arXiv subjects

C. D. Bailyn

Publications and source records attributed to C. D. Bailyn.

33 records · Page 2Linked to original sources

arXiv2004

Discovery of a supernova associated with GRB 031203: SMARTS Optical-Infrared Lightcurves from 0.2 to 92 days

Optical and infrared monitoring of the afterglow site of gamma-ray burst (GRB) 031203 has revealed a brightening source embedded in the host galaxy, which we attribute to the presence of a supernova (SN) related to the GRB ("SN 031203"). We present details of the discovery and evolution of SN 031203 from 0.2 to 92 days after the GRB, derived from SMARTS consortium photometry in I and J bands. A template type Ic lightcurve, constructed from SN 1998bw photometry, is consistent with the peak brightness of SN 031203 although the lightcurves are not identical. Differential astrometry reveals that the SN, and hence the GRB, occurred less than 300 h_71^-1 pc (3-sigma) from the apparent galaxy center. The peak of the supernova is brighter than the optical afterglow suggesting that this source is intermediate between a strong GRB and a supernova.

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arXiv2004

Optical-Infrared ANDICAM Observations of the Transient Associated with GRB 030329

We present photometry of the transient associated with GRB 030329 obtained with the CTIO 1.3--meter telescope and the ANDICAM instrument, a dual optical/infrared imager with a dichroic centered at one micron. Without the need for light curve interpolation to produce snapshot broadband spectra, we show that the transient spectrum remained statistically achromatic from day 2.7 to day 5.6, during a re-brightening episode. Associating the light in these early epochs with the GRB afterglow, we infer a modest level of extinction due to the host galaxy in the line--of--sight toward the GRB: A_V(host) = 0.30 +/- 0.03 mag for beta = -0.5 and A_V(host) < 0.4 mag (3 sigma) for any physically plausible value of beta (with flux f_nu ~ lambda^-beta). We conclude that the spectral slope of the afterglow component was more than beta = -0.8 between day 2.7-5.6 after the GRB, excluding the possibility that the synchrotron cooling break passed through the optical/IR bandpass over that period. Taking extinction into account, a decomposition of the light curve into an afterglow and supernova component requires the presence of a supernova similar to that of SN 1998bw, an afterglow that shows some evidence for a second break around day 8-10, and a fifth re-brightening event around day 15. Assuming an SN 1988bw-like evolution and a contemporaneous GRB and SN event, the peak SN brightness was M_V = -19.8 +/- 0.4 - 5 log h_65 mag.

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arXiv2004

The detailed optical light curve of GRB 030329

(Abridged) We present densely sampled BVRI light curves of the optical transient associated with the gamma-ray burst GRB 030329, the result of a coordinated observing campaign conducted at five observatories. Augmented with published observations of this GRB, the compiled optical dataset contains 2687 photometric measurements, obtained between 78 minutes and 79 days after the burst. We show that the underlying supernova 2003dh evolved faster than, and was probably somewhat fainter than the type Ic SN 1998bw, associated with GRB 980425. We find that our data can be described by a broken power-law decay perturbed by a complex variable component. The early- and late-time decay slopes are determined to be ~1.1 and ~2, respectively. Assuming this single power-law model, we constrain the break to lie between ~3 and ~8 days after the burst. This simple, singly-broken power-law model, derived only from the analysis of our optical observations, may also account for available multi-band data, provided that the break happened ~8 days after the burst. The more complex double-jet model of Berger et al. provides a comparable fit to the optical, X-ray, mm and radio observations of this event. We detect a significant change in optical colors during the first day. Our color analysis is consistent with a cooling break frequency sweeping through the optical band during the first day. The light curves of GRB 030329 reveal a rich array of variations, superposed over the mean power-law decay. We find that the early variations are asymmetric, with a steep rise followed by a relatively slower (by a factor of about two) decline. The variations maintain a similar time scale during the first four days, and then get significantly longer.

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arXiv2004

Evolution of Spectral States of Aql X-1 during the 2000 Outburst

We present the results of detailed analysis of X-ray data in 3-20 keV range from a ~70 day outburst of the neutron star transient Aquila X-1 during September-November 2000. Optical monitoring with the YALO 1m telescope was used to trigger X-ray observations with Rossi X-ray Timing Explorer (RXTE) in order to follow the outburst from a very early stage. In this paper we discuss the correlated evolution in time of features in the spectral and temporal domains, for the entire outburst. The state transition from low/hard state to high/soft state during the rise of the outburst occurs at higher luminosity than the transition back to low/hard state during the decay, as has also been observed in other outbursts. Fourier power spectra at low frequencies show a broken power law continuum during the rising phase, with the break frequency increasing with time. During the decline from maximum the source evolves to a position in the hardness-intensity plane as well as in the color-color diagram which is similar to, but distinct from, the canonical high/soft state. High frequency quasi-periodic oscillations from 636-870 Hz were seen only during this transitional state.

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arXiv2003

Can high-velocity stars reveal black holes in globular clusters?

We estimate the number of individual, fast-moving stars observable in globular clusters under the assumption that the clusters contain massive central black holes which follow the galactic black-hole mass vs. sigma relationship. We find that radial velocity measurements are unlikely to detect such stars, but that proper motion studies could reveal such stars, if they exist, in the most likely clusters. Thus, HST proper motion studies can test this hypothesis in a few nearby clusters.

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arXiv2003

Central Proper-Motion Kinematics of NGC 6752

We present proper motions derived from WFPC2 imaging for stars in the core of the peculiar globular cluster NGC 6752. The central velocity dispersion in both components of the proper motion is 12 km/s. We discuss the implications of this result as well as the intrinsic difficulties in making such measurements. We also give an alternative correction for the 34-row problem in the WFPC2 CCDs.

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arXiv2001

A Closer Look at the Soft X-ray Transient X1608-52: Long-term Optical/X-ray Observations

We report long-term simultaneous optical and (RXTE) X-ray observations of the soft X-ray transient and low mass X-ray binary X1608-52 spanning from 1999 to 2001. In addition to the usual X-ray outburst and quiescent states, X1608-52 also exhibits an extended low intensity state during which the optical counterpart, QX Nor, is found to be about two magnitudes brighter than during quiescence. We detect optical photometric variability on a possible period of 0.5370 days with a semi-amplitude of ~0.27 mag in the I band. The modulation could be orbital but is also consistent with a scenario invoking a superhump with decreasing period. Observations of QX Nor during quiescence indicate an F to G type main sequence secondary while theoretical considerations argue for an evolved mass donor. Only an evolved mass donor would satisfy the condition for the occurrence of superhumps.

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arXiv2001

Multiwavelength Observations of the Black Hole Candidate XTE J1550-564 during the 2000 Outburst

We report optical, infrared, and X-ray light curves for the outburst, in 2000, of the black hole candidate XTE J1550-564. We find that the start of the outburst in the H and V bands precedes that seen in the RXTE All Sky Monitor by 11.5 +/- 0.9 and 8.8 +/- 0.6 days, respectively; a similar delay has been observed in two other systems. About 50 days after the primary maxima in the VIH light curves, we find secondary maxima, most prominently in H. This secondary peak is absent in the X-ray light curve, but coincides with a transition to the low/hard state. We suggest that this secondary peak may be due to non-thermal emission associated with the formation of a jet.

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arXiv2001

X-ray states and radio emission in the black hole candidate XTE J1550-564

We report on radio and X-ray observations of the black hole candidate (BHC) XTE J1550-564 performed during its 2000 X-ray outburst. Observations have been conducted with the Australia Telescope Compact Array (ATCA) and have allowed us to sample the radio behavior of XTE J1550-564 in the X-ray Low Hard and Intermediate/Very High states. We observed optically thin radio emission from XTE J1550-564 five days after a transition to an Intermediate/Very High state, but we observed no radio emission six days later, while XTE J1550-564 was still in the Intermediate/Very High state. In the Low Hard state, XTE J1550-564 is detected with an inverted radio spectrum. The radio emission in the Low Hard state most likely originates from a compact jet; optical observations suggest that the synchrotron emission from this jet may extend up to the optical range. The total power of the compact jet might therefore be a significant fraction of the total luminosity of the system. We suggest that the optically thin synchrotron radio emission detected five days after the transition to the Intermediate/Very High state is due to a discrete ejection of relativistic plasma during the state transition. Subsequent to the decay of the optically thin radio emission associated with the state transition, it seems that in the Intermediate/Very High state the radio emission is quenched by a factor greater than 50, implying a suppression of the outflow. We discuss the properties of radio emission in the X-ray states of BHCs.

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arXiv1999

X-ray Nova XTE J1550-564: Discovery of a QPO Near 185 Hz

We have investigated the X-ray timing properties of XTE J1550-564 during 60 RXTE PCA observations made between 1998 September 18 and November 28. We detect quasi-periodic oscillations (QPOs) near 185 Hz during four time intervals. The QPO widths (FWHM) are near 50 Hz, and the rms amplitudes are about 1% of the mean flux at 2-30 keV. This is the third Galactic black hole candidate known to exhibit a transient X-ray timing signature above 50 Hz, following the 67 Hz QPO in GRS1915+105 and the 300 Hz QPO in GRO J1655-40. However, unlike the previous cases, which appear to show stationary frequencies, the QPO frequency in XTE J1550-564 must vary by at least 10% to be consistent with observations. The occurrences and properties of the QPO were insensitive to large changes in the X-ray intensity (1.5 to 6.8 Crab). However, the QPO appearance was accompanied by changes in the energy spectrum, namely, an increase in the temperature and a decrease in the normalization of the thermal component. The QPO is also closely related to the hard X-ray power-law component of the energy spectrum since the fractional amplitude of the QPO increases with photon energy. The fast QPOs in accreting black hole binaries are thought to be effects of general relativity; however, the relevance of the specific physical models that have been proposed remains largely uncertain. Low frequency QPOs in the range 3-13 Hz were often observed. Occasionally at high luminosity the rms QPO amplitude was 15% of the flux, a level previously reached only by GRS1915+105.

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arXiv1999

X-ray Nova XTE J1550-564: RXTE Spectral Observations

Excellent coverage of the 1998 outburst of the X-ray Nova XTE J1550-564 was provided by the Rossi X-ray Timing Explorer. XTE J1550-564 exhibited an intense (6.8 Crab) flare on 1998 September 19 (UT), making it the brightest new X-ray source observed with RXTE. We present a spectral analysis utilizing 60 Proportional Counter Array spectra from 2.5-20 keV spanning 71 days, and a nearly continuous All Sky Monitor light curve. The spectra were fit to a model including multicolor blackbody disk and power-law components. XTE J1550-564 is observed in the very high, high/soft, and intermediate canonical outburst states of Black Hole X-ray Novae.

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arXiv1999

X-ray Nova XTE J1550-564: Optical Observations

We report the identification of the optical counterpart of the X-ray transient XTE J1550-564 described in two companion papers by Sobczak et al (1999) and Remillard et al (1999). We find that the optical source brightened by approximately 4 magnitudes over the quiescent counterpart seen at B~22 on a SERC survey plate, and then decayed by approximately 1.5 magnitudes over the 7 week long observation period. There was an optical response to the large X-ray flare described by Sobczak et al (1999), but it was much smaller and delayed by roughly 1 day.

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arXiv1998

RXTE Observations of 0.1-300 Hz QPOs in the Microquasar GRO J1655-40

We have investigated 52 RXTE pointed observations of GRO J1655-40 spanning the X-ray outburst that commenced on 1996 April 25 and lasted for 16 months. Our X-ray timing analyses reveal four types of QPOs: three with relatively stable central frequencies at 300 Hz, 9 Hz, and 0.1 Hz, and a fourth that varied over the range 14-28 Hz. The 300 Hz and 0.1 Hz QPOs appear only at the highest observed luminosities (Lx > 0.15 Ledd), where the power-law component dominates the X-ray spectrum. At lower luminosity, the disk flux exceeds the power-law flux and only two of the QPOs are observed: the spectrally "soft" 9 Hz QPO, and the narrow, "hard" QPO that varies from 14-28 Hz as the hard flux decreases. The 300 Hz QPO is likely to be analogous to the stationary QPO at 67 Hz seen in the microquasar GRS1915+105. We discuss models of these high-frequency QPOs which depend on effects due to general relativity. The 9 Hz QPO displays a spectrum consistent with a thermal origin, but this frequency does not appear to be consistent with any of the natural time scales associated with the disk, or with the inferred values of the mass and rapid spin of the black hole. The mechanism for the 14-28 Hz QPOs appears to be linked to the power-law component, as do the 1-10 Hz QPOs in GRS1915+105. Finally, we show data for GRO J1655-40 and GRS1915+105 as each source teeters between relative stability and a state of intense oscillations at 0.1 Hz. A comparison of the sources' spectral parameters allows us to speculate that the black hole mass in GRS1915+105 is very large, possibly in the range 39-70 Msun.

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arXiv1996

The Quadruple Gravitational Lens PG1115+080: Time Delays and Models

Optical photometry is presented for the quadruple gravitational lens PG1115+080. A preliminary reduction of data taken from November 1995 to June 1996 gives component ``C'' leading component ``B'' by 23.7+/-3.4 days and components ``A1'' and ``A2'' by 9.4 days. A range of models has been fit to the image positions, none of which gives an adequate fit. The best fitting and most physically plausible of these, taking the lensing galaxy and the associated group of galaxies to be singular isothermal spheres, gives a Hubble constant of 42 km/s/Mpc for Omega=1, with an observational uncertainty of 14%, as computed from the B-C time delay measurement. Taking the lensing galaxy to have an approximately E5 isothermal mass distribution yields H0=64 km/sec/Mpc while taking the galaxy to be a point mass gives H0=84 km/sec/Mpc. The former gives a particularly bad fit to the position of the lensing galaxy, while the latter is inconsistent with measurements of nearby galaxy rotation curves. Constraints on these and other possible models are expected to improve with planned HST observations.

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arXiv1994

A Possible Optical Counterpart for the Triple Pulsar System PSR B1620-26

We have searched deep optical images of the globular cluster M4 for a possible optical counterpart for the third body in the PSR B1620-26 system. We identify as a possible optical counterpart a star located within $0.3''$ of the nominal pulsar position with $V\approx 20$. This magnitude is consistent with a main sequence cluster member with $M\approx 0.45M_\odot$. However, this star may be blended with fainter stars, and the probability of a chance superposition is non-negligible.

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