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M. Linares
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M. Linares

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High Energy Astrophysical Phenomena (46)
Astrophysics (4)
Solar and Stellar Astrophysics (3)
Astrophysics of Galaxies (2)

Publications Authored By M. Linares

Affiliations: 1Instituto de Astrofísica de Canarias, Tenerife, Spain, 2Instituto de Astrofísica de Canarias, Tenerife, Spain, 3Instituto de Astrofísica de Canarias, Tenerife, Spain, 4South African Astronomical Observatory, Cape Town, South Africa, 5INAR-Osservatorio Astronomico di Roma, Italy, 6Instituto de Astrofísica de Canarias, Tenerife, Spain, 7Instituto de Astrofísica de Canarias, Tenerife, Spain

The new recurrent X-ray transient MAXI J1957+032 has had four X-ray outbursts within 16 months, all very briefly detected (lasting <5 days). During the most recent event (Sep/Oct 2016), we obtained with SALT the first optical spectrum of the transient counterpart, showing the classic blue continuum of an X-ray irradiated disc in an LMXB and no other features. At high Galactic latitude below the plane (-13 deg) reddening is low but there is no quiescent counterpart visible on any of the existing sky surveys, nor any other known X-ray source in the region. Read More

In search for the counterpart to the Fermi-LAT source 3FGL J0838.8-2829, we report on 1) a new magnetic Cataclysmic Variable (mCV), RX J0838-2827, that we identify as an asynchronous system (therefore not associated with this Fermi-LAT source) and 2) on a new X-ray flaring source, XMM J083850.4-282759, that might be tentatively identified as new candidate Transitional Millisecond Pulsar, possibly associated with the gamma-ray source. Read More

We present the discovery of a variable optical counterpart to the unidentified gamma-ray source 3FGL J0212.1+5320, and argue this is a new compact binary millisecond pulsar (MSP) candidate. We show 3FGL J0212. Read More

Accretion of matter onto black holes is universally associated with strong radiative feedback and powerful outflows. In particular, black hole transients show outflows whose properties are strongly coupled to those of the accretion flow. This includes X-ray winds of ionized material, expelled from the accretion disc encircling the black hole, and collimated radio jets. Read More

We present the results of VLA, ATCA, and Swift XRT observations of the 2015 outburst of the transient neutron star X-ray binary (NSXB), EXO 1745$-$248, located in the globular cluster Terzan 5. Combining (near-) simultaneous radio and X-ray measurements we measure a correlation between the radio and X-ray luminosities of $L_R\propto L_X^\beta$ with $\beta=1.68^{+0. Read More

The Fermi Gamma Ray Burst Monitor (GBM) is an all sky gamma-ray monitor well known in the gamma-ray burst community. Although GBM excels in detecting the hard, bright extragalactic GRBs, its sensitivity above 8 keV and all-sky view make it an excellent instrument for the detection of rare, short-lived Galactic transients. In March 2010, we initiated a systematic search for transients using GBM data. Read More

Aql X-1 is a prolific transient neutron star low-mass X-ray binary that exhibits an accretion outburst approximately once every year. Whether the thermal X-rays detected in intervening quiescent episodes are the result of cooling of the neutron star or due to continued low-level accretion remains unclear. In this work we use Swift data obtained after the long and bright 2011 and 2013 outbursts, as well as the short and faint 2015 outburst, to investigate the hypothesis that cooling of the accretion-heated neutron star crust dominates the quiescent thermal emission in Aql X-1. Read More


We present time-resolved optical photometry of the binary millisecond `redback' pulsar PSR J1023+0038 (=AY Sex) during its low-mass X-ray binary phase. The light curves taken between 2014 January and April show an underlying sinusoidal modulation due to the irradiated secondary star and accretion disc. We also observe superimposed rapid flaring on time-scales as short as ~20 s with amplitudes of ~0. Read More

This is a White Paper in support of the mission concept of the Large Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We discuss the potential of LOFT for the study of thermonuclear X-ray bursts on accreting neutron stars. For a summary, we refer to the paper. Read More

Tracking the spectral evolution of transiently accreting neutron stars between outburst and quiescence probes relatively poorly understood accretion regimes. Such studies are challenging because they require frequent monitoring of sources with luminosities below the thresholds of current all-sky X-ray monitors. We present the analysis of over 30 observations of the neutron star low-mass X-ray binary SAX J1750. Read More

We search the literature for reports on the spectral properties of neutron-star low-mass X-ray binaries when they have accretion luminosities between 1E34 and 1E36 ergs/s. We found that in this luminosity range the photon index (obtained from fitting a simple absorbed power-law in the 0.5-10 keV range) increases with decreasing 0. Read More

We present Chandra, XMM-Newton, and Swift observations of the quiescent neutron star in the transient low-mass X-ray binary MAXI J0556-332. Observations of the source made during outburst (with the Rossi X-ray Timing Explorer) reveal tracks in its X-ray color--color and hardness--intensity diagrams that closely resemble those of the neutron-star Z sources, suggesting that MAXI J0556-332 had near- or super-Eddington luminosities for a large part of its ~16 month outburst. A comparison of these diagrams with those of other Z sources suggests a source distance of 46+/-15 kpc. Read More

Using the High Resolution Camera onboard the Chandra X-ray Observatory, we have measured an accurate position for the bright persistent neutron-star X-ray binary and atoll source GX 3+1. At a location that is consistent with this new position we have discovered the near-infrared (NIR) counterpart to GX 3+1 in images taken with the PANIC and FourStar cameras on the Magellan Baade Telescope. The identification of this K_s=15. Read More

In this work, the analysis of multi-epoch (1995-2010) X-ray observations of the Seyfert 1 galaxy H0557-385 is presented. The wealth of data presented in this analysis show that the source exhibits dramatic spectral variability, from a typical unabsorbed Seyfert 1 type spectrum to a Compton-thin absorbed state, on time scales of ~5 years. This extreme change in spectral shape can be attributed to variations in the column density and covering fraction of a neutral absorbing medium attenuating the emission from the central continuum source. Read More

Compact binary millisecond pulsars with main-sequence donors, often referred to as "redbacks", constitute the long-sought link between low-mass X-ray binaries and millisecond radio pulsars, and offer a unique probe of the interaction between pulsar winds and accretion flows. We present a systematic study of eight nearby redbacks, using more than 100 observations obtained with Swift's X-ray Telescope. We distinguish between three main states: pulsar, disk and outburst states. Read More

Both the broad iron (Fe) line and the frequency of the kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (LMXBs) can potentially provide independent measures of the inner radius of the accretion disc. We use XMM-Newton and simultaneous Rossi X-ray Timing Explorer observations of the LMXB 4U 1636-53 to test this hypothesis. We study the properties of the Fe-K emission line as a function of the spectral state of the source and the frequency of the kHz QPOs. Read More

Affiliations: 1University of Alberta, 2University of Alberta, 3University of Alberta, 4Astronomical Institute 'Anton Pannekoek', 5Astronomical Institute 'Anton Pannekoek', 6Kavli Institute for Astrophysics & Space Research, 7Instituto de Astrofisica de Canarias, 8Sam Houston State University, 9University of Michigan, 10University of Alberta

We report and study the outburst of a new transient X-ray binary (XRB) in Terzan 5, the third detected in this globular cluster, Swift J174805.3-244637 or Terzan 5 X-3. We find clear spectral hardening in Swift/XRT data during the outburst rise to the hard state, thanks to our early coverage (starting at L_X ~ 4x10^{34} ergs/s) of the outburst. Read More

The X-ray transient IGR J18245-2452 in the globular cluster M28 contains the first neutron star (NS) seen to switch between rotation-powered and accretion-powered pulsations. We analyse its 2013 March-April 25d-long outburst as observed by Swift, which had a peak bolometric luminosity of ~6% of the Eddington limit (L$_{E}$), and give detailed properties of the thermonuclear burst observed on 2013 April 7. We also present a detailed analysis of new and archival Chandra data, which we use to study quiescent emission from IGR J18245-2452 between 2002 and 2013. Read More

We report the discovery of kHz quasi periodic oscillations (QPOs) in three Rossi X-ray Timing Explorer observations of the low mass X-ray binary (LMXB) XTE J1701-407. In one of the observations we detect a kHz QPO with a characteristic frequency of 1153 +/- 5 Hz, while in the other two observations we detect twin QPOs at characteristic frequencies of 740 +/- 5 Hz, 1112 +/- 17 Hz and 740 +/- 11 Hz, 1098 +/- 5 Hz. All detections happen when XTE J1701-407 was in its high intensity soft state, and their single trial significance are in the 3. Read More

Circinus X-1 is a bright and highly variable X-ray binary which displays strong and rapid evolution in all wavebands. Radio flaring, associated with the production of a relativistic jet, occurs periodically on a ~17-day timescale. A longer-term envelope modulates the peak radio fluxes in flares, ranging from peaks in excess of a Jansky in the 1970s to an historic low of milliJanskys during the years 1994 to 2007. Read More

Affiliations: 1Groningen, 2Groningen, 3Groningen, 4Amsterdam, 5INAF-OAB, 6Canary Islands

We analysed the X-ray spectra of six observations, simultaneously taken with XMM-Newton and Rossi X-ray Timing Explorer (RXTE), of the neutron star low-mass X-ray binary 4U 1636-53. The observations cover several states of the source, and therefore a large range of inferred mass accretion rate. These six observations show a broad emission line in the spectrum at around 6. Read More

Affiliations: 1U. Groningen, 2U. Southampton, 3ESAC, 4INAF-OAB, 5INAF-OAR, 6U. Groningen, 7U. Amsterdam, 8IAC, 9U. Amsterdam, 10U. Southampton, 11U. Amsterdam

We present our monitoring campaign of the outburst of the black-hole candidate Swift J1753.5-0127, observed with the Rossi X-ray Timing Explorer and the Swift satellites. After ~4. Read More

We report on 6 RXTE observations taken during the 2010 outburst of the 11 Hz accreting pulsar IGR J17480-2446 located in the globular cluster Terzan 5. During these observations we find power spectra which resemble those seen in Z-type high-luminosity neutron star low-mass X-ray binaries, with a quasi-periodic oscillation (QPO) in the 35-50 Hz range simultaneous with a kHz QPO and broad band noise. Using well known frequency-frequency correlations, we identify the 35-50 Hz QPOs as the horizontal branch oscillations (HBO), which were previously suggested to be due to Lense-Thirring precession. Read More

Thermonuclear bursts from slowly accreting neutron stars (NSs) have proven difficult to detect, yet they are potential probes of the thermal properties of the neutron star interior. During the first year of a systematic all-sky search for X-ray bursts using the Gamma-ray Burst Monitor (GBM) aboard the Fermi Gamma-ray Space Telescope we have detected 15 thermonuclear bursts from the NS low-mass X-ray binary 4U 0614+09, when it was accreting at nearly 1% of the Eddington limit. We measured an average burst recurrence time of 12+/-3 d (68% confidence interval) between March 2010 and March 2011, classified all bursts as normal duration bursts and placed a lower limit on the recurrence time of long/intermediate bursts of 62 d (95% confidence level). Read More

We discuss the origin of two triggers of Swift's Burst Alert Telescope (BAT) that occurred in 2011. The triggers were identified with Swift J185003.2-005627, a previously unknown X-ray source, and the known but unclassified X-ray transient Swift J1922. Read More

We report on the first 180 days of RXTE observations of the outburst of the black hole candidate IGR J17091-3624. This source exhibits a broad variety of complex light curve patterns including periods of strong flares alternating with quiet intervals. Similar patterns in the X-ray light curves have been seen in the (up to now) unique black hole system GRS 1915+105. Read More

We present a comprehensive study of the thermonuclear bursts and millihertz quasi-periodic oscillations (mHz QPOs) from the neutron star (NS) transient and 11 Hz X-ray pulsar IGR J17480-2446, located in the globular cluster Terzan 5. The increase in burst rate that we found during its 2010 outburst, when persistent luminosity rose from 0.1 to 0. Read More

The X-ray transient XTE J1719-291 was discovered with RXTE/PCA during its outburst in 2008 March, which lasted at least 46 days. Its 2-10 keV peak luminosity is 7E35 erg/s assuming a distance of 8 kpc, which classifies the system as a very faint X-ray transient. The outburst was monitored with Swift, RXTE, Chandra and XMM-Newton. Read More

The recently-discovered accreting X-ray pulsar IGR J17480--2446 spins at a frequency of ~11 Hz. We show that Type I X-ray bursts from this source display oscillations at the same frequency as the stellar spin. IGR J17480--2446 is the first secure case of a slowly rotating neutron star which shows Type I burst oscillations, all other sources featuring such oscillations spin at hundreds of Hertz. Read More

The neutron star transient and 11 Hz X-ray pulsar IGR J17480-2446, recently discovered in the globular cluster Terzan 5, showed unprecedented bursting activity during its 2010 October-November outburst. We analyzed all X-ray bursts detected with the Rossi X-ray Timing Explorer and find strong evidence that they all have a thermonuclear origin, despite the fact that many do not show the canonical spectral softening along the decay imprinted on type I X-ray bursts by the cooling of the neutron star photosphere. We show that the persistent-to-burst power ratio is fully consistent with the accretion-to-thermonuclear efficiency ratio along the whole outburst, as is typical for type I X-ray bursts. Read More

We report on the analysis of all 65 pointed Rossi X-ray Timing Explorer observations of the recently discovered soft X-ray transient MAXI J1659-152 (initially referred to as GRB 100925A). The source was studied in terms of its evolution through the hardness-intensity diagram (HID) as well as its X-ray variability properties. MAXI J1659-152 traced out an anti-clockwise loop in the HID, which is commonly seen in transient low-mass X-ray binaries. Read More

Affiliations: 1MIT, 2Amsterdam, 3Amsterdam, 4Groningen, 5Amsterdam, 6Amsterdam, 7Amsterdam, 8Southampton, 9MIT, 10MIT, 11CSIC-IEEC, 12Amsterdam, 13Amsterdam, 14Amsterdam, 15Amsterdam, 16Amsterdam, 17Amsterdam

We report the detection of 15 X-ray bursts with RXTE and Swift observations of the peculiar X-ray binary Circinus X-1 during its May 2010 X-ray re-brightening. These are the first X-ray bursts observed from the source after the initial discovery by Tennant and collaborators, twenty-five years ago. By studying their spectral evolution, we firmly identify nine of the bursts as type I (thermonuclear) X-ray bursts. Read More

We report the discovery of burst oscillations at the spin frequency in ten thermonuclear bursts from the accreting millisecond X-ray pulsar (AMXP) IGR J17511-3057. The burst oscillation properties are, like those from the persistent AMXPs SAX J1808.4-3658 and XTE J1814-338, anomalous compared to burst oscillations from intermittent pulsars or non-pulsing LMXBs. Read More

We report on the discovery and the timing analysis of the first eclipsing accretion-powered millisecond X-ray pulsar (AMXP): SWIFT J1749.4-2807. The neutron star rotates at a frequency of ~517. Read More

Affiliations: 1NRAO, 2U. Virginia, 3U. Amsterdam, 4ASTRON, 5ESAC, 6NRAO, 7U. Southampton, 8ASTRON, 9U. Wisconsin-Madison, 10U. Paris Diderot, 11NASA/GSFC, 12MIT, 13U. Michigan, 14U. Amsterdam, 15JIVE, 16MIT, 17NRAO, 18U. Southampton, 19U. Amsterdam, 20U. Virginia, 21U. Manchester

The 2009 November outburst of the neutron star X-ray binary Aquila X-1 was observed with unprecedented radio coverage and simultaneous pointed X-ray observations, tracing the radio emission around the full X-ray hysteresis loop of the outburst for the first time. We use these data to discuss the disc-jet coupling, finding the radio emission to be consistent with being triggered at state transitions, both from the hard to the soft spectral state and vice versa. Our data appear to confirm previous suggestions of radio quenching in the soft state above a threshold X-ray luminosity of about 10% of the Eddington luminosity. Read More

In August 2008, the accreting milli-second X-ray pulsar (AMXP), IGR J00291+5934, underwent an outburst lasting ~ 100 days, the first since its discovery in 2004. We present data from the double-peaked outburst from Faulkes Telescope North, the INT, the Keck Telescope, PAIRITEL, the Westerbork Synthesis Radio Telescope and the Swift, XMM-Newton and RXTE X-ray missions. We study the outburst's evolution at various wavelengths. Read More

Affiliations: 1Amsterdam, 2Southampton, 3ASTRON, 4Michigan, 5Southampton, 6MIT, 7Amsterdam, 8Amsterdam, 9INAF-OAB, 10Southampton, 11NRAO, 12Manchester, 13Altran, 14ASTRON, 15Amsterdam

In studies of accreting black holes in binary systems, empirical relations have been proposed to quantify the coupling between accretion processes and ejection mechanisms. These processes are probed respectively by means of X-ray and radio/optical-infrared observations. The relations predict, given certain accretion conditions, the expected energy output in the form of a jet. Read More

We report the discovery of the second accreting millisecond X-ray pulsar (AMXP) in the globular cluster NGC 6440. Pulsations with a frequency of 205.89 Hz were detected with the Rossi X-Ray Timing Explorer on August 30th, October 1st and October 28th, 2009, during the decays of ~4 day outbursts of a newly X-ray transient source in NGC 6440. Read More

We have identified a new transient luminous low-mass X-ray binary, NGC 6440 X-2, with Chandra/ACIS, RXTE/PCA, and Swift/XRT observations of the globular cluster NGC 6440. The discovery outburst (July 28-31, 2009) peaked at L_X~1.5*10^36 ergs/s, and lasted for <4 days above L_X=10^35 ergs/s. Read More

Affiliations: 1ESA/ESAC, Spain, 2SRON, The Netherlands, 3LATT, France, 4MIT Kavli Center for Astrophysics, USA, 5Guilford College, USA, 6Guilford College, USA, 7Univ. of Amsterdam, The Netherlands, 8ISSI, Switzerland, 9ESA/ESAC, Spain, 10UMD & NASA-GSFC, USA, 11NASA/GSFC, USA, 12McGill University, Canada, 13ISAS-JAXA, Japan

[abridged] The LMXB 4U 0614+091 is a source of sporadic thermonuclear (type I) X-ray bursts. We find bursts with a wide variety of characteristics in serendipitous wide-field X-ray observations by EURECA/WATCH, RXTE/ASM, BeppoSAX/WFC, HETE-2/FREGATE, INTEGRAL/IBIS/ISGRI, and Swift/BAT, as well as pointed observations by RXTE/PCA and HEXTE. Most of them reach a peak flux of ~15 Crab, but a few only reach a peak flux below a Crab. Read More

We present a detailed study of the X-ray energy and power spectral properties of the neutron star transient IGR J17191-2821. We discovered four instances of pairs of simultaneous kilohertz quasi-periodic oscillations (kHz QPOs). The frequency difference between these kHz QPOs is between 315 Hz and 362 Hz. Read More

Affiliations: 1ASTRON, 2Southampton, 3Amsterdam, 4Amsterdam, 5Amsterdam

We study the accretion/ejection processes (i.e. disc/jet coupling) in the neutron star X-ray binary Aquila X-1 via a multi-wavelength approach. Read More

Affiliations: 1University of Amsterdam, 2University of Amsterdam, 3University of Amsterdam, 4University of Amsterdam, 5University of Amsterdam, 6University of Amsterdam, 7University of Amsterdam, 8University of Amsterdam, 9University of Amsterdam, 10University of Amsterdam, 11University of Amsterdam

We report the discovery of burst oscillations from the intermittent accretion-powered millisecond pulsar (AMP) HETE J1900.1-2455, with a frequency approximately 1 Hz below the known spin frequency. The burst oscillation properties are far more similar to those of the non-AMPs and Aql X-1 (an intermittent AMP with a far lower duty cycle), than those of the AMPs SAX J1808. Read More

XMM-Newton observed the accreting millisecond pulsar SAX J1808.4-3658 during its 2008 outburst. We present timing and spectral analyses of this observation, in particular the first pulse profile study below 2 keV, and the high-resolution spectral analysis of this source during the outburst. Read More

During the September-October 2008 outburst of the accreting millisecond pulsar SAX J1808.4-3658, the source was observed by both Suzaku and XMM-Newton approximately 1 day apart. Spectral analysis reveals a broad relativistic Fe K-alpha emission line which is present in both data-sets, as has recently been reported for other neutron star low-mass X-ray binaries. Read More

Authors: Manuel Linares1
Affiliations: 1University of Amsterdam
Category: Astrophysics

At present, ten years after they were first discovered, ten accreting millisecond pulsars are known. I present a study of the aperiodic X-ray variability in three of these systems, which led to the discovery of simultaneous kHz quasi periodic oscillations in XTE J1807-294 and extremely strong broadband noise at unusually low variability frequencies in IGR J00291+5934. Furthermore, we classified SWIFT J1756. Read More

Affiliations: 1Amsterdam, 2Amsterdam, 3Amsterdam, 4Amsterdam, 5Amsterdam, 6Amsterdam, 7Leicester, 8Amsterdam
Category: Astrophysics

XTE J1701-407 is a new transient X-ray source discovered on June 8th, 2008. More than one month later it showed a rare type of thermonuclear explosion: a long type I X-ray burst. We report herein the results of our study of the spectral and flux evolution during this burst, as well as the analysis of the outburst in which it took place. Read More

SWIFT J1756.9-2508 is one of the few accreting millisecond pulsars (AMPs) discovered to date. We report here the results of our analysis of its aperiodic X-ray variability, as measured with the Rossi X-ray Timing Explorer during the 2007 outburst of the source. Read More

Affiliations: 1Amsterdam, 2Amsterdam, 3Amsterdam
Category: Astrophysics

We report on the X-ray aperiodic timing analysis of two accreting millisecond pulsars: XTE J1807-294 and IGR J00291+5934. On the one hand, we discovered in XTE J1807-294 seven pairs of simultaneous kilohertz quasi-periodic oscillations (kHz QPOs) separated in frequency by nearly the spin frequency of the neutron star. This confirms the suspected dichotomy in the frequency separation of kHz QPOs: sometimes once and sometimes half the spin frequency. Read More