# Presentation: 158493

## The Radio Evolution of SN1987A

- Lister Staveley-Smith
- University of Western Australia

## Collaborators

**Lewis Ball (ATNF)**
**Bryan Gaensler (University of Sydney)**
**Mike Kesteven (ATNF)**
**Dick Manchester (ATNF)**
**Tasso Tzioumis (ATNF)**

## Summary of Early Radio Observations

**Prompt SN outburst lasting ~5 days**
- Optically thick RSN phase (Turtle et al. 1987)
- Initial expansion rate >19,000 km/s (Jauncey et al. 1987)
**Re-emergence as a radio source on day 1200**
- Optically thin SNR phase (Staveley-Smith et al. 1992)
- Expansion rate  ~3000 km/s (Gaensler et al. 1997)
- Accelerating flux increase near day 4600 (Manchester et al. 2002)
**Low Radio Luminosity**
- 10-4 times luminosity of SN1993J at maximum
**Unusual Evolution**
- Circumstellar model of Chevalier & Dwarkadas (1995) and CR shock acceleration model of Duffy, Ball & Kirk (1995) provided some explanation.

## MOST 843 MHz Light Curve

## ATCA 1.4 GHz light curve to day 7297 (2007 Feb 15)

- Re-emergence
- at day 1200

- Bump at
- day 2100

- First H
- hotspot

- Rapid rise in
- X-ray flux

- No turnover

## Spectral Evolution

## Day 7300 radio spectrum

## Spectral Evolution

**Spectral index (S************) is now ********=-0.75**
**Flattening at a rate ********=+0.02/yr, will reach canonical SNR spectral index (-0.5) in 2020**
**Electron energy spectral index is -2.5**

## First ATCA millimeter detection

- Day 6710:
- H75 array - 6 x 5 arcsec2
- 94 GHz
- Flux density 6.2 mJy

## 0.8-100 GHz Spectrum - day 6710

## Radio emission mechanism

**Cosmic rays accelerated in an CR-modified shock (Ball & Kirk 1992, Duffy et al. 1995).**
**Interaction with magnetic field produces synchrotron radiation**
**Toroidal geometry and slow expansion suggestive of production of CRs in reverse shock.**
**However B field and CR energy density probably too low in reverse shock for efficient emission (Dorfi 1991, Berezhko & Ksenofontov 2000)**

- Michael et al. (2003)

## Application to ATCA 1.4 GHz Light Curve

*t*2.2

- 3-zone model with modified
- Shock front and 10-2 particle
- Injection (Berezhko &
- Ksenofontov 2000)

## SN1987A as a new probe of the LMC

**1992 ATCA image/spectrum at 1.4 GHz (21cm HI)**

- SN1987A

- ‘Source 1’

- LMC

## SN1987A as a new probe of the LMC

**2006 ATCA image/spectrum at 1.4 GHz (21cm HI)**

- SN1987A

- ‘Source 1’

- LMC

## Line of sight absorption components

- HI(280 km/s)=0.48
- THI(280 km/s)=36K and NHI=2.37x1021 cm-2 from emission spectrum
- Tspin(280 km/s)<94K
- SN1987A behind bulk of the LMC’s disk which has more cool gas than the Milky Way

- Welty et al. (1999)

## Implications for ALMA and SKA

**ALMA (2012)**
- Resolution 0.1 arcsec at 100 GHz
- Mean S/N~3 per beam area at present flux density (8 hr observation)
**SKA Phase 1 (2014)**
- Resolution 0.1 arcsec at 6 GHz
- Mean S/N~4 per beam area at present flux density (8 hr observation)
**SKA (2020)**
- Resolution 0.01 arcsec at 1 GHz
- Mean S/N~100 per beam area, even at present flux density (8 hour observation)
- Detailed, spatially resolved structure at all frequencies 0.1-20 GHz

## Summary

- Rapid increase of flux density at all radio frequencies - lately St2.2
- No evidence of recent turning over of radio flux densities
- Spectral index becoming flatter - now at -0.75
- First millimeter (95 GHz) detection
- Some progress in modelling - but large number of poorly known variables (B field, shock velocity, CR acceleration efficiency, geometry and density profile)
- SNR 1987A now strong enough to be a useful probe of the foreground ISM