Justin D. Linford

Characteristics of Gamma-Ray Loud Blazars in the VLBA Imaging and Polarimetry Survey

The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed as part of the VLBA Imaging and Polarimetry Survey. This large, flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong γ-ray emission. At lower flux levels, radio flux density does not directly correlate with γ-ray flux. We find that the LAT-detected BL Lac objects tend to be similar to the non-LAT BL Lac objects, but that the LAT-detected FSRQs are often significantly different from the non-LAT FSRQs. The differences between the γ-ray loud and quiet FSRQs can be explained by Doppler boosting; these objects appear to require larger Doppler factors than those of the BL Lac objects. It is possible that the γ-ray loud FSRQs are fundamentally different from the γ-ray quiet FSRQs. Strong polarization at the base of the jet appears to be a signature for γ-ray loud AGNs.

CONTEMPORANEOUS VLBA 5 GHz OBSERVATIONS OF LARGE AREA TELESCOPE DETECTED BLAZARS

The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA). In total, 232 sources were observed with the VLBA. Ninety sources that were previously observed as part of the VLBA Imaging and Polarimetry Survey (VIPS) have been included in the sample, as well as 142 sources not found in VIPS. This very large, 5 GHz flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong γ-ray emission. In particular, we see that γ-ray emission is related to strong, uniform magnetic fields in the cores of the host AGN. Included in this sample are non-blazar AGNs such as 3C84, M82, and NGC 6251. For the blazars, the total VLBA radio flux density at 5 GHz correlates strongly with γ-ray flux. The LAT BL Lac objects tend to be similar to the non-LAT BL Lac objects, but the LAT flat-spectrum radio quasars (FSRQs) are significantly different from the non-LAT FSRQs. Strong core polarization is significantly more common among the LAT sources, and core fractional polarization appears to increase during LAT detection.

THE DISTANCE TO NOVA V959 MON FROM VLA IMAGING

Determining reliable distances to classical novae is a challenging but crucial step in deriving their ejected masses and explosion energetics. Here we combine radio expansion measurements from the Karl G. Jansky Very Large Array with velocities derived from optical spectra to estimate an expansion parallax for nova V959 Mon, the first nova discovered through its gamma-ray emission. We spatially resolve the nova at frequencies of 4.5-36.5 GHz in nine different imaging epochs. The first five epochs cover the expansion of the ejecta from 2012 October to 2013 January, while the final four epochs span 2014 February to 2014 May. These observations correspond to days 126 through 199 and days 615 through 703 after the first detection of the nova. The images clearly show a non-spherical ejecta geometry. Utilizing ejecta velocities derived from 3D modelling of optical spectroscopy, the radio expansion implies a distance between 0.9 +/- 0.2 and 2.2 +/- 0.4 kpc, with a most probable distance of 1.4 +/- 0.4 kpc. This distance implies a gamma-ray luminosity much less than the prototype gamma-ray-detected nova, V407 Cyg, possibly due to the lack of a red giant companion in the V959 Mon system. V959 Mon also has a much lower gamma-ray luminosity than other classical novae detected in gamma-rays to date, indicating a range of at least a factor of 10 in the gamma-ray luminosities for these explosions.

VLBI observations of the shortest orbital period black hole binary, MAXI J1659-152

The X-ray transient MAXI J1659−152 was discovered by Swift/Burst Alert Telescope and it was initially identified as a gamma-ray burst. Soon its Galactic origin and binary nature were established. There exists a wealth of multiwavelength monitoring data for this source, providing a great coverage of the full X-ray transition in this candidate black hole binary system. We obtained two epochs of European very long baseline interferometry (VLBI) Network (EVN) electronic-VLBI and four epochs of Very Long Baseline Array data of MAXI J1659−152 which show evidence for outflow in the early phases. The overall source properties (polarization, milliarcsecond-scale radio structure, flat radio spectrum) are described well with the presence of a compact jet in the system through the transition from the hard-intermediate to the soft X-ray spectral state. The apparent dependence of source size and the radio core position on the observed flux density (luminosity-dependent core shift) supports this interpretation as well. We see no evidence for major discrete ejecta during the outburst. For the source proper motion we derive 2σ upper limits of 115 μas d−1 in right ascension, and 37 μas d−1 in declination, over a time baseline of 12 d. These correspond to velocities of 1400 and 440 km s−1, respectively, assuming a source distance of ∼7 kpc.

Broad-band monitoring tracing the evolution of the jet and disc in the black hole candidate X-ray binary MAXI J1659−152

MAXI J1659−152 was discovered on 2010 September 25 as a new X-ray transient, initially identified as a gamma-ray burst, but was later shown to be a new X-ray binary with a black

Non-thermal radio emission from colliding flows in classical nova V1723 Aql

The importance of shocks in nova explosions has been highlighted by Fermis discovery of \gamma-ray producing novae. Over three years of multi-band VLA radio observations of the 2010 nova V1723 Aql show that shocks between fast and slow flows within the ejecta led to the acceleration of particles and the production of synchrotron radiation. Soon after the start of the eruption, shocks in the ejecta produced an unexpected radio flare, resulting in a multi-peaked radio light curve. The emission eventually became consistent with an expanding thermal remnant with mass

Shock-powered radio emission from V5589 Sagittarii (Nova Sgr 2012 #1)

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A Radio Emission Analysis of Classical Nova V351 Pup (1991)

and temperature

VLBI detection of the internal shocks in nova V959 Mon

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Binary orbits as the driver of γ-ray emission and mass ejection in classical novae

K. However, during the first two months, the