arXiv subjects

M. F. Bode

Publications and source records attributed to M. F. Bode.

At least 127 records · Page 7Linked to original sources

arXiv2005

The Early (<1 hr) Multi-Color Afterglow of GRB 050502a: Possible Evidence for a Uniform Medium with Density Clumps

The 2-m robotic Liverpool Telescope reacted promptly to the gamma-ray burst GRB 050502a discovered by INTEGRAL and started observing 3 min after the onset of the GRB. The automatic identification of a bright afterglow of r'~15.8 triggered for the first time an observation sequence in the BVr'i' filters during the first hour after a GRB. Observations continued for ~1 day using the RoboNet-1.0 network of 2-m robotic telescopes. The light curve in all filters can be described by a simple power law with index of 1.2 +/- 0.1. We find evidence for a bump rising at t~0.02 days in all filters. From the spectrum and the light curve we investigate different interpretative scenarios and we find possible evidence for a uniform circumburst medium with clumps in density, as in the case of GRB 021004. Other interpretations of such bumps, such as the effect of energy injection through refreshed shocks or the result of a variable energy profile, are less favored. The optical afterglow of GRB 050502a is likely to be the result of slow electron cooling with the optical bands lying between the synchrotron peak frequency and the cooling frequency.

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arXiv2005

Rotational velocities of the giants in symbiotic stars: I. D'-type symbiotics

We have measured the rotational velocities (v.sini) of the mass donors in a number of D'--type symbiotic stars, using the cross-correlation function method. Four from five D' symbiotic stars with known v.sini, appeared to be very fast rotators compared with the catalogues of v.sini for the corresponding spectral types. At least three of these stars rotate at a substantial fraction (>=0.5) of the critical velocity. This means that at least in D'-type symbiotics the cool components rotate faster than isolated giants. If these binary stars are synchronized, their orbital periods should be relatively short (4-60 days). We also briefly discuss the possible origin of the rapid rotation and its connection with mass loss and dust formation.

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arXiv2005

Emission line variability of RS Ophiuchi

We report that the H_alpha emission line of RS Oph was strongly variable during our 2004 observations on a time scale of 1 month. The line consisted of both a double peaked central narrow component (FWHM ~ 220 km/s) and a strongly variable broad one (FWHM ~ 2000 km/s). The base of the H_alpha line was very broad with FWZI 4600 km/s on all spectra from 1986 to 2004. The variability of the broad component extends from -2000 to +2000 km/s. Most probably this is due to either blobs ejected from the white dwarf (with a typical blob mass estimated to be ~10^{-10} M_solar or a variable accretion disk wind. We also detected variability of the HeII4686 line on a time scale shorter than 1 day. The possible origin is discussed.

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arXiv2005

Early GRB Optical and Infrared Afterglow Observations with the 2-m Robotic Liverpool Telescope

We present the first optical observations of a Gamma Ray Burst (GRB) afterglow using the 2-m robotic Liverpool Telescope (LT), which is owned and operated by Liverpool John Moores University and situated on La Palma. We briefly discuss the capabilities of LT and its suitability for rapid follow-up observations of early optical and infrared GRB light curves. In particular, the combination of aperture, site, instrumentation and rapid response (robotic over-ride mode aided by telescope's rapid slew and fully-opening enclosure) makes the LT ideal for investigating the nature of short bursts, optically-dark bursts, and GRB blast-wave physics in general. We briefly describe the LT's key position in the RoboNet-1.0 network of robotic telescopes. We present the LT observations of GRB041006 and use its gamma-ray properties to predict the time of the break in optical light curve, a prediction consistent with the observations.

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arXiv2005

The Liverpool Telescope Automatic Pipeline for Real-time GRB Afterglow Detection

The 2-m robotic Liverpool Telescope (LT) is ideally suited to the rapid follow-up of unpredictable and transient events such as GRBs. Our GRB follow-up strategy is designed to identify optical/IR counterparts in real time; it involves the automatic triggering of initial observations, on receipt of an alert from Gamma Ray Observatories HETE-2, INTEGRAL and Swift, followed by automated data reduction, analysis, OT identification and subsequent observing mode choice. The lack of human intervention in this process requires robustness at all stages of the procedure. Here we describe the telescope, its instrumentation and GRB pipeline.

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arXiv2004

Rapid H-alpha variability in T Coronae Borealis

We report our search for variability in the H-alpha emission line of the recurrent novae T CrB with time resolution 10-15 minutes. This is comparable with the time scale of the photometric flickering observed in this object. This is the first time that observations of the short time scale variation in emission lines have been made in this object. On two nights (990106 and 990107) we detected statistically significant variability (at 0.99 confidence level) in the line profile of H-alpha. This variability is confined in the central part of the emission line (\pm 100 km/s) although FWZI(H-alpha) is ~800 km/s. The variability in the line profile is accompanied with variability of the total equivalent width, EW(H-alpha), \pm 8% for 990106, and \pm 6% for 990107 (calculated from the mean value of EW). Assuming Keplerian motion, the variability is generated at a distance ~20-30 R_Solar from the white dwarf, which is approximately the radius of the ring the stream of gas forms as it flows away from L_1. On three other nights we are only able to put upper limits on the variability, ΔEW(H-alpha) \pm 2% for 980415, \pm 4% for 980802, and \pm 3% for 980803.

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arXiv2004

White dwarfs with jets as non-relativistic analogues of quasars and microquasars?

We explore the similarities between accreting white dwarfs (CH Cyg and MWC 560) and the much more energetic jet sources - quasars and microquasars. To-date we have identified several common attributes: (1) they exhibit collimated outflows (jets); (2) the jets are precessing; (3) these two symbiotic stars exhibit quasar-like emission line spectra; (4) there is a disk-jet connection like that observed in microquasars. Additionally they may have a similar energy source (extraction of rotational energy from the accreting object). Study of the low energy analogues could have important implications for our understanding of their higher energy cousins.

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arXiv2004

Rapid GRB Follow-up with the 2-m Robotic Liverpool Telescope

We present the capabilities of the 2-m robotic Liverpool Telescope (LT), owned and operated by Liverpool John Moores University and situated at ORM, La Palma. Robotic control and scheduling of the LT make it especially powerful for observations in time domain astrophysics including: (i) rapid response to Targets of Opportunity: Gamma Ray Bursts, novae, supernovae, comets; (ii) monitoring of variable objects on timescales from seconds to years, and (iii) observations simultaneous or coordinated with other facilities, both ground-based and from space. Following a GRB alert from the Gamma Ray Observatories HETE-2, INTEGRAL and Swift we implement a special over-ride mode which enables observations to commence in about a minute after the alert, including optical and near infrared imaging and spectroscopy. In particular, the combination of aperture, site, instrumentation and rapid response (aided by its rapid slew and fully-opening enclosure) makes the LT excellently suited to help solving the mystery of the origin of optically dark GRBs, for the investigation of short bursts (which currently do not have any confirmed optical counterparts) and for early optical spectroscopy of the GRB phenomenon in general. We briefly describe the LT's key position in the RoboNet-1.0 network of robotic telescopes.

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arXiv2004

Classical novae from the POINT-AGAPE microlensing survey of M31 -- I. The nova catalogue

The POINT-AGAPE survey is an optical search for gravitational microlensing events towards the Andromeda Galaxy (M31). As well as microlensing, the survey is sensitive to many different classes of variable stars and transients. Here we describe the automated detection and selection pipeline used to identify M31 classical novae (CNe) and we present the resulting catalogue of 20 CN candidates observed over three seasons. CNe are observed both in the bulge region as well as over a wide area of the M31 disk. Nine of the CNe are caught during the final rise phase and all are well sampled in at least two colours. The excellent light-curve coverage has allowed us to detect and classify CNe over a wide range of speed class, from very fast to very slow. Among the light-curves is a moderately fast CN exhibiting entry into a deep transition minimum, followed by its final decline. We have also observed in detail a very slow CN which faded by only 0.01 mag day$^{-1}$ over a 150 day period. We detect other interesting variable objects, including one of the longest period and most luminous Mira variables. The CN catalogue constitutes a uniquely well-sampled and objectively-selected data set with which to study the statistical properties of classical novae in M31, such as the global nova rate, the reliability of novae as standard-candle distance indicators and the dependence of the nova population on stellar environment. The findings of this statistical study will be reported in a follow-up paper.

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arXiv2004

Flickering variability of T Coronae Borealis

We present electro-photometric UBV and high-speed U-band flickering observations of the recurrent nova T CrB during a period when its U brightness varies by more than 2 mag. The V band is dominated by the ellipsoidal variability of the red giant, however, the variability of the hot component also causes 0.15 mag variations in V. We define a set of parameters which characterise the flickering. The Fourier spectra of all 27 nights are similar to each other. The power spectral density of the variations has a power law component (f^{-1.46} on average). We do not detect a dependence of the Fourier spectra and autocorrelation function on the brightness of the object. Having subtracted the contribution of the red giant, we show that the flickering amplitude correlates with the average flux of the accreting component. A comparison with CH Cyg and MWC 560 indicates that the flickering of T CrB is more stable (at least during the time of our observations), than that in the jet-ejecting symbiotic stars. The data are available in electronic form from the authors.

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arXiv2004

High Spatial Resolution Optical and Radio Imagery of the Circumbinary Environment

In this review, I concentrate on describing observations of spatially resolved emission in symbiotic stars at sub-arcsecond scales. In some of the closer objects, the highest resolutions discussed here correspond to linear dimensions similar to the supposed binary separation. A total of 17 stars well accepted as symbiotics are now observed to show sub-arcsecond structure, almost twice the number at the time of the last review in 1987. Furthermore, we now have access to HST imagery to add to radio interferometry. From such observations we can derive fundamental parameters of the central systems, investigate the variation of physical parameters across the resolved nebulae and probe the physical mechanisms of mass loss and interactions between ejecta and the circumstellar medium. Suggestions for future work are made and the potential of new facilities in both the radio and optical domains is described. This review complements that by Corradi (this volume) which mainly considers the larger scale emission from the ionized nebulae of these objects.

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arXiv2003

The Liverpool Telescope: Rapid follow-up observation of Targets of opportunity with a 2 m robotic telescope

The Liverpool Telescope, situated at Roque de los Muchachos Observatory, La Palma, Canaries, is the first 2-m, fully instrumented robotic telescope. It recently began observations. Among Liverpool Telescope's primary scientific goals is to monitor variable objects on all timescales from seconds to years. An additional benefit of its robotic operation is rapid reaction to unpredictable phenomena and their systematic follow up, simultaneous or coordinated with other facilities. The Target of Opportunity Programme of the Liverpool Telescope includes the prompt search for and observation of GRB and XRF counterparts. A special over-ride mode implemented for GRB/XRF follow-up enables observations commencing less than a minute after the alert, including optical and near infrared imaging and spectroscopy. In particular, the moderate aperture and rapid automated response make the Liverpool Telescope excellently suited to help solving the mystery of optically dark GRBs and for the investigation of currently unstudied short bursts and XRFs.

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arXiv2003

GRB optical and IR rapid follow-up with the 2 m Liverpool Robotic Telescope

The Liverpool Telescope, owned and operated by Liverpool John Moores University and situated at Roque de los Muchachos, La Palma, is the first 2-m, fully instrumented robotic telescope. We plan to use the LT in conjunction with Gamma Ray Observatories (HETE-2, INTEGRAL, Swift) to study GRB physics. A special over-ride mode will enable observations commencing less than a minute after the GRB alert, including optical and near infrared imaging and spectroscopy. These observations, together with systematic monitoring of the burst through the afterglow, will help to unravel the nature of prompt optical flashes, short bursts, optically dark bursts, redshift distribution, GRB - supernova connection and other questions related to the GRB phenomenon. In particular, the combination of aperture, instrumentation and rapid automated response makes the Liverpool Telescope excellently suited to the investigation of optically dark bursts and currently optically unstudied short bursts.

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arXiv2003

HST/WFPC2 snapshot imaging of symbiotic stars

The results of a HST/WFPC2 snapshot imaging survey of selected symbiotic stars in 1999/2000 are presented. Seven sources - HD 149427 (PC 11), PU Vul, RT Ser, He2-104 (Southern Crab), V1329 Cyg (HBV 475), V417 Cen, AS 201 - were observed in filters F218W (ultraviolet continuum), F502N ([OIII]lambda 4959,5007) and F656N (Halpha); an eighth source, RS Oph, was observed in F437N ([OIII]lambda 4363), F502N and F656N. The presence of extended emission was detected in He2-104, V1329 Cyg and possibly HD 149427. In He2-104 we detected the [OIII] and Halpha counterparts to the inner lobes found in [NII] by Corradi et al. For V1329 Cyg, comparison with previously published HST/FOC results indicates expanding ejecta which may be associated with an ejection event in 1982 (+/-2 years) at a velocity of 260 +/- 50 km/s in the plane of the sky and at an assumed distance of 3.4kpc. We also present previously unpublished radio images of HD 149427, which we have obtained from the archives of the Australia Telescope Compact Array and which reveal the presence of extended emission at a similar orientation to that of the possible optical extension. Finally we also include HST/WFPC2 GO observations of AG Peg and detect possible extended emission in the F218W filter.

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arXiv2002

Novae In External Galaxies From The POINT-AGAPE Survey And The Liverpool Telescope

We have recently begun a search for Classical Novae in M31 using three years of multicolour data taken by the POINT-AGAPE microlensing collaboration with the 2.5m Isaac Newton Telescope (INT) on La Palma. This is a pilot program leading to the use of the Liverpool Telescope (LT) to systematically search for and follow novae of all speed classes in external galaxies to distances up to around 5Mpc.

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arXiv2002

The symbiotic star CH Cygni. III. A precessing radio jet

VLA, MERLIN and Hubble Space Telescope imaging observations of the extended regions of the symbiotic system CH Cygni are analysed. These extensions are evidence of a strong collimation mechanism, probably an accretion disk surrounding the hot component of the system. Over 16 years (between 1985 and 2001) the general trend is that these jets are seen to precess. Fitting a simple ballistic model of matter ejection to the geometry of the extended regions suggests a period of 6520 +/- 150 days, with a precession cone opening angle of 35 +/- 1 degrees. This period is of the same order as that proposed for the orbital period of the outer giant in the system, suggesting a possible link between the two. Anomalous knots in the emission, not explained by the simple model, are believed to be the result of older, slower moving ejecta, or possibly jet material that has become disrupted through sideways interaction with the surrounding medium.

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arXiv2002

The central binary and surrounding nebula of the symbiotic star V1016 Cygni

We present HST/WFPC2 images of the symbiotic star V1016 Cyg which, for the first time, directly explore the inner regions of the nebula to AU scales at optical wavelengths. They also suggest that the [OIII] 4959,5007 emission takes place in a bipolar outflow. We use these images to determine the position of the two stars and hence a projected binary separation of 84 AU (assuming a distance of 2 kpc) and a position angle of 143.5 degrees. Furthermore, we combine our images with VLA radio imaging which enables diagnostic tests to be applied and properties of the circumstellar nebula to be determined. Finally we have obtained archive HST/STIS spectra of V1016 Cyg with which we were able to spatially resolve the source at various positions in the nebula. This enabled discovery of the ultraviolet counterpart to the ~25 arcsec extended emission found by Bang et al. (1992).

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arXiv2001

The symbiotic star CH Cygni. I. Non-thermal bipolar jets

VLA surface brightness and spectral index maps of the evolving extended emission of the triple symbiotic star CH Cygni are presented. These are derived from observations at 4.8, 8.4 and 14GHz between 1985 and 1999. The maps are dominated by thermal emission around the central bright peak of the nebula, but we also find unambiguous non-thermal emission associated with the extended regions. Our observations confirm that this is a jet. The central region has been associated with the stellar components through HST imaging. If the jets are due to ejection events at outburst, expansion velocities are consistent with those from other measurement methods. We propose that the non-thermal emission is caused by material ejected in the bipolar jets interacting with the circumstellar wind envelope. The resulting shocks lead to local enhancements in the magnetic field from the compact component of the order 3mG.

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