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NASA NTRS1995

Meteor stream activity. 2: Meteor outbursts

In the past two centuries, alert amateur and professional meteor astronomers have documented 35 outbursts of 17 individual meteor streams well enough to allow the construction of a homogeneous set of activity curves. These curves add to similar profiles of the annual streams in a previous paper (Paper 1). This paper attempts to define the type and range of phenomena that classify as meteor outbursts from which the following is concluded: Outbursts are associated with the return of the comet to perihelion (near-comet type outbursts), but occur also when the parent comet is far from perihelion and far from the Earth (far-comet type). All outbursts of a given type only, depending on encounter geometry. The activity curves, expressed in terms of Zenith Hourly Rates (ZHR), have a shape that is generally well described by: ZHR = ZHR(sub max) 10(sup(-B (the absolute value of lambda (sub dot in a circle) - lambda (sup max) (sub dot in a circle))). The steepness of the slopes varies from an exponent of B = 7 to B = 220 per degree of solar longitude, with a typical value of B = 30. In addition, most near-comet type outbursts have a broader component underlying the main peak with B approximately 1 - 7.The duration Delta t is approximately 1/B of the main peak is almost independent of location near the comet, while the background component varies considerably in duration and relative intensity from one return to another. The two components in the activity curve are due to two distinct structures in the dust distribution near the parent comet, where the main component can be due to a sheet of dust that emanates from the IRAS dust trail. This brings the total number of distinct structures in meteor streams to four, including the two structures from the annual stream activity in Paper 1.

Jenniskens, P.↗
NASA NTRS1995

The cooling of the white dwarf in U Geminorum following heating by two different outbursts

We present the analysis of 13 orbital phase-resolved IUE (large and small aperture) SWP spectra, sampling the quiescent intervals of the proptotype dwarf nova U Geminorum following two individual outbursts, the outburst of 1992, 29 August-14 September, and the outburst of 1993, 19 March-5 April. The quiescent interval following the outburst 29 August 1992 is the longest ever recorded. During quiescence, the photospheric radiation of the exposed white dwarf dominates the far ultrviolet. The variations in absorption line strengths and continum flux levels are analyzed as a function of both orbital phase and elapsed time, since the return to optical quiescence, by fitting the IUE spectra with a grid of high gravity, LTE, model atmospheres with solar composition constructed with TLUSTY and SYNSPEC (Hubeny, I. Tlusty and Synnspec: A Users Guide (1994)). We present evidence from both absorption line variations and continuum variations, as a function of time since the outbursts, that the white dwarf photosphere has cooled by several thousand degrees. Within the signal-to-noise limitations, we find no evidence of a difference in heating and cooling between the two outbursts.

Huang, Min↗
NASA NTRS1997

Effects of FU Orionis Outbursts on Protoplanetary Disks

In the early stages of work under this grant, we developed simulations to match the light curves of the three best studied systems: FU Ori, V1515 Cyg, & V1057 Cyg (Bell et al. 1995). We compared the details of model results to observations to test the validity of the thermal ionization instability model for outburst. In this paper, we were able to answer several of the key objections to the accretion disk outburst model for the FU Orionis phenomenon (eg. Herbig 1989). The declines in line width and reddening observed in V1057 Cyg following peak light had been used as arguments against the disk instability model. We showed these effects to be natural consequences of the slow outward progression and limited radial excursion of the ionization front during outburst. By the end of the grant period, we had begun combining the inner and outer disk models to derive the radiation expected in the planet forming region of the disk. A crucial step in this was the development of a radiative transfer model of the complete inner and outer disk system (Turner, Bodenheimer, & Bell 1997). In this work, wavelength dependent opacities were used to synthesize images and spectral energy distributions of FU Ori objects. New detailed opacities provided by Alexander (1995) allowed the resolution of coarse features such as silicate emission lines. Data for the fits were taken from the time dependent simulations in Bell et al. (1995) to which was added the effect of disk to disk or "self"-reprocessing which accounts for the illumination of the outer disk by the inner disk (Bell 1998). Through the course of work on this grant we have made considerable progress in computing detailed models of both the active outburst region of the disk and the outer quiescent disk. We have begun an investigation into the effects of a cocooning envelope. Direct comparisons with observations lend confidence that the basic underlying assumptions of the outburst model are reasonable. We are now ready to build upon these results to investigate the effects of outbursts on the central star and on the accumulation of small particles in the planet-forming regions.

Bodenheimer, Peter↗
NASA NTRS1999

Hard X-Ray Variability of the Black Hole Candidate GRO J0422+32 During its 1992 Outburst

We have studied the hard X-ray variability of the soft X-ray transient GRO J0422+32 with BATSE (Burst and Transient Source Experiment) in the 20-100 keV energy band. Our analysis covers 180 days following the first X-ray detection of the source on August 5, 1992, fully covering its primary and secondary X-ray outbursts. We compute power density spectra (PDSs) in the 20-50, 50-100, and 20-100 keV energy bands, in the frequency interval 0.002-0.488 Hz. The PDSs of GRO J0422+32 are approximately flat up to a break frequency, and decay as a power law above it, with index approximately 1. During the first 70 days of the X-ray outburst, the PDSs of GRO J0422+32 show a significant quasi-periodic oscillation (QPO) peak near approximately 0.2 Hz, superposed on the power-law tail. The break frequency of the PDSs obtained during the primary X-ray outburst of GRO J0422+32 occurs at 0.041 +/- 0.006 Hz; during the secondary outburst, the break is at 0.081 +/- 0.015 Hz. The power density at the break ranged between 44% and 89% / square root of Hz (20-100 keV). The canonical anticorrelation between the break frequency and the power density at the break, observed in Cyg X-1 and other BHCs in the low state, is not observed in the PDSs of GRO J0422+32. We compare our results with those of similar variability studies of Cyg X-1. The relation between the spectral slope and the amplitude of the X-ray variations of GRO J0422+32 is similar to that of Cyg X-1; however, the relation between the hard X-ray flux and the amplitude of its variation is opposite to what has been found in Cyg X-1. Phase lags between the X-ray flux variations of GRO J0422+32 at high and low photon energies could only be derived during the first 30 days of its outburst. During this period, the variations in the 50-100 keV band lag those in the 20-50 keV energy band by an approximately constant phase difference of 0.039(3) rad in the frequency interval 0.02-0.20 Hz. The time lags of GRO J0422+32 during the first 30 days of the outburst decrease with frequency as a power law with index 0.9 for v > 0.01 Hz.

vanderHooft, F.↗
NASA NTRS1999

The Outbursts and Orbit of the Accreting Pulsar GS 1843 - 02 = 2S 1845 - 024

We present observations of a series of 10 outbursts of pulsed hard X-ray flux from the transient 10.6 mHz accreting pulsar GS 1843-02, using the Burst and Transient Source Experiment on the Compton Gamma Ray Observatory. These outbursts occurred regularly every 242 days, coincident with the ephemeris of the periodic transient GRO J1849-03, which has recently been identified with the SAS 3 source 2S 1845-024. Our pulsed detection provides the first clear identification of GS 1843-02 with 2S 1845-024. We present a pulse timing analysis that shows that the 2S 1845-024 outbursts occur near the periastron passage of the neutron star's highly eccentric (e = 0.88 +/- 0.01) 242.18 +/- 0.01 day period binary orbit about a high-mass (M(sub c) greater than 7 solar mass) companion. The orbit and transient outburst pattern strongly suggest that the pulsar is in a binary system with a Be star. Our observations show a long-term spin-up trend, with most of the spin-up occurring during the outbursts. From the measured spin-up rates and inferred luminosities we conclude that an accretion disk is present during the outbursts.

Finger, Mark H.↗
NASA NTRS1998

The Outbursts and Orbit of the Accreting Pulsar GS 1843-02=2S 1845-024

We present observations of a series of 10 transient outbursts of pulsed hard x-ray flux from the 10.6 mHz accreting pulsar GS 1843-02 using the Burst and Transient Source Experiment (BATSE) on the Compton Observatory. These outbursts occurred regularly every 242 days, coincident with the ephemeris of the periodic transient GRO J1849-03 (Zhang et al. 1996)), which has recently been identified with the the SAS 3 source 2S 1845-024 (Soffitta et al. 1998). Our pulsed detection provides the first clear identification of GS 1843-02 with 2S 1845-024. We present a pulse timing analysis which shows that the 2S 1845-024 outbursts occur near the periastron passage of a highly eccentric (e = 0.88 q 0.01) 242.18 +/- 0.01 day period binary orbit about a high mass (M(sub opt) > 7 solar mass companion. The orbit and transient outburst pattern suggest a Be star/X-ray pulsar system, however the optical companion is unknown. Our observations show a long-term spin-up trend, with most of the spin-up occurring during the outbursts. From the measured spin-up rates and inferred mass accretion rates we conclude that an accretion disk is present during the outbursts.

Finger, Mark H.↗
NASA NTRS2011

The Be/X-Ray Binary A0535+26 During Its Recent 2009/2010 Outbursts

The Be/X-ray binary A0535+26 showed a giant outburst in December 2009 that reached approximately 5.14 Crab in thc 15-50 keV range. Unfortunately, due to Sun constraints it could not be observed by most X-ray satellites. The outburst was preceded by four weaker outbursts associated with the periastron passage of the neutron star. The fourth of them, in August 2009, presented a peculiar double-peaked light curve, with a first peak lasting about 9 days that reached a (15- 50 keV) flux of 440 mCrab. The tl ux then decreased to less than 220 mCrab, and increased again reaching 440 mCrab around the periastron. The outburst was monitored with INTEGRAL, RXTE, and Suzaku TOO observations. One orbital period (approximately 111 days) after the 2009 giant outburst, a new and unexpectedly bright outburst took place (approximately 1.4Crab in the 15-50 keV range). It was monitored with TOO observations with INTEGRAL, RXTE, Suzaku, and Swift. First results of the spectral and timing analysis of these observations are presented. with a specific focus on the cyclotron lines present in thc system and its variation with the mass accretion rate.

Caballero, I.↗
NASA NTRS2011

The Spectroscopic Evolution of the Symbiotic-like Recurrent Nova V407 Cygni During Its 2010 Outburst. 2. The Circumstellar Environment and the Aftermath

The nova outburst of V407 Cyg in 2010 Mar. 10 was the first observed for this star but its close resemblance to the well known symbiotic-like recurrent nova RS Oph suggests that it is also a member of this rare type of Galactic novae. The nova was the first detected at gamma-ray energies and is the first known nova explosion for this system. The extensive multiwavelength coverage of this outburst makes it an ideal comparison with the few other outbursts known for similar systems. We extend our previous analysis of the Mira and the expanding shock from the explosion to detail the time development of the photoionized Mira wind, circumstellar medium, and shocked circumstellar environment to derive their physical parameters and how they relate to large scale structure of the environment, extending the previous coverage to more than 500 days after outburst. We use optical spectra obtained at high resolution with the Nordic Optical Telescope (NOT) (R approx. =.45000 to 65000) and medium resolution Ondrejov Observatory (R approx. = 12000) data and compare the line variations with publicly available archival measurements at 30 GHz OVNR and at X-rays with Swift during the first four months of the outburst, through the end of the epoch of strong XR emission. We use nebular diagnostics and high resolution profile variations to derive the densities and locations of the extended emission. We find that the higher the ionization and/or the higher the excitation energy, the more closely the profiles resemble the He II/Ca V-type high velocity shock profile discussed in Paper I. This also accounts for the comparative development of the [N II] and [O III] isoelectronic transitions: the [O III] 4363A profile does not show the low velocity peaks while the excited [N II] 5754A does. If nitrogen is mainly N(+3) or higher in the shock, the upper state of the [N II] nebular lines will contribute but if the oxygen is O(+2) then this line is formed by recombination, masking the nebular contributor, and the lower states are collisionally quenched but emit from the low density surroundings. Absorption lines of Fe-peak ions formed in the Mira wind were visible as P Cyg profiles at low velocity before Day 69, around the time of the X-ray peak and we identified many absorption transitions without accompanying emission for metal lines. The H Balmer lines showed strong P Cyg absorption troughs that weakened during the 2010 observing period, through Day 128. The Fe-peak line profiles and flux variations were different for permitted and forbidden transitions: the E1 transitions were not visible after Day 128 but had shown a narrow peak superimposed on an extended (200 km/s) blue wing, while the M1 and E2 transitions persisted to Day 529, the last observation, and showed extended redshifted wings up of the same velocity. We distinguish the components from the shock, the photoionized environment, and the chromosphere and inner Mira wind using spectra taken more than one year after outburst. The multiple shells and radiative excitation phenomenology are similar to those recently cited for GRBs and SNIa .

Shore, S. N.↗
NASA NTRS1974

CNO abundances and hydrodynamic models of the nova outburst. II - 1.00 solar mass models with enhanced carbon and oxygen

Results of a computation of a variety of evolutionary sequences involving thermonuclear runaways in the hydrogen-rich envelopes of 1.00-solar-mass carbon-oxygen white dwarfs. The evidence concerning the location of the outburst in the nova system is reexamined, and it is concluded that the white dwarf is the seat of the outburst. An order-of-magnitude argument is presented which indicates that for a 1.00-solar-mass white dwarf it is impossible to achieve mass ejection without an energy generation of approximately 10 to the 16th ergs/g/sec. A description is given of models with low nuclear enhancements that do not produce an outburst, although their evolution has certain implications for the cause of the dwarf-nova outburst. The results for models that produced a nova outburst are then presented, and on the basis of these results it is found possible to explain continuous ejection, Kukarkin and Parenago's (1934) relationship, and other gross features of the nova phenomena.

Starrfield, S.↗
NASA NTRS1976

The cause of the nova outburst

A large number of models are evolved for thermonuclear runaways in the hydrogen-rich envelopes of 1.00-solar-mass carbon-oxygen white dwarfs. Models characterized by enhanced CNO abundances satisfy the observations of the common nova outburst, ejecting from 10 to the 27th to 10 to the 29th power g at velocities of 200 to 2400 km/s and kinetic energies of 10 to the 44th to 10 to the 45th power erg. The theoretical light curves are similar to the observed light curves of common novae during the early stages of the outbursts. Explanations are given for the continuous ejection of mass which is observed for long times after the initial outbursts, for the relationship between maximum magnitude and the decline to minimum, and for the constant luminosity phase of the outburst and the oval shapes of the ejected nebulae. The analysis is extended to models with extreme enhancements of C-12 and to models which include infalling material in the evolution. The extreme C-12 studies result in outbursts which reach near-supernova proportions, while the accretion models result in light curves which resemble observed light curves quite closely. The accretion studies also demonstrate the need for enhanced abundances.

Starrfield, S.↗
NASA NTRS1977

CNO nucleosynthesis and the nova outburst

Predictions for CNO nucleosynthesis by the classical nova outburst are presented. Properties of the nova phenomenon pertinent to the production of CNO isotopes are discussed, the effect of beta(+) unstable nuclei on outburst evolution is examined, and the need for enhanced CNO nuclei in the envelope is described. Possible mechanisms for producing such enhancement are considered, and recent observations of enhanced CNO nuclei in nova ejecta are reviewed. Results of model evolutionary calculations are outlined which show that a thermonuclear runaway in the hydrogen envelope of a carbon-oxygen white dwarf can reproduce the gross features of the classical nova outburst, that the behavior of the outburst depends at least on the hydrogen-envelope mass and the degree of CNO enhancement, and that all degrees of isotopic enhancement result in an outburst that may be compared with observed events. Two enhancement mechanisms are identified, both of which involve mixing in the envelope.

Starrfield, S.↗
NASA NTRS1985

High-speed photometry of Z Chamaeleontis covering the 1983 March normal outburst

High-speed photometry over a three-week period covering the Mar. 13, 1983 normal outburst of Z Cha is presented. Multicolor observations revealed significant reddening during eclipse in both the quiescent and outburst states. Quiescent primary eclipse timings remained consistent with an increasing orbital period. Hotspot eclipse timings revealed that the accretion disk had physically expanded in radius after the outburst. The duration of the eclipse during outburst, however, limited the optical emission to a region bounded by the radius of the preoutburst accretion disk. In the final stages of decline this emission region had shrunk in size by a factor of approximately 4. The postoutburst observations showed the hotspot eclipse to be less stable in structure compared to before the outburst.

Cook, M. C.↗
NASA NTRS1985

Multifrequency observations of dwarf novae outbursts

Studies using EXOSAT and IUE data combined with ground-based optical and IR photometry, spectroscopy and polarimetry of the transition timescales and physical properties of the high accretion rate states of the disks in cataclysmic variables are discussed. Implications for dwarf novae stem from comparison of the timing and amplitude of the optical and IR rise with that of the UV and X-ray; the development of the optical and UV line profile changes as the outburst develops; and the similarity of the outburst flux distributions in different systems and different types of outbursts (standstills and supermaxima). These features of dwarf novae outbursts present interesting comparisons with the outbursts of systems like TV Col and GK Per.

Szkody, P.↗
NASA NTRS1992

UV spectroscopy of Z Chamaeleontis. II - The 1988 January normal outburst

IUE observations taken during the 1988 January normal outburst of Z Cha are presented and a detailed comparison with the 1987 April superoutburst is made. The most important difference from the superoutburst is that the normal outburst continuum flux shows less than 10 percent orbital variation away from the eclipse, implying that there is no 'cool' bulge on the disk to occult the brighter inner disk periodically. The implications for the outburst mechanism in the types of outburst are discussed. The evolution of the continuum flux distribution and emission-line fluxes, the modulation of the continuum and line fluxes with orbital phase, and the behavior of the mideclipse spectral during normal outburst are investigated.

Harlaftis, E. T.↗
NASA NTRS1993

An April 1991 outburst from 4U0115+63 observed by BATSE

4U0115+63 is a recurrent transient X-ray pulsar in a moderately eccentric orbit with a Be star companion, V635 Cas. Many outbursts from this system have been reported over the past twenty years; yet despite the apparent relation between optical outbursts from the companion star and subsequent X-ray transient events, the physical mechanism for the mass transfer in the system remains unclear. In this paper, we present the preliminary results of analysis of observations made using BATSE during the 1991 April outburst from this system. This outburst does not fit the pattern of three year recurrence intervals previously suggested by Whitlock, Roussel-Dupre and Priedhorsky (1989). The orbital elements of the system have been updated and do not support the claim of Tamura et al., (1992) that apsidal motion was detected in this system based on the 1990 Ginga outburst.

Cominsky, Lynn↗
NASA NTRS1994

Disk instability and the spectral evolution of the 1992 outburst of the intermediate polar GK Persei

The disk instability model can explain the previous history of dwarf-nova-like outbursts in the intermediate polar GK Per, which occur about once every three years. Disk models that reproduce the recurrence time and outburst light curves suggest that GK Per has a large effective inner disk radius (approx. 30-40 white dwarf radii) truncated by a strong magnetic field (10(exp 7) G). In this context, the effective radius is that of the portion of the disk that participates in the disk thermal instability. The radius derived is larger than the corotation radius, which must be an upper limit on the true dynamical inner radius of the disk. Disk instability models with this large effective inner radius predict that the ultraviolet continuum should be rather flat. Here we compare the predictions of the disk instability model to IUE observations of the 1981 outburst and to IUE and ROSAT observations of the recent 1992 outburst of GK Per. The model disk continuum spectral evolution is consistent with the observed UV and optical spectra, especially at maximum and in the early decay phase of the outburst. The consistency of the model with the observed UV spectra suggests that the effective inner radius of the disk is almost constant, independent of mass accretion rate, and that whatever structure lies between the effective inner radius and the corotation radius neither participates in the disk instability nor radiates substantially in the UV. The related physics of the inner disk region will be briefly discussed.

Kim, S.-W.↗
NASA NTRS1999

Properties of the Second Outburst of the Bursting Pulsar (GRO J1744-28) as Observed with BASTE

One year after its discovery, the Bursting Pulsar (GRO J1744-28) went into outburst again, displaying the hard X-ray bursts and pulsations that make this source unique. We report on BATSE (Burst and Transient Source Experiment) observations of both the persistent and burst emission for this second outburst and draw comparisons with the first. The second outburst was smaller than the first in both duration and peak luminosity. The persistent flux, burst peak flux, and burst fluence were all reduced in amplitude by a factor of approximately 1.7. Despite these differences, the two outbursts were very similar with respect to the burst occurrence rate, the durations and spectra of bursts, the absence of spectral evolution during bursts, and the evolution of the ratio alpha of average persistent to burst luminosity. Although no spectral evolution was found within individual bursts, we find evidence for a small (20%) variation of the spectral temperature during the course of the second outburst.

Woods, Peter M.↗
NASA NTRS1999

Black Hole X-Ray Nova Outburst with XTE and HST

We obtained multiwavelength coverage of the soft X-ray transient GRO J1655-40 during its 1996 outburst, using HST, RXTE, CGRO, and ground-based facilities. This outburst was qualitatively different from other SXT outbursts and from previous outbursts of this source. The onset of hard X-ray activity occurred very slowly, over several months, and was delayed relative to the soft X-ray rise. During this period, the optical fluxes declined steadily. This apparent anticorrelation is not consistent with with the standard disk instability model of SXT outbursts, nor is it expected if the optical output is dominated by reprocessed X-rays, as in persistent low-mass X-ray binaries. .

Patterson, Joseph↗