Transient X-ray Pulsar Research Articles

The identification of the optical/IR counterpart of the 29.5-s transient X-ray pulsar GS 1843+009

We report on the identification of the optical/IR counterpart of the 29.5-s transient X-ray pulsar GS 1843+009. We re-analysed an archival ROSAT HRI observation of GS 1843+009 obtaining a new refined position. The optical and IR follow-up observations carried out for the new error circle allowed us to find a relatively faint () and variable early type reddened star (). The optical spectra show the Balmer and Paschen series in emission, while the IR observations confirm the presence of a flux excess (, ), suggesting that the star is surrounded by a circumstellar envelope. Spectroscopic and photometric data together indicate a B0-B2 IV-Ve spectral-type star located at a distance of ≥ 10 kpc confirming the Be-star/X-ray binary nature of GS 1843+009.

Discovery of the Orbit of the Transient X-Ray Pulsar SAX J2103.5+4545

Using X-ray data from the Rossi X-Ray Timing Explorer (RXTE), we carried out a pulse-timing analysis of the transient X-ray pulsar SAX J2103.5+4545. An outburst was detected by the All-Sky Monitor (ASM) in 1999 October 25 and reached a peak X-ray brightness of 27 mcrab on October 28. Between November 19 and December 27, the RXTE Proportional Counter Array (PCA) carried out pointed observations that provided us with pulse arrival times. These yield an eccentric orbit (e = 0.4 ± 0.2) with an orbital period of 12.68 ± 0.25 days and a light-travel time across the projected semimajor axis of 72 ± 6 s. The pulse period was measured to be 358.62171 ± 0.00088 s, and the spin-up rate was (2.50 ± 0.15) × 10-13 Hz s-1. The ASM data for the 1997 February-September outburst, in which F. Hulleman, J. J. M. in 't Zand, & J. Heise discovered SAX J2103.5+4545 using BeppoSAX, are modulated at timescales close to the orbital period. Folded light curves of the 1997 ASM data and the 1999 PCA data are similar and show that the intensity increases at periastron passages.

The discovery of the optical/IR counterpart of the 12-s transient X-ray pulsar GS 0834-43

We report the discovery of the optical counterpart of the 12.3-s transient X-ray pulsar GS 0834−43. We reanalysed archival ROSAT PSPC observations of GS 0834−43, obtaining two new refined positions, ∼14 and ∼18 arcsec away from the previously published one, and a new spin period measurement. Based on these results we carried out optical and infrared (IR) follow-up observations. Within the new error circles, we found a relatively faint (V=20.1) early-type reddened star (V−R=2.24). The optical spectrum shows a strong Hα emission line. The IR observations of the field confirm the presence of an IR excess for the Hα-emitting star (K′=11.4, J−K′=1.94), which is likely surrounded by a conspicuous circumstellar envelope. Spectroscopic and photometric data indicate a B0–2 V–IIIe spectral type star located at a distance of 3–5 kpc and confirm the Be-star/X-ray binary nature of GS 0834−43.

Broad-Band X-Ray Study of a Transient Pulsar RX J0059.2–7138

We report on the results of the ASCA and ROSAT observations on RX J0059.2-7138, a transient X-ray pulsar in the Small Magellanic Cloud. The barycentric pulse period has been precisely determined to be 2.763221 ± 0.000004 s. The pulse shape is almost identical in all of the energy bands. The pulse fraction increases with the photon energy below ∼ 2 keV, while it is nearly constant at ∼ 37% above ∼ 2 keV. The X-ray spectrum has been found to consist of two components. One is dominant above 2 keV, and exhibits sinusoidal pulsations. This component is well described by a typical model found in many X-ray binary pulsars, a power-law of photon index 0.4 with an exponential cut-off at 6.5 keV. The other is dominant below 1 keV and shows no significant pulsation. This component is represented by either a broken power-law with photon indices of 2.6 and 5.1 below and above a break energy of 0.9 keV, or a metal-poor thin-thermal plasma with a temperature of 0.37 keV. The phase-averaged luminosity is ∼ 1038 erg s-1 (0.1–10.0 keV) for both components. A hint of oxygen over-abundance is found in the absorbing column, possibly due to circumstellar gas ejected from an evolved companion.

BeppoSAX observation of the transient X-ray pulsar GS 1843+009

The transient X-ray pulsar GS 1843+009 was observed by BeppoSAX satellite on 1997 April 4, while it was at flux level of 50 mCrab in the 20–200 keV energy band. Using the MECS and LECS concentrators, the source position was measured with unprecedented accuracy of 30. In this poster we present results on both spectral and temporal analysis.

Great outburst of A0535+26 recorded in optical band in 28/29 October 1995

Abstract The observations in Johnson's B filter of the great outburst of transient X-ray pulsar A0535+26, recorded in the night 28/29 October 1995 (JD2450019) from UT = 22.90 to 24.61 h are presented. The outburst consist of a great number of transitory individual pulses. The amplitude of single pulse at the peak of the burst's intensity was about 1.74. The durations of the pulses were about 10–20 s and similar to the integration time. The bottom brightness level between the pulses was stable during the event.

Identification of the Periodic Hard X-Ray Transient GRO J1849−03 with the X-Ray Pulsar GS 1843−02 = X1845−024: A New B[CLC]e[/CLC]/X-Ray Binary

We identify the periodic transient hard X-ray source GRO J1849-03 with the transient X-ray pulsar GS 1843-02 = X1845-024 on the basis of the detection of X-ray outbursts from X1845-024 coincident with hard X-ray outbursts of GRO J1849-03. From its spin period of 94.8 s and its orbital period of 241 days, we classify the system as a Be/X-ray binary.

QPO in transient pulsars

QPOs have now been observed from five transient X-ray pulsars. Four of these are in Be/X-ray systems, and one is the newly discovered LMXB transient GRO J1744-28. I review the observations, and discuss their interpretation in terms of the beat or Keplerian frequency models. These models are successful in explaining the observations for two of the Be/X-ray transients. For one of these, A0535+262, the observations constrain the ratio of the radius of the accretion disk inner edge to the Alfvén radius, providing new information on the accretion disk-magnetosphere boundary region. Neither model can explain the QPO in the remaining two Be/X-ray systems, nor that in GRO J1744-28. It is likely therefore that two or more QPO mechanisms are at work. I discuss the potential for gaining new insight into QPOs from analysis tools unique to pulsed systems, and discuss what we can learn from new observations.

Discovery and Orbital Determination of the Transient X‐Ray Pulsar GRO J1750−27

We report on the discovery and hard X-ray (20-70 keV) observations of the 4.45 s period transient X-ray pulsar GRO J1750-27 with the BATSE all-sky monitor on board CGRO. A relatively faint outburst (<30 mcrab peak) lasting at least 60 days was observed during which the spin-up rate peaked at 38 pHz s^(-1) and was correlated with the pulsed intensity. An orbit with a period of 29.8 days was found. The large spin-up rate, spin period, and orbital period together suggest that accretion is occurring from a disk and that the outburst is a giant outburst typical of a Be/X-ray transient system. No optical counterpart has yet been reported.

Evolution of the Inner Radius of the Accretion Disk in the X‐Ray Pulsar A0535+26

In disk-fed X-ray pulsars, the inner radius R0 of the accretion disk is conventionally expressed in terms of the Alfven radius RA for spherical accretion, R0 = ξRA. The value of the dimensionless parameter ξ and its dependence on the accretion rate are poorly known. Applying the beat frequency model and accretion torque theory to the transient X-ray pulsar A0535+26, in which the spin variation and the quasi-periodic oscillations were measured simultaneously during a giant outburst, we calculate the value of ξ throughout the outburst, and find it generally close to unity, independent of the accretion rate, suggesting that the stellar field nearly fully threads the disk. It is also shown that during the initial rise of the outburst, ξ increased from ~0.6 to ~0.9. We believe that this phenomenon reflects the transition of the accretion process of the neutron star from spherical accretion before the outburst to disk accretion during the outburst.

On the optical variability of a be star, HDE 245770, ? the optical counterpart of the transient X-ray pulsar A0535+26

Photoelectric WBVR observations of Be star HDE 245770=V 725 Tau, the optical counterpart of the transient X-ray pulsar A0535+26, having a pulse period of about 104 s, were conducted for more than 10 years. An irregular long-term optical variability of the star with amplitudes of the order of a few tenths of magnitude was found to be a usual phenomenon. In some cases rapid changes of the star's optical luminosity with a characteristic period of a few tens of minutes or a few hours, and an amplitude of several hundredths of magnitude in all the spectral bands used, which have practically coincided or correlated with the X-ray pulsar outbursts detected by X-ray satellites, were observed.

Status of the Transient Gamma-Ray Spectrometer

The Transient Gamma-Ray Spectrometer (TGRS) was launched aboard the GGS/WIND spacecraft on November 1, 1994. After several deep space orbits (∼2 yrs) WIND will eventually be injected into a halo orbit around the Sun-EarthL1 point. TGRS consists of a 215 cm3 high purityn-type Ge crystal which is kept at cryogenic temperatures by a passive radiative cooler. The energy range covered by the instrument is ∼25–8000 keV with an energy resolution of ∼2–3 keV. The primary task of TGRS is to perform high resolution spectroscopy of gamma-ray bursts and solar flares. Additional objectives are the study of transient x-ray pulsars and, using an on-board passive occulter, the long-term monitoring of sources such as the Crab and the Galactic Center. Since launch, TGRS has been performing exceedingly well, and all the important experiment parameters such as background levels, gain, and resolution have proven to be very stable. To date, TGRS has detected 27 GRBs and three solar flares. Preliminary analysis of our data also indicates that TGRS is indeed sensitive to sources such as the Crab and the Galactic Center.

Discovery of the quasi-periodic oscillations from V0332+53

The discovery of quasi-periodic oscillations (QPOs) in the X-ray flux from the recurrent transient X-ray pulsar VO332+53 is reported. The centroid frequency, full width at half maximum (FWHM), and the relative root mean square (RMS) amplitude of the QPOs are (5.1 +/- 0.5) x 10<SUP>-2</SUP> Hz, (3.3 +/- 1.5) x 10<SUP>-2</SUP> Hz, and 4.8% +/- 1.2%, respectively. The beat frequency model is tested using these results and previously reported QPOs from other X-ray binary pulsars.

A new transient pulsar in the Small Magellanic Cloud with an unusual x-ray spectrum

This article reports the discovery of a luminous (3.5 x 10(exp 37) ergs/sec over the 0.2 to 2 keV band) transient X-ray pulsar in the Small Magellanic Cloud (SMC) with an extremely soft component to its X-ray spectrum. This is the first time that a spectrum of this type has been seen in this class of X-ray source. The pulse period is 2.7632 s, and the pulse modulation appears to vary with energy from nearly unpulsed in the low-energy band of the ROSAT Position Sensitive Proportional Counter (PSPC) (0.07 to 0.4 keV) to about 50% in the high-energy band (1.0 to 2.4 keV). The object, RX J0059.2-7138, also shows flickering variability in its X-ray emission on timescales of 50 to 100s. The pulse-phase-averaged PSPC X-ray spectrum can be well described by a two-component source model seen through an absorbing column density of approximately 10(exp 21) atoms cm(exp -2). One spectral component is a power law with photon index 2.4. The other component is significantly softer and can be described by either a steeply falling power law or a blackbody with a temperature KT(sub BB) approximately 35 eV. Ths component is transient, but evidently upulsed, and, for the blackbody model fits, requires a large bolometric luminosity: near, or even several times greater than, the Eddington luminosity for a 1.4 solar mass object. When these characteristics of its soft emission are considered, RX J0059.2-7138 appears quite similar to other X-ray sources in the magellanic Clouds, such as CAL 83, CAL 87, and RX J0527.8-6954, which show only extreme ultrasoft (EUS) X-ray spectra. The discovery of RX J0059.2-7138, a probably high-mass X-ray binary, clearly indicates that EUS spectra may arise from accretion-powered neutron-star X-ray sources. This result lends support to the idea that some of the 'pure' EUS sources may be shrouded low-mass X-ray binaries rather than accreting white dwarfs.

Two-component continuum spectrum X-ray pulsar EXO2030+375

We report the detection of a soft X-ray component in the spectrum of the transient X-ray pulsar EXO2030+375 at a high state in 1985. The spectrum of the soft X-ray component could be fitted by a blackbody with a temperature kT ∼1.1 keV and a radius of the emission areaR ∼ 3.6 – 6.1 km (assuming 5 kpc distance).

Pulse phase-resolved X-ray spectroscopy of the transient high-mass X-ray binary V0332 + 53

We present an analysis of the EXOSAT observations of the transient binary X-ray pulsar, V0332 + 53, obtained during a series of flares in the 1983–4 outburst. For many of these observations, the data were taken in a mode which provided high time resolution and energy resolution simultaneously. This meant that detailed pulse phase-resolved X-ray spectroscopy of the 4.37-s pulsar was possible for the first time. We consider the data in two sets, namely those showing a double peak in the pulse profile and those showing a single peak only. The spectra of both data sets can be adequately fitted in terms of a power law plus exponential cut-off model, and show significant changes in some of the spectral parameters as a function of pulse phase. We interpret our results in terms of a system in which our line of sight is not close to the magnetic axis of the neutron star and in which contributions from two active regions are seen to vary as the outburst evolves. We also investigate one particular data set which was distinct from any of the other observations. This data set had a large modulation in the flux level which is attributable to excess power at low frequencies. This represents a further novel property of V0332 + 53, which is already known to exhibit both pulsations and short-time-scale flicker.

Discovery of a cyclotron resonance feature at 30 keV from the transient X-ray pulsar Cepheus X-4

From Ginga observations of the transient X-ray pulsar Cep X-4, a spectral line feature attributable to electron cyclotron resonance was discovered at about 30 keV in the 1.2−37 keV X-ray spectrum. The detection, a fifth firm example of cyclotron resonance from X-ray pulsars, implies a surface magnetic field of about 2.6×10 12 (1+z) G for this pulsar, where z is the gravitational redshift. Throughout the 66.25 s pulses, the cyclotron feature appears in absorption, with at most ±5% variation in the resonance center energy around the mean value of 30.5±0.4 keV

Cyclotron line features in the spectrum of the transient X-ray pulsar X0115 + 634

An outburst of the transient X-ray pulsar X0115 + 634 was detected with the All Sky Monitor (ASM) on board Ginga on February 5, 1990. Follow-up observations with the large-area proportional counters (LACs) revealed complex changes in the energy spectrum which depend on the phase of the 3.6 s pulsation. Characteristic structures in the spectra above 10 keV can be best interpreted as two dips at about 12 and about 23 keV, although not at all phases. The results strongly suggest that the structures in the spectra are due to cyclotron resonant scattering and the two apparent absorption lines are ascribed to the fundamental and second harmonics. This indicates a magnetic field strength on the neutron star surface of about 1 {times} 10 to the 12th G. Equivalent widths of the second harmonic line are about 2 times larger than those of the first harmonic line, depending on the pulse phase. 25 refs.

A new X-ray pulsar GS 2138 + 56 (Cepheus X-4)

A transient X-ray pulsar was discovered with the Ginga satellite at the position of alpha(1950) = 21 h 38 m + or - 1 m, delta(1950) = 56 deg 50 arcmin + or - 6 arcmin (designed as GS 2138 + 56). The error box includes the previously reported transient source Cep X-4. An X-ray pulsation with a heliocentric pulse period of 66.2490 + or - 0.0001 sec (at MJD = 47263.5) was discovered. Assuming no intrinsic change of the pulse period during the observation, a lower limit of the orbital period of 23 days and projected semiaxis of 9 lt-sec are obtained. The X-ray spectrum has a typical shape for X-ray pulsars having power-law index of about 1.0 with an exponential cutoff at an energy typical shape for X-ray pulsars having power-law index of about 1.0 with an exponential cutoff at an energy of about 16 keV. It is suggested, based on circumstantial evidence, that GS 2138 + 56 is likely to be Be star binary. 13 refs.

Discovery of a prominent cyclotron absorption feature from the transient X-ray pulsar X0331 + 53

view Abstract Citations (114) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discovery of a Prominent Cyclotron Absorption Feature from the Transient X-Ray Pulsar X0331+53 Makishima, K. ; Mihara, T. ; Ishida, M. ; Ohashi, T. ; Sakao, T. ; Tashiro, M. ; Tsuru, T. ; Kii, T. ; Makino, F. ; Murakami, T. ; Nagase, F. ; Tanaka, Y. ; Kunieda, H. ; Tawara, Y. ; Kitamoto, S. ; Miyamoto, S. ; Yoshida, A. ; Turner, M. J. L. Abstract A remarkable absorption feature at 28.5 keV, attributable to electron cyclotron resonance, has been discovered in the 1.9-60-keV X-ray spectrum of the recurrent transient X-ray pulsar X0331 + 53. The observed resonance energy implies a neutron star surface magnetic field of 2.5(1 + z) x 10 to the 12th G, where z is the gravitational redshift. The detection was made with the Ginga observatory in October 1989, during an outburst of this transient with a flux level of about 0.3 Crab. The feature is very deep and has been resolved with excellent statistics. This is the fourth unambiguous detection of cyclotron resonant scattering features from X-ray pulsars, suggesting that these features are a common phenomenon among these objects. An empirical relation found between the cyclotron resonance energy and the spectral cutoff energy suggests that the magnetic field strengths of the known X-ray pulsars are clustered in a range (1-4) x 10 to the 12th G. Publication: The Astrophysical Journal Pub Date: December 1990 DOI: 10.1086/185888 Bibcode: 1990ApJ...365L..59M Keywords: Absorption Spectra; Cyclotron Resonance; Pulsars; X Ray Sources; Neutron Stars; Red Shift; Stellar Magnetic Fields; Transient Response; X Ray Binaries; X Ray Spectra; Astrophysics; PULSARS; STARS: MAGNETIC; X-RAYS: BINARIES; X-RAYS: SPECTRA full text sources ADS | data products SIMBAD (7)