arXiv subjects

P. G. Jonker

Publications and source records attributed to P. G. Jonker.

At least 145 records · Page 8Linked to original sources

arXiv2013

VLT/FORS2 observations of four high-luminosity ULX candidates

We obtained VLT/FORS2 spectra of the optical counterparts of four high-luminosity (L_X >= 10^40 erg/s) ULX candidates from the catalog of Walton (2011). We first determined accurate positions for the X-ray sources from archival Chandra observations and identified counterparts in archival optical observations that are sufficiently bright for spectroscopy with an 8 meter telescope. From the spectra we determine the redshifts to the optical counterparts and emission line ratios. One of the candidate ULXs, in the spiral galaxy ESO 306-003, appears to be a bona fide ULX in an HII region. The other three sources, near the elliptical galaxies NGC 533 and NGC 741 and in the ring galaxy AM 0644-741, turn out to be background AGN with redshifts of 1.85, 0.88 or 1.75 and 1.40 respectively. Our findings confirm the trend of a high probability of finding background AGN for systems with a ratio of log(F_X/F_opt) in the range of -1 to 1.

astro-ph.HE↗

arXiv2013

Identification of 5 Interacting Binaries in the Galactic Bulge Survey

We present optical lightcurves, spectroscopy, and classification of five X-ray sources in the Chandra Galactic Bulge Survey [CXOGBS J174009.1-284725 (CX5), CXOGBS J173935.7-272935 (CX18), CXOGBS J173946.9-271809 (CX28), CXOGBS J173729.1-292804 (CX37), CXOGBS J174607.6-261547 (CX561)]. These objects were selected based on bright optical counterparts which were quickly found to have emission lines in their optical spectra. This paper presents an illustration of GBS optical follow-up, targeting emission line objects. Of these five objects, four exhibit photometric variability in the Sloan r' band. CX5 shows a tentative period of 2.1 hours and is clearly an Intermediate Polar (IP). CX28 and CX37 both exhibit flickering with no clear period. Both are suggested to also be IPs. CX18 was observed to undergo 2 dwarf nova outbursts. Finally, CX561 shows no detectable variability, although its characteristics would be consistent with either a quiescent Low Mass X-ray Binary or Cataclysmic Variable.

astro-ph.SR↗

arXiv2013

A bright thermonuclear X-ray burst simultaneously observed with Chandra and RXTE

The prototypical accretion-powered millisecond pulsar SAX J1808.4-3658 was observed simultaneously with Chandra-LETGS and RXTE-PCA near the peak of a transient outburst in November 2011. A single thermonuclear (type-I) burst was detected, the brightest yet observed by Chandra from any source, and the second-brightest observed by RXTE. We found no evidence for discrete spectral features during the burst; absorption edges have been predicted to be present in such bursts, but may require a greater degree of photospheric expansion than the rather moderate expansion seen in this event (a factor of a few). These observations provide a unique data set to study an X-ray burst over a broad bandpass and at high spectral resolution (lambda/delta-lambda=200-400). We find a significant excess of photons at high and low energies compared to the standard black body spectrum. This excess is well described by a 20-fold increase of the persistent flux during the burst. We speculate that this results from burst photons being scattered in the accretion disk corona. These and other recent observations of X-ray bursts point out the need for detailed theoretical modeling of the radiative and hydrodynamical interaction between thermonuclear X-ray bursts and accretion disks.

astro-ph.HE↗

arXiv2013

IGR J19308+0530: Roche lobe overflow on to a compact object from a donor 1.8 times as massive

We present phase-resolved spectroscopy and photometry of the optical counterpart to the X-ray binary IGR J19308+0530. Ellipsoidal modulations in the light curve show that the F-type companion star in the system is Roche lobe filling. The optical spectra are dominated by absorption features from the donor star, with ~10-20 per cent disc contribution to the optical continuum. We measure an orbital period of 14.662+-0.001 h, a radial velocity semiamplitude for the companion star of K2 = 91.4+-1.4 kms-1 and a rotational broadening of vsini = 108.9+-0.6 kms-1. From K2 and vsini, given that the donor star is filling its Roche lobe, we derive a mass ratio of q = M2/M1=1.78+-0.04, which is typically considered to be too large for stable Roche lobe overflow. Our observations support an inclination of ~50 degrees. The accretor in IGR J19308+0530 is most likely a white dwarf, although a neutron star cannot entirely be excluded.

astro-ph.HE↗

arXiv2012

Time-resolved X-Shooter spectra and RXTE light curves of the ultra-compact X-ray binary candidate 4U 0614+091

In this paper we present X-Shooter time resolved spectroscopy and RXTE PCA light curves of the ultra-compact X-ray binary candidate 4U 0614+091. The X-Shooter data are compared to the GMOS data analyzed previously by Nelemans et al. (2004). We confirm the presence of C III and O II emission features at ~ 4650 Å and ~ 5000 Å. The emission lines do not show evident Doppler shifts that could be attributed to the motion of the donor star/hot spot around the center of mass of the binary. We note a weak periodic signal in the red-wing/blue-wing flux ratio of the emission feature at ~ 4650 Å. The signal occurs at P = 30.23 +/- 0.03 min in the X-Shooter and at P = 30.468 +/- 0.006 min in the GMOS spectra when the source was in the low/hard state. Due to aliasing effects the period in the GMOS and X-Shooter data could well be the same. We deem it likely that the orbital period is thus close to 30 min, however, as several photometric periods have been reported for this source in the literature already, further confirmation of the 30 min period is warranted. We compare the surface area of the donor star and the disc of 4U 0614+091 with the surface area of the donor star and the disc in typical hydrogen-rich low-mass X-ray binaries and the class of AM Canum Venaticorum stars and argue that the optical emission in 4U 0614+091 is likely dominated by the disc emission. Additionally, we search for periodic signals in all the publicly available RXTE PCA light curves of 4U 0614+091 which could be associated with the orbital period of this source. A modulation at the orbital period with an amplitude of ~ 10% such as those that have been found in other ultra-compact X-ray binaries (4U 0513-40, 4U 1820-30) is not present in 4U 0614+091.

astro-ph.HE↗

arXiv2012

CXOGBSJ174444.7-260330: a new long orbital period cataclysmic variable in a low state

We present phase-resolved spectroscopy and photometry of a source discovered with the Chandra Galactic Bulge Survey (GBS), CXOGBSJ174444.7-260330 (aka CX93 and CX153 in the previously published GBS list). We find two possible values for the orbital period P, differing from each other by 13 seconds. The most likely solution is P =5.69014(6) hours. The optical lightcurves show ellipsoidal modulations, whose modeling provides an inclination of 32+-1 degrees for the most likely P. The spectra are dominated by a K5V companion star (the disc veiling is <~5%). Broad and structured emission from the Balmer lines is also detected, as well as fainter emission from HeI. From the absorption lines we measure K2 =117+-8km/s and v sin i = 69+-7km/s. By solving the system mass function we find M1=0.8+-0.2Msun for the favored P and i, consistent with a white dwarf accretor, and M2=0.6+-0.2Msun. We estimate a distance in the range 400-700 pc. Although in a low accretion state, both spectroscopy and photometry provide evidence of variability on a timescale of months or faster. Besides finding a new, long orbital period cataclysmic variable in a low accretion state, this work shows that the design of the GBS works efficiently to find accreting X-ray binaries in quiescence, highlighting that the spectra of CVs in a low-accretion state can at times appear suggestive of a quiescent neutron star or a black hole system.

astro-ph.HE↗

arXiv2012

Identification of Galactic Bulge Survey X-ray Sources with Tycho-2 Stars

We identify 69 X-ray sources discovered by the Galactic Bulge Survey (GBS) that are coincident with, or very close to bright stars in the Tycho-2 catalog. Additionally, two other GBS sources are resolved binary companions to Tycho-2 stars where both components are separately detected in X-rays. Most of these are likely to be real matches, but we identify nine objects with large and significant X-ray to optical offsets as either detections of resolved binary companions or chance alignments. We collate known spectral types for these objects, and also examine 2MASS colors, variability information from the All-Sky Automated Survey (ASAS), and X-ray hardness ratios for the brightest objects. Nearly a third of the stars are found to be optically variable, divided roughly evenly between irregular variations and periodic modulations. All fall among the softest objects identified by the GBS. The sample forms a very mixed selection, ranging in spectral class from O9 to M3. In some cases the X-ray emission appears consistent with normal coronal emission from late-type stars, or wind emission from early-types, but the sample also includes one known Algol, one W UMa system, two Be stars, and several X-ray bright objects likely to be coronally active stars or binaries. Surprisingly, a substantial fraction of the spectroscopically classified, non-coincidental sample (12 out of 38 objects) have late B or A type counterparts. Many of these exhibit redder near-IR colors than expected for their spectral type and/or variability, and it is likely that the X-rays originate from a late-type companion star in most or all of these objects.

astro-ph.SR↗

arXiv2012

Formation of the planet orbiting the millisecond pulsar J1719-1438

In 2011, Bailes et al. reported on the discovery of a detached companion in a 131 minute orbit around PSR J1719-1438, a 173 Hz millisecond pulsar. The combination of the very low mass function and such a short orbital period is unique. The discoverers suggested that the progenitor system could be an ultracompact X-ray binary (UCXB), which is a binary with a sub-hour orbital period in which a (semi-)degenerate donor fills its Roche lobe and transfers mass to a neutron star. The standard gravitational-wave driven UCXB scenario, however, cannot produce a system like PSR J1719-1438 as it would take longer than the age of the Universe to reach an orbital period of 131 min. We investigate two modifications to the standard UCXB evolution that may resolve this discrepancy. The first involves significant heating and bloating of the donor by pulsar irradiation, and in the second modification the system loses orbital angular momentum via a fast stellar wind from the irradiated donor, additional to the losses via the usual gravitational wave radiation. In particular a donor wind is effective in accelerating orbital expansion, and even a mild wind could produce the 131 minute period within the age of the Universe. We note that UCXBs could be an important class of progenitors of solitary millisecond radio pulsars.

astro-ph.SR↗

arXiv2012

The nature of the bright ULX X-2 in NGC3921: a Chandra position and HST candidate counterpart

We report on Chandra observations of the bright ultra-luminous X-ray (ULX) source in NGC3921. Previous XMM observations reported in the literature show the presence of a bright ULX at a 0.5-10 keV luminosity of 2x10^40 erg/s. Our Chandra observation finds the source at a lower luminosity of ~8x10^39 erg/s, furthermore, we provide a Chandra position of the ULX accurate to 0.7" at 90% confidence. The X-ray variability makes it unlikely that the high luminosity is caused by several separate X-ray sources. In 3 epochs of archival Hubble Space Telescope (HST) observations we find a candidate counterpart to the ULX. There is direct evidence for variability between the two epochs of WFPC2 F814W observations with the observation obtained in 2000 showing a brighter source. Furthermore, converting the 1994 F336W and 2000 F300W WFPC2 and the 2010 F336W WFC3 observations to the Johnson U-band filter assuming a spectral type of O7I we find evidence for a brightening of the U-band light in 2000. Using the higher resolution WFC3 observations the candidate counterpart is resolved into two sources of similar color. We discuss the nature of the ULX and the probable association with the optical counterpart(s). Finally, we investigate a potential new explanation for some (bright) ULXs as the decaying stages of flares caused by the tidal disruption of a star by a recoiled supermassive black hole. However, we find that there should be at most only 1 of such systems within z=0.08.

astro-ph.HE↗

arXiv2012

Accurate positions for the ULXs NGC 7319-X4 and NGC 5474-X1 and limiting magnitudes for their optical counterparts

In this paper we report accurate Chandra positions for two ultraluminous X-ray sources: NGC 7319-X4 at Right Ascension (RA) = 339.02917(2) deg, Declination (Dec) = 33.97476(2) deg and NGC 5474-X1 at RA = 211.24859(3) deg, Dec = 53.63584(3) deg. We perform bore-sight corrections on the Chandra X-ray Satellite observations of these sources to get to these accurate positions of the X-ray sources and match these positions with archival optical data from the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope. We do not find the optical counterparts: the limiting absolute magnitudes of the observations in the WFPC2 standard magnitude system are B = -7.9, V = -8.7 and I = -9.3 for NGC 7319-X4 and U = -6.4 for NGC 5474-X1. We report on the X-ray spectral properties and we find evidence for X-ray variability in NGC 5474-X1. Finally, we briefly discuss several options for the nature of these ULXs.

astro-ph.HE↗

arXiv2012

Initial data release of the Kepler-INT Survey

This paper describes the first data release of the Kepler-INT Survey (KIS), that covers a 116 deg2 region of the Cygnus and Lyra constellations. The Kepler field is the target of the most intensive search for transiting planets to date. Despite the fact that the Kepler mission provides superior time series photometry, with an enormous impact on all areas of stellar variability, its field lacks optical photometry complete to the confusion limit of the Kepler instrument necessary for selecting various classes of targets. For this reason, we follow the observing strategy and data reduction method used in the IPHAS and UVEX galactic plane surveys in order to produce a deep optical survey of the Kepler field. This initial release concerns data taken between May and August 2011, using the Isaac Newton Telescope on the island of La Palma. Four broadband filters were used, U, g, r, i, as well as one narrowband one, Halpha, reaching down to a 10-sigma limit of around 20th mag in the Vega system. Observations covering around 50 deg2, thus about half of the field, passed our quality control thresholds and constitute this first data release. We derive a global photometric calibration by placing the KIS magnitudes as close as possible to the Kepler Input Catalog (KIC) photometry. The initial data release catalogue containing around 6 million sources from all the good photometric fields is available for download from the KIS webpage, as well as via MAST.

astro-ph.GA↗

arXiv2012

The black hole candidate XTE J1752-223 towards and in quiescence: optical and simultaneous X-ray - radio observations

We present optical, X-ray and radio observations of the black hole transient (BHT) XTE J1752-223 towards and in quiescence. Optical photometry shows that the quiescent magnitude of XTE J1752-223 is fainter than 24.4 magnitudes in the i'-band. A comparison with measurements of the source during its 2009-2010 outburst shows that the outburst amplitude is more than 8 magnitudes in the i'-band. Known X-ray properties of the source combined with the faintness of the quiescence optical counterpart and the large outburst optical amplitude point towards a short orbital period system (Porb<~6.8 h) with an M type (or later) mass donor, at a distance of 3.5<~d<~8 kpc. Simultaneous X-ray and radio data were collected with Chandra and the EVLA, allowing constraints to be placed on the quiescent X-ray and radio flux of XTE J1752-223. Furthermore, using data covering the final stage of the outburst decay, we investigated the low luminosity end of the X-ray - radio correlation for this source and compared it with other BHTs. We found that XTE J1752-223 adds to the number of outliers with respect to the `standard' X-ray - radio luminosity relation. Furthermore, XTE J1752-223 is the second source, after the BHT H1743-322, that shows a transition from the region of the outliers towards the `standard' correlation at low luminosity. Finally, we report on a faint, variable X-ray source we discovered with Chandra at an angular distance of ~2.9" to XTE J1752-223 and at a position angle consistent with that of the radio jets previously observed from the BHT. We discuss the possibility that we detected X-ray emission associated with a jet from XTE J1752-223.

astro-ph.HE↗

arXiv2012

Formation of the planet around the millisecond pulsar J1719-1438

Context. Recently the discovery of PSR J1719-1438, a 5.8 ms pulsar with a companion in a 2.2 hr orbit, was reported. The combination of this orbital period and the very low mass function is unique. The discoverers, Bailes et al., proposed an ultracompact X-ray binary (UCXB) as the progenitor system. However, the standard UCXB scenario would not produce this system as the time required to reach this orbital period exceeds the current estimate of the age of the Universe. The detached state of the system aggravates the problem. Aims. We want to understand the evolutionary history of PSR J1719-1438, and determine under which circumstances it could have evolved from an UCXB. Methods. We model UCXB evolution varying the donor size and investigate the effect of a wind mass loss from the donor, and compare the results with the observed characteristics of PSR J1719-1438. Results. An UCXB can reach a 2.2 hr orbit within the age of the Universe, provided that 1) the millisecond pulsar can significantly heat and expand the donor by pulsar irradiation, or 2) the system loses extra orbital angular momentum, e.g. via a fast wind from the donor. Conclusions. The most likely scenario for the formation of PSR J1719-1438 is UCXB evolution driven by angular momentum loss via the usual gravitational wave emission, which is enhanced by angular momentum loss via a donor wind of ~3x10^-13 Msun/yr. Depending on the size of the donor during the evolution, the companion presently probably has a mass of ~1-3 Jupiter masses, making it a very low mass white dwarf as proposed by Bailes et al. Its composition can be either helium or carbon-oxygen. A helium white dwarf companion makes the long (for an UCXB) orbital period easier to explain, but the required inclination makes it a priori less likely than a carbon-oxygen white dwarf.

astro-ph.SR↗

arXiv2011

Optical spectroscopy of the quiescent counterpart to EXO 0748-676: a Black Widow scenario?

We present phase-resolved optical spectroscopy of the counterpart to the neutron star low mass X-ray binary EXO 0748-676, almost one year after it turned into quiescence. The spectra display prominent Hbeta and Hgamma and weak Fe II lines in emission. An average of all the spectra (corrected for the orbital motion) also exhibits a very weak line from Mg I. Tomographic reconstructions show that the accretion disc is not contributing to the optical line emission, which is instead dominated by the irradiated hemisphere of the companion star facing the neutron star. We could not detect absorption features from the mass donor star in the spectra. The emission lines appear broad, with an intrinsic FWHM of 255+-22 km/s. Under the assumption that the width of the Fe II emission lines is dominated by rotational broadening, we obtain a lower limit on the compact object mass which is inconsistent with a NS accretor. We discuss this incongruity and conclude that either the lines are blends of unresolved features (although this requires some fine tuning) or they are broadened by additional effects such as bulk gas motion in an outflow. The fact that the Fe II lines slightly lag in phase with respect to the companion star can be understood as outflowing gas consistent with a Black-Widow like scenario. Nevertheless, we can not rule out the possibility that blends of various emission lines cause the apparent phase lag of the Fe II emission lines as well as their large width.

astro-ph.HE↗

arXiv2011

A late jet rebrightening revealed from multi-wavelength monitoring of the black hole candidate XTE J1752-223

We present optical monitoring of the black hole candidate XTE J1752-223 during its 2009 - 2010 outburst and decay to quiescence. The optical light curve can be described by an exponential decay followed by a plateau, then a more rapid fade towards quiescence. The plateau appears to be due to an extra component of optical emission that brightens and then fades over ~ 40 days. We show evidence for the origin of this optical 'flare' to be the synchrotron jet during the decaying hard state, and we identify and isolate both disc and jet components in the spectral energy distributions. The optical flare has the same morphology and amplitude as a contemporaneous X-ray rebrightening. This suggests a common origin, but no firm conclusions can be made favouring or disfavouring the jet producing the X-ray flare. The quiescent optical magnitudes are B >= 20.6, V >= 21.1, R >= 19.5, i' >= 19.2. From the optical outburst amplitude we estimate a likely orbital period of < 22 h. We also present near-infrared (NIR) photometry and polarimetry and rare mid-infrared imaging (8 - 12 microns) when the source is nearing quiescence. The fading jet component, and possibly the companion star may contribute to the NIR flux. We derive deep mid-IR flux upper limits and NIR linear polarization upper limits. With the inclusion of radio data, we measure an almost flat jet spectral index between radio and optical; F_nu ~ nu^(~ +0.05). The data favour the jet break to optically thin emission to reside in the infrared, but may shift to frequencies as high as the optical or UV during the peak of the flare.

astro-ph.HE↗

arXiv2011

Multiwavelength campaign on Mrk 509. I. Variability and spectral energy distribution

(Abridged) Active galactic nuclei show a wealth of interesting physical processes, some of which are poorly understood. We want to address a number of open questions, including the location and physics of the outflow from AGN, the nature of the continuum emission, the geometry and physical state of the X-ray broad emission line region, the Fe-K line complex, the metal abundances of the nucleus and finally the interstellar medium of our own Galaxy. We study one of the best targets for these aims, the Seyfert 1 galaxy Mrk 509 with a multiwavelength campaign using five satellites (XMM-Newton, INTEGRAL, Chandra, HST and Swift) and two ground-based facilities (WHT and PAIRITEL). Our observations cover more than five decades in frequency, from 2 um to 200 keV. The combination of high-resolution spectroscopy and time variability allows us to disentangle and study the different components. Our campaign covers 100 days from September to December 2009, and is centred on a simultaneous set of deep XMM-Newton and INTEGRAL observations with regular time intervals, spanning seven weeks. We obtain a continuous light curve in the X-ray and UV band, showing a strong, up to 60% flux increase in the soft X-ray band during the three weeks in the middle of our deepest monitoring campaign, and which is correlated with an enhancement of the UV flux. This allows us to study the time evolution of the continuum and the outflow. By stacking the observations, we have also obtained one of the best X-ray and UV spectra of a Seyfert galaxy ever obtained. In this paper we also study the effects of the spectral energy distribution (SED) that we obtained on the photo-ionisation equilibrium. Thanks to our broad-band coverage, uncertainties on the SED do not strongly affect the determination of this equilibrium.

astro-ph.CO↗

arXiv2011

A deep radio survey of hard state and quiescent black hole X-ray binaries

We have conducted a deep radio survey of a sample of black hole X-ray binaries in the hard and quiescent states, to determine whether any systems were sufficiently bright for astrometric follow-up with high-sensitivity very long baseline interferometric (VLBI) arrays. The one hard-state system, Swift J1753.5-0127, was detected at a level of 0.5 mJy/beam. All eleven quiescent systems were not detected. In the three cases with the highest predicted quiescent radio brightnesses (GRO J0422+32, XTE J1118+480, and GRO J1655-40), the new capabilities of the Expanded Very Large Array were used to reach noise levels as low as 2.6 microJy/beam. None of the three sources were detected, to 3-sigma upper limits of 8.3, 7.8, and 14.2 microJy/beam, respectively. These observations represent the most stringent constraints to date on quiescent radio emission from black hole X-ray binaries. The uncertainties in the source distances, quiescent X-ray luminosities at the times of the observations, and in the power-law index of the empirical correlation between radio and X-ray luminosities, make it impossible to determine whether these three sources are significantly less luminous in the radio band than expected. Thus it is not clear whether that correlation holds all the way down to quiescence for all black hole X-ray binaries.

astro-ph.HE↗

arXiv2011

Deep Chandra observations of TeV binaries II: LS 5039

We report on Chandra observations of the TeV emitting High Mass X-ray Binary LS 5039, for a total exposure of ~70ks, using the ACIS-S camera in Continuos Clocking mode to search for a possible X-ray pulsar in this system. We did not find any periodic or quasi-periodic signal in the 0.3-0.4 and 0.75-0.9 orbital phases, and in a frequency range of 0.005-175 Hz. We derived an average pulsed fraction 3sigma upper limit for the presence of a periodic signal of ~15% (depending on the frequency and the energy band), the deepest limit ever reached for this object. If the X-ray emission of LS 5039 is due (at least in part) to a rotational powered pulsar, the latter is either spinning faster than ~5.6 ms, or having a beam pointing away from our line of sight, or contributing to ~15% of the total X-ray emission of the system in the orbital phases we observed.

astro-ph.GA↗