Small Outbursts Research Articles

Spectrum and timing phenomena in IGR J17091-3624 2011 outburst

AbstractX-ray source IGR J17091-3624 was discovered by INTEGRAL observatory on 2003 April (Kuulkers 2003). A outburst was detected with Swift/Burst Alert Telescope (BAT) in late January 2011 (Krimm 2011). IGR J17091-3624 has a similar timing phenomena to microquasar GRS 1915+105(Belloni 2000; Altamirano 2011). We have analyzed the evolution of temporal and spectral characteristic of IGR J17091-3624 during the 2011 outburst. We find that (1) all the QPOs can be divided into two types, QPO-AB and QPO-C, (2) a small outburst tracks clockwise in the HID, (3) the relationship between hardness and disk color temperature forms a V-shape. Those results will give a strong constraint on the disk radiative process.

Dwarf Novae in the Shortest Orbital Period Regime. I A New Short Superhump Period Dwarf Nova, OT J055717+683226

Abstract We report on the observation of a new dwarf nova (DN), OT J055717$+$683226 (OT: optical transient), during the period of its first-recorded superoutburst in 2006 December. Our observation shows that this object is an SU UMa-type dwarf nova having a very short superhump period of 76.67$\pm$0.03 min (0.05324$\pm$0.00002 d). The next superoutburst was observed in 2008 March. The recurrence time of superoutbursts (supercycle) is, hence, estimated to be $\sim$480 d. The supercycle ($\sim$ 480 d) is much shorter than those ($>rsim$10 yr) of WZ Sge-type dwarf novae which are in the major of dwarf novae in the shortest orbital period regime ($\lesssim$85 min). Using a hierarchical cluster analysis, we divided the dwarf nova in the shortest orbital period regime in seven groups. We found that objects, which have short supercycles, small outburst amplitudes, and large superhump period excesses compared with those of WZ Sge stars, form a small group. OT J055717$+$683226 probably belongs to this group.

Seismic observations of transient subglacial water‐flow beneath MacAyeal Ice Stream, West Antarctica

New seismic observations of harmonic tremors beneath MacAyeal Ice Stream, West Antarctica are reported. Each of the two tremor events that we recorded during a six week period had sustained arrival of 3 Hz energy for approximately 10 minutes. During that time the source location migrated a few kilometers. The harmonic nature of the tremors is interpreted as the result of resonance in subglacial water‐filled cracks and conduits. The duration, monochromatic nature, and movement of the tremor indicate that the source mechanism is likely flow in the subglacial water system resulting from the discharge from a small subglacial lake. Our results suggest that the subglacial water system produces repeated, small outburst floods, with possible implications for ice‐stream dynamics.

A mechanism for short-lived cometary outbursts at sunrise as observed by Deep Impact on 9P/Tempel 1

Abstract We explore a possible mechanism that may explain the outbursts observed by the Deep Impact mission on comet 9P/Tempel 1 that appear to occur near sunrise on a particular area. Assuming that the area is covered by a porous, poorly conducting dust layer, the heat wave generated by solar radiation at local noon propagates through the dust layer towards the ice-rich layer underneath it. The heated ice sublimates and the vapour flows towards the surface. However, by the time the heat wave reaches the ice, the spot has moved out of sunlight and its temperature has started dropping. As the vapour flows outwards, the surface has become so cold that it refreezes. Thus, at night some ice accumulates in the dust layer, very close to the surface. At sunrise, it immediately evaporates, producing a short-lived surge of activity. Numerical simulations of this mechanism provide the duration and water production of such outbursts, which are compatible with the 9P/Tempel 1 observations of small outbursts.

Rock avalanches that travel onto glaciers and related developments, Karakoram Himalaya, Inner Asia

Catastrophic rock slope failures in rugged terrain commonly generate rock avalanches. When these occur in glacier basins the extent of landslide run out and its emplacement geometry are affected by movement over ice. Substantial modifications of glacier activity and sedimentation can follow. Ice activity leads to rapid modification, transport and dispersal of landslide debris. The nature of these interactions is described from observations over 20 years at Bualtar Glacier in the Karakoram. In August 1986 rock avalanches descended onto the ablation zone of the glacier. Their moisture content and patterns of deposition were affected by travel over ice. Glacier movement increased sharply at and below the rock avalanche deposits and, within a few months, the glacier surged. A second surge occurred 2 years later. Major slope failures and debris flows were triggered beyond the ice margins, and ponded melt water led to small outburst floods. By 2005 the landslide material had been transported some 9 km, about one third of this distance in the surges. Eventually it was fully reworked to become less readily distinguishable from other heavy supraglacial debris. A large area of thickened ice persisted where the debris reduced ablation; a positive impact on mass balance equivalent to a 20% increase in annual accumulation. However, it occurred as a moving segment of the ablation zone. In 10 years it had, in effect, replaced the mass transferred in the surges. Data for the mid-1980s indicate the rock avalanches exceeded pre-existing supraglacial debris by roughly five times and, over a 30 year period, will equal almost 500 years of normal supraglacial transport to the glacier margins. Other impacts of the episode suggest a doubling of this contribution to denudation. Similar developments were observed at three other glaciers where recent rock avalanches occurred and at twenty-one prehistoric rock avalanches newly identified as having spread over glaciers. It seems inadequate to treat such events only as singular extremes, or the landslide and glacial processes separately. Here they are interpreted as contributing to ‘disturbance regime’ landscapes, whose history reflects episodic and regionally specific responses to strong interference among different earth surface processes. They generate polygenetic deposits and landforms that are morphologically complex. Individual episodes involve decades to millennia; their numbers and repetition can over-ride or redirect geotectonic and climatic conditions. It is suggested they are major, but hitherto misread or neglected, elements of landform evolution in the Karakoram and, perhaps, in other high mountains.

Recent photometry of symbiotic stars

AbstractWe present new photometric observations of 15 symbiotic stars covering their last orbital cycle(s) from 2003.9 to 2007.2. We obtained our data by both classical photoelectric and CCD photometry. Main results are: EG And brightened by ∼0.3 mag in U from 2003. A ∼0.5 mag deep primary minimum developed in the U light curve (LC) at the end of 2006. ZAnd continues its recent activity that began during the 2000 autumn. A new small outburst started in summer of 2004 with a peak U magnitude of ∼ 9.2. During the spring of 2006 the star entered a massive outburst. It reached its historical maximum at U ∼ 8.0 in 2006 July. AEAra erupted in 2006 February with Δmvis ∼ 1.2 mag. BF Cyg entered a new active stage in 2006 August. A brightness maximum (U ∼ 9.4) was measured during 2006 September. CH Cyg persists in a quiescent phase. During 2006 June–December a ∼ 2 mag decline in all colours was measured. CI Cyg started a new active phase during 2006 May–June. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A “Combination Nova” Outburst in Z Andromedae: Nuclear Shell Burning Triggered by a Disk Instability

We describe observational evidence for a new kind of interacting-binary-star outburst that involves both an accretion instability and an increase in thermonuclear shell burning on the surface of an accreting white dwarf. We refer to this new type of eruption as a combination nova. In late 2000, the prototypical symbiotic star Z Andromedae brightened by roughly two magnitudes in the optical. We observed the outburst in the radio with the VLA and MERLIN, in the optical both photometrically and spectroscopically, in the far ultraviolet with FUSE, and in the X-rays with both Chandra and XMM. The two-year-long event had three distinct stages. During the first stage, the optical rise closely resembled an earlier, small outburst that was caused by an accretion-disk instability. In the second stage, the hot component ejected an optically thick shell of material. In the third stage, the shell cleared to reveal a white dwarf whose luminosity remained on the order of 10^4 Lsun for approximately one year. The eruption was thus too energetic to have been powered by accretion alone. We propose that the initial burst of accretion was large enough to trigger enhanced nuclear burning on the surface of the white dwarf and the ejection of an optically thick shell of material. This outburst therefore combined elements of both a dwarf nova and a classical nova. Our results have implications for the long-standing problem of producing shell flashes with short recurrence times on low-mass white dwarfs in symbiotic stars.

A Frequency Glitch in an Accreting Pulsar

Frequency glitches have been observed so far only in radio pulsars and anomalous X-ray pulsars. Here we present evidence of a glitch in a neutron star accreting from a Be companion. The transient KS 1947+300 reappeared in 2000 October as a moderately strong X-ray source that exhibited 18.7 s pulsations, leading to an identification with the BATSE source GRO J1948+32, last detected in 1994. We have analyzed Rossi X-Ray Timing Explorer (RXTE) observations taken during the 2000-2001 outburst, as well as additional observations taken during a smaller outburst in 2002 July. Orbital Doppler shifts are apparent in the temporal variation of the pulse frequency. A joint fit of the RXTE data together with BATSE measurements from an outburst in 1994 yields the orbital period Porb = 40.415 ± 0.010 days, the projected orbital radius aX sin i = 137 ± 3 lt-s, and the eccentricity e = 0.033 ± 0.013. This degree of eccentricity is unexpectedly low for such a wide orbit. Pulse timing results also show that the intrinsic pulse frequency increased from 53.30 to 53.47 mHz at a rate approximately proportional to the X-ray flux. This is about the degree of spin-up expected from the accretion torques that must be present when the X-ray luminosity reaches ~1038 ergs s-1. On one occasion during the 2000-2001 outburst, the pulse frequency increased by ~1.8 × 10-6 Hz in 10 hr over and above the mean trend seen around that time, without any indication of a correspondingly large increase in X-ray flux. The fractional change in frequency of 3.7 × 10-5 during this event is significantly larger than the values observed in the glitches in radio pulsars and anomalous X-ray pulsars. We discuss other similarities and differences between these events.

Hot white dwarfs and the UV delay in dwarf novae

ABSTRA C T We calculate the effect of illumination of dwarf nova accretion discs by radiation from a hot, central, white dwarf. We show that, only for very hot white dwarfs (Teff < 40 000 K), the inner regions of quiescent dwarf nova discs are partially depleted so that the delay between the rise to outburst of the optical and UV fluxes would be increased as suggested recently by King. This depletion, however, must create several small outbursts between the main outbursts, contrary to observations. Lower white dwarf temperatures may cause the outbursts to be of the ‘insideout’ type, thus removing the UV delay. We conclude that white dwarf irradiation of dwarf nova discs is not very efficient because, for example, the UV radiation from the hot white dwarf does not penetrate deep enough in the disc atmosphere. The total ablation of the inner disc by, e.g., evaporation (possibly related to illumination) appears to be a very promising possibility, accounting for both the extreme UV (EUV) delay and the general properties of the light curves.

Discovery of a Magnetic White Dwarf in the Symbiotic Binary Z Andromedae

We report the first result from our survey of rapid variability in symbiotic binaries: the discovery of a persistent oscillation at P=1682.6 ± 0.6 s in the optical emission from the prototype symbiotic Z Andromedae. The oscillation was detected on all eight occasions on which the source was observed over a time span of nearly 1 yr, making it the first such persistent periodic pulse found in a symbiotic binary. The amplitude was typically 2-5 mmag, and it was correlated with the optical brightness during a relatively small outburst of the system. The most natural explanation is that the oscillation arises from the rotation of an accreting magnetic (BS105G) white dwarf. This discovery constrains the outburst mechanisms, since the oscillation emission region near the surface of the white dwarf was visible during the outburst.

THE 1994 SUPEROUTBURST OF THE NEW SU UMA-TYPE DWARF NOVA, SX LEONIS MINORIS

ABSTRACT We present observations of SX LMi obtained during the 1994 long outburst at Ouda Station. Superhumps, with a period of 0.06950 (± 0.00002) d, are detected. This confirms SX LMi as a new member of the SU UMa-type dwarf novae. We measured the recurrence cycle of normal outbursts and superoutbursts to be about 35 d and 250 d, repsectively, from outburst records by RoboScope (Indiana University) and amateur observers. These recurrence cycles are typical values for normal SU UMa stars. However, the outburst amplitude (∼3.8 mag) of SX LMi is small for an SU UMa star and close to those of ER UMa stars. This small outburst amplitude might be understood if the viscosity at quiescence and the mass-transfer rate are slightly high in SX LMi.

The Visual Light Curve Of C/1995 O1 (Hale-Bopp) From Discovery To Late 1997

We present a light curve of C/1995 O1 (Hale-Bopp) compiledfrom more than 3000 visual observations of the comet made by members of the The Astronomer Group world-wide. These observations cover the period from discovery through to the end of 1997. The light curve shows that the rate of brightening of the comet varied widely at different times, with rapid rates of brightening at high heliocentric distance pre-perhelion and a comparably rapid post-perihelion fade. There is no evidence that the comet was suffering a large photometric outburst when first discovered, although a small outburst can be identified at perihelion. At least five difficult brightening regimes can be identified in the light curve between discovery and perihelion. From 2.5 AU to perihelion the rate of brightening with decreasing heliocentric distance was typical for “fairly” new comets(n ∼ 3.5, where “n” is the power law exponent of the heliocentric distance), although this was preceded by a period of very slow brightening with n ∼ 1 from r ∼ 4.0 AU to r ∼ 2.8 AU and followed by an initially more rapid brightening which appears to be related to the on-set of rapid water sublimation activity. We derive the light curve parameters at different stages of the comet's apparition.

The peculiar interacting binary V Sagittae: Brightness variations in 1932 – 1994

The analysis of the historical light curve revealed several kinds of variations not connected with the orbital modulation: a) large outbursts consisting of a primary (amplitude about 2 magvis:) and a fainter secondary peak; b) transitions from the high to the low state and vice versa; c) small outbursts (amplitude about 0.7 magvis: )o n the time scale of 15-20 days in the high state; d) year-to-year variations of brightness. It is shown that drastic changes of the photometric activity occurred in the course of the last six decades. An interpretation of this activity in terms of mass transfer events in a strongly interacting binary containing an accreting white dwarf is oered.

A survey for highly variable objects on the SRC-J plates. 1: Faint new cataclysmic variables in the Galactic halo

We present finding charts and spectra of seven new, faint (J approximately 19-21) cataclysmic variables discovered during a deep survey for highly variable objects in the overlapping regions of the SRC-J plates. Four of them are probably members of the halo population. The He II lambda 4686 emission line is strong in two objects. One of them has been confirmed as a member of the AM Her class; its orbital period (2.66 h), well determined by photometry, spectroscopy, and polarimetry, lies within the period gap of cataclysmic variables (CVs). The seven variables have relatively small outburst amplitudes (1.6 mag on average), in contrast with most high latitude cataclysmics studied previously; this indicates that we sample a different sub-population of CVs than previous surveys which may suffer from selection effects.

Mass transfer rate and outburst cycle of SS Cygni

From an analysis of the SS Cygni light curve, we have recently shown (Hempelmann & Kurths 1990) that the rate of mass transfer, M˙ T , from the secondary star to the white dwarf primary is inversely correlated with the outburst cycle, t c . This has been criticized as being of a trivial nature by Cannizzo & Mattei (1992). We demonstrate the nontrivial character of our finding by means of a gedankenexperiment which is based on the static outburst parameters observed. We show in this experiment that a positive M˙ T -t c correlation is possible. The negative correlation found by Hempelmann & Kurths (1990) is a consequence of the dynamics of small and strong outbursts

Z Andromedae: Quiescence and Activity

Z Andromedae, often considered as the prototype of symbiotic stars, experimented, after several years of quiescence, a small outburst in March-April 1984, followed by a larger one in September-October 1985. The imminence of a new activity phase was predicted by Viotti et al. (1982). Z And is, together with AG Draconis, the only symbiotic star observed both during quiescence and activity with the IUE satellite. The early photometric and spectroscopic history of Z And has been recently reviewed by Kenyon (1986).The behaviour of Z And in the ultraviolet during quiescence has been studied by Fernåndez-Castro et al. (1988), on the basis of data obtained by the International Ultraviolet Explorer from 1978 to 1982. In that period of time, the UV continuum and the emission line fluxes varied quasiperidically with a period of about two years, in phase with the Hα variability found by Altamore et al. (1979), with the UBV photometry by Belyakina (1985) and also in agreement with the ephemeris given by Kenyon and Webbink (1984). The electron density derived from Si III/C III] flux ratio, also varied in phase with the UV flux. In particular, a correlation was found between the electron density variations, and the UV continuum flux at 2900 A. This fact, together with the presence of a Balmer jump in emission, indicates that the principal contributor at those wavelengths is nebular emission, mainly free-bound transitions.

Materials for a study in animal competition

The incidence of the sewage fly, Psychoda alternata Say, breeding almost free from other insect competitors in a bacteria bed at Huddersfield is examined. Its general seasonal trend is marked by periods of peak output explained on the theory that there are two successions of generations running persistently and alternating with one another. Such behaviour has previously been demonstrated for another sewage fly, Spaniotoma minima, and has been shown to be instituted by irregular temperatures in autumn and spring. In Psychoda alternata a special type of intraspecific competition is set‐up in the warmer months when the cycles are rapid, for the larvae of one succession must start life in a bed just depleted of food by the other. Therefore large and small outbursts of the fly tend to alternate. The discharges of solids from the bed have a detailed periodicity corresponding to the alternations in the successions of the fly.

Afferent Impulses in the Carotid Sinus and Aortic Nerves.

Afferent impulses in the carotid sinus nerve of the rabbit have been recorded by means of a vacuum tube amplifier and either a string galvanometer or Matthews oscillograph and the arterial pulse curve registered simultaneously with a Wiggers manometer. The experiments show that there is a burst of impulses accompanying each heart cycle followed by comparative inactivity. This discharge is coincident with the rapid rise in arterial pressure revealed by the carotid pulse curve. The duration of the nerve activity extends usually to about the incisura although frequently there are scattered impulses continuing throughout diastole. In some cases there is a second smaller outburst which coincides with the rise in pressure following the incisura. At high blood pressures the discharge becomes continuous, an effect which is likewise produced as a result of asphyxia. The general character of the discharge in the carotid sinus nerve agrees closely with that found in the aortic (cardiac depressor) nerve. The impulses in this nerve have been recorded by Adrian and several other workers and simultaneous records of the impulses and pulse curves have recently been reported by the author. Here, too, there is a large outburst of impulses synchronous with the rapid rise in pressure the major part of the discharge usually continuing to the incisura. The activity of the sensory nerve endings in both the aorta and the carotid sinus appears, on the basis of these experiments, to be a function of both the absolute level of pressure and the rate of change of pressure.