laser topic problem and gazebo model [closed]

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I am using pioneer3at gazebo model. But when I added hokuyo lidar on pionner3at model in sdf file , ı can not see /scan topic or another topic with $rostopic list. How can ı add scan topic as ı see with rostopic echo /scan or rviz.

this is my sdf model:

    <?xml version="1.0" ?>
<sdf version="1.5">
  <world name='default'>
    <light name='sun' type='directional'>
      <cast_shadows>1</cast_shadows>
      <pose>0 0 10 0 -0 0</pose>
      <diffuse>0.8 0.8 0.8 1</diffuse>
      <specular>0.2 0.2 0.2 1</specular>
      <attenuation>
        <range>1000</range>
        <constant>0.9</constant>
        <linear>0.01</linear>
        <quadratic>0.001</quadratic>
      </attenuation>
      <direction>-0.5 0.1 -0.9</direction>
    </light>
    <model name='ground_plane'>
      <static>1</static>
      <link name='link'>
        <collision name='collision'>
          <geometry>
            <plane>
              <normal>0 0 1</normal>
              <size>100 100</size>
            </plane>
          </geometry>
          <surface>
            <friction>
              <ode>
                <mu>100</mu>
                <mu2>50</mu2>
              </ode>
            </friction>
            <contact>
              <ode/>
            </contact>
            <bounce/>
          </surface>
          <max_contacts>10</max_contacts>
        </collision>
        <visual name='visual'>
          <cast_shadows>0</cast_shadows>
          <geometry>
            <plane>
              <normal>0 0 1</normal>
              <size>100 100</size>
            </plane>
          </geometry>
          <material>
            <script>
              <uri>file://media/materials/scripts/gazebo.material</uri>
              <name>Gazebo/Grey</name>
            </script>
          </material>
        </visual>
        <self_collide>0</self_collide>
        <kinematic>0</kinematic>
        <gravity>1</gravity>
      </link>
    </model>
    <physics name='default_physics' default='0' type='ode'>
      <max_step_size>0.001</max_step_size>
      <real_time_factor>1</real_time_factor>
      <real_time_update_rate>1000</real_time_update_rate>
      <gravity>0 0 -9.8</gravity>
      <magnetic_field>6e-06 2.3e-05 -4.2e-05</magnetic_field>
    </physics>
    <scene>
      <ambient>0.4 0.4 0.4 1</ambient>
      <background>0.7 0.7 0.7 1</background>
      <shadows>1</shadows>
    </scene>
    <spherical_coordinates>
      <surface_model>EARTH_WGS84</surface_model>
      <latitude_deg>0</latitude_deg>
      <longitude_deg>0</longitude_deg>
      <elevation>0</elevation>
      <heading_deg>0</heading_deg>
    </spherical_coordinates>
    <model name='pioneer3at'>
      <pose>0 0 0.18 0 -0 0</pose>
      <static>0</static>
      <link name='chassis'>
        <inertial>
          <mass>14</mass>
          <inertia>
            <ixx>0.3338</ixx>
            <ixy>0</ixy>
            <ixz>0</ixz>
            <iyy>0.4783</iyy>
            <iyz>0</iyz>
            <izz>0.3338</izz>
          </inertia>
        </inertial>
        <collision name='collision'>
          <geometry>
            <box>
              <size>0.501 0.4 0.19</size>
            </box>
          </geometry>
          <max_contacts>10</max_contacts>
          <surface>
            <contact>
              <ode/>
            </contact>
            <bounce/>
            <friction>
              <ode/>
            </friction>
          </surface>
        </collision>
        <visual name='visual'>
          <geometry>
            <mesh>
              <uri>model://pioneer3at/meshes/chassis.dae</uri>
            </mesh>
          </geometry>
        </visual>
        <self_collide>0</self_collide>
        <kinematic>0</kinematic>
        <gravity>1</gravity>
      </link>
      <link name='right_front_wheel'>
        <pose>0.125 -0.201 -0.06 1.5707 -0 0</pose>
        <collision name='collision'>
          <geometry>
            <cylinder>
              <radius>0.11</radius>
              <length>0.075</length>
            </cylinder>
          </geometry>
          <surface>
            <friction>
              <ode>
                <mu>1</mu>
                <mu2>1</mu2>
                <slip1>0.5</slip1>
                <slip2>0</slip2>
              </ode>
            </friction>
            <contact>
              <ode/>
            </contact>
            <bounce/>
          </surface>
          <max_contacts>10</max_contacts>
        </collision>
        <visual name='visual'>
          <geometry>
            <mesh>
              <uri>model://pioneer3at/meshes/wheel.dae</uri>
            </mesh>
          </geometry>
        </visual>
        <self_collide>0</self_collide>
        <inertial>
          <inertia>
            <ixx>1</ixx>
            <ixy>0</ixy>
            <ixz>0</ixz>
            <iyy>1</iyy>
            <iyz>0</iyz>
            <izz>1</izz>
          </inertia>
          <mass>1</mass>
        </inertial>
        <kinematic>0</kinematic>
        <gravity>1</gravity>
      </link>
      <link name='left_front_wheel'>
        <pose>0.125 0.201 -0.06 ...