arXiv subjects

R. H. D. Corbet

Publications and source records attributed to R. H. D. Corbet.

At least 19 recordsLinked to original sources

arXiv2026

Multi-mission Investigation of X-ray Superorbital Modulation in the Supergiant High Mass X-ray Binary 4U 1538-52

Superorbital modulations has been detected in the supergiant High-Mass X-ray binary 4U 1538-52 using long-term monitoring with the Neil Gehrels Swift Observatory Burst Alert Telescope (BAT). The source also exhibits a long-term pulse period evolution as seen with Rossi X-ray Timing Explorer (RXTE), INTEGRAL, and Fermi Gamma-Ray Burst Monitor (GBM) that appears uncorrelated with changes in its X-ray flux. To investigate the mechanisms causing these superorbital modulations and its possible dependence on pulse period changes, we analyzed long-term monitoring with Swift-BAT and Monitor of All Sky X-ray Image Gas Slit Camera (MAXI-GSC) to construct dynamic power spectra and superorbital intensity profiles. In addition, we used pointed X-ray observations from Nuclear Spectroscopic Telescope Array (NuSTAR) and Neutron Star Interior Composition Explorer mission (NICER) to investigate the pulsation and spectral properties across different superorbital and orbital phase intervals. We find the presence of superorbital modulations in the MAXI-GSC 2-20 keV lightcurves, consistent with the periodicity observed with the Swift-BAT lightcurves. However, no significant changes are detected in the pulse profiles or spectral parameters across different superorbital, orbital, or pulse-change intervals. This lack of spectral or timing variations with orbital and superorbital phases suggests that the mechanisms driving the observed superorbital modulation and pulse period changes are likely associated with large-scale stellar wind structures, such as Co-Rotating Interaction regions, within the stellar wind of the supergiant companion.

astro-ph.HE↗

arXiv2025

Swift/XRT monitoring of the orbital and superorbital modulations in 4U 1909+07

We report on an observational campaign performed with Swift/XRT on the wind-fed supergiant X-ray binary 4U 1909+07 to investigate the nature of the orbital and superorbital modulation of its X-ray emission. A total of 137 XRT observations have been carried out, summing up to a total effective exposure time of 114 ks and covering a total of 66 orbital and 19 superorbital cycles of the source. The XRT data folded on the orbital period of the source confirmed and improved the previously reported variability in intensity and absorption column density, which can be ascribed to the neutron star accreting from the wind of its B supergiant companion across a fairly circular orbit. The XRT data folded on the superorbital period did not provide evidence of significant variations in either the absorption column density and/or the power-law photon index. This may be due to a significant weakening of the superorbital modulation during the times when the XRT observations were carried out, as confirmed by the BAT dynamic power spectrum. We discuss the implications of these findings within the corotating interaction region model proposed to interpret the superorbital variability in wind-fed supergiant X-ray binaries.

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arXiv2023

Swift/XRT observations of superorbital modulations in wind-fed supergiant X-ray binaries

We present the first Swift/XRT long-term monitoring of 2S 0114+650, a wind-fed supergiant X-ray binary for which both orbital and superorbital periods are known (P_orb~11.6d and P_sup~0.8d). Our campaign, summing up to ~ 79ks, is the most intense and complete sampling of the X-ray light curve of this source with a sensitive pointed X-ray instrument, and covers 17 orbital, and 6 superorbital cycles. The combination of flexibility, sensitivity, and soft X-ray coverage of XRT allowed us to confirm previously reported spectral changes along the orbital cycle of the source and unveil the variability in its spectral parameters as a function of the superorbital phase. For completeness, we also report on a similar analysis carried out by exploiting XRT archival data on three additional wind-fed supergiant X-ray binaries IGR J16418-4532, IGR J16479-4514, and IGR J16493-4348. For these sources, the archival data provided coverage along several superorbital cycles but our analysis could not reveal any significant spectral variability.

astro-ph.HE↗

arXiv2022

Gamma-ray Eclipses and Orbital Modulation Transitions in the Candidate Redback 4FGL J1702.7-5655

Observations with the Fermi Large Area Telescope (LAT) of the gamma-ray source 4FGL J1702.7-5655, previously classified as a candidate millisecond pulsar, show highly-significant modulation at a period of 0.2438033 days (~ 5.85 hours). Further examination of the folded light curve indicates the presence of narrow eclipses, suggesting this is a redback binary system. An examination of the long-term properties of the modulation over 13 years of LAT observations indicates that the orbital modulation of the gamma-rays changed from a simple eclipse before early 2013, to a broader, more easily detected, quasi-sinusoidal modulation. In addition, the time of the eclipse shifts to ~0.05 later in phase. This change in the orbital modulation properties is, however, not accompanied by a significant overall change in gamma-ray flux or spectrum. The quasi-sinusoidal component peaks ~0.5 out of phase with the eclipse, which would indicate inferior conjunction of the compact object in the system. Swift X-ray Telescope observations reveal a possible X-ray counterpart within the LAT error ellipse. However, radio observations obtained with the Australia Telescope Compact Array do not detect a source in the region. 4FGL J1702.7-5655 appears to have changed its state in 2013, perhaps related to changes in the intrabinary shock in the system. We discuss how the properties of 4FGL J1702.7-5655 compare to other binary millisecond pulsars that have exhibited orbital modulation in gamma rays.

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arXiv2019

Discovery of the Galactic High-Mass Gamma-ray Binary 4FGL J1405.1-6119

We report the identification from multi-wavelength observations of the Fermi Large Area Telescope (LAT) source 4FGL J1405.1-6119 (= 3FGL J1405.4-6119) as a high-mass gamma-ray binary. Observations with the LAT show that gamma-ray emission from the system is modulated at a period of 13.7135 +/- 0.0019 days, with the presence of two maxima per orbit with different spectral properties. X-ray observations using the Neil Gehrels Swift Observatory X-ray Telescope (XRT) show that X-ray emission is also modulated at this period, but with a single maximum that is closer to the secondary lower-energy gamma-ray maximum. A radio source, coincident with the X-ray source, is also found from Australia Telescope Compact Array (ATCA) observations, and the radio emission is modulated on the gamma-ray period with similar phasing to the X-ray emission. A large degree of interstellar obscuration severely hampers optical observations, but a near-infrared counterpart is found. Near-infrared spectroscopy indicates an O6 III spectral classification. This is the third gamma-ray binary to be discovered with the Fermi LAT from periodic modulation of the gamma-ray emission, the other two sources also have early O star, rather than Be star, counterparts. We consider at what distances we can detect such modulated gamma-ray emission with the LAT, and examine constraints on the gamma-ray binary population of the Milky Way.

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arXiv2018

A Luminous and Highly-variable Gamma-ray Flare Following the 2017 Periastron of PSR B1259-63/LS 2883

Three periastron passages of the PSR B1259$-$63/LS 2883 binary system, consisting of a 48 ms rotation-powered pulsar and a $\sim30$ M$_{\odot}$ Be star, have been observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope, in 2010, 2014, and 2017. During the most-recent periastron passage, sustained low-level gamma-ray emission was observed over a $\sim3$-week long interval immediately after periastron, which was followed by an interval of no emission. Sporadic flares were detected starting 40 days post-periastron and lasted approximately 50 days, during which the emission displayed significant spectral curvature, variability on timescales as short as 1.5 minutes, and peak flux levels well in excess of the pulsar spin-down power. By contrast, during the 2010 and 2014 periastron passages, significant gamma-ray emission was not observed with the LAT until 30 and 32 days post-periastron, respectively. The previous flares did not exhibit spectral curvature, showed no short term variability, and did not exceed the pulsar spin-down power. The high flux and short timescales observed in 2017 suggest significant beaming of the emission is required and constrain the size of the emission region. The flares occur long enough after periastron that the neutron star should already have passed through the extended disk-like outflow, thus constraining options for target material and seed photon sources for inverse Compton models.

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arXiv2016

Multi-wavelength observations of the Be/X-ray binary IGR J01217-7257 (=SXP 2.16) during outburst

We present simultaneous, multi-wavelength observations of the Small Magellanic Cloud Be/XRB IGR J01217-7257 (=SXP 2.16) during outbursts in 2014, 2015 and 2016. We also present the results of RXTE observations of the Small Magellanic Cloud during which the source was initially discovered with a periodicity of 2.1652$\pm$0.0001 seconds which we associate with the spin period of the neutron star. A systematic temporal analysis of long term Swift/BAT data reveals a periodic signal of 82.5$\pm$0.7 days, in contrast with a similar analysis of long base line OGLE I-band light curves which reveals an 83.67$\pm$0.05 days also found in this work. Interpreting the longer X-ray periodicity as indicative of binary motion of the neutron star, we find that outbursts detected by INTEGRAL and Swift between 2014 and 2016 are consistent with Type I outbursts seen in Be/XRBs, occurring around periastron. Comparing these outbursts with the OGLE data, we see a clear correlation between outburst occurrence and increasing I-band flux. A periodic analysis of subdivisions of OGLE data reveals three epochs during which short periodicities of $\sim$1 day are significantly detected which we suggest are non-radial pulsations (NRPs) of the companion star. These seasons immediately precede those exhibiting clear outburst behaviour, supporting the suggested association between the NRPs, decretion disk growth and the onset of Type I outbursts.

astro-ph.HE↗

arXiv2016

A Luminous Gamma-ray Binary in the Large Magellanic Cloud

Gamma-ray binaries consist of a neutron star or a black hole interacting with a normal star to produce gamma-ray emission that dominates the radiative output of the system. Only a handful of such systems have been previously discovered, all within our Galaxy. Here we report the discovery with the Fermi Large Area Telescope (LAT) of a luminous gamma-ray binary in the Large Magellanic Cloud from a search for periodic modulation in all sources in the third Fermi LAT catalog. This is the first such system to be found outside the Milky Way. The system has an orbital period of 10.3 days and is associated with a massive O5III star located in the supernova remnant DEM L241, previously identified as the candidate high-mass X-ray binary (HMXB) CXOU J053600.0-673507. X-ray and radio emission are also modulated on the 10.3 day period, but are in anti-phase with the gamma-ray modulation. Optical radial velocity measurements suggest that the system contains a neutron star. The source is significantly more luminous than similar sources in the Milky Way at radio, optical, X-ray and gamma-ray wavelengths. The detection of this extra-galactic system, but no new Galactic systems raises the possibility that the predicted number of gamma-ray binaries in our Galaxy has been overestimated, and that HMXBs may be born containing relatively slowly rotating neutron stars.

astro-ph.HE↗

arXiv2016

Fermi LAT Gamma-ray Detections of Classical Novae V1369 Centauri 2013 and V5668 Sagittarii 2015

We report the Fermi Large Area Telescope (LAT) detections of high-energy (>100 MeV) gamma-ray emission from two recent optically bright classical novae, V1369 Centauri 2013 and V5668 Sagittarii 2015. At early times, Fermi target-of-opportunity observations prompted by their optical discoveries provided enhanced LAT exposure that enabled the detections of gamma-ray onsets beginning ~2 days after their first optical peaks. Significant gamma-ray emission was found extending to 39-55 days after their initial LAT detections, with systematically fainter and longer duration emission compared to previous gamma-ray detected classical novae. These novae were distinguished by multiple bright optical peaks that encompassed the timespans of the observed gamma rays. The gamma-ray light curves and spectra of the two novae are presented along with representative hadronic and leptonic models, and comparisons to other novae detected by the LAT are discussed.

astro-ph.HE↗

arXiv2015

Gamma-ray flaring activity from the gravitationally lensed blazar PKS 1830-211 observed by Fermi LAT

The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope routinely detects the highly dust-absorbed, reddened, and MeV-peaked flat spectrum radio quasar PKS 1830-211 (z=2.507). Its apparent isotropic gamma-ray luminosity (E>100 MeV) averaged over $\sim$ 3 years of observations and peaking on 2010 October 14/15 at 2.9 X 10^{50} erg s^{-1}, makes it among the brightest high-redshift Fermi blazars. No published model with a single lens can account for all of the observed characteristics of this complex system. Based on radio observations, one expects time delayed variability to follow about 25 days after a primary flare, with flux about a factor 1.5 less. Two large gamma-ray flares of PKS 1830-211 have been detected by the LAT in the considered period and no substantial evidence for such a delayed activity was found. This allows us to place a lower limit of about 6 on the gamma rays flux ratio between the two lensed images. Swift XRT observations from a dedicated Target of Opportunity program indicate a hard spectrum and with no significant correlation of X-ray flux with the gamma-ray variability. The spectral energy distribution can be modeled with inverse Compton scattering of thermal photons from the dusty torus. The implications of the LAT data in terms of variability, the lack of evident delayed flare events, and different radio and gamma-ray flux ratios are discussed. Microlensing effects, absorption, size and location of the emitting regions, the complex mass distribution of the system, an energy-dependent inner structure of the source, and flux suppression by the lens galaxy for one image path may be considered as hypotheses for understanding our results.

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arXiv2014

Fermi-LAT Detection of Gravitational Lens Delayed Gamma-ray Flares from Blazar B0218+357

Using data from the Fermi Large Area Telescope (LAT), we report the first clear gamma-ray measurement of a delay between flares from the gravitationally lensed images of a blazar. The delay was detected in B0218+357, a known double-image lensed system, during a period of enhanced gamma-ray activity with peak fluxes consistently observed to reach >20-50 times its previous average flux. An auto-correlation function analysis identified a delay in the gamma-ray data of 11.46 +/- 0.16 days (1 sigma) that is ~1 day greater than previous radio measurements. Considering that it is beyond the capabilities of the LAT to spatially resolve the two images, we nevertheless decomposed individual sequences of superposing gamma-ray flares/delayed emissions. In three such ~8-10 day-long sequences within a ~4-month span, considering confusion due to overlapping flaring emission and flux measurement uncertainties, we found flux ratios consistent with ~1, thus systematically smaller than those from radio observations. During the first, best-defined flare, the delayed emission was detailed with a Fermi pointing, and we observed flux doubling timescales of ~3-6 hrs implying as well extremely compact gamma-ray emitting regions.

astro-ph.HE↗

arXiv2013

Spin period change and the magnetic fields of neutron stars in Be X-ray binaries in the Small Magellanic Cloud

We report on the long-term average spin period, rate of change of spin period and X-ray luminosity during outbursts for 42 Be X-ray binary systems in the Small Magellanic Cloud. We also collect and calculate parameters of each system and use these data to determine that all systems contain a neutron star which is accreting via a disc, rather than a wind, and that if these neutron stars are near spin equilibrium, then over half of them, including all with spin periods over about 100 s, have magnetic fields over the quantum critical level of 4.4x10^13 G. If these neutron stars are not close to spin equilibrium, then their magnetic fields are inferred to be much lower, of the order of 10^6-10^10 G, comparable to the fields of neutron stars in low-mass X-ray binaries. Both results are unexpected and have implications for the rate of magnetic field decay and the isolated neutron star population.

astro-ph.SR↗

arXiv2013

Contrasting behaviour from two Be/X-ray binary pulsars: insights into differing neutron star accretion modes

In this paper we present the identification of two periodic X-ray signals coming from the direction of the Small Magellanic Cloud (SMC). On detection with the Rossi X-ray Timing Explorer (RXTE), the 175.4s and 85.4s pulsations were considered to originate from new Be/X-ray binary (BeXRB) pulsars with unknown locations. Using rapid follow-up INTEGRAL and XMM-Newton observations, we show the first pulsar (designated SXP175) to be coincident with a candidate high-mass X-ray binary (HMXB) in the northern bar region of the SMC undergoing a small Type II outburst. The orbital period (87d) and spectral class (B0-B0.5IIIe) of this system are determined and presented here for the first time. The second pulsar is shown not to be new at all, but is consistent with being SXP91.1 - a pulsar discovered at the very beginning of the 13 year long RXTE key monitoring programme of the SMC. Whilst it is theoretically possible for accreting neutron stars to change spin period so dramatically over such a short time, the X-ray and optical data available for this source suggest this spin-up is continuous during long phases of X-ray quiescence, where accretion driven spin-up of the neutron star should be minimal.

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arXiv2012

The Search for High-Mass X-ray Binaries in the Phoenix Dwarf Galaxy

We report on the first X-ray images of the Phoenix dwarf galaxy, taken with \emph{XMM-Newton} in July 2009. This local group dwarf galaxy shares similarities with the Small Magellanic Cloud (SMC) including a burst of star formation $\sim$50 Myr ago. The SMC has an abundance of High Mass X-ray Binaries (HMXBs) and so we have investigated the possibility of an HMXB population in Phoenix with the intention of furthering the understanding of the HMXB-star formation rate relation. The data from the combined European Photon Imaging Cameras (EPIC) were used to distinguish between different source classes (foreground stars, background galaxies, AGN and supernova remnants) using EPIC hardness ratios and correlations with optical and radio catalogues. Of the 81 X-ray sources in the field of view, six are foreground stars, four are galaxies and one is an AGN. The remaining sources with optical counterparts have log($\frac{f_X}{f_{opt}}$) consistent with AGN in the local universe. Further investigation of five sources in the field of view suggests they are all background AGN. Their position behind the gas cloud associated with Phoenix makes them a possible tool for further probing the metallicity of this region. We find no evidence for any HMXBs in Phoenix at this time. This rules out the existence of the X-ray persistent supergiant X-ray binary systems. However the transient nature of the Be/X-ray binaries means we cannot rule out a population of these sources but can conclude that it is not extensive.

astro-ph.HE↗

arXiv2012

Long-term monitoring of the high-energy gamma-ray emission from LS I +61° 303 and LS 5039

The Fermi Large Area Telescope (LAT) reported the first definitive GeV detections of the binaries LS I +61\degree 303 and LS 5039 in the first year after its launch in June, 2008. These detections were unambiguous as a consequence of the reduced positional uncertainty and the detection of modulated gamma-ray emission on the corresponding orbital periods. An analysis of new data from the LAT, comprising 30 months of observations, identifies a change in the gamma-ray behavior of LS I +61\degree 303. An increase in flux is detected in March 2009 and a steady decline in the orbital flux modulation is observed. Significant emission up to 30GeV is detected by the LAT; prior datasets led to upper limits only. Contemporaneous TeV observations no longer detected the source, or found it -in one orbit- close to periastron, far from the phases at which the source previously appeared at TeV energies. The detailed numerical simulations and models that exist within the literature do not predict or explain many of these features now observed at GeV and TeV energies. New ideas and models are needed to fully explain and understand this behavior. A detailed phase-resolved analysis of the spectral characterization of LS I +61\degree 303 in the GeV regime ascribes a power law with an exponential cutoff spectrum along each analyzed portion of the system's orbit. The on-source exposure of LS 5039 is also substantially increased with respect to our prior publication. In this case, whereas the general gamma-ray properties remain consistent, the increased statistics of the current dataset allows for a deeper investigation of its orbital and spectral evolution.

astro-ph.HE↗

arXiv2012

A giant radio flare from Cygnus X-3 with associated Gamma-ray emission

With frequent flaring activity of its relativistic jets, Cygnus X-3 is one of the most active microquasars and is the only Galactic black hole candidate with confirmed high energy Gamma-ray emission, thanks to detections by Fermi/LAT and AGILE. In 2011, Cygnus X-3 was observed to transit to a soft X-ray state, which is known to be associated with high-energy Gamma-ray emission. We present the results of a multi-wavelength campaign covering a quenched state, when radio emission from Cygnus X-3 is at its weakest and the X-ray spectrum is very soft. A giant (~ 20 Jy) optically thin radio flare marks the end of the quenched state, accompanied by rising non-thermal hard X-rays. Fermi/LAT observations (E >100 MeV) reveal renewed Gamma-ray activity associated with this giant radio flare, suggesting a common origin for all non-thermal components. In addition, current observations unambiguously show that the Gamma-ray emission is not exclusively related to the rare giant radio flares. A 3-week period of Gamma-ray emission is also detected when Cygnus X-3 was weakly flaring in radio, right before transition to the radio quenched state. No Gamma rays are observed during the ~ one-month long quenched state, when the radio flux is weakest. Our results suggest transitions into and out of the ultrasoft X-ray (radio quenched) state trigger Gamma-ray emission, implying a connection to the accretion process, and also that the Gamma-ray activity is related to the level of radio flux (and possibly shock formation), strengthening the connection to the relativistic jets.

astro-ph.HE↗

arXiv2011

On the orbital parameters of Be/X-ray binaries in the Small Magellanic Cloud

The orbital motion of a neutron star about its optical companion presents a window through which to study the orbital parameters of that binary system. This has been used extensively in the Milky Way to calculate these parameters for several high-mass X-ray binaries. Using several years of RXTE PCA data, we derive the orbital parameters of four Be/X-ray binary systems in the SMC, increasing the number of systems with orbital solutions by a factor of three. We find one new orbital period, confirm a second and discuss the parameters with comparison to the Galactic systems. Despite the low metallicity in the SMC, these binary systems sit amongst the Galactic distribution of orbital periods and eccentricities, suggesting that metallicity may not play an important role in the evolution of high-mass X-ray binary systems. A plot of orbital period against eccentricity shows that the supergiant, Be and low eccentricity OB transient systems occupy separate regions of the parameter space; akin to the separated regions on the Corbet diagram. Using a Spearman's rank correlation test, we also find a possible correlation between the two parameters. The mass functions, inclinations and orbital semimajor axes are derived for the SMC systems based on the binary parameters and the spectral classification of the optical counterpart. As a by-product of our work, we present a catalogue of the orbital parameters for every high-mass X-ray binary in the Galaxy and Magellanic Clouds for which they are known.

astro-ph.HE↗

arXiv2011

The bright unidentified gamma-ray source 1FGL J1227.9-4852: Can it be associated with an LMXB?

We present an analysis of high energy (HE; 0.1-300 GeV) gamma-ray observations of 1FGL J1227.9-4852 with the Fermi Gamma-ray Space Telescope, follow-up radio observations with the Australia Telescope Compact Array, Giant Metrewave Radio Telescope and Parkes radio telescopes of the same field and follow-up optical observations with the ESO VLT. We also examine archival XMM-Newton and INTEGRAL X-ray observations of the region around this source. The gamma-ray spectrum of 1FGL J1227.9-4852 is best fit with an exponentially cutoff power-law, reminiscent of the population of pulsars observed by Fermi. A previously unknown, compact radio source within the 99.7% error circle of 1FGL J1227.9-4852 is discovered and has a morphology consistent either with an AGN core/jet structure or with two roughly symmetric lobes of a distant radio galaxy. A single bright X-ray source XSS J12270-4859, a low-mass X-ray binary, also lies within the 1FGL J1227.9-4852 error circle and we report the first detection of radio emission from this source. The potential association of 1FGL J1227.9-4852 with each of these counterparts is discussed. Based upon the available data we find the association of the gamma-ray source to the compact double radio source unlikely and suggest that XSS J12270-4859 is a more likely counterpart to the new HE source. We propose that XSS J12270-4859 may be a millisecond binary pulsar and draw comparisons with PSR J1023+0038.

astro-ph.HE↗