Gamma Ray Burst Precursor
Approximately 15 percent of all astronomical gamma-ray bursts show one or more precursors, these are called gamma ray burst precursors . This is radiation that occurs up to 100 seconds before the main eruption and has about 100 times less luminosity. Before the main eruption there is usually a phase in which no radiation is detected. The spectrum corresponds to that of the main eruption. If several precursors are observed, there are rest phases of around 10 seconds between them.
properties
The precursors of gamma-ray bursts have the following properties:
- There is a phase between the precursor and the main eruption in which no radiation can be detected.
- Gamma-ray bursts with and without a precursor do not differ in spectral properties or in their light curves .
- The spectrum and the temporal variability of the radiation from the precursors and the main event are approximately the same.
- Several precursors can occur in a gamma-ray flash.
- Precursors appear in both short and long bursts of gamma rays . More precursors are observed with long gamma-ray flashes.
- The time difference between the main eruption and the precursor is between fractions of a second and a few hundred seconds.
Interpretations
Original hypotheses of a two-stage model were invalidated by the observation of several precursors in some gamma-ray flashes. Instead, the central mechanism that creates the main outbreak is likely to be responsible for the precursors as well.
- In the fireball model, the emission of the precursor is interpreted as the thermal radiation of the explosion cloud. However, the spectrum of the precursors differs from that of a black body .
- In the Progenior Precursor Model, the precursors are created in the context of the Kollapsar model through the interaction of the jets with the stellar envelope. This model also has difficulties with the non-thermal spectrum.
- In the magnetar model, radiation is produced by accretion of matter onto a magnetar . The torque transmitted in the process accelerates the neutron star so that it cannot temporarily absorb any further matter until the rotational speed has fallen below a critical value again.
- Flares caused by the breaking of the crust of a neutron star during a merger of two compact stars.
- Interaction of the magnetospheres of the neutron stars in a merger of two neutron stars.
None of the listed hypotheses can explain all observed precursors and predict their properties.
Definition of terms
A supernova is detected for some of the long gamma-ray bursts after the afterglow has subsided . According to the Induced Gravitational Collapse hypothesis , gamma-ray bursts arise in close binary star systems in which a stripped-envelope supernova initiates the collapse of a companion, a neutron star . When the neutron star collapses, the gamma-ray burst occurs. In the context of this model, the Ib / c type supernovae are also referred to as precursors.
literature
- F. Nappo et al .: Afterglows from precursors in Gamma Ray Bursts. Application to the optical afterglow of GRB 091024 . In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1405.3981v1 .
- MG Bernardini et al .: A magnetar powering the ordinary monster GRB 130427A? In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1401.1972v1 .
- Lech Wiktor Piotrowski: Constraints on the optical precursor to the naked-eye burst GRB080319B from Pi of the Sky observations . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1202.5322v1 .
- Eleonora Troja, Stephan Rosswog, Neil Gehrels: Precursors of short gamma-ray bursts . In: Astrophysics. Solar and Stellar Astrophysics . 2010, arxiv : 1009.1385v1 .
Individual evidence
- ↑ Maria Grazia Bernardini et al .: How to switch on and off a Gamma-ray burst through a magnetar . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1306.0013v1 .