant spectral variability [45]. On the other hand, long low flux 'states' are observed in Holmberg IX X-1 [46], follo modulation in terms of a super-orbital period causeddisc/jet the proposed by Foster et in has [44]. been system al. by the precession of the inner- 3.2 Monitoring with Swift/XRT is particularly successfull in identifying structured long- A dedicated monitoring campaign performed with ledSwift/XRT to the discovery of a periodicity of 155.5 days in the light curve of NGC 5408 X-1 [41]. This value was later revisited in 243 days using 1240 days of monitoring of the source [42]. However, the result could not be confirmed by etGrise’ al. [43] using an even longer baseline (1532 days). The significance ofdisappears after a few equallyAn cycles. interesting interpretation of this thenon-persistent detection decreases with time and the periodicity Thanks to its flexible monitoring strategy, Swift has shown to be the best suited X-ray facility to search for long-term (months-to-years) periodicities and variability in ULXs. Here I will summarize shortly of the some significant Swift. most obtained with results 3.1 Swift contribution to our understandingof contributionSwift ULXs to 3. PoS(SWIFT 10)048 erg/s. 42 L. Zampieri L. blackbody component is 5 arguing that the source is highly compact and [55]. solar masses . rom the normalisation of the multi-colour disc (e.g. [57]). Detection of ballistic radio jets allows for an even higher mass solar masses HLX-1 in ESO 243-49: a recurrent hyper-luminous transient ULX transient hyper-luminous a HLX-1 recurrent ESO in 243-49: Conclusions In the coming years expected a to significantcome from improvement the instudy discoveryof our and theirfollow understandinguplong of term ofthe stillX-ray ULXslargely variabilityunknown This population is and requires of fromatransient flexiblesources. the and fast scheduling strategy. suited X-ray facility purpose. for this Swift has shown to be the best their long-term X-ray flux variabilityfollow-up (flux transients transitions, flaring ULXs, activity, recurrent including timescales); hyper-luminous transient and intermediate mass BH candidate HLX-1 in ESO the remarkable 243-49. transients in M31 and the make the intepretation of the feeding debated. mechanism of the intermediate mass BH still 4. Thanks to its unprecedented coverage Swift long-termhas periodicities (orbital allowedand super-orbital periods)us in ULXs; to:start characterizing place constraints on the thermal-viscous timescale of a Outbursts arestandard instead believed to be discinduced by bursts of massaround transfer occurring when an intermediatethe donor,mass in anBH. eccentric orbit, grazes the tidal radius accretion[58]. However, discthe inferredsize fromof the optical-through-X-ray spectral fitting turns large outfor to the beobserved too decay time [59]. Furthermore, outburststhe intervalseems betweento successive increase with time and it may not be strictly periodic. These fact solar masses between 90000 9000 and The X-ray light curve of all thereveals interestingvery decay properties. The timescale is too to short be consistent with outbursts has been carefully sampled by Swift and recurrent transient ULX that, at maximum, in 2009,Since itits reachesunderwentdiscovery, 6 outburts, all followed by Swift. Luminosity- a peak luminosity of 10 correlated spectral variability similar to that observed in Galactic BH binaries is seen in this source, with the X-ray spectrum at blackbody maximummodel [56]. The relativelywell low disk fittedtemperature in this bydisc-dominated state a multi-colour disc (0.2-0.3 keV) suggests the presence of an intermediate mass BH with a mass of ~20000 powered by accretion close the onto to Eddington limit stellar a mass [52]. black hole 3.4 The most luminous ULX and strongest intermediate mass BH condidate to date hyperluminousis the X-ray source HLX-1 in the galaxy ESO 243-49 [53,54,55]. It is a mass inferred f 12-14 M31 ULX-2 was jointly Simultaneous X-ray and radio measurements monitored demonstrated a clear bright sub-Eddington in the radio state, with radio flaring (on timescales andas short as minutes) analogous to that seen in the X-rays by severalGalatic facilities. BH binary GRS 1915+105, Swift contribution to our understandingof contributionSwift ULXs to luminosity the source was in a disc dominated state and for moderate inclinations, the PoS(SWIFT 10)048
514 416
741 financial , A&A 429 A&A , L. Zampieri L. (2006) 491 (2006) (2013) 3380 (2001) L27 (2001) 311
436
551
(2001) L109 (2001) Sci , 552
MNRAS , , ApJS 157 (2005) 59 157 (2005) ApJS , 6 (2009) 677 (2009) L39 (2009) 400
690 Low-metallicity natal environments and black masse hole in environments Low-metallicity natal
Production of globular intermediate-mass black clusters, in holes Production 09, (2004) 724 (2004) Formation of massive black holes through runaway collisions in dense runaway collisions in massive blackFormation through of holes Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High ROSAT Galaxies in Nearby from X-Ray Sources Ultraluminous 428
A catalogue of ultraluminous X-ray sources in external galaxies sources X-ray of ultraluminous catalogue A Massive Black Holes as Population III Remnants, ApJ Population HolesMassive III Remnants, Black as (2011) 166 (2011) 55 Ultraluminous X-ray sources in the and XMM-Newton New era, in Chandra X-ray sources Ultraluminous A Complete Sample of Ultraluminous X-ray Source Host Galaxies, ApJ ApJ Galaxies, Host Ultraluminous SampleComplete X-ray Source of A , 2XMM ultraluminous X-ray source candidates in candidates nearby MNRAS galaxies, source X-ray 2XMM ultraluminous An ultraluminous X-ray source powered by an accreting neutron star, Natur star, neutron an accreting by powered X-ray source An ultraluminous (2014) 198 Low metallicity and ultra-luminous X-ray sources in the Cartwheel galaxy, in Cartwheel the galaxy, Low X-ray sources metallicity and ultra-luminous Ultraluminous X-Ray Sources in External Galaxies, ApJ in Galaxies, External Ultraluminous X-Ray Sources Discovery of a 6.4 h black hole binary in NGC 4490 ofDiscovery a 6.4 h black in binary NGC hole A mass of less than 15 solar masses for the black the masses X-ray in hole an ultraluminous of for thanmass less 15 solar A The orbital period of the ultraluminous X-ray source in M 82 in M ultraluminous source period the The orbital X-ray of Puzzling accretion onto a black hole in the ultraluminous X-ray source M 101 ULX- M source hole ultraluminous the onto a black X-ray in accretion Puzzling Hubble Space Telescope Monitoring Reveals a 6.1 Day for Period Monitoring an Ultraluminous Space Hubble Telescope 514
(2013) 500 (2013) (2002) 232 (2009) L71 (1999) 89 503 330 395
519 MNRAS young star clusters, Natur clusters, young star ApJ, ApJ, MNRAS source, Natur source, (2014) 202 X-Ray Source in NGC 1313, ApJL in NGC X-Ray Source 1, Natur ultraluminous X-ray sources, MNRAS X-ray sources, ultraluminous Reviews Astronomy (2011) id. 49 (2011) 1844 (2011) P. Madau & M. J. Rees, P. R. A. al., King et al., M. Mapelli et E. J. M. Colbert & R. F. Mushotzky, The Nature of Accreting Black Holes Nearby Black in Galaxy Nuclei, Accreting Nature of The Mushotzky, R. F. E. J. M. Colbert & Hamilton, Miller & P. D. M. C. al., et Portegies-Zwart F. S. C. MotchC. al., et al., M. Bachetti et J.-F. Liu et Liu al., J.-F. Esposito al., et P. et Liu al., J.-F. H. Feng & R. Soria, Feng &H. R. Kaaret al., et P. D. A. Swartz al., et A. D. et al., Walton J. D. 20 Roberts P. T. & L. Zampieri J.-F. Liu & Bregman,J. N. Liu J.-F. Analysis Imager Observations Data Resolution I. Mirabel, Z. LiuQ. & I.F. 1125 (2005) [8] [9] [6] [7] [3] [4] [5] [1] [2] [11] [16] [17] [18] [13] [14] [15] [12] [10] We acknowledge financial support from the INAF research grant PRIN-2011-1 (“Challenging grant from PRIN-2011-1 research the financial INAF support acknowledge We and formation black holes theirand pathways”) X-ray Ultraluminous chasing sources: I/037/12/0. ASI-INAF contribution the from agreement References Swift contribution to our understandingof contributionSwift ULXs to Acknowledgments PoS(SWIFT 10)048
398
696
L. Zampieri L. (2011) 644 (2011) ApJ , 411 411 (2007) 580 660 (2014) 74 (2014) (2010) 1217 513
(2003) L61 (2003) 714
586
(2006) 1123 (2006) 1123 365
(2009) 1836 (2006) 191 (2007) 941 397
(2013) 1758 (2013) (2015) 3926 (2015) 365
668
435 446
(2013) id. 163 (2013) 7 778
Discovery of X-Ray Quasi-periodic Oscillations from an Oscillations ofDiscovery X-Ray Quasi-periodic from (2012) 1107 1107 (2012) (2013) L9 420
black MNRAS hole, 773 ○ Spectral variability of ultraluminous X-ray sources, MNRAS X-ray sources, ultraluminous variabilitySpectral of Quasi-periodic Variability in NGC 5408 X-1, ApJ ApJ 5408 X-1, in NGC Quasi-periodic Variability Discovery of a quasi-periodic oscillation in the ultraluminous X-rayDiscovery in ultraluminous oscillation the of a quasi-periodic X-ray spectral states and metallicity in the ultraluminous X-ray sources X-ray and metallicity sources in ultraluminous the X-ray states spectral (2010) L137 (2010) Challenging times: a re-analysis of NGC 5408 X-1, of NGC MNRAS times:Challenging a re-analysis Broad absorption features in wind-dominated ultraluminous X-ray sources?, X-raywind-dominated sources?, ultraluminous in features absorption Broad X-ray spectral evolution in the ultraluminous X-ray source M33 MNRAS X-8, X-rayX-ray source evolution in ultraluminous the spectral Origin of the X-Ray Quasi-periodic Oscillations and Identification of a of X-Ray the and Identification Quasi-periodic of Oscillations Origin The ultraluminous state, MNRAS The ultraluminous 710 Spectral States and Evolution of Ultraluminous X-Ray States and EvolutionSpectral Sources of On the Maximum Mass of Stellar Black Holes, ApJ of Holes, Stellar Maximum Mass the Black On A variable Quasi-Periodic Oscillation in M82 X-1. Timing and spectral and spectral M82 Oscillation Timing X-1. Quasi-Periodic in variable A A 400-solar-mass black hole the Natur black M82, in galaxy 400-solar-mass A The ultraluminous state revisited: fractional variability and spectral as variability shape fractional state revisited: The ultraluminous X-Ray Outflows and Super-Eddington Accretion in the Ultraluminous X-Ray in Ultraluminous the Accretion X-Ray and Super-Eddington Outflows A deep XMM-Newton observation of the ultraluminous X-ray source Holmberg II Holmberg XMM-Newton X-ray of ultraluminous source observation the deep A The Ultraluminous X-Ray Sources NGC 1313 X-1 and X-2: A Broadband Study Study Broadband A NGC and X-2: 1313 X-1 The Ultraluminous X-Ray Sources A systematic study of variability in a sample of ultraluminous X-ray sources, X-ray sources, ultraluminous in a sample of study variability of systematic A Weighing the black holes in ultraluminous X-ray sources through timing, MNRAS timing, through ultraluminous sources black the X-ray in holes Weighing Ultraluminous X-ray sources: a deeper insight into evolution, a deeper insight their spectral X-ray sources: Ultraluminous Discovery of Millihertz X-Ray Oscillations in a Transient Ultraluminous X-Ray Ultraluminous Discovery in X-Ray a Transient of Oscillations Millihertz (2009) 1061 (2014) 3461 (2014) L51 397 439 438
(2011) 464 (2011) (2008) 1707 387 Transient Ultraluminous X-Ray Source in M82, ApJ in M82, X-Ray Source Ultraluminous Transient X-1: a 1000-M case the against Source in M82, ApJL ApJL in M82, Source Ultraluminous X-Ray Source in M82: Evidence against Beaming, ApJ in M82: against Evidence Beaming, Ultraluminous X-Ray Source and RossiXTEanalysis of MNRAS XMM-Newton observations, MNRAS MNRAS MNRAS ApJL X-1, IX Holmberg Source NGC and X-2,X-1 1313 MNRAS MNRAS accretion, diagnostics of super-Eddington (2009) 1712 (2009) 1450 with NuSTAR and XMM-Newton 2013, ApJ and XMM-Newton 2013, NuSTAR with 417 P. Casella al., et P. H. Feng & P. Kaaret, Feng &H. P. Goad al., et M. R. T. E. Strohmayer 2007, al. et T. Nandi, A. & Agrawal K. V. MNRAS XMM-Newton results, IC 342 X-1: source al., Feng et H. P. Mucciarelli al., et P. R. al., D. et Pasham M. J. Middleton et al., et M. J. Middleton al., et L. M. Heil Mushotzky, E. Strohmayer F. & R. T. M. J. Middleton et al., et M. J. Middleton et al., Walton J. D. F. Pintore & L. Zampieri, F. et Sutton D. A. al., al., Pintore et F. H. Feng & P. Kaaret, Feng &H. P. J. J. E. Kajava & J. Poutanen, J. C. Gladstone al., et J. C. al., M. Bachetti et al., et M. J. Middleton K. Belczynski et Belczynski K. al., [40] [38] [39] [35] [37] [33] [34] [30] [31] [32] [28] [29] [25] [26] [27] [23] [24] [20] [21] [22] [19] [36] Swift contribution to our understandingof contributionSwift ULXs to PoS(SWIFT 10)048
724
(2004) L. Zampieri L. 351
(2012) id. 34 752
(2012) id. 152 (2012) 750
(2010) L102 (2010) (2013) 1023 (2013) 721
433
ApJL , (2013) id. 93 (2013) 764
8 (2013) 1944 428
(2011) id. 6 (2011) Evidence for Quasi-periodic X-Ray Dips from an Ultraluminous X-Ray from Dips forEvidence Quasi-periodic 743
(2015) 1153 (2015) (2012) 554 (2012) 448 right radio emission from an ultraluminous stellar-mass microquasar in M in M microquasar an ultraluminous stellar-mass from emission right radio (2011) id. 89 (2011)
337 (2009) 73 Radio Detections During Two State Transitions of Intermediate-Mass the State Transitions Radio Detections During Two A dipping black hole X-ray binary candidate in NGC 55, MNRAS black in X-ray NGC candidate hole dipping binary A Swift Observations of the Ultraluminous X-ray Source Holmberg IX X-1, ApJ IX X-1, Holmberg Ultraluminous the Swift Observations X-ray Source of (2013) 2480 (2013) 735 (2009) L210 iscovery of a 115 Day Orbital Period in the Ultraluminous X-Ray Source NGC X-Ray Orbital Source in Period Ultraluminous the Day a 115 iscovery of A Redshift for the BlackRedshift Candidate for Intermediate-mass Hole HLX-1: A 460 An intermediate-mass black hole of over 500 solar masses in galaxy the An intermediate-mass black 500 solar masses of hole over Interpretation of the 115 Day Modulation Periodic in X-ray of the Flux NGC of 115 the Interpretation
(2010) 2480 X-Ray Variability and Hardness of 243-49 Clear ESO Evidence HLX-1: for and Hardness X-Ray Variability The Origin of Variability of the Black-hole ULX System of Intermediate-mass HLX-1 The Origin of Variability Swift observations of the ultraluminous X-ray source XMMU J004243.6+412519 X-ray of source ultraluminous observations the Swift 428 XMMU J004243.6+412519 - a new X-ray transient in M 31 seen XMM in M with XMMU a new X-ray J004243.6+412519 - transient
Spectral variability in Swift and Chandra observations of the ultraluminous source source Swift and Chandra of ultraluminous observations the variabilitySpectral in 706 Investigating Slim Disk Solutions for HLX-1 in ESO 243-49, ApJ for in 243-49, HLX-1 ESO Solutions SlimInvestigating Disk A long-term X-ray monitoring of the ultraluminous X-ray source NGC 5408 X-1 NGC with X-ray of ultraluminous source X-ray the monitoring long-term A ApJL X-1, II in Holmberg Luminosity with X-ray State is Spectral not Correlated 725 The Birth of an Ultraluminous X-Ray Source in M83, ApJ in M83, X-Ray Source of an Ultraluminous The Birth (2013) 187 (2013)
493 Eccentricity MNRAS of HLX-1, ster et al., et ster , ATel #3890 (2012) ATel , (2010) 1816 Spectral State Transitions, ApJ Transitions, Spectral State ApJ in 243-49, ESO Confirmation of its Association with the Galaxy the with ESOAssociation 243-49 Confirmation of its Black HLX-1, Hole Sci in M31, MNRAS in M31, 31, Natur ESO243-49, Natur Newton 722 NGC 55 ULX1, MNRAS 1063 5408 X-1, ApJ 5408 X-1, (2010) L148 X-Ray Source: Implications for the Binary Motion, ApJ Implications for Motion, Binary the X-Ray Source: MNRAS period, but no orbital of dips presence the Swift reveals 5408 X-1, ApJL ApJL 5408 X-1, R. Soria,R. M. Servillat etM. Servillat al., et Godet O. al., Lasota al., et J.-P. K. Wiersema et al., al., et Wiersema K. 2012, al. et Webb N. M. J. Middleton et al., et M. J. Middleton B Farrell al., et A. S. R. SoriaR. al., et al., et M. Henze Esposito al., et P. F. Pintore et al., Pintore et F. al., M. Stobbart et A. D. L. FoD. al., et Grise’ F. H. K. A. al., et Kong D. R. Pasham & T. E. Strohmayer, E. Strohmayer, T. R. &D. Pasham al., et Grise’ F. T. E. Strohmayer, D E. Strohmayer, T. [59] [56] [57] [58] [54] [55] [52] [53] [49] [50] [51] [47] [48] [44] [45] [46] [42] [43] [41] Swift contribution to our understandingof contributionSwift ULXs to