Method for Detecting Gravitational Wave Electromagnetic Counterparts Based on Optical Telescope System

Abstract

A detection method for a gravitational wave electromagnetic counterpart based on an optical telescope system relates to the field of optical telescope detection technology, solves the problem that the existing optical telescope cannot simultaneously measure the luminosity and spectrum of a celestial body, resulting in limited use of the optical telescope, obtains the spot signal of each celestial body in the sky area through two visual observation optical telescopes, and the spot signal is received by a CCD detector to obtain an imaging image; uses astronomical positioning software to determine the position of the transient source celestial body target; and performs photometric analysis to obtain the photometric value of the transient source celestial body target; the common-view optical telescope obtains the transient source celestial body target and performs spectral measurement on it through a multi-channel spectrometer; the photometric value and spectral data of the transient source celestial body target are simultaneously transmitted to a PC terminal to obtain the distance and mass of the gravitational wave electromagnetic counterpart. The present invention simultaneously measures the luminosity and spectrum of a celestial body, more conclusively determines the gravitational wave electromagnetic counterpart, and increases the determination confidence of the existing equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of optical telescope detection, and particularly relates to a method for detecting gravitational wave electromagnetic counterparts based on an optical telescope system. Background Art

[0002] Currently, a simple photometric telescope alone cannot determine the gravitational wave source counterpart relying solely on the light curve. Many samples of transient sources can be observed every day. Which one is the gravitational wave counterpart depends on a variety of devices such as gamma-ray telescopes and X-ray telescopes to comprehensively determine the electromagnetic counterpart of the gravitational wave.

[0003] There are mainly two defects in the existing optical telescopes for detecting the optical counterparts of gravitational wave sources:

[0004] First, it mainly detects the photometric changes of the optical counterparts of gravitational waves. Whether it is detecting transient sources or the afterglow of a merger event with a longer duration, it measures the light curve of celestial bodies and does not detect the spectrum of celestial bodies. For the instantaneous photometric changes, the search for electromagnetic counterparts mainly comes from the forecasts of gamma-ray telescopes or gravitational wave observatories for post-event search and matching.

[0005] Second, for existing optical telescopes, photometric measurement and spectral measurement cannot be carried out simultaneously. Because the celestial body signal to be observed is already very weak. When measuring the photometry, it is impossible to split the light and then measure the spectrum. When measuring the spectrum, photometric measurement cannot be carried out.

[0006] In summary, the existing optical telescopes cannot independently complete the detection and determination of the electromagnetic counterparts of gravitational wave sources and must rely on other devices to determine the specific information of the gravitational wave sources.

[0007] For a large-field optical telescope, the function of the telescope is to collect as much energy of electromagnetic waves as possible. The two important parameters of the telescope are the aperture and the resolution. The larger the aperture, the more light energy is collected, and of course, it is more beneficial for us to process and analyze the optical signal. The resolution is the ability to distinguish two very close targets on the celestial sphere. The larger the aperture of the telescope, the greater the resolution. The present invention mainly searches for transient source phenomena. Currently known main transient sources include: supernovae (including kilonovae), gamma-ray bursts, gravitational lenses, events where a star is disrupted by a massive black hole, etc. At the same time, it measures the photometric and spectral information of transient sources, determines the position information of the electromagnetic counterparts of gravitational wave sources, calculates the mass information and matches it with the observed gravitational waves. The system of the present invention has a certain forecasting function for gravitational waves. Through theoretical calculations, it can estimate the magnitude of gravitational waves that a celestial event can emit and whether it can be observed by existing devices.

[0008] The present invention determines the electromagnetic counterpart of a gravitational wave source by using the photometric change and spectral redshift information of electromagnetic waves. In particular, for black hole mergers or black hole-neutron star mergers, which are non-luminous gravitational wave events, the position of the electromagnetic counterpart of the gravitational wave is determined by the gravitational redshift perturbation of the electromagnetic waves emitted by the black hole accretion disk or the orbiting celestial body. Summary of the Invention

[0009] In order to solve the problem that existing optical telescopes cannot simultaneously measure the photometry and spectrum of celestial bodies, resulting in limited use of optical telescopes, the present invention provides a method for detecting the electromagnetic counterpart of a gravitational wave based on an optical telescope system.

[0010] A method for detecting the electromagnetic counterpart of a gravitational wave based on an optical telescope system is realized by the following process:

[0011] Receive the satellite time signal through the GPS clock and send the time signal to the first optically co-visible telescope and the second optically co-visible telescope for observation simultaneously.

[0012] Obtain the spot signals of each celestial body in the sky area through the first optically co-visible telescope, and the spot signals are received by the CCD detector to obtain an imaging image.

[0013] Use astronomical positioning software to perform comparative analysis on the imaging image to obtain a target image containing transient source celestial bodies; at the same time, determine the position of the transient source celestial body target in the target image.

[0014] The CCD detector performs photometric analysis on the transient source celestial body target to obtain the photometric value of the transient source celestial body target.

[0015] The second optically co-visible telescope obtains the transient source celestial body target and performs spectral measurement on it through a multi-channel spectrometer.

[0016] Transmit the photometric value and spectral data of the transient source celestial body target to the PC terminal simultaneously to obtain the distance and mass of the electromagnetic counterpart of the gravitational wave.

[0017] Advantages of the present invention: The method of the present invention can simultaneously measure the photometry and spectrum of celestial bodies. Through spectral information and photometric information, information such as the distance and mass of the gravitational wave source can be analyzed, and the electromagnetic counterpart of the gravitational wave can be determined more conclusively, increasing the determination confidence of existing equipment. First, use the stellar background to perform astronomical positioning on the transient source, exclude the targets in near-Earth space from the astronomical positioning, and then perform photometric analysis and spectral analysis on the transient source target. Through theoretical calculation, the magnitude of gravitational waves that a celestial event can emit can be obtained. By comparing and analyzing with the measured data of the gravitational wave observatory, the electromagnetic counterpart of the gravitational wave can be determined.

[0018] In the present invention, the telescope system adopts a co-visual observation mode of a large-aperture telescope and an array telescope system of four small-aperture telescopes. Among them, the fields of view of the four small-aperture telescopes are stitched into a refractive telescope array system with a large field of view to obtain photometric information, and spectral information is obtained through a large-aperture reflective telescope. The photometric information and spectral information data are summarized and analyzed by a computer terminal.

[0019] The telescope system in the method of the present invention consists of a large-aperture telescope and an array of four small-aperture telescopes to form different types of telescope array systems, which not only meet the requirements of measurement performance indicators but also minimize the price. Brief Description of the Drawings

[0020] Figure 1 It is a principle block diagram of the method for detecting gravitational wave electromagnetic counterparts based on the optical telescope system described in the present invention. Detailed Embodiment

[0021] Combined with Figure 1 This embodiment is described to illustrate the method for detecting gravitational wave electromagnetic counterparts based on the optical telescope system. In this embodiment, by searching and analyzing transient source targets, matching analysis is performed on the gravitational wave sources to determine the corresponding gravitational wave source electromagnetic counterparts. The transient source celestial bodies that generate gravitational waves are too far away and their brightness is very weak, so it is not suitable to measure the photometric and spectral information by using the method of splitting the light of a single telescope. The co-visual observation mode of two telescopes is adopted, and then the photometric signals and spectral signals of the two telescopes are processed and analyzed to match the observed gravitational wave information.

[0022] This method is implemented through an optical telescope system, and the optical telescope system includes a first co-visual observation optical telescope, a second co-visual observation optical telescope, a GPS clock, a CCD detector, astronomical positioning software, and a multi-channel fiber optic spectrometer;

[0023] The GPS clock receives the time signal from the satellite and then sends the time signal to the first co-visual observation optical telescope and the second co-visual observation optical telescope simultaneously;

[0024] The first co-visual observation optical telescope collects the spot signals in the sky area, images them by the CCD detector and performs photometric analysis; obtains the target image containing the transient source celestial body, and locates the position of the transient source celestial body through the astronomical file positioning software and then transmits it to the second co-visual observation large-aperture optical telescope;

[0025] The second co-visual observation optical telescope collects the light signals of the transient source celestial body and receives them through the multi-channel fiber optic spectrometer. The multi-channel fiber optic spectrometer obtains the spectral signal and performs spectral detection through the computer terminal.

[0026] The specific process is as follows:

[0027] Receive satellite time signals through a GPS clock and send the time signals to the optical telescope for the first common-view observation and the optical telescope for the second common-view observation simultaneously;

[0028] Obtain the spot signals of each celestial body in the sky area through the optical telescope for the first common-view observation, and the spot signals are received by a CCD detector to obtain an imaging image;

[0029] Use astronomical positioning software to perform comparative analysis on the imaging image to obtain a target image containing transient source celestial bodies; at the same time, determine the position of the transient source celestial body target in the target image;

[0030] The CCD detector performs photometric analysis on the transient source celestial body target to obtain the photometric value of the transient source celestial body target;

[0031] The optical telescope for the second common-view observation obtains the transient source celestial body target and performs spectral measurement on it through a multi-channel spectrometer;

[0032] Transmit the photometric value and spectral data of the transient source celestial body target to a PC terminal simultaneously to obtain the distance and mass of the gravitational wave electromagnetic counterpart.

[0033] In this embodiment, the optical telescope for the first common-view observation adopts a refracting small-aperture telescope mirror array mode. Specifically, a horizontal mounting system with four sub-tubes is used to splice the fields of view of four small telescopes into a large-field refracting telescope; the characteristic of the refracting telescope array is that the imaging is clear and sharp. Although there is chromatic aberration, it has little impact on photometric measurement. Moreover, the refracting telescope technology is mature and the cost is low. Using a horizontal mounting system with four sub-tubes, the fields of view of four small telescopes are spliced into a large field of view. Since the photometry of transient source celestial bodies is collected, the spliced large field of view can fully meet the observation requirements, and the cost can be significantly reduced.

[0034] The optical telescope for the second common-view observation adopts a large-aperture reflecting telescope mirror system. The biggest advantage of the reflecting telescope is that there is no chromatic aberration, which is very important for spectral measurement.

[0035] In this embodiment, the photometric measurement and imaging observation of celestial bodies can often be carried out simultaneously, and CCD images can be used for photometric analysis. The specific process of performing photometric analysis and astronomical positioning is as follows:

[0036] The observation mode of the two optical telescope systems adopts the stellar synchronization mode, that is, the stellar targets in the telescope remain stationary in the field of view. When new targets appear, there are trailing targets and targets with unchanged positions but changing luminosities. For targets with trailing relative to the stars, they are considered near-Earth targets and are automatically excluded. The transient source celestial object targets that remain unchanged in position but change in luminosity relative to the theoretical stellar background are taken as the key observation targets, and then it is determined whether they are gravitational wave electromagnetic counterparts through spectral analysis.

[0037] The relative positions of the targets and the background stars in the target images obtained by the CCD detector are used to calculate the image coordinates of the targets, that is, the pixel coordinates in the image, and then the pixel coordinates of the corresponding theoretical stars in the image are converted into celestial sphere coordinates through numerical calculation. The right ascension and declination of the targets in the celestial sphere are obtained.

[0038] Luminosity calculation: The total luminosity value of the transient source celestial object imaged in the CCD is calculated through aperture photometry. The transient source celestial object is a bright spot in the CCD image. A certain aperture is selected to make a circle that exactly encloses the entire bright spot, and the radiation flux of this circle is statistically analyzed. Subtracting the background value gives the luminosity of the target relative to the device. The curve of luminosity changing with time is the light curve.

[0039] Photometry of variable celestial bodies can obtain light variation data or light curves of important stars such as eclipsing variables, pulsating variables, flare stars, novae, and supernovae, as well as active galaxies, so that their physical properties and dynamical properties can be further studied.

[0040] In this embodiment, the result of celestial body luminosity measurement is related to the characteristics of the used telescope and detector, and the properties of various analyzers (mainly filters) added in the optical path. Such a system with a certain configuration of telescope, detector, and filter is called a photometric system. Photometric work usually measures the radiation of celestial bodies in some wavelength intervals that respond to the measured radiation with a combination of specified filters and detectors. Such a photometric system established is called a multicolor photometric system, and the photometry performed with it is called multicolor photometry.

[0041] In this embodiment, the described astronomical positioning method refers to finding the target by imaging and storing the celestial sphere, and then through the comparative analysis of two consecutive front and back photos, discovering the differences between the target and the theoretical star map. The theoretical star map uses the Tycho star map. When a target is found in the poor analysis of consecutive several-second pictures, it is determined as a valid target.

[0042] Astronomical positioning gives the right ascension and declination of the target in the celestial sphere coordinate system at a certain moment. For near-Earth targets, the right ascension and declination will have a slow movement, while for distant celestial bodies, they are a fixed value within this observation time period.

[0043] Based on this characteristic, near-earth targets can be quickly excluded, and the focus is on spectral measurement of distant transient targets.

[0044] Use astronomical positioning software to find the transient source celestial body. The time scale of the transient source celestial body is generally a few minutes. For long transient sources, it can be several hours or even days, and for short transient sources, it is only a few seconds. The stellar background is constant, and it is easy to find the target from the stellar background. Use the movement of the transient source relative to the stellar background to exclude near-earth transient source targets.

[0045] CCD photometric measurement, abbreviated as photometry, is to calculate the total photometric value of the celestial body's image in the CCD, which reflects the radiation flux of the celestial body within the CCD sensing range. The two-dimensional photometry using CCD can directly obtain important physical parameters such as the light curve, apparent magnitude, and color index of the celestial body through CCD photometry.

[0046] In this embodiment, spectral measurement is that the light of the star is dispersed by the spectrometer into red, orange, yellow, green, cyan, blue, and purple bands, and the white light becomes a continuous spectrum and some absorption lines and emission lines.

[0047] One content of spectral analysis is to study the spectral line displacement and broadening caused by the Doppler effect, and thus study the motion state of the celestial body and the spectral line generation region.

[0048] Another main content of spectral analysis is to study the redshift of the spectrum. If there are some features in the spectrum, which can be absorption lines, emission lines or other changes in optical density, redshift analysis can be performed. Performing redshift analysis of the spectrum requires a standard characteristic spectral line. For example, hydrogen in an atom has clear characteristic spectral lines when it emits light, and a series of characteristic spectral lines have a certain interval. If the characteristics are generally recognized, redshift analysis can be performed. There are many types of burst mechanisms of transient sources. Since the celestial bodies that generate gravitational waves all come from outside the Milky Way, through spectral analysis, the mass and distance of the central celestial body of the transient source can be determined.

[0049] In this embodiment, the specific process of spectral measurement is as follows:

[0050] Discover the transient source target through the first co-visual observation telescope, quickly transmit the information of this target to the second co-visual observation telescope, and focus on spectral measurement of the transient source. The spectrometer is the basic instrument for obtaining the celestial body's spectrum. It decomposes the radiation from the celestial body into a spectrum composed of monochromatic lights of various wavelengths. Spectral imaging. The receiving system is the detector, which is used to record the obtained celestial body's spectrum for spectral analysis. The weak information obtained is spectroscopically analyzed by a multi-channel spectrometer, and the spectroscopically analyzed spectral information is transmitted to the computer terminal. The computer terminal compares the received spectral information with the standard spectrum, and then through photometric analysis, obtains the total spectral redshift amount; the standard spectrum is prepared in advance in the laboratory.

[0051] In this embodiment, Doppler redshift refers to the change in phase and frequency caused by the difference in propagation path when an astronomical object moves in a certain direction at a constant rate. When the astronomical object moves closer to the Earth, the wave is compressed, the wavelength becomes shorter, and the frequency becomes higher. When the astronomical object moves away from the Earth, the opposite effect occurs, the wavelength becomes longer, and the frequency becomes lower.

[0052] In this embodiment, the Doppler redshift formula used is:

[0053]

[0054] ν′ is the frequency after redshift, and ν0 is the original frequency of the spectral line. Among them, θ is the angle between the line connecting the receiver and the wave source and the velocity direction, and β is the ratio of the astronomical object's velocity to the speed of light. It is positive when approaching the observer and negative when moving away from the observer.

[0055] The multi-object fiber optic spectrometer can simultaneously perform spectral measurements on multiple objects. Through spectral analysis and photometric analysis, the distance of the object and approximate astronomical collision or explosion events can be calculated, and then combined with the general relativity formula, the approximate magnitude of gravitational waves generated can be calculated.

[0056] In this embodiment, the GPS clock receives the time signal from the satellite and then sends the time signal to two telescopes for common-view observation, so that the time synchronization of the two telescopes can be achieved. However, some time parameters are uncontrollable. For example, the time for the two telescopes to receive and record optical signals cannot be absolutely synchronized, and only through mathematical interpolation can the optical parameters of the two analyses be strictly synchronized.

[0057] The CCD detector is a device for presenting images. As the abbreviation of Charge Coupled Device, the CCD can convert optical signals into electrical signals. After the electrical signals are amplified, the storage and restoration of images can be realized.

[0058] The working principle of the multi-channel fiber optic spectrometer in this embodiment is to first disperse the optical signal with a slit, and then use a collimating mirror to turn the scattered light into a collimated parallel light and reflect it onto the grating. After the light is dispersed, it is expanded according to different wavelengths to form a spectral plane. Each channel of the multi-channel spectrometer can cover different wavelength ranges. Any tiny spectral band can be selected to pass through different channels, and after the optical signal is converted into an electrical signal, it is output through the terminal to complete various spectral signal measurement and analysis. The multi-channel fiber optic spectrometer is particularly suitable for detecting weak signals and transient signals.

[0059] This embodiment uses the redshift information of the spectrum to determine the distance information and mass change information of the transient source. By inverting the gravitational wave signal through the mass change information and matching it with the observed gravitational wave signal, the electromagnetic counterpart of the gravitational wave source can be determined. It takes advantage of the fact that the propagation speeds of electromagnetic waves and gravitational waves are the same, and the luminosity information and spectral information of electromagnetic waves can reflect the changes in the gravitational field, so that the electromagnetic counterpart of the gravitational wave source can be determined. It has the characteristics of good positioning and coexistence of multiple information.

Claims

1. A method for detecting gravitational wave electromagnetic counterparts based on an optical telescope system, characterized in that: The specific implementation process of this method is as follows: Receive the satellite time signal through the GPS clock, and send the time signal to the optical telescope for the first common-view observation and the optical telescope for the second common-view observation simultaneously; Obtain the spot signals of each celestial body in the sky area through the optical telescope for the first common-view observation, and the spot signals are received by the CCD detector to obtain an imaging image; Use astronomical positioning software to conduct comparative analysis on the imaging image to obtain a target image containing transient source celestial bodies; at the same time, determine the position of the transient source celestial body target in the target image; The CCD detector conducts photometric analysis on the transient source celestial body target to obtain the photometric value of the transient source celestial body target; The optical telescope for the second common-view observation obtains the transient source celestial body target and conducts spectral measurement on it through a multi-channel spectrometer; Transmit the photometric value and spectral data of the transient source celestial body target to the PC terminal simultaneously to obtain the distance and mass of the gravitational wave electromagnetic counterpart.

2. The method for detecting gravitational wave electromagnetic counterparts based on an optical telescope system according to claim 1, characterized in that: The method for the astronomical positioning software system to position the transient source celestial body target is as follows: First, calculate the pixel coordinates of the transient source celestial body target in the target image, and then numerically calculate and convert the pixel coordinates of the corresponding theoretical star in the target image into celestial sphere coordinates, that is, obtain the right ascension and declination of the transient source celestial body target in the sky area.

3. The method for detecting gravitational wave electromagnetic counterparts based on an optical telescope system according to claim 1, characterized in that: The specific method for the CCD detector to conduct photometric analysis is: calculate the photometry of the transient source celestial body target through aperture photometry; The transient source celestial body is a bright spot in the image obtained by the CCD detector. Encircle the entire bright spot, calculate the gray value of the bright spot, subtract the background value from the gray value to obtain the photometric value of the target; and transmit the photometric value to the PC terminal.

4. The method for detecting gravitational wave electromagnetic counterparts based on an optical telescope system according to claim 1, characterized in that: The optical telescope for the second common-view observation transmits the optical signal of the transient source celestial body target to the multi-channel spectrometer for spectral splitting, and transmits the obtained spectral information after spectral splitting to the computer terminal. The computer terminal compares the received spectral information with the standard spectrum to obtain the total spectral redshift; The computer terminal determines the distance and mass of the transient source celestial body target according to the received photometric value and spectral redshift.

5. The detection method for gravitational wave electromagnetic counterparts based on an optical telescope system according to any one of claims 1-4, characterized in that: The optical telescope system includes an optical telescope for the first common-view observation, an optical telescope for the second common-view observation, a GPS clock, a CCD detector, astronomical positioning software, and a multi-channel fiber optic spectrometer; The GPS clock receives the time signal of the satellite, and then sends the time signal to the optical telescope for the first common-view observation and the optical telescope for the second common-view observation simultaneously; The optical telescope for the first co-visual observation collects the spot signals in the sky area and is imaged by a CCD detector. The transient source celestial body is positioned by the sky file positioning software, and the CCD detector performs photometric analysis of the transient source celestial body to obtain a target image. The target image is transmitted to the large optical telescope for the second co-visual observation. The optical telescope for the second co-visual observation collects the optical signals of the transient source celestial body and is received by a multi-channel fiber optic spectrometer. The multi-channel fiber optic spectrometer obtains spectral signals and performs spectral detection through a PC terminal to obtain the distance and mass of the gravitational wave electromagnetic counterpart.

6. The detection method for gravitational wave electromagnetic counterparts based on an optical telescope system according to claim 5, characterized in that: The optical telescope for the first co-visual observation uses a small-aperture large-field-of-view optical telescope array. The small-aperture large-field-of-view optical telescope array is an equatorial mounting system with four sub-tubes, and the fields of view of the four small telescopes are spliced into a large-field-of-view refractive telescope.

7. The detection method for gravitational wave electromagnetic counterparts based on an optical telescope system according to claim 5, wherein: The optical telescope for the second co-visual observation uses a large-aperture large-field-of-view reflective optical telescope.

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