Blazars are a rare category of active galactic nuclei (AGN) as their luminous core powered by black holes is aligned directly along the observer’s line of sight. These black holes can contain up to million times more material than our Sun. In some of the most luminous Blazars, their visible light surpasses the combined luminosity of stars contained by an entire galaxy. This makes Blazars one of the most luminous objects in the universe which like other galaxies gets its energy through matter falling into its central black hole. Some parts of this material form particle jets that travel outwards in opposite direction from the central black hole. What makes Blazars so luminous to the observer is that we are observing them directly down the jet. The material in these jets can travel at more than 99% of the speed of light and these blazars can appear to move faster than light when jets are pointed directly towards the earth. Despite astronomers knowing the relative speed of these jets, it is still a great mystery as to what these jets are composed of or their birth. (Ref.1)
When studying blazars, it is important to notice their luminosity is boosted by several magnitudes because the jet strongly beams emission along the line of sight toward the observer. Blazars are known to observe variability on timescales from hours to years, and due to Doppler-boosting (beams close to the speed of light appear to move faster than the speed of light), the observed timescale of variability is shortened when compared to the rest frame. So it can be concluded the variations within the jet are Doppler-boosted and can be greatly amplified. (Ref. 1)
Most blazars are best studied using gamma telescopes due to their high energies, but in this study the high resolution images were taken using optical telescopes (CMT) and a V filter spanning a time of two hours. The Mira software is then used to reduce the images to collect data where the optimal image was uploaded to nova.astrometry.net to obtain the final field star image. (Ref. 3)
In Figure 1 we are able to observe the jet that is often found in objects with spinning accretion disks. Ground based telescopes such as ones used in this experiment are able to pick up the low frequency radiation while space based telescopes are able to pick up their high frequency radiation. The predicted gamma-ray luminosity peaks at around 100 GeV for M87, making this ideal source for high sensitivity gamma telescopes. M87 is not classified to be a Blazar due to its jet not pointing directly towards the earth but is a great depiction of a jet observed from a black hole in a Blazar. (Ref.2)
Firstly in this experiment ,we are challenged to find the plate scale of the final optimal star image we obtain, then using the pixel count and plate-scale we are able to find the field of view and focal length of the CMT telescope. Then accounting for the magnitudes of several surrounding stars we can then estimate the luminosity of the Blazar by first finding the apparent magnitude using the Mira photometry tool. FInally we are able to find the variability of the Blazar by finding the difference in instrumental magnitude between the blazar and surrounding stars over the given time interval. These are some of the main objectives that were achieved in this experiment. (Ref. 3)
In the first section of the experiment, high resolution images are made in the MIRA software using the variety of tools available. First, the whole set of raw images is combined into one image using the median combine tool. Next, a map of the vignetting for the CMT is created as an image of the background sky profile in the combined image. This vignetting is then divided by its median value to normalize the image. Each individual raw image is divided by the normalized sky profile to remove the telescope vignetting. Images with poor declination tracking are removed from further analysis. The images that have not been removed are registered once using a single bright star and then registered a second time using at least twenty stars. These registered images are median combined into a final image. A 180degree rotation is performed on the image to orient it properly. This final image is uploaded to Astrometry.net [1] to use its world coordinate system calibration feature. The calibrated image is downloaded, this is the final processed image. The Simbad website [2] is used to obtain the right ascension and declination of BL Lac and the AladinLite Viewer is used to compare the obtained star field with those of the 2MASS and DSS surveys to confirm the location of BL Lac.
The header of the final processed image is used to obtain the plate scale. Using this plate scale, the field of view of the telescope and camera configuration as well as the effective focal length of the telescope are calculated. Using the statistics and cursor box tools on MIRA, the mean and standard deviation of the sky counts in the two registered images as well as the final processed image are determined and compared. This is done by placing the cursor box in a dark spot of sky without stars in each image.
The magnitudes of seven standard stars are used to determine the zero point of the final image. This is done using the photometry tool of MIRA. The standard stars used are the stars of which the magnitude is known from using Simbad’s [2] query around tool. An appropriate aperture and annulus size are used on the MIRA photometry tool and are kept constant throughout the experiment. The known magnitudes are input into MIRA for the standard stars, improving the zero point value for each magnitude entered. The magnitude of BL Lac is then measured using the photometry tool. NASA’s Astronomical Data Service [3] is then used to find a value for the distance to BL Lac. This distance, along with its uncertainty, is used to calculate the absolute magnitude and solar luminosity of the blazar.
The Nasa ADS [3] is used furthermore to find an image of a few blazars in order to analyze the visual properties of the objects. Image analyzing tools in MIRA are used to look for evidence of these properties in the final processed image of BL Lac in order to discern the blazar’s host galaxy.
In order to determine the variability of the blazar’s magnitude over time, differential photometry is used on the set of dual registered images. This is done by finding the difference in instrumental magnitude between the blazar and at least thirty stars and taking an average of these values to produce as small of an uncertainty as possible. This minimized uncertainty will allow for a more confident analysis of the variability. The instrumental magnitudes are measured using the photometry tool with the chosen annulus and aperture size from before. Important measurements are output for each star by MIRA. The track button on the photometry tool is used to obtain these measurements for the thirty stars and blazar in every image. This data is imported to Excel and used to produce a light curve plot for the blazar. This same method is used to plot a light curve of an ordinary field star in order to observe if the plot remains constant over time as expected.