August Outburst Research Articles

Supernova 2009ip Outbursts in 2012: From Scenario to Model

Spherical and aspherical models are presented for two outbursts in 2012 of supernova 2009ip. Models are based on a scenario which suggests that the August 2012 outburst is caused by the explosive shell ejection from LBV-presupernova. The model predicts an emergence of an unobserved outburst in late July 2012 related to a shock breakout and a subsequent diffusive radiative cooling of the ejected envelope. The luminosity of the first observed outburst in August 2012 was presumably powered by the central source, whereas the second, more powerful outburst in late September 2012, was caused by the ejecta interaction with the circumstellar envelope. Models provide estimates of the ejecta energy and mass along with the mass of the circumstellar shell.

New SU UMa-type star ZTF18abdlzhd in the Zwicky Transient Facility data

We carried out a search for unknown dwarf novae in a public data release of the Zwicky Transient Facility survey and suspected that the object ZTF18abdlzhd is a SU UMa-type star. Performed multicolor CCD observations permit us to follow its fading from an outburst in August and an entire superoutburst in October 2020. The duration of the superoutburst is 13 days. We detected superhumps with period P = 0.06918(3) d that are characteristic of UGSU type stars.

The quiescent state of the neutron-star X-ray transient GRS 1747−312 in the globular cluster Terzan 6

We studied the transient neutron-star low-mass X-ray binary GRS 1747−312, located in the globular cluster Terzan 6, in its quiescent state after its outburst in August 2004, using an archival XMM–Newton observation. A source was detected in this cluster and its X-ray spectrum can be fitted with the combination of a soft, neutron-star atmosphere model and a hard, power-law model. Both contributed roughly equally to the observed 0.5–10 keV luminosity (∼4.8 × 1033 erg s−1). This type of X-ray spectrum is typically observed for quiescent neutron-star X-ray transients that are perhaps accreting in quiescence at very low rates. Therefore, if this X-ray source is the quiescent counterpart of GRS 1747−312, then this source is also accreting at low levels in-between outbursts. Since source confusion is a likely problem in globular clusters, it is quite possible that part, if not all, of the emission we observed is not related to GRS 1747−312, and is instead associated with another source or conglomeration of sources in the cluster. Currently, it is not possible to determine exactly which part of the emission truly originates from GRS 1747−312, and a Chandra observation (when no source is in outburst in Terzan 6) is needed to be conclusive. Assuming that the detected emission is due to GRS 1747−312, we discuss the observed results in the context of what is known about other quiescent systems. We also investigated the thermal evolution of the neutron star in GRS 1747−312, and inferred that GRS 1747−312 can be considered a typical quiescent system under our assumptions.

Truncation of the Accretion Disk at One-third of the Eddington Limit in the Neutron Star Low-mass X-Ray Binary Aquila X-1

Abstract We perform a reflection study on a new observation of the neutron star (NS) low-mass X-ray binary Aquila X-1 taken with NuSTAR during the 2016 August outburst and compare with the 2014 July outburst. The source was captured at ∼32% L Edd, which is over four times more luminous than the previous observation during the 2014 outburst. Both observations exhibit a broadened Fe line profile. Through reflection modeling, we determine that the inner disk is truncated (where R g = GM/c 2) and (errors quoted at the 90% confidence level). Fiducial NS parameters (M NS = 1.4 M ⊙, R NS = 10 km) give a stellar radius of R NS = 4.85 R g ; our measurements rule out a disk extending to that radius at more than the 6σ level of confidence. We are able to place an upper limit on the magnetic field strength of B ≤ 3.0–4.5 × 109 G at the magnetic poles, assuming that the disk is truncated at the magnetospheric radius in each case. This is consistent with previous estimates of the magnetic field strength for Aquila X-1. However, if the magnetosphere is not responsible for truncating the disk prior to the NS surface, we estimate a boundary layer with a maximum extent of and . Additionally, we compare the magnetic field strength inferred from the Fe line profile of Aquila X-1 and other NS low-mass X-ray binaries to known accreting millisecond X-ray pulsars.

A DOUBLE-PEAKED OUTBURST OF A 0535+26 OBSERVED WITH INTEGRAL , RXTE , AND SUZAKU

The Be/X-ray binary A 0535+26 showed a normal (type I) outburst in August 2009. It is the fourth in a series of normal outbursts associated with the periastron, but is unusual by presenting a double-peaked light curve. The two peaks reached a flux of ~450 mCrab in the 15-50 keV range. We present results of the timing and spectral analysis of INTEGRAL, RXTE, and Suzaku observations of the outburst. The energy dependent pulse profiles and their evolution during the outburst are studied. No significant differences with respect to other normal outbursts are observed. The centroid energy of the fundamental cyclotron line shows no significant variation during the outburst. A spectral hardening with increasing luminosity is observed. We conclude that the source is accreting in the sub-critical regime. We discuss possible explanations for the double-peaked outburst.

Discovery of a Cyclotron Resonance Feature in the X-Ray Spectrum of GX 304−1 with RXTE and Suzaku during Outbursts Detected by MAXI in 2010

Abstract We report on the discovery of a cyclotron resonance scattering feature (CRSF) in the X-ray spectrum of GX 304 $-$ 1, obtained by RXTE and Suzaku during major outbursts detected by MAXI in 2010. The peak intensity in August reached 600 mCrab in the 2–20 keV band, which is the highest ever observed from this source. The RXTE observations on more than twenty occasions and one Suzaku observation revealed a spectral absorption feature at around 54 keV, which is the first CRSF detection from this source. The estimated strength of the surface magnetic field, 4.7 $\times$ 10 $^{12}$ G, is one of the highest among binary X-ray pulsars from which CRSFs have ever been detected. The RXTE spectra taken during the August outburst also suggest that the CRSF energy changed over 50–54 keV, possibly in a positive correlation with the X-ray flux. The behavior is qualitatively similar to that observed from Her X-1 on long time scales, or from A 0535 $+$ 26, but different from the negative correlation observed from 4U 0115 $+$ 63 and X 0331 $+$ 53.

Spin down during quiescence of the fastest known accretion-powered pulsar

We present a timing solution for the 598.89 Hz accreting millisecond pulsar, IGR J00291+5934, using Rossi X-ray Timing Explorer data taken during the two outbursts exhibited by the source on 2008 August and September. We estimate the neutron star spin frequency and we refine the system orbital solution. To achieve the highest possible accuracy in the measurement of the spin frequency variation experienced by the source in-between the 2008 August outburst and the last outburst exhibited in 2004, we re-analysed the latter considering the whole data set available. We find that the source spins down during quiescence at an average rate of {\nu}dot_{sd}=(-4.1 +/- 1.2)E-15 Hz/s. We discuss possible scenarios that can account for the long-term neutron star spin-down in terms of either magneto-dipole emission, emission of gravitational waves, and a propeller effect. If interpreted in terms of magneto-dipole emission, the measured spin down translates into an upper limit to the neutron star magnetic field, B<=3E+08 G, while an upper limit to the average neutron star mass quadrupole moment of Q<=2E+36 g cm^2 is set if the spin down is interpreted in terms of the emission of gravitational waves.

DISCOVERY OF A SECOND TRANSIENT LOW-MASS X-RAY BINARY IN THE GLOBULAR CLUSTER NGC 6440

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. Four other outbursts (May 29-June 4, Aug. 29-Sept. 1, Oct. 1-3, and Oct. 28-31 2009) have been observed with RXTE/PCA (identifying millisecond pulsations, Altamirano et al. 2009a) and Swift/XRT (confirming a positional association with NGC 6440 X-2), with similar peak luminosities and decay times. Optical and infrared imaging did not detect a clear counterpart, with best limits of V>21, B>22 in quiescence from archival HST imaging, g'>22 during the August outburst from Gemini-South GMOS imaging, and J>~18.5$ and K>~17 during the July outburst from CTIO 4-m ISPI imaging. Archival Chandra X-ray images of the core do not detect the quiescent counterpart, and place a bolometric luminosity limit of L_{NS}< 6*10^31 ergs/s (one of the lowest measured) for a hydrogen atmosphere neutron star. A short Chandra observation 10 days into quiescence found two photons at NGC 6440 X-2's position, suggesting enhanced quiescent emission at L_X~6*10^31 ergs/s . NGC 6440 X-2 currently shows the shortest recurrence time (~31 days) of any known X-ray transient, although regular outbursts were not visible in the bulge scans before early 2009. Fast, low-luminosity transients like NGC 6440 X-2 may be easily missed by current X-ray monitoring.

Warm and hot circumstellar gas in V1647 Ori during the 2008-2009 outburst

AbstractThe pre-main sequence star V1647 Ori started a new outburst in August 2008. From October 2008 to February 2009 we monitored V1647 Ori, obtaining quasi-simultaneous VLT-CRIRES near-IR spectroscopy, VLT-VISIR mid-IR spectroscopy and VLT-FORS2 optical spectroscopy. We studied the evolution of H2 and CO emission from hot and warm gas and Hα and forbidden line-emission during the initial outburst phase of V1647 Ori. Hα is observed in emission displaying P-Cygni profiles with blue-shifted absorption up to –700 km/s, suggesting the presence of a high velocity wind (Fig. 1a). [OI] emission at 6300 Å is observed displaying a blue-shifted emission shoulder, indicating the presence of material moving away from the star (Fig. 1b). We detect H2 1-0 S(1) and CO (P4 to P14 and P30-P38) ro-vibrational lines centered at the velocity of the star at all epochs (Fig. 1c &amp; d). This strongly suggests that the H2 and CO emission originates from a disk and not from a warm outflow. The H2 1–0 S(0) and 2-1 S(1) ro-vibrational lines at 2.22 and 2.24 μm and the pure-rotational H2 0–0 S(1) and 0–0 S(2) lines at 17 and 12 μm were not detected in our spectra. Changes in the Hα and [OI] profiles and the H2 and CO emission observed do not correlate. We modeled the H2 and CO line profiles assuming emission from a flat disk in keplerian rotation with line intensity decreasing with radius (I ~ I0(R/Rmin)−α). We found that the disk of V1647 Ori is observed nearly face-on and that the line emission is produced within a fraction of an AU of the star (Fig. 1d).

Pulsed thermal emission from the accreting pulsar XMMU J054134.7-682550

Aims. Soft X-ray excesses have been detected in several Be/X-ray binaries and interpreted as the signature of hard X-ray reprocessing in the inner accretion disk. The system XMMU J054134.7-682550, located in the LMC, featured a giant Type II outburst in August 2007. The geometry of this system can be understood by studying the response of the soft excess emission to the hard X-ray pulses. Methods. We have analyzed series of simultaneous observations obtained with XMM-Newton/EPIC-MOS and RXTE/PCA in order to derive spectral and temporal characteristics of the system, before, during and after the giant outburst. Spectral fits were performed and a timing analysis has been carried out. Spectral variability, spin period evolution and energy dependent pulse shapes are analysed. Results. The outburst (LX = 3 × 10 38 erg/s ≈ LEDD) spectrum could be modeled successfully using a cutoff powerlaw, a cold disk emission, a hot blackbody, and a cyclotron absorption line. The magnetic field and magnetospheric radius could be constrained. The thickness of the inner accretion disk is broadened to a width of 75 km. The hot blackbody component features sinusoidal modulations indicating that the bulk of the hard X-ray emission is emitted preferentially along the magnetic equator. The spin period of the pulsar decreased very significantly during the outburst. This is consistent with a variety of neutron star equations of state and indicates a very high accretion rate.

Photometric Studies of New Southern SU UMa-Type Dwarf Novae, FL Trianguli Australis and CTCV J0549–4921

We report on the time-resolved optical CCD photometry of newly discovered SU UMa-type dwarf novae, FL TrA and CTCVJ0549$-$4921. During a 2006 August outburst, we detected superhumps with a period of 0.59897(11) days for FL TrA, clarifying the SU UMa nature of the system. On the first night of our observations of FL TrA, the object showed no superhumps. This implies that it takes a few days for the full development of superhumps. The superhump period variation diagram of FL TrA was similar to that observed in some WZ Sge stars and short-period SU UMa-type stars. This indicates that the system is closely related to WZ Sge stars and SU UMa stars having short orbital periods. For CTCV J0549$-$4921, the candidates of the mean superhump period are 0.083249(10) days and 0.084257(8) days, respectively. Due to a lack of observations, we cannot determine the true superhump period, but the latter period is favorable. Using the ASAS-3 archive, it turned out that the system showed only four outbursts over the past 6 years. The outburst amplitude of CTCV J0549$-$4921 was relatively small, with about 4.5 mag. One possibility is that mass evaporation may play a role during quiescence.

A Study of the Evolution of the Accretion Disk of V2051 Ophiuchi through Two Outburst Cycles

We follow the changes in the structure of the accretion disk of the dwarf nova V2051 Oph along two separate outbursts in order to investigate the causes of its recurrent outbursts. We apply eclipse-mapping techniques to a set of light curves covering a normal (2000 July) and a low-amplitude (2002 August) outburst to derive maps of the disk surface brightness distribution at different phases along the outburst cycles. The sequence of eclipse maps of the 2000 July outburst reveal that the disk shrinks at outburst onset while an uneclipsed component of 13% of the total light develops. The derived radial intensity distributions suggest the presence of an outward-moving heating wave during rise and an inward-moving cooling wave during decline. The inferred speed of the outward-moving heating wave is 1.6 km s-1, while the speed of the cooling wave is a fraction of that. A comparison of the measured cooling wave velocity on consecutive nights indicates that the cooling wave accelerates as it travels toward disk center, in contradiction with the prediction of the disk instability model. From the inferred speed of the heating wave we derive a viscosity parameter αhot 0.13, comparable to the measured viscosity parameter in quiescence. The 2002 August outburst had a lower amplitude (ΔB 0.8 mag), and the disk at outburst maximum was smaller than on 2000 July. For an assumed distance of 92 pc, we find that along both outbursts the disk brightness temperatures remain below the minimum expected according to the disk instability model. The results suggest that the outbursts of V2051 Oph are caused by bursts of increased mass transfer from the mass-donor star.

Multicolour Photometry and Spectroscopy of the Slow Nova V475 Sct (Nova Scuti 2003)

The UBVRI photometry and 460–900 nm spectroscopy of a classical nova V475 Sct obtained after its outburst in August 2003 is discussed. The nova was classified as a Fe II slow nova with the t2,V = 48 d, t3,V = 53 d. The absolute magnitudes of the nova at maximum MVmax = −7.16±0.15, MBmax = −6.96±0.39, the color excess E(B−V) = 0.69±0.05 and the distance to the nova d = 4.8±0.9 kpc was determined. Observed 13.4-day periodicity of flares can be explained either by pulsation of the nova envelope or by the mass transfer bursts from the red to the white dwarf probably caused by a periastron passage of the third body. The rapid fade of the brightness, which started 57 days after the maximum, is related to a dust formation in the ejecta of the nova. The early optical spectra display the forest of low ionization emission lines, primarily Fe II and Balmer H, accompanied by two P Cygni absorptions, arising in the inner and outer envelope of the expanding nova shell ejected at brightness maximum and accelerated by continuous stellar wind. The spectrum taken in the nebular stage of the nova, which started in March 2004, shows very strong emission [O III] 495.9 nm and 500.7 nm lines, responsible for discrepancy of the B and V magnitudes determined from observations taken by different instruments. The nebular emission line profiles suggest a nonspherical ejection of the shell.

Discovery of a redshifted X-ray emission line in the symbiotic neutron star binary 4U 1700+24

We present the spectral analysis of an XMM-Newton observation of the X-ray binary 4U 1700+24, performed during an outburst in August 2002. The EPIC-PN spectrum above 1 keV can be modeled by a blackbody plus Comptonization model, as in previous observations. At lower energies, however, we detect a prominent soft excess, which we model with a broad Gaussian centered at ~0.5 keV. In the high resolution RGS spectrum we detect a single emission line, centered at 19.19^{+0.05}_{-0.09} \AA. We discuss two possible interpretations for this line: O VIII at redshift z=0.012^{+0.002}_{-0.004} or Ne IX at redshift z~0.4.

Search for an Infrared Counterpart to SGR 1900+14

We used the Palomar 1.5 m telescope to obtain infrared (IR) images of the field of the soft gamma-ray repeater SGR 1900+14 on 1998 June 4 UT, shortly after its 1998 May/June outburst. We find no IR counterpart within a 2'' radius of the position of SGR 1900+14 down to limiting magnitudes of J > 18.1 mag, H > 16.6 mag, and Ks > 15.3 mag (90% confidence level). Given the estimated distance and extinction to SGR 1900+14, we can rule out any possible counterpart more luminous than a B8 main-sequence star, including any star of luminosity class I or II. We can also rule out a luminous synchrotron afterglow such as the one seen following the 1998 August outburst.

The 1993 August Minioutburst of GRO J0422+32

We report on observations of the soft X-ray transient (SXT) GRO J0422+32 made with the ROSAT Position Sensitive Proportional Counter (PSPC) and the ASCA GIS and SIS X-ray imaging spectrometers during its 1993 August outburst. This event occurred approximately one year after the primary outburst of the source and was characterized by an X-ray-to-optical luminosity ratio much smaller than that typically seen in SXT outbursts or in steady, low-mass X-ray binaries. Our X-ray observations with the ROSAT PSPC, spread over 6.2 days and totalling 28.8 ks, combined with our archival analysis of 17 ks of ASCA observations, indicate an approximately 1 mcrab source that turned and subsequently back on over a 10 day period, with distinct spectral characteristics in each case. In addition to our analysis of the X-ray spectra, we report on optical photometry and spectroscopy bracketing the X-ray observations. It is noteworthy that the optical light curves remain approximately constant, at least in our data's almost daily sampling, during the turning and turning on sequence seen in the X-rays. Optical spectroscopy reveals large, asymmetric redshifted and blueshifted components in the double-peaked emission lines He II λ4686 and Hβ λ4861, which can be interpreted as evidence for a wind emanating from the secondary. The phasing of these shifts ruled out a wind originating from the disk. On the other hand, the X-ray power illuminating the star seems insufficient for driving such a wind. Comparisons are made with the primary (1992) outburst and decay phase of GRO J0422+32. Implications for X-ray reprocessing scenarios of the production of optical and UV emission and for other possible scenarios, such as advection-dominated accretion, are briefly considered. An upper limit to the quiescent X-ray luminosity is estimated using data acquired during the X-ray off state. A similarity between the X-ray-to-optical behavior of GRO J0422+32 during this minioutburst and previously documented optical-to-EUV behavior of certain SU Ursae Majoris system outbursts is noted. A physical interpretation of this analogous behavior, suggesting that the hot and cold branches of the S-shaped stability curve may be relatively closely spaced in GRO J0422+32, is offered.

The Radio Outburst from GRO J1655-40

Strong variable radio emission from the bright transient X-ray source GRO J1655-40 (X-ray Nova Scorpii 1994) has been detected at 843 MHz with the Molonglo Observatory Synthesis Telescope (MOST). As the hard X-ray intensity from the 1994 August outburst declined the radio output increased rapidly, reaching a peak of nearly 8 Jy some 12 days after the first X-ray peak. VLBI images obtained at this time showed two main components separating with an apparent transverse velocity &gt; c. The evolution of the radio spectrum suggests that the time delay between X-ray and radio emissions is due, at least in part, to opacity effects associated with this expansion.

EUVE Observations of the Anomalous 1993 August Outburst of SS Cygni

EUVE Observations of the Anomalous 1993 August Outburst of SS Cygni

Observations of the X-ray transient 4U 0115+63

view Abstract Citations (39) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of the X-Ray Transient 4U 0115+63 Whitlock, L. ; Roussel-Dupre, D. ; Priedhorsky, W. Abstract Six recurrences of the X-ray transient 4U 0115+63 are observed in the Vela 5B data base during the interval from May 1968 to June 1979. The outbursts occurring in August 1969, January 1970, August 1970, and January 1971 are roughly 180 days apart. This pattern then stops, and a quasi-periodic 2.9-3.5-yr recurrence time appears which accounts for the January 1971, August 1974, and December 1977 outbursts. The known 3.6-sec pulsations of this pulsar are seen during a major outburst in August 1974, and imply a spin-up between the 1971 and 1974 events. The intermittent stellar-wind accretion model of Stella et al. (1986) can be successfully applied to the pulse period and intensity history if a spin-up of the neutron star is allowed while it is in the inhibited accretion regime. Publication: The Astrophysical Journal Pub Date: March 1989 DOI: 10.1086/167206 Bibcode: 1989ApJ...338..381W Keywords: Stellar Flares; X Ray Binaries; B Stars; Neutron Stars; Stellar Mass Accretion; Transient Response; Astrophysics; STARS: INDIVIDUAL ALPHANUMERIC: 4U 0115; 63; STARS: BINARIES; X-RAYS: SOURCES; X-RAYS: BINARIES; X-RAYS: BURSTS full text sources ADS | data products SIMBAD (3) Related Materials (1) Erratum: 1989ApJ...344.1051W