The Fermi ScienceTools

The Fermi analysis team has produced a suite of software tools for the purpose of reducing and analyzing data from the spacecraft. These tools are collectively called theFermi ScienceTools, and may be downloaded from the Fermi website3_{. Step-by-step examples and walkthroughs concerning}

the use of these tools can be found on separate pages in the Analysis Threads section of the website4_{. This subsection will briefly describe the purpose and usage of a selection of the analysis}

tools within the ScienceTools suite, which will be used in the following chapters.

TheGTLIKEScienceTool performs the unbinned (and binned) maximum likelihood analysis of the LAT data as described earlier in this section. Before this tool can be used, however, the raw data from the LAT must be prepared using several other ScienceTools. To perform a likelihood analysis of LAT data, the following tools need to be run in the order presented below:

• GTSELECTfor applying event class, energy range, region-of-interest (ROI - the field of view surrounding the science target), and field center (location of the science target on the sky, usually defined by radio coordinates) cuts.

• GTMKTIMEfor convolving the photons selected above with the pointing history of the space- craft to select Good Time Intervals (GTIs) that satisfy any pointing requirements specified by 3_{http://fermi.gsfc.nasa.gov/ssc/data/analysis/software/}

the user (e.g. restrict the off-axis pointing angle of the spacecraft with respect to the center of the field, avoid pointing near the Earth’s limb or towards the Sun, etc.).

• GTLTCUBE for computing “livetime cubes” for the field of view, which involves using the spacecraft pointing history and the file created by GTMKTIME to calculate a function (the livetime) describing the inclination of the spacecraft and position on the sky within a given time period. This step is necessary due to the dependance of the LAT response functions on the angle between the direction to a source and the instrument z-axis.

• GTLTCUBEfor creating exposure maps which are used to compute the predicted number of photons with the ROI, using the output fromGTLTCUBEand the spacecraft pointing history. In order to account for the large point spread function of the LAT at low energies, the region specified for this tool should be larger than the ROI and is referred to as the Source Region. The GTLIKE tool itself uses the output files from the GTMKTIME, GTLTCUBE, and GTLTCUBE tools to perform its function. It is also necessary to provide a file written in the XML language describing the location and spectral parameters of all the sources in the Source Region, as well as the galactic and extragalactic diffuse background components. Construction of TS Maps (see below) can help identify sources which were not included in the initial model. Some sources within the ROI, including the target of interest, should be flagged so that their spectral parameters are left free to vary during the likelihood analysis. The initial selection of which sources should be left to vary depends on, for example, the average intensity of an individual source and its individual history of variability, and is subject to change based on the results of successive fits withGTLIKE and/or changing of the exposure time for the field.

TheGTFINDSRCScienceTool finds the optimal spatial position of a given source, and is primar- ily used to localize the positions of newly-discovered sources. This is accomplished by finding the optimal Test Statistic for a given point source over a grid of positions around some initial guess (i.e. the radio coordinates of a RL NLS1) using a multidimensional minimization routine. The output of this tool provides not only the best-fit position, but also the offset between the best-fit and original

positions as well as the 68% confidence error circle about the best-fit position. The literature often cites the 95% error circle when describing the location of a newly-discovered source. A standard metric for determining the degree of confidence in the association of a newly-discovered gamma-ray source and an established source at lower energy bands is to show that the coordinates of the established source lie within the 95% error circle - in other words, that the error circle is larger than the separation between the best-fit position for the gamma-ray centroid and the starting coordinates. The 95% error circle can be calculated by simply multiplying the radius of the 68% error circle by a factor of 1.6225. The size of an error circle should be less than a degree for a good localization - 0.2º would be a typical value.

The GTTSMAP ScienceTool is used to create a significance map (TS map) of the likelihood test statistic for a specified region. This is done to aid the localization of newly-discovered point sources or to detect un-modeled sources within the field, which may interfere with the model fits of known (or newly-discovered) sources by distorting their spectral shapes, erroneously increasing their measured flux levels, or with source localization and error circle constraint viaGTFINDSRC. Sources dominated by low-energy (less than 1 GeV) photons are especially susceptible to these issues, due to the larger PSFs at such energies. Since all of the RL NLS1 sources detected at gamma-ray energies at the time of writing are dominated by such low-energy photons, the construction of TS maps is employed for all gamma-ray detected sources in this dissertation.

3 OBSERVATIONS

The data obtianed for the sample of RL NLS1 galaxies are described and summarized in this chapter. The photopolarimetric data for all 33 objects in the sample are displayed graphically in Figures 3.6 thru 3.62, while the tabular form of the data can be found in Appendix B. Each object has been observed polarimetrically over at least 6 separate nights, for a total of 343 polarimetric measurements for the sample.

This chapter is divided into 3 sections. Section 3.1 details the data collected for the 17 objects which have been detected at gamma-ray energies above a threshold of TS 9, orsv 3. The ob- jects are presented in order of increasing right ascension, with two exceptions: PMN J0948+0022 and QSO J0849+5108. These objects were subjects of intense study by the the author and fellow PEGA group members, especially Jeremy D. Maune - and those investigations are included in this dissertation.

In order to test for gamma-ray emissions from the objects in this sample, gamma-ray data were downloaded from the Fermi/LAT data server covering a period of time beginning on August 04, 2008, and ending on February 20, 2014. The details concerning event class selection, energy range, and pointing cuts are the same as those described in Section 3.1.1.4, below. However, this longer-term analysis utilized the latest-available version of the Fermi ScienceTools (v9r32p5) and latest instrument response functions (P7REP_SOURCE_V15). The data were divided into 66 equally-sized time bins per object, with a bin size of 30.5 days, and JD = 2454683.155 being the start time of the first bin. The determination of gamma-ray detectability for a particular object was achieved by analyzing the bin during which the object displayed the highest TS value. In some

cases multiple bins were used if the highest TS was roughly equal between two bins, or if the TS values in adjacent bins indicated that combining those bins into a single, larger bin would yield more robust results.

For each object detected at gamma-ray energies, the task GTFINDSRC was run and a TS map was constructed for the bin(s) in which the TS value was highest. TheGTFINDSRCtool was used to determine the degree of separation (in degrees on the sky) between the coordinates of the centroid of the gamma-ray emissions and the radio coordinates (epoch: J2000.0) of the object as given by the NASA/IPAC Extragalactic Database (NED).GTFINDSRCis also used to compute the size of the 95% confidence error circle in degrees, which is centered on the gamma-ray centroid. These two quantities are presented in the gamma-ray data tables for the associated objects as <95% error circle radius>(<separation of centroid & radio coordinates>). If a RL NLS1 is detected at gamma-ray energies, the separation of the centroid and radio coordinates should be equal to or less than the radius of the error circle.

The TS maps were calculated using a square field of view measuring 60x60 pixels with each pixel measuring 0.2° on the sky, resulting in images 12°x12° in size. Each TS map was centered on the radio coordinates of the RL NLS1. The purpose of the TS maps was to determine if there were any significant gamma-ray sources near the line of sight to the RL NLS1 that were not included in the source model, which could influence the measured flux, spectral shape, and/or location of the gamma-ray centroid of the RL NLS1. Also note that the gamma-ray spectra of these sources are not best-viewed in the manner familiar to IR, optical, UV, or even x-ray astronomers: the photon fluxes at gamma-ray wavelengths are much too low to allow meaningful figures of flux vs. photon energy to be constructed.

This work identifies 16 RL NLS1 galaxies at gamma-ray energies. Eight of these objects are identified at the level of 9T S<16, or between 3svand 4sv. One object is identified at the level of 16T S<25, or between 4svand 5sv. The remaining seven objects are detected above a T S 25 detection threshold, and are thereby considered “full” detections by the standards of the Fermi/LAT analysis community. Two of these high-confidence detections are the objects J1443+4725 and

J1644+2619, which have not been observed to be detected at gamma-ray energies before this work. The photopolarimetric data for the remaining 16 objects in the sample are presented in Section 3.2. Almost all of these objects were not detected at 3 standard deviations or better in the gamma- ray regime. The two exceptions - IRAS 09426+1926 & J1633+4718 - were discovered to be spurious detections due to the influence of bright, previously unidentified field sources near the lines of sight to the RL NLS1s.

Section 3.3 displays the polarimetric results of a sample of 17 Radio-Quiet Narrow Line Seyfert 1 galaxies, obtained and reduced under the same conditions as the RL NLS1 sample. These radio- quiet objects serve as a control sample for the polarimetric properties of the RL NLS1s, as the vast majority of NLS1 are radio-quiet. The majority of the objects in this control sample were found to possess little to no intrinsic polarization, with the only exceptions being objects which were suspected in earlier studies of being polarized due to the presence of interstellar dust. These objects were selected for their relative brightnesses (with respect to the RL NLS1s in this sample), which helped to maximize photon statistics and decrease observing time and thereby decrease the overall uncertainty of their polarimetric measurements.

Table 3.1, below, provides a summary of the polarimetric and gamma-ray observations of each object in the sample. Photometric ranges are taken from the work presented in Maune (2014), which deals with the photometric variability of these objects in great detail. The radio loudnesses of these sources are taken from Yuan et al. (2008), Komossa et al. (2006), Whalen et al. (2006), and Calderone et al. (2012).

Table 3.1: The Radio-Loud Narrow Line Seyfert 1 Sample: Photopolarimetry &g-ray Results Columns are: 1) Object ID, 2)DR (max. - min. brightness in magnitudes), 3) minimum P (and

error), 4) maximum P (and error), 5) number of photopolarimetric observations, 6) radio-loudness, and 7) the TS level of the bestg-ray detection, if applicable

Object ID DR (Rmax-Rmin) Pmin Pmax Nobs log(R) Best TS

J0100-0200 0.42 (18.82-19.24) 0.00(0.78) 3.21(0.56) 18 1.77 9.65 IRAS 01506+2554 0.56 (16.39-16.95) 0.62(0.10) 2.40(0.28) 23 1.40 – 1H 0323+342 1.08 (15.28-16.36) 0.00(0.13) 2.27(0.27) 22 2.50 280.31 J0706+3901 0.60 (16.77-17.37) 0.00(0.02) 1.63(0.13) 20 1.21 10.50 J0723+5054 0.45 (18.15-18.60) 0.00(0.06) 2.57(0.30) 10 1.29 – J0744+5149 0.33 (17.55-17.88) 0.00(0.75) 3.40(0.26) 8 1.62 – J0804+3853 0.64 (16.37-17.01) 1.30(0.11) 2.22(0.07) 16 1.18 10.77 J0849+5108 4.11 (14.46-18.57) 2.94(0.84) 15.44(0.34) 10 3.16 790.76 IRAS 09426+1926 0.29 (16.52-16.81) 0.00(0.12) 1.15(0.31) 10 1.56 – PMN J0948+0022 3.33 (16.70-20.03) 0.72(0.49) 12.26(1.14) 21 2.93 402.14 J0956+2515 0.70 (15.39-16.09) 1.44(0.07) 10.52(0.32) 8 3.56 95.95 J1038+4227 0.24 (17.06-17.30) 0.11(0.58) 3.51(0.05) 9 1.30 – J1047+4725 0.28 (18.77-19.05) 0.19(0.13) 5.48(0.93) 10 4.09 – J1102+2239 0.53 (18.71-19.24) 0.0(0.95) 8.84(0.29) 8 1.28 14.57 J1140+4622 0.52 (15.92-16.44) 0.00(0.14) 0.32(0.24) 7 1.36 – J1146+3236 0.99 (17.66-18.65) 0.14(0.14) 2.14(0.99) 8 2.19 12.61 J1227+3214 0.21 (16.75-16.96) 5.88(0.20) 8.83(0.18) 7 2.16 – J1246+0238 0.78 (16.46-17.24) 0.00(0.17) 1.17(0.12) 7 2.38 17.13 J1333+4141 0.43 (18.36-18.79) 0.16(0.05) 2.88(0.46) 7 1.06 – J1358+2658 0.29 (17.49-17.78) 1.18(0.54) 3.00(0.38) 8 1.11 – J1405+2657 0.25 (16.94-17.19) 0.00(0.43) 1.44(0.40) 6 1.09 – J1421+2824 0.20 (18.84-19.04) 0.00(0.13) 1.36(0.18) 7 2.14 – J1435+3132 0.46 (18.53-18.99) 0.00(0.17) 5.39(0.13) 8 2.98 – J1443+4725 0.26 (17.94-18.20) 0.00(0.38) 2.87(0.13) 7 3.03 27.81 PKS 1502+036 0.67 (17.71-18.38) 0.00(0.55) 2.77(0.41) 8 3.53 36.60 RX 16290+4007 0.27 (17.82-18.09) 0.00(0.57) 1.65(0.72) 7 1.61 – J1633+4718 0.74 (16.88-17.62) 0.00(0.18) 0.76(0.36) 6 2.19 – J1644+2619 0.71 (17.23-17.94) 0.10(0.16) 1.85(0.42) 7 2.73 52.25 B3 1702+457 0.54 (14.86-15.40) 0.89(0.09) 1.78(0.14) 7 2.01 – J1709+2348 0.56 (18.93-19.49) 0.24(0.39) 1.94(0.31) 6 1.06 – J1713+3523 0.34 (16.78-17.12) 0.19(0.32) 1.42(0.05) 7 1.05 12.03 IRAS 20181-2244 0.48 (18.30-18.78) 0.00(0.14) 1.03(0.25) 11 1.57 9.42 J2314+2243 0.29 (15.82-16.11) 0.00(0.06) 0.82(0.21) 19 1.25 11.59

3.1 RL NLS1 Galaxies With Gamma-ray Detections

This section describes the observations of the gamma-ray detected portion of our sample. These objects have been detected in at least one 1-month (30.5 days) bin at a significance of TS 9. Further checks to confirm the gamma-ray nature of these sources include confirming that the radio location of the source lies within the the 95% confidence circle, which is concentric about the centroid of the gamma-ray emissions. TS maps were also created to ensure that no un-modeled sources were within at least 6º of the target, which could lead to false detections as the likelihood analysis routine would attempt to incorrectly assign photons from un-modeled sources to modeled ones.

The process of searching for gamma-ray emissions from these sources began with an analysis of the first 66 months of LAT data in a single bin, which revealed no new sources. The individual analysis of each 1-month bin revealed that almost all of the objects in this sample were not detectable in a majority of the single-month bins, but were instead only provisionally detectable (TS > 9) in one or a few months out of 66. Objects which were detected above a TS > 4 threshold in consecutive months were re-analyzed by combining those months into a single bin, which generally improved the confidence of the detection.