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Miller, H. R.

Publications and source records attributed to Miller, H. R..

13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A VERITAS/Breakthrough Listen Search for Optical Technosignatures

The Breakthrough Listen Initiative is conducting a program using multiple telescopes around the world to search for “technosignatures”: artificial transmitters of extraterrestrial origin from beyond our solar system. The Very Energetic Radiation Imaging Telescope Array System (VERITAS) Collaboration joined this program in 2018 and provides the capability to search for one particular technosignature: optical pulses of a few nanoseconds in duration detectable over interstellar distances. We report here on the analysis and results of dedicated VERITAS observations of Breakthrough Listen targets conducted in 2019 and 2020 and of archival VERITAS data collected since 2012. Thirty hours of dedicated observations of 136 targets and 249 archival observations of 140 targets were analyzed and did not reveal any signals consistent with a technosignature. The results are used to place limits on the fraction of stars hosting transmitting civilizations. We also discuss the minimum pulse sensitivity of our observations and present VERITAS observations of CALIOP: a space-based pulsed laser on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations. The detection of these pulses with VERITAS, using the analysis techniques developed for our technosignature search, allows a test of our analysis efficiency and serves as an important proof of principle.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1992

The timescales of the optical variability of blazars. III - OJ 287 and BL Lacertae

The BL Lacertae objects OJ 287 and BL Lac have been photometrically monitored in an effort to study the nature of optical variations which may occur on timescales ranging from years to less than a day. The results of ten years of photometric monitoring of these two objects show variations which are consistent with those reported by other authors. No strong dependence of color with source brightness was detected, although both sources exhibited a weak tendency to be bluer when brighter. Microvariability was observed for both objects; variations as large as 0.1 mag/hr were observed for BL Lac and changes as large as 0.08 mag/hr were observed for OJ 287. No evidence for a periodicity was found in the observed variations of either object.

Carini, M. T.↗
NASA NTRS1992

The optical variability of PKS 2155 - 304

Results of photometric monitoring of the BL Lacertae object PKS 2155 - 304 between 1979 and 1990 are presented. Optical variations were observed on time scales ranging from several minutes to several years. The variations detected with time scales on the order of minutes are among the fastest optical variations detected for a BL Lacertae object. These rapid variations provided constraints on the mass of the supermassive black hole, assumed to be present at the center of the object, of the range between 5.5 +/-0.4 x 10 exp 8 and 8.1 +/-1.0 x 10 exp 9 solar masses. The results indicate that the characteristic variability time scale for the optical variability is shorter than the characteristic variability time scale established for the UV of approximately 50 d reported by Treves et al. (1989).

Carini, Michael T.↗
NASA NTRS1992

A search for microvariability in five OVV quasars

We present results of monitoring a sample of five OVV qausars in an effort to determine if these types of AGNs exhibit microvariability similar to that detected for BL Lacertae objects. Three of the five quasars investigated clearly exhibited microvariability. The timescales for the variations for both BL Lacertae objects and OVV quasars are similar which suggests that the radiation is generated in similar spatial volumes. These variations are consistent with the results of models which explain the observed microvariability as the result of excess emission produced by flares or hot spots randomly appearing and disappearing on the accretion disks around supermassive black holes.

Miller, H. R.↗
NASA NTRS1988

The ultraviolet/optical variability of PG 1553+11

Ultraviolet optical observations of the BL Lacertae object, PG 1553+11, indicate that significant color variations are associated with the luminosity variations seen in the ultraviolet and the optical regions of the spectrum. The color variations are consistent with the presence of an accretion disk in this system.

Miller, H. R.↗
NASA NTRS1986

Observations of three BL Lacertae objects - Constraints on inhomogeneous relativistically beamed jet models

Multifrequency observations are presented of three BL Lac objects, including the first UV measurements of 0912 + 297 and 1219 + 285. An eight day optical flare was measured from 0422 = 004 in which a doubling in visual flux density was noted; other sources displayed smaller daily fluctuations. The 5-15 GHz radio flux from these three objects remained constant for two months, although the 15-20 GHz emission from 0912 + 297 varied slightly over a period of a month. Constraints which are provided by these and other Bl Lac data are discussed for inhomogeneous relativistically beamed jet models. It is concluded that a tapered jet model is in good agreement with the data for each source and that additional emission regions are not required.

Worrall, D. M.↗
NASA NTRS1984

Multifrequency-spectral behavior of the BL Lacertae objects OI 90.4 and 3C 66A

Single-epoch multifrequency data for the BL Lac objects OI 90.4 and 3C 66A, spanning radio through ultraviolet wavelengths, are presented, as well as other measurements relevant to intensity and spectral-shape variability. Both BL Lac objects exhibit spectral curvature in the infrared-to-ultraviolet region, a properity that is inferred to be usual for this object class. Variability in the ultraviolet spectral index of OI 90.4 is found, whereas the spectral index of 3C 66A is the same in two observations 17 months apart. A synchrotron self-Compton jet model is applied to each BL Lac object. The OI 90.4 data are found to be best satisfied by a jet with a relatively high degree of relativistic beaming, but emission at frequencies below about 50 GHz is not described by the model. Furthermore, 3C 66A may not always undergo strong relativistic beaming, and the model may incorporate the small fraction of the total radio emission below about 20 GHz that is from within about 1.5 milliarcsec of the core.

Worrall, D. M.↗
NASA NTRS1984

Multifrequency observations of the BL Lacertae objects OQ 530 and ON 325

Spectral measurements of the two BL Lac objects OQ 530 and ON 325 are presented. The measurements were taken at frequencies ranging from radio to ultraviolet. Both sources show spectral curvature between the infrared and ultraviolet frequencies. The intensity and spectral shape of OQ 530 vary, but the spectral shape of ON 325 appears to remain constant during intensity variability. A nonthermal theoretical model of jet emission is developed which incorporates both the spectral and time variability data. The model predicts that ON 325 radiates at X-ray frequencies with Compton radiation dominating over synchrotron emission. The angular size of the jet emission is predicted to be less than 0.1 milli-arcsec at high radio frequencies.

Worrall, D. M.↗
NASA NTRS1984

Multifrequency observations of the quasi-stellar object Ton 1542

Single-epoch multifrequency data are presented for the radio-quiet low-redshift QSO Ton 1542, spanning radio through ultraviolet wavelengths. A 3 Sigma upper limit of 9.2 mJy is obtained for the 20.3 GHz flux density; the first ultraviolet spectrum of this object is presented and discussed. A particularly strong excess of flux density is found at about 3000 A, which is likely to be dominated by Balmer continuum emission. An L-alpha/beta-hydrogen flux ratio of about 17 is also found, which is higher than that usually observed in QSOs.

Worrall, D. M.↗
NASA NTRS1984

Two multifrequency observations of 3C 371

Observations of 3C371 made at frequencies from the radio to the ultraviolet and coordinated during two short time intervals separated by 3 months are presented. Also presented are 1 keV X-ray flux densities measured at a different time. The multifrequency measurements indicate spectral steepening at visual wavelengths, and that an extrapolation of the ultraviolet continuum falls below the X-ray data. The infrared through X-ray data is explained as relativistically beamed synchrotron self-Compton emission, and source parameters are derived for two possible models. The present ultraviolet spectra both show strong Lyman-alpha emission at the same redshift as weak optical emission lines reported previously. Production of these lines by recombination of gas, after its ionization by the ultraviolet to X-ray continuum radiation, is favored as an explanation. C IV and N V absorption lines are tentatively identified in one ultraviolet spectrum, which, if real, suggest the presence of a hot (about 300,000 K) gaseous halo in 3C 371.

Puschell, J. J.↗
NASA NTRS1980

Optical and infrared variability of B2 1308+326

Optical and infrared polarimetric and photometric observations of the BL Lacertae object B2 1308+326 during its high-luminosity outburst in the spring of 1978 are reported. The energy distribution, polarization at 0.6 and 2.2 microns, flux and polarization variability and position angle and strength of polarization variations of B2 1308+326, which has a luminosity greater than 10 to the 48th ergs/sec, are observed to be similar to those of BL Lac objects of much lower luminosity, suggesting the same emission process. Models of BL Lac object emission accounting for the high luminosity of B2 1308+326 are examined, and the isotropic synchrotron model is found to be more applicable to the optical and infrared emission of BL Lac objects than a model invoking relativistically enhanced emission.

Moore, R. L.↗