Gamma-Ray Burst/Supernovae:�a Review

Paolo A. Mazzali

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GRB Duration:

Bimodal distribution:

Short-hard v. Long-soft

short

long

Short-hard bursts are produced by NS-NS or NS-BH mergers (see Monday talks)

Most nearby long-soft GRBs come with a Supernova� GRB980425: the optical counterpart

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GRB/SNe are Broad-Lined SNe Ic

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SN 1998bw / GRB980425

Matheson et al. 2003

Patat et al. 2001

SN2003dh / GRB030329

Stripped-envelope SN: classification

SNe Ib/IIb: amount of He/H

SNe Ic: width (nr) of lines

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SNe Ic: meaning of broad lines

• Broad lines indicate sufficient line opacity at high velocity
• indicative of high Kinetic Energy
• As lines get broader (larger velocity span) they blend more

🡺Broader-lined SNe have fewer lines

• Number of lines is a more accurate and quantitative criterion for spectral classification than “broad-lined”
• Vel increasing as N_lin decreases indicates that Ek ~ (Mej)ⁿ

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07gr

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04aw

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97ef

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98bw

Core-Collapse SNe�Massive Star (>8M_⊙)

• Si burning
• Core collapse
• Compact object (NS/BH)
• ν emission
• KE deposited
• Explosion 🡪 NSE

🡪 ⁵⁶Ni (~0.1-1M_⊙)

• SNe Ib/c: “stripped-envelope”

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H

He

^C

^O

^Si

^core

^{SN Type SN Ic SN Ib IIb SN II}

^{Prog. Star WO WC WN R/BSG}

Distribution by subtype

• SN Lum fn, Li et al. 2011
• SE-SNe NOT dominated by H/He rich SNe: numbers of He-rich and He-poor actually similar
• IIb: 7% of all, 9% of CC-SNe, 27% of all SE-SNe
• Ib: 4% 5% 15%
• Ic: 15% 20% 58%

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SE SNe:Different LC distributions

SNe Ib/IIb: more homogeneous

On average less luminous

SNe Ic: wider range of Lum

On average more luminous

84 SNe, Prentice et al. 2016

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SNe IIb – Ib are a continuum

• different strength of Balmer lines: range of H shell masses, although capped at a few 0.1 M_◉ to preserve Type I light curve
• Many SNe classified as Ib show weak or intermediate strength Balmer lines (in part. Hα)

(Prentice & PM 2017)

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It takes little He to make a SN Ib

• HeI requires non-thermal processes
• SNe Ib: M(He) >~ 0.1 M_◉
• SNe IIb: M(H)~0.02 M_◉
• Different spectral subclasses are sharply separated

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(Hachinger et al., 2012)

All GRB/XRF SNe are Ic�SNe Ib v. Ic: Helium

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Ib

Ic

Ic

2.058µm

1.083µm

Taubenberger et al. 2006

Strongest HeI lines in IR. 1μ can cause confusion, 2μ line unique

Line blending and number of features

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• As velocity increases, features blend:
• Fewer features
• Higher E/M
• As velocity increases, features just shift
• Larger M
• Constant E/M

Typical N=7 spectrum

N=6 spectra with different velocities

Outer density slope determines line width

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PM+ 2017

Refined classification

Presence of H in Ib quite common

• Many SNe classified as Ib show weak or intermediate strength Balmer lines (in part. Hα)
• More SNe with H
• SN IIb—IIb(I)—Ib(II)—Ib by decreasing H line strength

50 SNe with good spectral coverage out of 82 SNe with good LC (Prentice & PM 2017)

No trace of He in Ic

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• SNe Ic can be ordered by line width/number

Updated distribution by subtype

• Relative numbers close to Li et al.’s rates
• Considering weak Hα lines, n(IIb) >> n(Ib)
• Difficult to strip all H, as would be expected in single star evolution
• n(Ic)~n(IIb+Ib): are all SNe Ic the product of close binary interaction?

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SN Ic IIb Ib

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46% 40% 14%

50 SNe, Prentice & PM 2017

GRB/SNe are luminous

• SN1998bw was as luminous as a SN Ia
• LC powered by ⁵⁶Ni decay
• It produced much more ⁵⁶Ni than `normal’ core-collapse SNe (~0.5 M_◉)

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GRB/SNe are highly energetic

• GRB/SNe have very high expansion velocities (optical velocities up to 0.1c track relativistic properties)
• XRF/SNe have lower velocities

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after Pian et al. 2006, Nature

Explosion Parameters

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Arnett 1982

Use of line width

• Single velocity measurement often used combined with LC shape to obtain Mass AND Ek: this is VERY RISKY (euphemism)
• Velocity is time-dependent: what epoch do you choose?
• Maximum does not always happen at the same epoch
• Blending depends on velocity (line id uncertain)
• Highest velocities may carry most Ek if they contain sufficient mass
• Width and breadth may not always correlate: distribution of mass with velocity may not be constant

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SN 1998bw: high mass and KE

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Iwamoto et al. 1998

GRB/SNe are all similar �SN 2003dh/GRB030329

SN 2003dh was

almost as bright

and powerful as

SN 1998bw:

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KE = 3.8 10⁵² erg

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Mazzali et al. 2003

GRB/SNe are driven by ⁵⁶NI

• Strong nebular Fe lines in nebular spectrum resemble SNe Ia, and testify to the large amount of ⁵⁶Ni synthesised
• Oxygen line are broader than Fe lines, indicating an aspherical explosion (Mazzali et al. 2001)

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SN 2013dx has the lowest Ek �of any GRB(130702A)/SN so far

Mej ~ 9 M_◉, Ek ~ 9 10⁵¹ erg

M(⁵⁶Ni) ~ 0.25 M_◉

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• cf. SN2010ah (no GRB):

Mej ~ 3 M_◉, Ek ~ 10⁵² erg

M(⁵⁶Ni) ~ 0.25 M_◉

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• GRB/SN 2013dx has smaller E/M but larger M

(PM+ 2021)

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Spherical

Aspherical

FeII] 5200A

[OI] 6300A

Observed

Aspherical explosion:

line shape depends

on orientation

Orientation 15 deg

GRB

More Ek: ⁵⁶Ni

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Less Ek: Oxygen

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Prediction from asphericity: off-axis (GRB?)/SNe

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• Narrow, single peaked [OI] line: polar view (like 98bw)

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• Broad, double-peaked [O I] line: aspherical SN viewed edge-on

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SN 2003jd:

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• The [O I] 6300A line shows a double peak, suggesting an explosion similar to SN1998bw but viewed ~70° from the axis

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(Subaru and Keck data,

PM + 2005)

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an off-axis aspherical SN

How common is asphericity?

• SNe Ib/c are consistent with being aspherical
• BL-SNe are the most aspherical
• They have the widest range of nebular properties (Maeda et al. 2008, Tanaka et al. 2009): double peaks have wider separation

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Mazzali et al. 2008, Tanaka et al. 2009

HN SN Ib 2008D / XRF 080109

Intermediate mass/energy

SN2008D / XRF080109: the nebular phase

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Mazzali et al. 2008, Tanaka et al. 2009

• [O I] line has double-peaked profile, like SN2003jd
• Not a normal SN w/ shock b/out!
• An energetic, highly aspherical explosion, viewed far from the polar axis
• He shell blocked any jet

SN2016jca/GRB161219B

One of the best observed GRB/SNe

• Early data show highest velocities ever recorded
• Ek estimate higher than other GRB/SNe because outermost layers better probed
• Mej ≅ 8 M_◉
• Ek ≅ 5 10⁵² erg
• M(⁵⁶Ni) ≅ 0.4 M_◉

Ashall et al 2017

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SN2016jca/GRB161219B

Higher velocities than 1998bw, UV suppressed: more Ni

Early data allow better models: increasing O ab. at low velocities, indicative of aspherical props.

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Ashall et al. 2017

SN 2016jca: more ⁵⁶Ni early on: head-on Fe jet

As time passes, see deeper into aspherical ejecta

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O-rich

Ni-rich

GRB jet

Modelling results

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Ek and Mej seem to be correlated, ⁵⁶Ni less so

Props of SNe Ibc as f(prog. mass)

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A minimum mass and energy seem to be required for GRBs

What is the “driving force”?�Compare energies of GRBs and SNe

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SN kinetic energy always dominates, and it is close to the maximum expected magnetar energy (PM+2014)

SN GRB

GRB+SN

GRB

GRB+SN

GRB

A Magnetar in SN Ib 2005bf?

SN 2005bf (Tominaga et al. 2007) showed a bright, late 2nd LC peak

Magnetar activity may have been responsible for the rebrightening (Maeda et al. 2007)

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A magnetar in XRF/SN bl-Ic 2006aj?

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SN2006aj, a BL-SN Ic, dimmer than GRB/SNe (98bw, 03dh, 03lw)

M(⁵⁶Ni) ~ 0.2M_⊙

Difficult to produce a lot of ⁵⁶Ni from a small mass core.

Remnant likely a NS

Extra energy from Magnetar?

SN2006aj: intermediate M, KE

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Mazzali et al. 2006

SLSNe and ULGRBs?

• Ultra-long (>10⁴ s) GRB111209 showed a SN bump (SN2011kl)
• SN LC intermediate in Lum between GRB/SNe and SLSNe
• Blue spectrum, consistent with high Ek SLSN

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Consistent with Magnetar powering

Are all luminous SNe magnetars? Greiner et al 2015, Nature

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Non-thermal spectra of SLSNe-I

“peculiar” OII lines are result of non-thermal excitation/ionization at high Temp

HeI lines appear via same process only later, when Temp is “right” (lower) (PM+2016)

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Composition

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06D4eu PTF13ajg

Most lines are C/O, Int. Mass or Fe-group elements, as in SNe Ic

(He visible late sometimes) (PM+2016)

The OII ion

Optical OII lines come from lower levels with higher excitation energy than HeI (>22eV).

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Not thermally excited

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Velocity evolution: SNe Ic v. SLSNe

• Both SLSNe and HNe have high velocities,
• but in SLSNe high vel is sustained over a much longer time
• ULGRB/SLSN has higher vel than other SLSNe
• Slow decline of vel in SLSNe suggestive of Magnetar powering in SLSNe

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Comparing properties

• ULGRB/SNe can have He and H (like SNe Ib/c, IIb)
• Highly excited OII (and He I) lines due to non-thermal excitation
• These are all cores of massive stars (binaries?)
• GRB/SNe, ULGRB/SNe have the highest Ek, Ek/Mej
• ULGRB/SNe NOT at massive end of range
• GRB/SNe driven by ⁵⁶Ni, ULGRB/SNe probably not.
• Magnetar powering likely in both GRB/HNe and ULGRB/SNe

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Comparing SNe Ib/c and SLSNe-I

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In SNe Ib/c, correlation between ejected mass and both ⁵⁶Ni mass and Kin En

SLSNe cover similar Ek range, may have larger Mej and have typically lower E/M (ULGRB/SN is the exception). Little info on M(⁵⁶Ni).

Origin of two groups could be similar.

Magnetar parameters?

• GRB, XRF require rapid energy injection, large E/M
• SLSNe powered by interaction: late injection

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GRB/SNe

XRF/SNe

SLSN-”I”

SN2005bf

SN2011kl-GRB111209

After Metzger+ 2015

A Grand Scheme

• Collapse of very massive (~35-50 M_⊙), stripped stars to BHs makes aspherical GRB-HN (GRB can be very different, HN much less).
• Collapse of less massive star (~ 20 M_⊙) to NS can cause a less energetic, less aspherical SN and an XRF (via magnetic activity ?).
• Presence of too much He prevents GRB, still allows XRF (fast/aspherical breakout)
• Are all energetic SNe energised by a magnetar (or a jet?)

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A possible scenario

• Ek, M(⁵⁶Ni) of SNe Ib/c increases with M(prog)
• Very large Ek (Ek/Mej >1) of GRB/SNe likely to be the result of magnetic energisation
• SLSNe-I have lower Ek/Mej (~1, like SNe Ib/c), their luminous LCs may be energised by magnetar energy at a later stage
• Jets may be the result of the collapse of the NS to a BH (collapsar)
• What role do NS/proto-NS really play?

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