Summary and Future Work - Trojans in Wireless Sensor Networks

The research presented in this dissertation has investigated the optical variability of a sample of radio-loud, narrow-line Seyfert 1 galaxies on both long (yearly) and short (intra-night) time scales.

Table 5.5: Potentially Blazar-Like Objects

Object DC Intra-night Long-term log(R) log(G) TS

4mR 4mR

1H 0323+342 2% 0.14 1.05 2.50 6.81 280

J1435+132 30% 0.11 0.46 2.98 — —

RX 16290+4007 29% 0.24 0.27 1.61 — —

Two exceptional objects – J0849+5108 and J0948+0022 – were confirmed to demonstrate frequent and violently variable optical activity on all measured time scales. Of particular note were the discovery of extremely high-amplitude microvariability from J0948+0022, the determination of a very rapid doubling time scale of approximately 40 minutes for the same object, and the occurrence of a 4-magnitude optical flare from J0849+5108 that has been unequalled since 1975. This flare was accompanied by quasi-simultaneous data from the radio, infrared, x-ray, andg-ray regimes.

Population studies failed to find significant correlations between the duty cycles of the radio- loud NLSy1 sample to parameters such as radio loudness, g-ray loudness, black hole mass, or amplitude of variability. However, the sample was found to demonstrate microvariability at amplitudes with a distribution very similar to that of LBL blazars. Based on their observed duty cycles, the amplitudes of the short and long time scale optical variability, and detections atg-ray energies, 7 of the 33 objects in the sample were found to be most similar to LBL-type blazars. Another three objects may also be LBLs. Only 10 objects were definitively found to be non-blazar-like, with the remainder of the sample having traits similar to both blazars and Seyfert galaxies.

Perhaps most importantly, it was discovered that whileg-ray emission was required for an object to demonstrate blazar-like optical variability2_{, the presence of high energy emission did not}

ensure such variability would be found. Many of the objects shown in Table 5.3 demonstrated little or even no evidence of microvarying behavior, despite hundreds of observations over multiple years; this makes it unlikely that the lack of detection was purely due to chance. Additionally, the radio loudness of the objects was completely independent of the level of optical variability the ob-

2_{It is true that not all known blazars have been detected at}_g_{-ray energies, so a lack of any such detection does not}

completely rule out that a given NLSy1 is a blazar-like object. But within the observations of this study, only theg-ray loud NLSy1s showed blazar-like variability.

jects demonstrated. Blazar-like variability was present in NLSy1s with radio loudness parameters as low as log(R) = 1.2, absent in objects as radio loud as log(R) > 3, and vice versa.

Several potential lines of research are suggested by these results. First, two objects (RX 16290+4007 and J1435+132) that currently lack evidence of g-ray emission were found to have moderately high duty cycles. If a dedicated investigation reveals that these objects have been detected by the Fermi instrument, it would significantly enhance the argument that the optical variability seen in radio-loud NLSy1s is due to the same phenomenon as found in blazars.

In addition, Abdo et al. (2009b) presents a g-ray detected radio-loud NLSy1 not included in this study. The object, PKS 2004-447 (2XMM J200755.2-443444), was found to possess a double- peaked, LBL-like SED. PKS 2004-447 was not included in the sample presented here due to the fact that its southern declination precluded the possibility of observing it with the telescopes at Lowell. While the object could have been observed at CTIO, the amount of observing time available to this study was insufficient to collect the high cadence intra-night data that would have been required. Astronomers with access to telescopes in the southern hemisphere are strongly encouraged to study the optical variability of this object.

This study presents a large set of optical data for radio-loud NLSy1s. The PEGA group at GSU possesses an even larger volume of data pertaining to BL Lacs and OVV blazars, and other groups such as Stalin et al. (2004) have amassed a considerable number of observations on radio-quiet quasars, radio- loud quasars, and other AGN. A large-scale analysis of the properties of all types of AGN would be highly informative if these samples could be combined. For example, the duty cycles of radio-quiet quasars and HBLs are commonly cited to be ~10% and ~45% respectively. However, these are known to be averages. How widely does this value range within each population? Is there a significant overlap with the duty cycles of other classes of objects – the results of this study indicate that this may be the case. What about other parameters, such as variability time scales or amplitude? This information would be invaluable to astronomers studying all types of AGNs, and could form the basis of a variety of new studies.

duty cycle for an object. A very simple equation was used for this document, and results may be slightly inconsistent when compared to data from other sources (for example, as was done in Table 2.3. The broad trends between object types should remain distinguishable, in that (for example) LBLs show much larger duty cycles than HBLs, which in turn are larger than what is found for radio-quiet NLSy1s. However, a consistent methodology across object types will be required for any future large-scale study as discussed in the previous paragraph.

Finally, astronomers are encouraged to collect the necessary multi-wavelength observations for the construction of SEDs for these and similar objects. This remains the most definitive way of demonstrating whether a radio-loud NLSy1 is blazar-like or not. Should one or more of the objects showing significant microvariability be shown to possess an SED lacking the double-peaked structure of a blazar, then many of the conclusions presented in this dissertation will have been challenged.

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Appendix A

Object Data

The following pages present the data that was acquired for each object as part of this investigation. Each section includes the following information: a finding chart for the object, a table detailing the apparent magnitudes of any comparison stars appearing in the finding chart, a table listing the optical observations for each night of data for the object, and chronologically organized light curves for any nights the object demonstrated microvariability.

All finding charts were produced by the author as part of this project. The base images used to create them were obtained from the Palomar Observatory Sky Survey (POSSII) using the imag- ing tools available through the SIMBAD Astronomical Database1_{. The Sloan Digital Sky Survey}

(SDSS) was later used to estimate the brightnesses of field stars when selecting comparison objects for differential photometry; these estimates were later refined to true apparent magnitudes as detailed in Chapter 2.

As the reader reviews this appendix, (s)he may find several nights that appear to show high amplitude variations with low average uncertainties that are not claimed as detections of microvariability. An example of such an event can be seen in Figure A.1. Almost universally, these nights demonstrate a relatively small number of high-variance, high uncertainty data (few enough that the average uncertainty remains low) while the remaining low-uncertainty data shows little evidence of variability. This is indicative of temporary atmospheric effects such as poor seeing or passing

clouds that are affecting part of the data set, and so the variability cannot be assumed to be intrinsic to the source object. Therefore, no claim of detection of microvariability is made.

Figures A.2-A.10 show light curves for objects undergoing events of various amplitude and at various epochs. These light curves also show the activity of one of the comparison stars on the same night; as they should be, the comparison star light curves are flat compared to the activity of the associated object. These figures are shown so that the reader may have confidence that the reported variations of the objects in this study are genuine.

Figure A.1: Example of false microvariability

Although this night demonstrates a high amplitude of variability (0.19 magnitudes) and the average uncertainty is low (0.02 magnitudes), these values are misleading. Upon examination of the light curve, it can be seen that the high-variance data has much higher uncertainties than the data found within the main trend. There is a high probability that these variations are not intrinsic to the source, but were instead caused by a transient atmospheric effects.

(a) Light curve showing a ~0.05 magnitude event