Image of the Week

Gaia sees exploding stars next door

   
 

Fig. 1: The lightcurve of Gaia16aeg shows a steady decline consistent with a radioactively powered supernova lightcurve.

 

Alongside its main mission to chart the sky at unprecedented resolution, Gaia is moonlighting as a survey for transients under the Gaia Photometric Science Alerts project. After reporting the discovery of hundreds of transients, Gaia Alerts had a six-month pause in the second half of 2015. This break allowed for upgrades to the detection algorithms used to find transients. In early 2016, the improved Gaia Alerts pipeline was turned on again. To date we have published in excess of 140 transients at a rate of a little over 3 per day. Many of these transients are supernovae. All Gaia transients are being published on the Photometric Science Alerts web page.

The first exciting supernova to be discovered by Gaia in 2016 was Gaia16aeg. This supernova was first discovered independently by the ASAS-SN survey (as ASASSN-15lv) in mid 2015, and classified as a Type IIb supernova, at a relatively close distance of around 60 million parsecs (Mpc). Type IIb supernovae arise from the core-collapse of a massive star which has retained only a thin layer of its hydrogen envelope.

The photometric measurements of Gaia16aeg show a steady decline in brightness over six months (see Figure 1), as the radioactive elements that are responsible for powering the lightcurve of the supernova decay to iron. The Gaia spectra (Figure 2), measured through this decline in brightness, become dominated by strong emission lines from Calcium, Oxygen and Iron. These elements have been ejected from inside the core of the star, or synthesized in the explosion. The spectra shown below provide a diagnostic of the mass of the star that exploded.

   
 

Fig. 2: This sequence of spectra charts the evolution of Gaia16aeg as it transitions towards a nebular spectrum. Over a five month period, the continuum fades while strong emission lines of Calcium (including the Ca NIR triplet), Oxygen and Iron are seen to emerge in the red spectrum. The spectra were measured with Gaia's own Blue and Red Prism Photometers (BP/RP). These spectra are uncalibrated, with the Y-axis showing normalised counts, and the X-axis showing channel number (i.e. no attempt is made to measure wavelength). The gap between channels 50-70 is the gap between the BP and RP photometers as imaged on the detectors.

 

The second interesting find in the Gaia data was the detection of one of the closest supernovae of the last ten years (Figure 3). SN 2016adj was first discovered by a group of Australian amateur astronomers, and lies in Centaurus A, which at only 3.5 Mpc is extremely nearby. Spectroscopy shows that SN 2016adj is a hydrogen-rich Type II supernova, and likely comes from the collapse of a massive red supergiant star.

Cen A is dominated by striking dust lanes, and unfortunately the supernova lies within one of these. The supernova is hence heavily obscured; while it has a faint blue magnitude of ~17, it is much brighter (i~13) in the redder bands. Despite the reddening, the proximity of SN 2016adj means that it is feasible to search the many archival Hubble Space Telescope images of the galaxy to try and identify the supernova progenitor. The astrometric precision of Gaia can be used to accurately locate the supernova on archival images.

Together, these two supernovae provide yet another example of the fantastic quality of Gaia data, and some of the varied (and unintended) ways in which it can be used.

   
 

Fig. 3: The spectrum of SN 2016adj as seen by Gaia is extremely red, with almost no flux seen in the blue spectrum on the left of the figure. As with Fig. 2, this is an uncalibrated spectrum, and the gap between channels 50-70 is the gap between the BP and RP photometers as imaged on the detectors.

 

Credits: ESA/Gaia/DPAC/Gaia Science Alerts Team/Morgan Fraser/Simon Hodgkin/Lukasz Wyrzykowski

[Published: 29/02/2016]

 

Image of the Week Archive

2017
24/03: Pulsating stars to study Galactic structures
09/02: Known exoplanetary transits in Gaia data
31/01: Successful second DPAC Consortium Meeting
2016
23/12: Interactive and statistical visualisation of Gaia DR1 with vaex
16/12: Standard uncertainties for the photometric data (in GDR1)
25/11: Signature of the rotation of the galactic bar uncovered
15/11: Successful first DR1 Workshop
27/10: Microlensing Follow-Up
21/10: Asteroid Occultation
16/09: First DR1 results
14/09: Pluto Stellar Occultation
15/06: Happy Birthday, DPAC!
10/06: 1000th run of the Initial Data Treatment system
04/05: Complementing Gaia observations of the densest sky regions
22/04: A window to Gaia - the focal plane
05/04: Hipparcos interactive data access tool
24/03: Gaia spots a sunspot
29/02: Gaia sees exploding stars next door
11/02: A new heart for the Gaia Object Generator
04/02: Searching for solar siblings with Gaia
28/01: Globular cluster colour-magnitude diagrams
21/01: Gaia resolving power estimated with Pluto and Charon
12/01: 100th First-Look Weekly Report
06/01: Gaia intersects a Perseid meteoroid
2015
18/12: Tales of two clusters retold by Gaia
11/11: Lunar transit temperature plots
06/11: Gaia's sensors scan a lunar transit
03/11: Celebrity comet spotted among Gaia's stars
09/10: The SB2 stars as seen by Gaia's RVS
02/10: The colour of Gaia's eyes
24/09: Estimating distances from parallaxes
18/09: Gaia orbit reconstruction
31/07: Asteroids all around
17/07: Gaia satellite and amateur astronomers spot one in a billion star
03/07: Counting stars with Gaia
01/07: Avionics Model test bench arrives at ESOC
28/05: Short period/faint magnitude Cepheids in the Large Magellanic Cloud
19/05: Visualising Gaia Photometric Science Alerts
09/04: Gaia honours Einstein by observing his cross
02/04: 1 April - First Look Scientists play practical joke
05/03: RR Lyrae stars in the Large Magellanic Cloud as seen by Gaia
26/02: First Gaia BP/RP deblended spectra
19/02: 13 months of GBOT Gaia observations
12/02: Added Value Interface Portal for Gaia
04/02: Gaia's potential for the discovery of circumbinary planets
26/01: DIBs in three hot stars as seen by Gaia's RVS
15/01: The Tycho-Gaia Astrometric Solution
06/01: Close encounters of the stellar kind
2014
12/12: Gaia detects microlensing event
05/12: Cat's Eye Nebula as seen by Gaia
01/12: BFOSC observation of Gaia at L2
24/11: Gaia spectra of six stars
13/11: Omega Centauri as seen by Gaia
02/10: RVS Data Processing
12/09: Gaia discovers first supernova
04/08: Gaia flag arrives at ESAC
29/07: Gaia handover
15/07: Eclipsing binaries
03/07: Asteroids at the "photo finish"
19/06: Calibration image III - Messier 51
05/06: First Gaia BP/RP and RVS spectra
02/06: Sky coverage of Gaia during commissioning
03/04: Gaia source detection
21/02: Sky-background false detections in the sky mapper
14/02: Gaia calibration images II
06/02: Gaia calibration image I
28/01: Gaia telescope light path
17/01: First star shines for Gaia
14/01: Radiation Campaign #4
06/01: Asteroid detection by Gaia
2013
17/12: Gaia in the gantry
12/12: The sky in G magnitude
05/12: Pre-launch release of spectrophotometric standard stars
28/11: From one to one billion pixels
21/11: The Hipparcos all-sky map
15/10: Gaia Sunshield Deployment Test
08/10: Initial Gaia Source List
17/09: CU1 Operations Workshop
11/09: Apsis
26/08: Gaia arrival in French Guiana
20/08: Gaia cartoons
11/07: Model Soyuz Fregat video
01/07: Acoustic Testing
21/06: SOVT
03/06: CU4 meeting #15
04/04: DPCC (CNES) 
26/03: Gaia artist impression 
11/02: Gaia payload testing  
04/01: Space flyby with Gaia-like data
2012
10/12: DPAC OR#2. Testing with Planck
05/11: Galaxy detection with Gaia
09/10: Plot of part of the GUMS-10 catalogue
23/07: "Gaia" meets at Gaia
29/06: The Sky as seen by Gaia
31/05: Panorama of BAM clean room
29/03: GREAT school results
12/03: Scanning-law movie
21/02: Astrometric microlensing and Gaia
03/02: BAM with PMTS
12/01: FPA with all the CCDs and WFSs
2011
14/12: Deployable sunshield
10/11: Earth Trojan search
21/10: First Soyuz liftoff from the French Guiana
20/09: Fast 2D image reconstruction algorithm
05/09: RVS OMA
10/08: 3D distribution of the Gaia catalogue
13/07: Dynamical Attitude Model
22/06: Gaia's view of open clusters
27/05: Accuracy of the stellar transverse velocity
13/05: Vibration test of BAM mirrors
18/04: L. Lindegren, Dr. Honoris Causa of the Observatory of Paris
19/01: Detectability of stars close to Jupiter
05/01: Delivery of the WFS flight models
2010
21/12: The 100th member of CU3
17/11: Nano-JASMINE and AGIS
27/10: Eclipsing binary light curves fitted with DPAC code
13/10: Gaia broad band photometry
28/09: Measuring stellar parameters and interstellar extinction
14/09: M1 mirror
 
Please note: Entries from the period 2003-2010 are available in this PDF document.