SGR 1806-20
Reference data for magnetar SGR 1806-20: 7.56-second spin period, 2×10¹⁵ gauss magnetic field, 28,400 ly distance, and the 2004 giant flare.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Distance | 28400 ly | ± 4200 ly | Spectrophotometric and radio H I absorption distance (~8.7 kpc) in the W31 star-forming complex (Bibby et al. 2008). | high-confidence | SIMBAD Astronomical Database (CDS) |
| Spin Period | 0.00008745 d | ± 1e-8 d | X-ray rotation period of 7.5559 seconds, rapidly braking under magnetar torque. | definitive | SIMBAD Astronomical Database (CDS) |
| Estimated Mass | 1.45 M☉ | ± 0.2 M☉ | Dynamical binary mass function or relativistic Shapiro delay | model-dependent | SIMBAD Astronomical Database (CDS) |
| Quiescent X-Ray Luminosity | 10.5 L☉ | ± 2.5 L☉ | Persistent 2–10 keV X-ray output (~4 × 10³⁴ erg/s) powered by magnetic field decay. | high-confidence | SIMBAD Astronomical Database (CDS) |
| Characteristic Age | 2.4e-7 Gyr | ± 5e-8 Gyr | Instantaneous dipole braking age; true physical age in the cluster is ~1–5 kyr. | model-dependent | SIMBAD Astronomical Database (CDS) |
| Surface X-Ray Temperature | 6500000 K | ± 600000 K | Blackbody thermal component ~0.56 keV heated by internal magnetic dissipation. | high-confidence | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots SGR 1806-20 — Extreme Galactic Magnetar at RA 18h 08m 39.34s, Dec -20° 24′ 39.8″ within Sagittarius, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
First identified in 1979 as a source of recurring soft gamma-ray bursts in Sagittarius, SGR 1806-20 became a cornerstone proof of the magnetar model developed by Robert Duncan and Christopher Thompson. In 1998, Rossi X-Ray Timing Explorer observations measured its 7.56-second spin period and an extraordinary spin-down rate, revealing a surface dipole magnetic field near 2.0 × 10¹⁵ gauss—roughly a thousand times stronger than a typical radio pulsar and a hundred trillion times stronger than a refrigerator magnet. Rather than drawing energy from rotation, SGR 1806-20 shines via the decay and twisting of this colossal magnetic field.
On December 27, 2004, a catastrophic crust-cracking starquake and magnetospheric reconnection event on SGR 1806-20 unleashed the brightest extrasolar flash ever detected at Earth. During its initial 0.2-second spike, the magnetar released more than 10⁴⁶ ergs of gamma-ray energy—outshining the full Moon at high energies, saturating nearly every X-ray and gamma-ray detector in space, and measurably ionizing Earth's upper daylit ionosphere across 28,400 light-years of space. A 400-second oscillating tail followed, modulated by the neutron star's 7.56-second spin and crust seismic vibrations.
Buried behind roughly 30 magnitudes of visual interstellar dust extinction in the W31 giant molecular cloud complex, SGR 1806-20 resides inside a compact cluster of young, ultra-massive stars—including Luminous Blue Variables and Wolf-Rayet stars—indicating that its progenitor star likely exceeded 40 solar masses before collapsing.
Practical Visual Observing Guide
- Completely obscured in optical light (AV ~ 29 mag) by dense galactic-plane dust clouds in Sagittarius.
- Faintly detected in the K band (K ~ 20–21) during active outbursts using 8-meter adaptive-optics infrared telescopes.
- Produced an expanding relativistic radio nebula tracked by the VLA and VLBA for months after its 2004 giant flare.
Catalog Cross-Identifications & Aliases
Common Aliases: PSR J1808-2024 · AX J1808.6-2024
| Catalog Authority | Identifier |
|---|---|
| SIMBAD | PSR J1808-2024 |
Related Objects, Comparisons & Guides
Vela Pulsar (PSR B0833-45) — Neutron Star
Reference data for the Vela Pulsar: 89.3 ms spin period, VLBI parallax distance of 936 ly, pulsar wind nebula jet, and superfluid glitch physics.
Crab Pulsar (PSR B0531+21 Neutron Star)
Coordinates, 33.08 ms spin period, 16.5-mag optical flashes, spin-down luminosity, and high-aperture observing guide for the Crab Pulsar.
Sagittarius A* (Galactic Center Black Hole)
Coordinates, GRAVITY S2 stellar orbit distance (8,277 pc) & mass (4.297 × 10^6 M☉), EHT 51.8 μas shadow, and Galactic Center guide for Sgr A*.
Measurement Uncertainty & Optics in Astronomy
How random vs systematic errors, asymmetric error bars, model dependencies, and optical aperture/exit-pupil limits shape astronomical measurements.
Celestial Coordinates (RA & Dec) Explained
Practical reference to J2000 equatorial coordinates: Right Ascension (RA in hours, minutes, seconds), Declination (Dec in degrees), and sexagesimal conversion.
Scientific Sources & Dataset Provenance
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg