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Two new transient ultra-luminous X-ray sources found in galaxy NGC 4552

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2026-07-09 06:34 UTC pith:GTYOBO5Q

load-bearing objection Two transient ULX candidates in NGC 4552, but T1's classification is model-dependent the 3 major comments →

arxiv 2607.07568 v1 pith:GTYOBO5Q submitted 2026-07-08 astro-ph.HE

Transient and Variable Ultra-luminous X-ray Sources in NGC 4552

V. Jithesh , A. S. Sreya , Riya Elza Mathew , E. Sreeraj , R. Arun This is my paper
classification astro-ph.HE
keywords ultra-luminous X-ray sourcestransient X-ray sourcesNGC 4552super-Eddington accretionX-ray binariesChandraXMM-NewtonJWST
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

Two sources (T1 and T14) in the elliptical galaxy NGC 4552 at 16.25 Mpc exceed the ULX luminosity threshold of 10^39 erg/s in their peak observations and show variability ratios of >=14.3 and >=8.7 between peak and non-detection states. Their soft spectral characteristics, including steep power-law indices and low disk temperatures, are consistent with super-Eddington accretion onto stellar-mass compact objects. The paper also identifies 12 additional transient or variable X-ray sources in the galaxy, most consistent with neutron-star or black-hole X-ray binaries at luminosities of 10^37-10^38 erg/s, and finds near-infrared counterparts for three mildly variable sources using JWST imaging, with magnitudes suggesting red supergiant companions.

Core claim

The central discovery is the identification of two sources that cross the ULX luminosity threshold of 10^39 erg/s during transient outbursts in NGC 4552, an elliptical galaxy previously not known to host ULXs. T1 reached a luminosity of ~10^39.4 erg/s in a 2001 Chandra observation before becoming undetectable in subsequent observations, while T14 brightened to above 10^39 erg/s in a 2003 XMM-Newton observation after being fainter by nearly an order of magnitude. Both sources show soft spectra (steep photon indices ~2.3-2.7 or low inner disk temperatures ~0.25-0.8 keV), placing them among the growing population of transient ULXs that serve as transitional objects between normal X-ray binaries

What carries the argument

transient ULXs

Load-bearing premise

The ULX classification depends on the peak luminosities of T1 and T14 being intrinsic rather than inflated by statistical noise, but T1 has only 363 net counts and T14 has as few as 33 counts in one observation, making the spectral fits and luminosity estimates subject to large uncertainties and model degeneracies.

What would settle it

Deeper X-ray observations that fail to detect either source above 10^39 erg/s, or that show the peak detections were statistical fluctuations, would undermine the ULX classification.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • If T1 and T14 are genuinely transient ULXs, deep X-ray monitoring of NGC 4552 could catch recurrent outbursts and enable spectral studies with sufficient counts to detect the high-energy spectral turnover characteristic of super-Eddington accretion.
  • The association of T1 with a globular cluster, if confirmed, would add to the evidence that globular clusters can host ULXs, constraining formation channels involving dynamical interactions in dense stellar environments.
  • The absence of supersoft sources among 14 transients, despite expectations of 25-35% from other galaxies, suggests that sensitivity and distance limit detection of this class at 16 Mpc, with implications for completeness of transient source populations in distant galaxies.
  • JWST near-infrared counterparts for three variable sources suggest red supergiant companions, which would link these X-ray systems to high-mass X-ray binary evolution channels in an elliptical galaxy environment.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

3 major / 7 minor

Summary. This paper searches for transient and variable X-ray sources in the elliptical galaxy NGC 4552 using archival Chandra and XMM-Newton observations (2001–2012), supplemented by JWST NIR imaging. The authors identify 14 transient/variable sources within 4 effective radii, classify them by luminosity ratio, and perform spectral fitting. Two sources (T1 and T14) are classified as transient/variable ULXs based on peak luminosities exceeding 10^39 erg/s. NIR counterparts are identified for three mildly variable sources using JWST, with magnitudes consistent with red supergiants. The analysis uses standard tools (CIAO, SAS, XSPEC) and is broadly self-contained.

Significance. The identification of transient ULXs in an elliptical galaxy is of interest for understanding the ULX population and its connection to X-ray binary evolution. The inclusion of JWST NIR counterpart analysis adds value, though the ULX candidates themselves fall outside the JWST field. The spectral and temporal analysis is standard but the photon statistics are low for the key sources, which limits the robustness of the central claims. The paper provides full spectral fit tables and upper-limit calculations, which is commendable for reproducibility.

major comments (3)
  1. §3.3, Table 4: The ULX classification of T1 is model-dependent in a consequential way. The diskbb model with fixed Galactic N_H yields log L_X = 38.99 (below the 10^39 threshold) with an acceptable fit (χ²/d.o.f = 19/14). Only the power law with N_H freed to 2.87×10^21 cm^-2 (~10× Galactic) produces log L_X = 39.40, above threshold. While the Δχ² improvement from freeing N_H is formally significant, the paper does not adequately discuss that an acceptable alternative model places T1 below the ULX threshold. The diskbb 90% upper bound (10^39.08) only marginally crosses. The paper should explicitly acknowledge this model-dependence and discuss whether freeing N_H for the diskbb model is physically motivated or warranted, or whether the elevated N_H could indicate local absorption within the galaxy rather than intrinsic source properties.
  2. §3.3, Table 4: For T14 in XMM1, the power law fit gives log L_X = 39.04+0.08/-0.09; the 90% lower bound (10^38.95) falls below the 10^39 ULX threshold. The double-thermal model (Table 5) gives 10^39.13+0.13/-0.11, with the lower bound above threshold, but this adds two free parameters to a 237-count spectrum. The F-test significance (98.4%) is noted, but the paper should more transparently state that the single-component power law classification is marginal, and discuss the reliability of the F-test for this low-count regime.
  3. §3.2, Table 3: The hardness ratio classification for T1 in the XMM1 observation yields 'SNR', which is inconsistent with its proposed ULX nature. This inconsistency is not discussed. While the paper notes that colour-based classifications should be considered indicative, the SNR classification for a source claimed as a ULX deserves at least a brief comment, particularly given the large HR uncertainties in XMM1 (HR1 = -0.40 ± 0.28).
minor comments (7)
  1. Table 2: The luminosity ratio column header says 'Luminosity Ratio' but the values for MVS sources (e.g., T3 with ratio 0.97, T4 with 0.36) are below 1, which is confusing given the definition as peak-to-undetected ratio. Please clarify whether these are ratios of peak to the strict upper limit on the non-detection, and how a ratio below 1 arises.
  2. §3.3: The paper states 'When using the χ² statistic, the lowest χ² model is chosen as the preferred model.' For T1, the diskbb (χ²/d.o.f = 19/14) and power law with free N_H (12.36/13) have different numbers of free parameters (different N_H treatment). A direct χ² comparison without accounting for the extra parameter is not strictly valid; an F-test or AIC/BIC comparison would be more appropriate.
  3. Table 4: For T14 XMM1, the diskbb fit has reduced χ² > 2 and parameter errors could not be estimated. The table entry shows '63.77/19' with a dash for goodness. Please clarify what the dash means and whether this fit should be reported at all if it is formally rejected.
  4. §3.4: The search radius of 1.5 arcsec for NIR counterparts is stated without justification. Given the Chandra positional uncertainties listed in Table 2 (0.04–0.45 arcsec), please comment on the choice of 1.5 arcsec and the resulting contamination probability.
  5. §4: The statement that T1's double-thermal fit 'suggests NS LMXB nature' with kTin ~ 2.9 keV seems inconsistent with the simultaneously claimed ULX status (L_X > 10^39). Please reconcile the NS LMXB interpretation with the super-Eddington luminosity.
  6. Table 6: The magnitudes are stated as not dereddened. Given that NGC 4552 is in the Virgo cluster with potentially significant foreground extinction, please comment on the expected impact of reddening on the RSG classification.
  7. Figure 2: The top panel y-axis label is difficult to read. Please ensure axis labels are legible in the final version.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for a careful and constructive report. The referee's three major comments all concern the robustness of the ULX classification for T1 and T14, given the low photon statistics and model-dependence of the spectral fits. We agree that these are legitimate concerns. We will revise the manuscript to explicitly acknowledge the model-dependence of the T1 classification, state more transparently that the T14 power-law classification is marginal, and add discussion of the SNR hardness ratio classification for T1 in XMM1. We also address the referee's points on the physical motivation for freeing N_H and the reliability of the F-test in the low-count regime.

read point-by-point responses

  1. Referee: §3.3, Table 4: The ULX classification of T1 is model-dependent. The diskbb model with fixed Galactic N_H yields log L_X = 38.99 (below 10^39) with an acceptable fit, while only the power law with N_H freed to ~10x Galactic produces log L_X = 39.40. The paper should explicitly acknowledge this model-dependence and discuss whether freeing N_H is physically motivated.

    Authors: We agree with the referee that the ULX classification of T1 carries model-dependent caveats that should be stated more explicitly. We will revise the manuscript to acknowledge that the diskbb model with fixed Galactic N_H yields a luminosity marginally below the 10^39 threshold (log L_X = 38.99, with the 90% upper bound at 10^39.08 only marginally crossing), and that the ULX classification rests on the power-law model with N_H freed. Regarding the physical motivation for freeing N_H: the power-law model with fixed Galactic N_H yields a reduced chi-s2 > 2, which is a poor fit. Freeing N_H improves the fit to chi^2/d.o.f = 12.36/13. The best-fit N_H = 2.87 x 10^21 cm^-2 is ~10x the Galactic column, but this is not implausible for a source in an elliptical galaxy with a steep density profile. As we note in Section 3.2, NGC 4552 exhibits a steep density profile, and sources in the inner regions may experience higher local absorption. T1 is located ~90 arcsec from the center, where the local gas density could plausibly elevate the column density above the Galactic foreground. We will add a discussion of whether the elevated N_H could indicate local absorption within the galaxy rather than intrinsic source properties, as the referee suggests. We will also note that the double-thermal model (Table 5) yields log L_X = 39.07, which is above the threshold, providing some support for the ULX classification from an independent model. However, we acknowledge that none of the models alone provides a definitive classification, and we will state this transparently in the revised manuscript. revision: yes

  2. Referee: §3.3, Table 4: For T14 in XMM1, the power law fit gives log L_X = 39.04 with the 90% lower bound (10^38.95) below the 10^39 threshold. The double-thermal model gives 10^39.13 with the lower bound above threshold, but adds two free parameters to a 237-count spectrum. The paper should more transparently state that the single-component power law classification is marginal, and discuss the reliability of the F-test for this low-count regime.

    Authors: We agree that the single-component power-law classification for T14 is marginal, and we will revise the manuscript to state this more transparently. The 90% lower bound on the power-law luminosity (10^38.95) does fall below the 10^39 threshold, and we will explicitly acknowledge this. Regarding the F-test: the referee is correct to raise the question of F-test reliability for a 237-count spectrum. The F-test assumes that the test statistic follows an F-distribution, which is strictly valid for Gaussian statistics and nested models. While our spectra are binned to a minimum of 20 counts per bin (justifying the use of chi^2 statistics), the low total count number means the F-test result should be treated with caution. We will add a caveat noting that the F-test significance (98.4%) should be interpreted as indicative rather than definitive given the photon statistics, and that the double-thermal model improvement, while suggestive, is not conclusive. We also note that both the power-law and double-thermal models yield central luminosity values above 10^39, and the double-thermal model's lower bound is above threshold. We will present both models and their caveats side by side so the reader can assess the robustness of the classification. revision: yes

  3. Referee: §3.2, Table 3: The hardness ratio classification for T1 in the XMM1 observation yields 'SNR', which is inconsistent with its proposed ULX nature. This inconsistency is not discussed. The paper should comment on this, particularly given the large HR uncertainties in XMM1 (HR1 = -0.40 ± 0.28).

    Authors: We agree that the SNR classification for T1 in XMM1 deserves at least a brief comment, and we will add one in the revised manuscript. The SNR classification arises because HR1 = -0.40 ± 0.28 and HR2 = -0.29 ± 0.48, which fall in the SNR region of the Kilgard et al. (2005) classification scheme (HR2 < -0.2, HR1 < -0.3). However, the uncertainties are very large — HR1 is consistent with -0.3 (the boundary between SNR and XRB classifications) within 1 sigma, and HR2 is consistent with zero within 1 sigma. The XMM1 observation has only 83 net counts for T1, so the hardness ratios are poorly constrained. We will note that the SNR classification is driven by the large statistical uncertainties rather than a physically meaningful spectral characterization, and that the Chandra HR classification for T1 in C1 (where the source is brighter, with 363 counts) yields 'XRB', which is more reliable. We will also reiterate our existing caveat that colour-based classifications should be considered indicative rather than definitive, particularly for sources with low counts and in regions of potentially elevated local absorption. revision: yes

Circularity Check

0 steps flagged

No significant circularity; the paper is self-contained against external benchmarks.

full rationale

The paper's central claim—that T1 and T14 are transient/variable ULXs—is derived from standard observational analysis using external tools (CIAO, SAS, XSPEC), external benchmarks (Galactic N_H from HI4PI, distance from Tonry et al. 2001), and the standard ULX definition (L_X > 10^39 erg/s) from external reviews (Kaaret et al. 2017; Fabrika et al. 2021). The transient classification scheme (ratio > 10 for TS, 5-10 for VS) is cited to Jithesh & Wang 2016, a prior work by the lead author. However, this is a straightforward empirical threshold definition, not a derived result that reduces to its own inputs. The luminosity estimates come from spectral fits to the actual X-ray data, not from any self-referential chain. While the ULX classification of T1 is model-dependent (the diskbb fit with fixed N_H gives log L_X = 38.99, below threshold, while the power law with freed N_H gives 39.40, above threshold), this is a model-selection sensitivity issue—a correctness risk, not circularity. The paper does not fit a parameter to data and then 'predict' the same data, nor does it define a quantity in terms of itself. The self-citations (Jithesh & Wang 2015, 2016, 2017) are used for methodology context and comparison populations, not as load-bearing mathematical premises. The derivation chain is self-contained.

Axiom & Free-Parameter Ledger

1 free parameters · 3 axioms · 0 invented entities

The paper relies on standard astrophysical assumptions (distance, Galactic absorption) and one fitted parameter (N_H for T1). No new physical entities or forces are postulated. The classification scheme is an observational definition, not a theoretical axiom.

free parameters (1)
  • N_H (for T1 power law fit) = 2.87e21 cm^-2
    The absorption column density was left as a free parameter for the T1 power law fit because the fixed Galactic value yielded reduced chi^2 > 2.
axioms (3)
  • domain assumption Distance to NGC 4552 is 16.25 Mpc
    Used throughout to convert flux to luminosity, taken from Tonry et al. (2001).
  • domain assumption Galactic N_H = 2.67e20 cm^-2
    Fixed absorption column density used in TBABS model, taken from HI4PI Collaboration et al. (2016).
  • domain assumption Transient classification threshold: luminosity ratio > 10
    The definition of a transient source used in Section 3.1, sourced from the authors' own prior work (Jithesh & Wang 2016).

pith-pipeline@v1.1.0-glm · 25222 in / 2294 out tokens · 389804 ms · 2026-07-09T06:34:51.239991+00:00 · methodology

0 comments
read the original abstract

We searched for transient and variable X-ray sources in the elliptical galaxy NGC 4552 using the {\it Chandra} and {\it XMM-Newton} observations from 2001-2012. We detected 14 transient and variable X-ray sources within the 4$R_{e}$ region of the galaxy, which exhibited peak state and undetected flux behaviour in the {\it Chandra} observations. Among them, two sources (T1 and T14) exceed the X-ray luminosity $10^{39}\rm~erg~s^{-1}$ in the detected observations and have the peak state and undetected luminosity ratio of $\geq 14.3$ and $\geq 8.7$, respectively, which we classified as transient and variable ultra-luminous X-ray sources (ULXs). For the third relatively bright transient source, the flux varies by a factor of 3 across the detected observations, and the hardness ratio analysis suggests a normal X-ray binary system. The remaining sources have luminosities in the $10^{37}-10^{38} \rm~erg~s^{-1}$ range, and the spectral analysis indicates that the sources may belong to neutron star or black hole X-ray binary systems, either in the hard or thermal-dominated state. The identified transient and variable ULXs exhibited high variability and soft spectral characteristics, which are consistent with ULXs accreting at super-Eddington rates. The near-infrared (NIR) counterpart search using {\it JWST} observations identified potential NIR counterparts for three mildly variable sources, and their magnitudes in different NIR bands suggest a red supergiant companion for each source. Deep X-ray monitoring observations can shed further light on the new transient and variable ULXs.

Figures

Figures reproduced from arXiv: 2607.07568 by A. S. Sreya, E. Sreeraj, R. Arun, Riya Elza Mathew, V. Jithesh.

Figure 1
Figure 1. Figure 1: Smoothened Chandra ACIS image of NGC 4552 from C1 obser￾vation. The dashed green circle represents the 4𝑅𝑒 region of the galaxy. The detected transient sources are represented as solid white circles with a radius of 3 arcseconds. To avoid false detection of these sources, we have put stringent cri￾teria that the source should be detected in at least one of the obser￾vations at a > 4𝜎 confidence level with … view at source ↗
Figure 2
Figure 2. Figure 2: Spectral fit of transient and variable ULXs in NGC 4552. Top Panel: Energy (keV) T1 spectrum from C1 observation is fitted with a power law model. Bottom Panel: T14 spectra from XMM1 observation fitted with blackbody plus disk blackbody model. In the XMM1 observation, the black and red data points represent the PN and combined MOS spectra, respectively. 𝑉𝑒𝑔𝑎mag = −2.5 log10 ( flux density × PIXAR_SR fluxVe… view at source ↗
Figure 3
Figure 3. Figure 3: 4.5 × 4.5 arcsec NIRCam F090W image cutout around the X-ray positions of sources T6, T7, and T11 that have potential counterparts. The centre of the dashed white circle (1.5′′ radius) represents the Chandra X-ray position, and the solid yellow circles (0.3′′ radius) represent possible NIR counterparts detected at 3𝜎 threshold. identified them as transient and variable sources. Based on the peak￾state and u… view at source ↗

discussion (0)

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Reference graph

Works this paper leans on

112 extracted references · 112 canonical work pages · 68 internal anchors

  1. [1]

    Monthly Notices of the Royal Astronomical Society , volume=

    X-ray outbursts from a new transient in NGC 55 , author=. Monthly Notices of the Royal Astronomical Society , volume=. 2015 , publisher=

    work page 2015

  2. [2]

    Astronomy & Astrophysics , volume=

    Three X-ray transients in M 31 observed with Swift , author=. Astronomy & Astrophysics , volume=. 2008 , publisher=

    work page 2008

  3. [3]

    A Wavelet-Based Algorithm for the Spatial Analysis of Poisson Data

    A Wavelet-Based Algorithm for the Spatial Analysis of Poisson Data. , keywords =. doi:10.1086/324017 , archivePrefix =. astro-ph/0108429 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/324017

  4. [4]

    and Lockman, Felix J

    Dickey, John M. and Lockman, Felix J. , title =. Annual Review of Astronomy and Astrophysics , volume =

    work page

  5. [5]

    The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances. , keywords =. doi:10.1086/318301 , archivePrefix =. astro-ph/0011223 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/318301

  6. [6]

    , keywords =

    Parameter estimation in astronomy through application of the likelihood ratio. , keywords =. doi:10.1086/156922 , adsurl =

    work page doi:10.1086/156922

  7. [7]

    Astronomical Data Analysis Software and Systems V , year = 1996, editor =

    XSPEC: The First Ten Years. Astronomical Data Analysis Software and Systems V , year = 1996, editor =

    work page 1996

  8. [8]

    A Chandra Survey of Nearby Spiral Galaxies. I. Point Source Catalogs. , keywords =. doi:10.1086/430443 , adsurl =

    work page doi:10.1086/430443

  9. [9]

    doi:10.1111/j.1365-2966.2005.08999.x , keywords =

    An XMM-Newton view of M101 - II. Global X-ray source properties. , keywords =. doi:10.1111/j.1365-2966.2005.08645.x , archivePrefix =. astro-ph/0411535 , primaryClass =

    work page doi:10.1111/j.1365-2966.2005.08645.x 2005

  10. [10]

    ChandraStudy of X‐Ray Point Sources in the Early‐Type Galaxy NGC 4552 (M89) , volume=

    Xu, Yueheng and Xu, Haiguang and Zhang, Zhongli and Kundu, Arunav and Wang, Yu and Wu, Xiang‐Ping , year=. ChandraStudy of X‐Ray Point Sources in the Early‐Type Galaxy NGC 4552 (M89) , volume=. The Astrophysical Journal , publisher=. doi:10.1086/432636 , number=

    work page doi:10.1086/432636

  11. [11]

    Trinchieri, G. , year=. Evidence from the HOT ISM from X-ray observations in external galaxies , volume=. doi:10.1051/eas/1256037 , journal=

    work page doi:10.1051/eas/1256037

  12. [12]

    New Astronomy Reviews , year=

    Ultraluminous X-ray sources in the Chandra and XMM-Newton era , author=. New Astronomy Reviews , year=

    work page

  13. [15]

    and Wang, Zhongxiang , year=

    Jithesh, V. and Wang, Zhongxiang , year=. TRANSIENT X-RAY SOURCE POPULATION IN THE MAGELLANIC-TYPE GALAXY NGC 55 , volume=. The Astrophysical Journal , publisher=. doi:10.3847/0004-637x/821/1/24 , number=

    work page doi:10.3847/0004-637x/821/1/24

  14. [16]

    and Wang, Zhongxiang , year=

    Jithesh, V. and Wang, Zhongxiang , year=. Transient X-Ray Sources in the Magellanic-type Galaxy NGC 4449 , volume=. The Astrophysical Journal , publisher=. doi:10.3847/1538-4357/836/1/44 , number=

    work page doi:10.3847/1538-4357/836/1/44

  15. [17]

    X-ray Binaries , year = 1995, month = jan, pages =

    The properties of X-ray binaries. X-ray Binaries , year = 1995, month = jan, pages =

    work page 1995

  16. [18]

    Broadband reflection spectroscopy of MAXI J1535-571 using AstroSat: Estimation of black hole mass and spin

    X-Ray Properties of Black-Hole Binaries. , keywords =. doi:10.1146/annurev.astro.44.051905.092532 , archivePrefix =. astro-ph/0606352 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1146/annurev.astro.44.051905.092532

  17. [19]

    Central UV Spikes in two Galactic Spheroids

    Central UV Spikes in Two Galactic Spheroids. The Formation of Galactic Bulges , year = 1999, editor =. doi:10.48550/arXiv.astro-ph/9901381 , archivePrefix =. astro-ph/9901381 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.48550/arxiv.astro-ph/9901381 1999

  18. [20]

    , keywords =

    Compact-core-dominated radio emission from bright E/SO galaxies. , keywords =. doi:10.1086/162662 , adsurl =

    work page doi:10.1086/162662

  19. [21]

    and Coughenour, Benjamin M

    Tomsick, John A. and Coughenour, Benjamin M. and Hare, Jeremy and Krivonos, Roman and Bodaghee, Arash and Chaty, Sylvain and Clavel, Maïca and Fornasini, Francesca M. and Rodriguez, Jerome and Shaw, Aarran W. , year=. Using Chandra Localizations and Gaia Distances and Proper Motions to Classify Hard X-Ray Sources Discovered by INTEGRAL , volume=. The Astr...

    work page doi:10.3847/1538-4357/abfa1a

  20. [22]

    Annual Review of Astronomy and Astrophysics , volume=

    Ultraluminous X-ray sources , author=. Annual Review of Astronomy and Astrophysics , volume=. 2017 , publisher=

    work page 2017

  21. [23]

    Bregman and Ed Lloyd-Davies and Jimmy Irwin and Catherine Espaillat and Patrick Seitzer , title =

    Ji-Feng Liu and Joel N. Bregman and Ed Lloyd-Davies and Jimmy Irwin and Catherine Espaillat and Patrick Seitzer , title =. 2005 , month =

    work page 2005

  22. [24]

    Portegies Zwart and Stephen L

    Simon F. Portegies Zwart and Stephen L. W. McMillan , title =. 2002 , month =

    work page 2002

  23. [25]

    Monthly Notices of the Royal Astronomical Society , volume=

    The transient ultraluminous X-ray source, ULX-4, in M51 , author=. Monthly Notices of the Royal Astronomical Society , volume=. 2022 , publisher=

    work page 2022

  24. [26]

    Monthly Notices of the Royal Astronomical Society , volume=

    A transient ultraluminous X-ray source in NGC 55 , author=. Monthly Notices of the Royal Astronomical Society , volume=. 2022 , publisher=

    work page 2022

  25. [27]

    Chandra X-Ray Observatory (CXO):Overview

    Chandra X-ray Observatory (CXO): overview. X-Ray Optics, Instruments, and Missions III , year = 2000, editor =. doi:10.1117/12.391545 , archivePrefix =. astro-ph/0004127 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1117/12.391545 2000

  26. [28]

    , keywords =

    The European Photon Imaging Camera on XMM-Newton: The pn-CCD camera * , DOI= "10.1051/0004-6361:20000066", url= "https://doi.org/10.1051/0004-6361:20000066", journal =

    work page doi:10.1051/0004-6361:20000066

  27. [29]

    The European Photon Imaging Camera on XMM-Newton: The MOS Cameras

    The European Photon Imaging Camera on XMM-Newton: The MOS cameras. , year = 2001, month = jan, volume =. doi:10.1051/0004-6361:20000087 , archivePrefix =. astro-ph/0011498 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361:20000087 2001

  28. [30]

    XMM-Newton observatory. I. The spacecraft and operations. , keywords =. doi:10.1051/0004-6361:20000036 , adsurl =

    work page doi:10.1051/0004-6361:20000036

  29. [31]

    HI4PI: A full-sky HI survey based on EBHIS and GASS

    HI4PI: A full-sky H I survey based on EBHIS and GASS. , keywords =. doi:10.1051/0004-6361/201629178 , archivePrefix =. 1610.06175 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361/201629178

  30. [32]

    The (re)appearance of NGC 925 ULX-3, a new transient ULX

    The (Re)appearance of NGC 925 ULX-3, a New Transient ULX. , keywords =. doi:10.3847/1538-4357/ab77b8 , archivePrefix =. 2001.00642 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-4357/ab77b8 2001

  31. [33]

    Quasi periodic whispers from a transient ULX in M\,101: signatures of a fast-spinning neutron star?

    Quasi-periodic whispers from a transient ULX in M 101: signatures of a fast-spinning neutron star?. , keywords =. doi:10.1093/mnras/stac195 , archivePrefix =. 2201.07252 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stac195

  32. [34]

    A transient ultraluminous X-ray source in NGC 55

    A transient ultraluminous X-ray source in NGC 55. , keywords =. doi:10.1093/mnras/stac2018 , archivePrefix =. 2207.09447 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stac2018

  33. [35]

    A new sample of transient ultraluminous X-ray sources serendipitously discovered by Swift/XRT

    A New Sample of Transient Ultraluminous X-Ray Sources Serendipitously Discovered by Swift/XRT. , keywords =. doi:10.3847/1538-4357/acd18a , archivePrefix =. 2305.01693 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-4357/acd18a

  34. [36]

    New Transient ULX Candidate in NGC 4254: Evidence of Circumbinary Disk?

    New transient ULX candidate in NGC 4254: evidence of circumbinary disc?. , keywords =. doi:10.1093/mnras/stad3175 , archivePrefix =. 2310.09421 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stad3175

  35. [37]

    NGC 2403 XMM4: evidence for a super-Eddington neutron star with a possible transient pulsation

    NGC 2403 XMM4: evidence for a super-Eddington neutron star with a possible transient pulsation. , keywords =. doi:10.1093/mnras/stae023 , archivePrefix =. 2401.02177 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stae023

  36. [38]

    The X-ray Globular Cluster Population in NGC 1399

    The X-Ray Globular Cluster Population in NGC 1399. , keywords =. doi:10.1086/323026 , archivePrefix =. astro-ph/0107362 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/323026

  37. [39]

    X-ray Source Population in the Elliptical Galaxy NGC 720 with Chandra

    X-Ray Source Population in the Elliptical Galaxy NGC 720 with Chandra. , keywords =. doi:10.1086/346074 , archivePrefix =. astro-ph/0211192 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/346074

  38. [40]

    50 M31 black hole candidates identified by Chandra and XMM-Newton

    Fifty M31 Black Hole Candidates Identified by Chandra and XMM-Newton. , keywords =. doi:10.1088/0004-637X/791/1/33 , archivePrefix =. 1406.6091 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1088/0004-637x/791/1/33

  39. [41]

    Globular Cluster Ultraluminous X-ray Sources in the Furthest Early-Type Galaxies

    Globular cluster ultraluminous X-ray sources in the furthest early-type galaxies. , keywords =. doi:10.1093/mnras/stac3244 , archivePrefix =. 2211.07699 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stac3244

  40. [42]

    Discovery of a transient ultraluminous X-ray source in the elliptical galaxy M86

    Discovery of a transient ultraluminous X-ray source in the elliptical galaxy M86. , keywords =. doi:10.1093/mnras/sty3221 , archivePrefix =. 1811.10595 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/sty3221

  41. [43]

    X-Ray Spectral Variability of Ultraluminous X-Ray Sources in Extragalactic Globular Clusters

    X-ray spectral variability of ultraluminous X-ray sources in extragalactic globular clusters. , keywords =. doi:10.1093/mnras/stz479 , archivePrefix =. 1902.05073 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stz479 1902

  42. [44]

    The first two transient supersoft X-ray sources in M 31 globular clusters and the connection to classical novae

    The first two transient supersoft X-ray sources in M 31 globular clusters and the connection to classical novae. , keywords =. doi:10.1051/0004-6361/200811122 , archivePrefix =. 0811.0718 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361/200811122

  43. [45]

    The Chandra ACIS Survey of M33 (ChASeM33): Transient X-ray Sources Discovered in M33

    The Chandra ACIS Survey of M33 (ChASeM33): Transient X-Ray Sources Discovered in M33. , keywords =. doi:10.1086/587885 , archivePrefix =. 0802.3724 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/587885

  44. [46]

    , year = 2010, month = mar, volume =

    Ten facts of life for distant supersoft sources. , year = 2010, month = mar, volume =. doi:10.1016/j.newar.2010.09.006 , adsurl =

    work page doi:10.1016/j.newar.2010.09.006 2010

  45. [47]

    , year = 1997, month = jan, volume =

    Luminous Supersoft X-Ray Sources. , year = 1997, month = jan, volume =. doi:10.1146/annurev.astro.35.1.69 , adsurl =

    work page doi:10.1146/annurev.astro.35.1.69 1997

  46. [48]

    Luminous Supersoft X-Ray Sources in External Galaxies

    Luminous Supersoft X-Ray Sources in External Galaxies. , keywords =. doi:10.1086/375858 , archivePrefix =. astro-ph/0301162 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/375858

  47. [49]

    The Nature of Composite LINER/HII Galaxies, As Revealed from High-Resolution VLA Observations

    The Nature of Composite LINER/H II Galaxies as Revealed from High-Resolution VLA Observations. , keywords =. doi:10.1086/313412 , archivePrefix =. astro-ph/0002404 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/313412

  48. [50]

    , year = 1995, month = nov, volume =

    An ultraviolet flare at the centre of the elliptical galaxy NGC4552. , year = 1995, month = nov, volume =. doi:10.1038/378039a0 , adsurl =

    work page doi:10.1038/378039a0 1995

  49. [51]

    , keywords =

    X-ray spectral states and metallicity in the ultraluminous X-ray sources NGC 1313 X-1 and X-2. , keywords =. doi:10.1111/j.1365-2966.2011.20072.x , archivePrefix =. 1110.6277 , primaryClass =

    work page doi:10.1111/j.1365-2966.2011.20072.x 2011

  50. [52]

    NuSTAR and Swift observations of the ultraluminous X-ray source IC 342 X-1 in 2016: witnessing spectral evolution

    NuSTAR and Swift Observations of the Ultraluminous X-Ray Source IC 342 X-1 in 2016: Witnessing Spectral Evolution. , keywords =. doi:10.3847/1538-4357/aa67e7 , archivePrefix =. 1703.06399 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-4357/aa67e7 2016

  51. [53]

    The Broadband Spectral Variability of Holmberg IX X-1

    The Broadband Spectral Variability of Holmberg IX X-1. , keywords =. doi:10.3847/1538-4357/aa683e , archivePrefix =. 1610.06611 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-4357/aa683e

  52. [54]

    doi:10.1111/j.1365-2966.2009.15310.x , keywords =

    The ultraluminous state. , keywords =. doi:10.1111/j.1365-2966.2009.15123.x , archivePrefix =. 0905.4076 , primaryClass =

    work page doi:10.1111/j.1365-2966.2009.15123.x 2009

  53. [55]

    , keywords =

    XMM-Newton observations of the brightest ultraluminous X-ray sources. , keywords =. doi:10.1111/j.1365-2966.2006.10112.x , archivePrefix =. astro-ph/0601651 , primaryClass =

    work page doi:10.1111/j.1365-2966.2006.10112.x 2006

  54. [56]

    , keywords =

    Ultraluminous X-ray sources. , keywords =. doi:10.1016/j.newar.2022.101672 , archivePrefix =. 2302.10605 , primaryClass =

    work page doi:10.1016/j.newar.2022.101672 2022

  55. [57]

    Ultraluminous X-Ray Sources

    Ultraluminous X-Ray Sources. Astrophysical Bulletin , keywords =. doi:10.1134/S1990341321010077 , archivePrefix =. 2105.10537 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1134/s1990341321010077

  56. [58]

    A New Transient Ultraluminous X-ray Source in NGC 7090

    A new transient ultraluminous X-ray source in NGC 7090. , keywords =. doi:10.1093/mnras/staa3666 , archivePrefix =. 2011.08870 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/staa3666 2011

  57. [59]

    , keywords =

    The missing link: a low-mass X-ray binary in M31 seen as an ultraluminous X-ray source. , keywords =. doi:10.1111/j.1365-2966.2011.20145.x , archivePrefix =. 1111.1188 , primaryClass =

    work page doi:10.1111/j.1365-2966.2011.20145.x 2011

  58. [60]

    A new Ultraluminous X-ray source in the galaxy NGC 5907

    A new ultraluminous X-ray source in the galaxy NGC 5907. , keywords =. doi:10.1093/mnrasl/sly048 , archivePrefix =. 1806.03633 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnrasl/sly048

  59. [61]

    The Ultraluminous X-ray sources population of the galaxy NGC 7456

    The Ultraluminous X-Ray Sources Population of the Galaxy NGC 7456. , keywords =. doi:10.3847/1538-4357/ab6ffd , archivePrefix =. 2001.08752 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-4357/ab6ffd 2001

  60. [62]

    Swift monitoring of M51: A 38-day super-orbital period for the pulsar ULX7 and a new transient ULX

    Swift Monitoring of M51: A 38 day Superorbital Period for the Pulsar ULX7 and a New Transient Ultraluminous X-Ray Source. , keywords =. doi:10.3847/1538-4357/ab7e2a , archivePrefix =. 1912.04431 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-4357/ab7e2a 1912

  61. [63]

    The Birth of an Ultra-Luminous X-ray Source in M83

    The Birth of an Ultraluminous X-Ray Source in M83. , keywords =. doi:10.1088/0004-637X/750/2/152 , archivePrefix =. 1203.2335 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1088/0004-637x/750/2/152

  62. [64]

    An Ultraluminous X-ray Source Powered by An Accreting Neutron Star

    An ultraluminous X-ray source powered by an accreting neutron star. , keywords =. doi:10.1038/nature13791 , archivePrefix =. 1410.3590 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1038/nature13791

  63. [65]

    Super-Eddington accretion onto a stellar mass ultraluminous X-ray source NGC 4190 ULX1

    Super-Eddington accretion on to a stellar mass ultraluminous X-ray source NGC 4190 ULX1. , keywords =. doi:10.1093/mnras/stab774 , archivePrefix =. 2103.10265 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stab774

  64. [66]

    A spectral-timing model for ULXs in the super-critical regime

    A spectral-timing model for ULXs in the supercritical regime. , keywords =. doi:10.1093/mnras/stu2644 , archivePrefix =. 1412.4532 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stu2644

  65. [67]

    X-ray spectral residuals in NGC 5408 X-1: diffuse emission from star formation, or the signature of a super-Eddington wind?

    X-Ray Spectral Residuals in NGC 5408 X-1: Diffuse Emission from Star Formation, or the Signature of a Super-Eddington Wind?. , keywords =. doi:10.1088/0004-637X/814/1/73 , archivePrefix =. 1510.03853 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1088/0004-637x/814/1/73

  66. [68]

    The Nature of Accreting Black Holes in Nearby Galaxy Nuclei

    The Nature of Accreting Black Holes in Nearby Galaxy Nuclei. , keywords =. doi:10.1086/307356 , archivePrefix =. astro-ph/9901023 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/307356

  67. [69]

    Intermediate-Mass Black Holes

    Intermediate-Mass Black Holes. International Journal of Modern Physics D , keywords =. doi:10.1142/S0218271804004426 , archivePrefix =. astro-ph/0308402 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1142/s0218271804004426

  68. [70]

    An accreting pulsar with extreme properties drives an ultraluminous x-ray source in NGC 5907

    An accreting pulsar with extreme properties drives an ultraluminous x-ray source in NGC 5907. Science , keywords =. doi:10.1126/science.aai8635 , archivePrefix =. 1609.07375 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1126/science.aai8635

  69. [71]

    Discovery of pulsations from NGC 300 ULX1 and its fast period evolution

    Discovery of pulsations from NGC 300 ULX1 and its fast period evolution. , keywords =. doi:10.1093/mnrasl/sly030 , archivePrefix =. 1802.10341 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnrasl/sly030

  70. [72]

    Discovery of a 2.8 s pulsar in a 2 d orbit High-Mass X-ray Binary powering the Ultraluminous X-ray source ULX-7 in M51

    Discovery of a 2.8 s Pulsar in a 2 Day Orbit High-mass X-Ray Binary Powering the Ultraluminous X-Ray Source ULX-7 in M51. , keywords =. doi:10.3847/1538-4357/ab8a44 , archivePrefix =. 1906.04791 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-4357/ab8a44 1906

  71. [73]

    , year = 1996, month = jan, volume =

    X-ray Novae. , year = 1996, month = jan, volume =. doi:10.1146/annurev.astro.34.1.607 , adsurl =

    work page doi:10.1146/annurev.astro.34.1.607 1996

  72. [74]

    A study of the population of LMXBs in the bulge of M31

    A study of the population of LMXBs in the bulge of M \, 31. , keywords =. doi:10.1051/0004-6361:20066614 , archivePrefix =. astro-ph/0610649 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361:20066614

  73. [75]

    Time variability of X-ray sources in the M 31 centre field

    Time variability of X-ray sources in the M 31 centre field. , keywords =. doi:10.1051/0004-6361:20078858 , archivePrefix =. 0801.4226 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361:20078858

  74. [76]

    A Catalog of Transient X-ray Sources in M31

    A Catalog of Transient X-Ray Sources in M31. , keywords =. doi:10.1086/501496 , archivePrefix =. astro-ph/0601287 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/501496

  75. [77]

    Bright X-ray Transients in M31: 2004 July XMM-Newton Observations

    Bright X-Ray Transients in M31: 2004 July XMM-Newton Observations. , keywords =. doi:10.1086/504072 , archivePrefix =. astro-ph/0512260 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/504072 2004

  76. [78]

    Three X-ray transients in M31 observed with Swift

    Three X-ray transients in M ;31 observed with Swift. , keywords =. doi:10.1051/0004-6361:20078970 , archivePrefix =. 0807.2949 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361:20078970

  77. [79]

    X-Ray Binary Systems in the Small Magellanic Cloud

    X-ray binary systems in the Small Magellanic Cloud. , keywords =. doi:10.48550/arXiv.astro-ph/9706075 , archivePrefix =. astro-ph/9706075 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.48550/arxiv.astro-ph/9706075

  78. [80]

    Optical identification of the transient supersoft X-ray source RX J0527.8-6954, in the LMC

    Optical identification of the transient supersoft X-ray source RX J0527.8-6954, in the LMC. , keywords =. doi:10.1051/0004-6361/201014773 , archivePrefix =. 1006.4820 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361/201014773

  79. [81]

    Detection of a 522 s Pulsation from the Transient X-ray Source Suzaku J0102.8--7204 (SXP 523) in the Small Magellanic Cloud

    Detection of a 522 s Pulsation from the Transient X-Ray Source Suzaku J0102.8-7204 (SXP 523) in the Small Magellanic Cloud. , keywords =. doi:10.1093/pasj/65.2.L2 , archivePrefix =. 1303.0119 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/pasj/65.2.l2

  80. [82]

    Discovery of a new Transient X-ray Pulsar in the Small Magellanic Cloud

    Discovery of a new transient X-ray pulsar in the Small Magellanic Cloud. , keywords =. doi:10.1051/0004-6361:20020150 , archivePrefix =. astro-ph/0201468 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361:20020150

Showing first 80 references.