Night 3:In an Unknown Land

Keep an eye on the landscape

Sometimes, we start a journey and don’t reach our final destination. This can be because the weather takes a turn for the worst, we run out of energy or we’ve gone the wrong way. Sometimes, we have no choice but to turn back.

However, we can always make the most of a bad situation. We can warn other mountaineers what path they ought to take or let them know that the weather has changed up ahead.

If we also look at the landscape with each step we take, we may find unexpected surprises, that is, things that are completely different to what we were looking for.

The same thing happens when hunting gammas. Dark matter will have to wait. But, does that mean that the hundreds of hours we’ve spent on observation have been a waste of time? No way! There’s a lot of analysis to be done and we can still be surprised.

There are many ways to analyse data. Sometimes we start the analysis with a certain objective and we lose things along the way.

My boss always tells me not to waste time doing extra things and to concentrate on the search for dark matter.

Although I never find anything. I like to check ans see if something else has appeared in the data. appears in the data. If you want, you can look at my notebook and see how I create a skymap of the region and look beyond what I had planned to do.

Dark matter is distributed around the centre of the cluster of galaxies. That’s why we’re going to look for it there. But, what if we don’t focus on the centre of the cluster?

Enter

import numpy as np
import pandas as pd
import matplotlib.pyplot as pl
import scipy.ndimage as ndimage
%matplotlib inline

  warnings.warn('Matplotlib is building the font cache using fc-list. This may take a moment.')

The sky map sometimes comes with surprises

Even though we can’t see anything in the centre of the Perseus cluster, isince we already have the data, let’s look at what the sky (the gamma ray) looks like around Perseus. We can do this with the same data we used to make the theta plot, just like Daniel did for Cas A.

# We read the files and give them a name
perseus_ON= pd.read_csv('data/EvtList_ON_Perseus_All.txt', sep=' ')
perseus_OFF= pd.read_csv('data/EvtList_OFF_Perseus_All.txt', sep=' ')

# We define the cut variables
had_cut = 0.20

# We select the data:
perseus_ON_cut = perseus_ON[perseus_ON['had'] < had_cut]
perseus_OFF_cut = perseus_OFF[perseus_OFF['had'] < had_cut]

# We check waht our loaded and selected data looks like
perseus_ON_cut.head(5)

	had	theta2	XCam	YCam
0	0.077	0.139	-0.323	0.185
27	0.083	0.253	0.064	0.498
31	0.119	0.279	0.452	-0.271
34	0.117	0.545	-0.688	-0.266
42	0.119	0.478	0.677	-0.136

You’ll see that now we have two new columns: XCam and YCam. These indicate the direction we think it comes from for each event. Each position on the camera indicates a position in the sky.

Let’s look in detail what Daniel did for his skymap function.

In contrast to the theta plot, here we want to show the data in 2 dimensions: positions X and Y. To do so, we have to use the function np.histogram2d instead of pl.hist. It works in a very similar way. We just need to provide two variables, for example camX_perseus and camY_perseus.

Also, there’s an error in the arrival address of each event. This implies that each event is likely to come, not only from a specific point but from a region of the sky. This is done with the gaussian filter as seen below for both OFF and ON data.

img1 = ndimage.gaussian_filter(hist_off, sigma=(5, 2), order=0)

img2 = ndimage.gaussian_filter(hist_perseus, sigma=(5, 2), order=0)

Now we can calculate the excesses by substracting OFF from ON:

hist_excess = np.subtract(img2, img1)

In addition, we know that the level of efficiency to detect events is not the same for the whole camera. A simple way to evaluate this efficiency is to divide the excesses by the OFF data that can be found at each point of the camera. To do so, we have:

hist_excess = np.divide(hist_excess, img1)

Then, we just need to show the 2D chart that remains after carrying out these operations.

# Skymap of the selected data:
hist_perseus, xedge, yedge = np.histogram2d(perseus_ON_cut.XCam, perseus_ON_cut.YCam, bins=71)
hist_off, xedge, yedge = np.histogram2d(perseus_OFF_cut.XCam, perseus_OFF_cut.YCam, bins=71)
img1 = ndimage.gaussian_filter(hist_off, sigma=(5, 2), order=0)
img2 = ndimage.gaussian_filter(hist_perseus, sigma=(5, 2), order=0)
hist_excess = np.subtract(img2, img1)
hist_excess = np.divide(hist_excess, img1)
pl.imshow(hist_excess, interpolation='gaussian', extent=[3.41,3.25,41.75,41.25],aspect="auto")
pl.xlabel('Ascencion Recta [deg]')
pl.ylabel('Declinacion [deg.]')
pl.show()

png

Wait! There’s something there…And I actually don’t remember ever seeing that before. Let’s see if it’s always been there or if it only appeared in the data that we collected yesterday.

# We read the files and give them a name:
perseus_ON= pd.read_csv('data/EvtList_ON_Perseus_LastDay.txt', sep=' ')
perseus_OFF= pd.read_csv('data/EvtList_OFF_Perseus_LastDay.txt', sep=' ')

# We define the cut variables:
had_cut = 0.20

# We select the data:
perseus_ON_cut = perseus_ON[perseus_ON['had'] < had_cut]
perseus_OFF_cut = perseus_OFF[perseus_OFF['had'] < had_cut]

# We represent the Skymap:
hist_perseus, xedge, yedge = np.histogram2d(perseus_ON_cut.XCam, perseus_ON_cut.YCam, bins=71)
hist_off, xedge, yedge = np.histogram2d(perseus_OFF_cut.XCam, perseus_OFF_cut.YCam, bins=71)
img1 = ndimage.gaussian_filter(hist_off, sigma=(5, 2), order=0)
img2 = ndimage.gaussian_filter(hist_perseus, sigma=(5, 2), order=0)
hist_excess = np.subtract(img2, img1)
hist_excess = np.divide(hist_excess, img1)
pl.imshow(hist_excess, interpolation='gaussian', extent=[3.41,3.25,41.75,41.25],aspect="auto")
pl.xlabel('Ascencion Recta [deg]')
pl.ylabel('Declinacion [deg.]')
pl.show()

png

Yesterday it was very clear … let’s check what happened with the rest of the data …

# We read the files and give them a name:
perseus_ON= pd.read_csv('data/EvtList_ON_Perseus_Other.txt', sep=' ')
perseus_OFF= pd.read_csv('data/EvtList_OFF_Perseus_Other.txt', sep=' ')

# We define the cut variables:
had_cut = 0.20

# We select the data:
perseus_ON_cut = perseus_ON[perseus_ON['had'] < had_cut]
perseus_OFF_cut = perseus_OFF[perseus_OFF['had'] < had_cut]

# We create the Skymap:
hist_perseus, xedge, yedge = np.histogram2d(perseus_ON_cut.XCam, perseus_ON_cut.YCam, bins=71)
hist_off, xedge, yedge = np.histogram2d(perseus_OFF_cut.XCam, perseus_OFF_cut.YCam, bins=71)
img1 = ndimage.gaussian_filter(hist_off, sigma=(5, 2), order=0)
img2 = ndimage.gaussian_filter(hist_perseus, sigma=(5, 2), order=0)
hist_excess = np.subtract(img2, img1)
hist_excess = np.divide(hist_excess, img1)
pl.imshow(hist_excess, interpolation='gaussian', extent=[3.41,3.25,41.75,41.25],aspect="auto")
pl.xlabel('Ascencion Recta [deg]')
pl.ylabel('Declinacion [deg.]')
pl.show()

png

There is nothing in the rest of the data. This is what we call a flare and it seems to be very intense. If you want to know more about flares, spend a night with Leyre. I’ll call her right now and tell her I’ve seen this one.

Dictionary of the gamma ray hunter

Active Galactic Nuclei

There's party going on inside!

This type of galaxy (known as AGN) has a compact central core that generates much more radiation than usual. It is believed that this emission is due to the accretion of matter in a supermassive black hole located in the centre. They are the most luminous persistent sources known in the Universe.

Find out more:

Black Hole

We love everything unknown. And a black hole keeps many secrets.

A black hole is a supermassive astronomical object that shows huge gravitational effects so that nothing (neither particles nor electromagnetic radiation) can overcome its event horizon. That is, nothing can escape from within.

Blazar

No, it's not a 'blazer', we aren't going shopping

A blazar is a particular type of active galactic nucleus, characterised by the fact that its jet points directly towards the Earth. In other words, it’s a very compact energy source associated with a black hole in the centre of a galaxy that’s pointing at us.

Cherenkov Radiation

It may sound like the name of a ames Bond villain, but this phenomenon is actually our maximum object of study

Cherenkov radiation is the electromagnetic radiation emitted when a charged particle passes through a dielectric medium at a speed greater than the phase velocity of light in that medium. When a very energetic gamma photon or cosmic ray interacts with the Earth’s atmosphere, a high-speed cascade of particles is produced. The Cherenkov radiation of these charged particles is used to determine the origin and intensity of cosmic or gamma rays.

Find out more:

Cherenkov Telescopes

Our favourite toys!

Cherenkov telescopes are high-energy gamma photon detectors located on the Earth’s surface. They have a mirror to gather light and focus it towards the camera. They detect light produced by the Cherenkov effect from blue to ultraviolet on the electromagnetic spectrum. The images taken by the camera allow us to identify if the particular particle in the atmosphere is a gamma ray and at the same time determine its direction and energy. The MAGIC telescopes at Roque de Los Muchachos (La Palma) are an example.

Find out more:

Cosmic Rays

You need to know how to distinguish between rays, particles and sparks!

Cosmic rays are examples of high-energy radiation composed mainly of highly energetic protons and atomic nuclei. They travel almost at the speed of light and when they hit the Earth’s atmosphere, they produce cascades of particles. These particles generate Cherenkov radiation and some can even reach the surface of the Earth. However, when cosmic rays reach the Earth, it is impossible to know their origin, because their trajectory has changed. This is due to the fact that they have travelled through magnetic fields which force them to change their initial direction.

Find out more:

Dark Matter

What can it be?

How can we define something that is unknown? We know of its existence because we detect it indirectly thanks to the gravitational effects it causes in visible matter, but we can’t study it directly. This is because it doesn’t interact with the electromagnetic force so we don’t know what it is composed of. Here, we are talking about something that represents 25% of everything known! So, it’s better not to discount it, but rather try to shed light on what it is …

Find out more:

Duality Particle Wave

But, what is it?

A duality particle wave is a quantum phenomenon in which particles take on the characteristics of a wave, and vice versa, on certain occasions. Things that we would expect to always act like a wave (for example, light) sometimes behave like a particle. This concept was introduced by Louis-Victor de Broglie and has been experimentally demonstrated.

Find out more:

Event

These really are the events of the year

When we talk about events in this field, we refer to each of the detections we make via telescopes. For each of them, we have information such as the position in the sky, the intensity, and so on. This information allows us to classify them. We are interested in having many events so that we can carry out statistical analysis a posteriori and draw conclusions.

Gamma Ray

Yes, we can!

Gamma rays are extreme-frequency electromagnetic ionizing radiation (above 10 exahertz). They are the most energetic range on the electromagnetic spectrum. The direction from which they reach the Earth indicates where they originate from.

Find out more:

Lorentz Covariance

The privileges of certain equations.

Certain physical equations have this property, by which they don’t change shape when certain coordinates changes are given. The special theory of relativity requires that the laws of physics take the same form in any inertial reference system. That is, if we have two observers whose coordinates can be related by a Lorentz transformation, any equation with covariant magnitudes will be written the same in both cases.

Find out more:

@ Wikipedia

Microquasar

Below you will learn what a quasar is...well a microquasar is the same, but smaller!

A microquasar is a binary star system that produces high-energy electromagnetic radiation. Its characteristics are similar to those of quasars, but on a smaller scale. Microquasars produce strong and variable radio emissions often in the form of jets and have an accretion disk surrounding a compact object (e.g. a black hole or neutron star) that’s very bright in the range of X-rays.

Find out more:

@ Wikipedia

Nebula

What shape do the clouds have?

Nebulae are regions of the interstellar medium composed basically of gases and some chemical elements in the form of cosmic dust. Many stars are born within them due to condensation and accumulation of matter. Sometimes, it’s just the remains of extinct stars.

Find out more:

@ Wikipedia

Particle Shower

The Niagara Falls of particles!

A particle shower results from the interaction between high-energy particles and a dense medium, for example, the Earth’s atmosphere. In turn, each of these secondary particles produced creates a cascade of its own, so that they end up producing a large number of low-energy particles.

Pulsar

Now you see me, now you don't

The word ‘pulsar’ comes from the shortening of pulsating star and it is precisely this, a star from which we get a discontinuous signal. More formally speaking, it’s a neutron star that emits electromagnetic radiation while it’s spinning. The emissions are due to the strong magnetic field they have and the pulse is related to the rotation period of the object and the orientation relative to the Earth. One of the best known and studied is the pulsar of the Crab Nebula, which, by the way, is very beautiful.

Find out more:

Quantum Gravity

A union of 'grave' importance ...

This field of physics aims to unite the quantum field theory, which applies the principles of quantum mechanics to classical systems of continuous fields, and general relativity. We want to define a unified mathematical basis with which all the forces of nature can be described, the Unified Field Theory.

Find out more:

@ wikipedia

Quasar

A 'quasi' star

Quasars are the furthest and most energetic members of a class of objects called active core galaxies. The name, quasar, comes from ‘quasi-stellar’ or ‘almost stars’. This is because, when they were discovered, using optical instruments, it was very difficult to distinguish them from the stars. However, their emission spectrum was clearly unique. They have usually been formed by the collision of galaxies whose central black holes have merged to form a supermassive black hole or a binary system of black holes.

Find out more:

@ Wikipedia

Supernova Remnant

A candy floss in the cosmos

When a star explodes (supernova) a nebula structure is created around it, formed by the material ejected from the explosion along with interstellar material.

Find out more:

Theory of relativity

In this life, everything is relative...or not!

Albert Einstein was the genius who, with his theories of special and general realtivity, took Newtonian mechanics and made it compatible with electromagnetism. The first theory is applicable to the movement of bodies in the absence of gravitational forces and in the second theory, Newtonian gravity is replaced with more complex formulas. However, for weak fields and small velocities it coincides numerically with classical theory.

Find out more:

@ Wikipedia