Gamma-Ray Bursts
description
Transcript of Gamma-Ray Bursts
![Page 1: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/1.jpg)
Gamma-Ray Bursts
![Page 2: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/2.jpg)
• Short (sub-second to minutes) flashes of gamma-rays, for ~ 30 years not associated with any counterparts in other wavelength bands
• First dedicated GRB detector: BATSE on the Compton Gamma-Ray Observatory
![Page 3: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/3.jpg)
GRB Light Curves
Long GRBs (duration > 2 s) Short GRBs (duration < 1 s)
Possibly two different types of GRBs: Long and short bursts
![Page 4: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/4.jpg)
General Properties
• Random distribution in the sky• Approx. 1 GRB per day observed• No repeating GRB sources
![Page 5: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/5.jpg)
BeppoSAX(1996 – 2003)
Wide-field Camera and Narrow-Field
Instrument (NFI; X-ray telescope) allowed
localization of GRBs to arc-minute
accuracy
First identification of X-ray and optical
afterglows of -ray bursts in 1997
![Page 6: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/6.jpg)
Afterglows of GRBs
Most GRBs have gradually decaying afterglows in X-rays, some also in optical and radio.
X-ray afterglow of GRB 970228
(GRBs are named by their date: Feb. 28, 1997)
On the day of the GRB 3 days after the GRB
![Page 7: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/7.jpg)
Optical afterglow of GRB 990510 (May 10, 1999)
Optical afterglows of GRBs are extremely difficult to localize:
Very faint (~ 18 – 20 mag.); decaying within a few days.
1 day after GRB 2 days after GRB
![Page 8: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/8.jpg)
Optical Afterglows of GRBs
Optical afterglow of GRB 990123, observed with Hubble Space
Telescope (HST/STIS)
Long GRBs are often found in the spiral arms (star forming regions!) of very faint host
galaxies
Host Galaxy
Optical Afterglow
![Page 9: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/9.jpg)
Energy Output of GRBs
Observed brightness combined with large
distance implies huge energy output of GRBs, if they are
emitting isotropically:
E ~ 1054 erg
L ~ 1051 erg/s
Energy equivalent to the entire mass of the sun (E = mc2), converted into gamma-rays in just a few seconds!
… another one, observed by us with the MDM 1.3 m
telescope on Kitt Peak!
![Page 10: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/10.jpg)
BeamingEvidence that GRBs are not
emitting isotropically (i.e. with the same intensity in all
directions), but they are beamed:
E.g., achromatic breaks in afterglow light curves.
GRB 990510
![Page 11: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/11.jpg)
Models of GRBs (I)
Hypernova:
There’s no consensus about what causes GRBs. Several models have been suggested, e.g.:
Supernova explosion of a very massive (> 25 Msun) star
Iron core collapse forming a black hole;
Material from the outer shells accreting onto
the black hole
Accretion disk =>
Jets => GRB!
![Page 12: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/12.jpg)
Models of GRBs (II)Supranova:
If a neutron star is rotating extremely rapidly, it could escape collapse (for a few months) due to
centrifugal forces.
Neutron star will gradually lose angular momentum, then
collapse into a black hole => collapse triggers the GRB
![Page 13: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/13.jpg)
Results of the BeppoSAX Era• During the BeppoSAX era, X-ray, optical,
radio afterglows were only found for long GRBs.
• In afterglows and host galaxies, redshifts, clustered around ~ 1, were measured; unambiguously established the cosmological origin of GRBs.
• Association with star-forming region, similarities of some optical light curves and spectra with type Ic supernovae provided strong support for hypernova/collapsar model for long GRBs
![Page 14: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/14.jpg)
Swift (launched 2004)
Localization of the first short GRBs;
Some with significant offsets from host galaxies, favoring binary-compact-
object merger models:
Dedicated GRB misssion with on-board soft -ray, X-ray, and optical telescopes;
Rapid automated localization and electronic distribution of GRBs with
arc-second precision
![Page 15: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/15.jpg)
Models of GRBs (II)Black-hole – neutron-star merger:
Black hole and neutron star (or 2 neutron stars) orbiting each
other in a binary system
Neutron star will be destroyed by tidal effects;
neutron star matter accretes onto black hole
=> Accretion disk
=> Jets => GRB!
Model works probably only for short GRBs.
![Page 16: Gamma-Ray Bursts](https://reader035.fdocuments.us/reader035/viewer/2022062323/56815496550346895dc2a8a1/html5/thumbnails/16.jpg)
Most successful model: