Exploring the Universe’s extreme events

Galactic transients
DANIELA HADASCH, AUGUST 8, 2023
superbossa/MPP

Definition of Transient sources• A transient event refers to a sudden and temporary change in the brightness of a celestial
object and is characterized by significant changes in the emitting object's properties.
• Unlike variability, transient events are not part of the regular behavior (e.g. AGN flares) of
the object but are caused by specific and often rare processes or interactions.

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Transitional
milli-second
pulsars

Supernovae

Magnetars
Fast radio
burstsNovae

Instruments
Fermi

Cherenkov
telescopes
50GeV - 50TeVMAGIC

VERITAS

Fermi-GBM
8keV - 30MeV
Fermi- LAT
100MeV - 300GeV

CTA-LST1
LHAASO

HAWC
100GeV - 100TeV

HAWC

H.E.S.S.

LHAASO
1TeV - 1PeV

Adapted M. Strzys

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Transitional milli-second pulsars

Milli-second pulsars (MSPs)• Weakly magnetized neutron stars• Neutron star: collapsed core of a massive
star; densest known stellar object: r ~10km, m~1.4 M☉• Pulsar: rotating neutron stars emitting
beams of electromagnetic radiation• Often found in globular clusters• Old systems• Often part of close binary systems➡ Recycled low-mass
X-ray binaries [Backer+1982, Alpar+1982]
Slide adapted from Papitto

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Transitional milli-second pulsars (tMSPs)
Composed by milli-second pulsar + low mass star
Low Mass X-Ray Binary (LMXB)

Switch between two states

Radio MSPHigh mass in-flow rate:
Gravity dominates

Low mass in-flow rate:
Magnetic field dominates

Accretion disc

Rotation powered MSP

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Swinging milli-second pulsar in M28
X-ray luminosity ~ few x 10 36 erg/s → accretion power

Papitto+2013

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Transitional milli-second pulsars

Papitto, VGGRS, 2023

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9Transitional milli-second pulsars

Brighter gamma-ray emission

Papitto, VGGRS, 2023

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10tMSPs at high energies• Search for transitions in 7 years of FermiLAT data [Torres+2017]

Radio pulsar

Sub-luminous

Sub-luminousRadio pulsar• Transition found in 2 out of 3 known systems(PSR J1824−2452I not included in analysis since
it is located in globular cluster M28 that is abright gamma-ray source)• gamma-ray flux varies by a factor of 2–5• High gamma-ray state is variable• Shorter-timescale phenomena like in radio/Xray/optical• High-energy cutoffs at a few GeV• TeV emission possible? Second component?
• Non-detection of J1023 at TeV by VERITAS[Aliu+2016]

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Open questions• What drives variations of the mass in-flow rate?
• Tidal interactions? Mass accumulation?

• Origin of the gamma-ray emission during the intermediate accretion stage?
• Propeller/magnetospheric origin?

• Are all millisecond pulsars in close binary systems transitional?
• Do they emit in the TeV range?
• Cutoff at GeV does not look promising, but another component coming from much farther out than thesurroundings on the pulsar might be possible.

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12Open questions• What drives variations of the mass in-flow rate?
• Tidal interactions? Mass accumulation?

• Origin of the gamma-ray emission during the intermediate accretion stage?
• propeller/magnetospheric origin?

• Are all millisecond pulsars in close binary systems transitional?
• Do they emit in the TeV range?
• Cutoff at GeV does not look promising, but another component coming from much farther out than thesurroundings on the pulsar might be possible.
Observation strategy
Look for distinctive variability in the optical and X-ray band in the error bar of unidentified
Fermi-LAT sources.
For TeV: Search for the closes ones (e.g. PSR J1023-0038 which is at 1.4 kpc)
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Magnetars
Fast radio bursts

NASAMagnetars
X-rays• Neutron stars with ultra-high magnetic
fields (B~10 14-1015G)• ~30 Magentars known• Bright X-ray pulsars• LX ~1033-10 35 erg/s• Rotating with periods of 2-12s

NASA
ICRC SATELLITE 2023 - D. HADASCHSlide from N. Rea

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Slide from A. Lopez

Slide from A. Lopez

Fast radio bursts (FRBs)• Transient radio pulses of milli-sec duration• Likely extragalactic, several confirmed with host galaxy ID(z~0.034-0.66)• Outer regions of galaxies within spiral arms or beyond central bulge• Over 150 FRBs have been discovered (http://frbcat.org/ ), ~20
repeating• Radio analysis pipelines tailored to search for short bursts inalmost real-time —> emit alerts for multi wavelength
observations• No counterpart to radio emission was detected before April 27,
2020...

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FRB200428: a unique case
• April 28, 2020: CHIME detects FRB incoincidence with a magnetar (ATel #13681)

CHIME 2020

• The burst had a double-peak structure with twocomponents ~5 ms wide separated by ~30 ms• Confirmation at different wavelengths:• STARE2 (Bochenek et al. 2020) and European dishes:
Westerbork, Onsala, Toruń (Kirsten et al. 2020)• X-ray bursts by Swift (Barthelmy et al. 2020), INTREGRAL(Mereghetti et al. 2020)• AGILE (Tavani et al. 2021), Konus-Wind (Ridnaia et al. 2021),NICER(Younes et al. 2021), Insight HXMT (Li et al. 2021)• MAGIC (TeV) could not observe due to pandemic
lockdown, H.E.S.S. put upper limits.
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Source of interest: SGR 1935+2154• Galactic magnetar located at 6.6 kpc [Zhou+2020]• Spin period P=3.24 sec• Dipole magnetic field Bm=2x1014G• Started period of X-ray bursting on April 22, 2020

• Hosted in an evolved SNR (G57.2+0.8) and (likely)interacting with a surrounding molecular cloud• April 2020: a fast radio burst (FRB) is detected by
CHIME/FRB in coincidence with this magnetar [Andersen+2020]
SGR 1935 +2154 is
the first FRB in the Galaxy andthe first identified FRB source.
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Very high energy constraints• It was not a giant flare but
intermediate burst• Different models for the site ofemission (see Zhang 2020 for areview):• inside magnetosphere• relativistic outflow interacting withsurrounding ISM• TeV emission can be expectedaccording to theoretical models[Lyubarsky 2014, Murase et al. 2016, Metzger et al. 2020]

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Supernovae

https://www.arcetri.inaf.it/science/SNe/zoo.jpg

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Cosmic Ray acceleration by SNe• Core-collapse (cc-)SNe, occurring in dense circumstellar medium (CSM), arepossible candidates for accelerating Cosmic Rays to PeV energies. Needvery dense environment (progenitor wind). [Katz et al. 2011; Murase et al. 2011; Bell et al. 2013,
Cristofari et al. 2022, Brose et al. 2022]• SN shock propagates in very dense CSM -> a collision-less shock [Ptuskin 2005, Murase
et al 2011, Katz et al 2011, Cardillo 2015, Marcowith 2014,2018, ]• High density: more p-p collisions -> gamma-ray emission• Fast magnetic field amplification [Bell 2004].
• High magnetic field of the order of Gauss are recorded in radio SNe,
instead of the 10 to 100 μG measured in young SNRs.
• Necessary to accelerate particles to very high energies at an early stage.
• Nearby Type IIb SN 1993J, a magnetic field as high as 100 G and shock speeds ashigh as 20,000 km s-1 [Fransson & Björnsson 1998, Tatischeff 2009]• TeV Gamma ray emission should have been detected weeks after theoutburst [Tatisheff 2009, Markowith et al 2018]
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https://www.mpi-hd.mpg.de/HESS/pages/home/som/2019/07/

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Core-collapse Supernovae occuring
in a dense environment are possible
candidates for PeV cosmic-ray
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acceleration.
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[Vink 2017]

Supernova (SN)

Multiwavelength image of Kepler’s SNR• Most recent SN in our Galaxy visible by unaided eye: SN 1604
(Kepler’s Supernova)• Type Ia supernova (d=3.2-12 kpc [Danziger and Goss 1980; van den Bergh et al. 1973] )• Most recent extra-galactic unaided eye SN: SN 1987A in the
Large Magellanic Cloud [Arnett et al. 1989]• Type II SN; d~50kpc• Beginning of neutrino astronomy: (Kamiokande II: 12 antineutrinos;
IMB: 8; Baksan: 5) in ∼ 10 s burst (core collapse)• What is happening at higher energies?

http://www.eso.org/public/images/eso1401a/• Brighter than stars and planets at its peak [Vink 2017]

Composite image of SN1987A remnant
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The case of SN 1987A• Laboratory for SN explosion and SNR expansion
modeling and particle acceleration on the shockmodeling.

[Frank 2016]• Hints in X-rays that the blast wave is leaving thedense equatorial ring [Frank 2016].

• Within Diffuse Shock Acceleration (DSA) models
emission from SNR 1987 A is expected [Berezhko 2015]:• Emission is variable (variable density of themedium + acceleration timescale)[Berezhko 2015]• The emission is hadronic (cosmic ray protons areaccelerated on the shock).

• Maximum of emission expected 2008-2018• NO emission detected in GeV (Fermi) nor TeV(H.E.S.S.) [Fermi Coll. 2015; H.E.S.S. Coll. 2015] But…
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GeV brightening of SN 1987A region[Malyshev 2019]• Enhancement (4σ) of the GeV
emission from the SN 1987A region as
observed with Fermi-LAT [Malyshev 2019]• Signal is seen only at >1 GeV energies
and comparable to predictions by
DSA models.
• Poor localization allows several othercounterparts• No clear variability in X-rays – a hint
for hadronic emission from SN 1987A?
• Let’s stay tuned!
• More sensitive instrument to come:Cherenkov telescope array (CTA)
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Core-collapsed SNe searches

H.E.S.S. Coll. 2019• Non-detection -> environment before
outburst was not dense enough.
• Constraints on progenitor’s mass loss rates[Dwarkadas 2013]• No detection in Fermi-LAT data search [FermiLAT Coll. 2015]• Transient γ-ray signal tentatively associated withSN iPTF14hls by Yuan et al. (2018), but quasar in
FoV.
• Search by Xi et al. 2020: fading GeV gamma ray
source spatial coincidence with SN 2004dj(chance coincidence 0.2%)

R. Simoni

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Expected Flux versus Distance

H.E.S.S. Coll. 2019

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What to expect at very high energies?
• Very high energy emission is expected, but• gamma-ray signal can be attenuated in the first days when photosphere and the shock are the closest,
and the photosphere luminosity is the highest. [Cristofari 2022]• Rise again about 5-10 days later and even show enhanced emission ~20-30 days later.

• Only very local SNe visible with typical detection distances from 20 kpc (HAWC) to 3 Mpc (CTASouth), e.g. within our Galaxy or in the Magellanic Clouds [Brose 2022: Cristofari 2022]

GALACTIC TRANSIENTS

Cristofari 2022

Brose 2022

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31Type Ia and super luminous SNe• Closest Type Ia supernova (d=3.6Mpc in M82) observed by
MAGIC: SN 2014J [MAGIC Coll. 2017]• No detection. Expected emission ≈10−24photons cm−2 s−1 -> notdetectable, even by future CTA.

• Super luminous supernovae (SLSNe) have luminosities ∼10–100
times greater than ordinary core-collapse SNe [review Gal-Yam 2019]• Additional power source from standard SNe Types I and II: injection
from a rapidly spinning magnetar? [Woosley&Heger2012;Quataert&
Kasen2012;Margalit&Metzger2016;Moriyaetal. 2018]• 0.4 and 4 events per year can be observed by VERITAS
from 10hr and 50hr observation, respectively.

Acharyya et al. 2023

• No detection of 2 candidates with VERITAS and Fermi-LAT,
but predictions are [Acharyya et al. 2023]:• 8 and 80 events per year can be expected by CTA.
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Most recent: SN2023ixf• Discovered on May 19 (17:27:15 UTC) and reported (21:42:21) by
K. Itagaki [TNS #178084]• Estimated explosion time: May 18, 18:00 UTC (MJD 60082.75)[Hosseinzadeh et al. 2023]• Mag 14.9; z= 0.000804 (~6.4 Mpc), located in M101 [Perley et al., AstroNote
2023-119]• Closest core-collapse (type II, possible II-L) SN in the northernhemisphere in the last few decades [Biancardi 2023]• SN 2023ixf is the second brightest supernova (SN) among all-type
SNe discovered after the discovery of SN 1987A in optical bands[Yamanaka et al. 2023]• X-ray: detected by Chandra [ATel #16073 ]• Fermi-LAT reported no GeV emission [ATel #16075]• Constraints on particle acceleration models to be expected• No reports from TeV instruments yet.
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Novaesuperbossa/MPP

Novae - White Dwarfs in Close Binary Systems

T. Cheung VGGRS 2023

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Processes and electromagnetic signals

Chomiuk+2021

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Fermi Discovery of a gamma-ray nova
• Particle acceleration in nova ejecta throughinteractions with dense wind of Red Giantcompanion (proposed for RS Oph by Tatischeff &Hernanz 2007)• Initial Fermi-LAT detection 2010 March 10, same
day as nova V407 Cyg optical discovery by
Nishiyama & Kabashima• γ-ray identification via spatial (r95%=3.7’) &temporal coincidence with a symbiotic- likerecurrent nova
• Observation with VERITAS during days 9–16
• No detection; Upper limits constrain hadronic model
parameters. [Aliu et al. 2012]
Abdo+2010

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Gamma-ray properties• Durations ~ 5-55 days
• trise ~ tfall ~ 2-7 days (shortest duration = 0.75
days in fastest nova Her 2021; Sokolovsky+23)• Flux peaks (>0.1 GeV) ~ 0.1- 5 x 10-6 ph cm-2 s-1• Power law ( = 1.8-2.3); many with cutoffs (Ec ~GeV) (slightly harder in symbiotics) [Frankowiack 2018]• Average luminosities (>0.1 GeV) ~ 1034 - 4 x 1036
erg s-1 (highest in the bulge)

Chomiuk+2021

𝜞

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explanation• Otherwise, populations indistinguishable (e.g., absolute optical mag, lightcurve decline times, optical spectral types)

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• Bayesian distances to 402 Galactic novae using Gaia DR3 parallax (74 “good”, i.e., with <30% uncertainty) and nonparallax distance measures (220 distances with <30% uncertainty) [Schaefer 2022]• 124 novae occurred in Fermi-era (2008 - 2021.6)• Two observed populations:39

Fermi-LAT GeV Novae population• Total N =19 LAT detections from 2008 - 2023
• Majority (N=15) of LAT detections in the Galactic disk (2/15 are seen through the sightline of the bulge)• 4 LAT detections in the Galactic Bulge (including symbiotic recurrent nova V3890 Sgr)T. Cheung VGGRS 2023

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Fermi-LAT GeV Novae: 2008 - 2023
• Fermi-LAT detected novae in Galactic disk tend
to be closest and brightest.
• In fact, LAT detected 13/17 of the opticallybrightest novae during Fermi era; Exceptions:• two recurrent novae: KT Eri (V = 5.4), T Pyx (V = 6.4)
• FM Cir 2018 (V = 5.9) – larger end of distance range?
• V5583 Sgr 2009 (V = 7) viewed through the Galacticbulge• 4 LAT detections (including symbiotic-recurrent
V3890 Sgr) are in the Galactic bulge with range ofV peaks consistent with general population.
T. Cheung VGGRS 2023

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Searching for very high energy emission• High energy data alone not enough to disentangle electron and proton acceleration models• Particles are accelerated in nova shock: non-thermal processes• Protons can reach much higher energies due to lower energy losses and thus possibly produce a second
component detectable by Cherenkov Telescopes• Cherenkov Telescopes had searched for a VHE component in novae for more than a decade (Aliu et al. 2012, Ahnen
et al. 2015)

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First detection of nova at VHE: RS Ophiuchi

Slide from A. Lopez

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First detection of Nova at very high energies• First nova detected in the very high energy regime(HESS coll. Science 2022, MAGIC coll. Nature Astr. 2022)• CTA-LST1 obtained comparable results.

Novae established as new sourceclass at VHE gamma rays

H.E.S.S. coll. 2022

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First detection of Nova at very high energies• Emission peaked at optical and GeV• MAGIC VHE emission is consistent with being constant over the first 4 days;
H.E.S.S. VHE emission peaks with 2 days delay to Fermi-LAT• Fast decay at high energies: 2.2 day halving timescale• During the nova outburst the photospheric emission creates thedominant radiation field

H.E.S.S. coll. 2022

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RS Ophiuchi - spectral energy distribution• Hadronic scenarios isfavored, because• Better fit to the data
• Protons injected withstandard parameters, whileelectrons would need an adhoc strong spectral break.
• Protons have slow cooling,
electrons cool too fast toreach that high energies.
• Spectral hardening withtime: behaviour in line withthe expectations from thecooling and acceleration timescales for protons.
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Hadronic scenario is favored.

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Acceleration

Slide from A. Lopez

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Comparison with other novae

Slide from A. Lopez

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Galactic novae and Cosmic rays

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T CrB Watch – keystone system• T CrB (T Coronae Borealis)• RA, Dec (J2000) = 15 59, +25 55 (north)• M4.5 III red giant companion, Porb = 227.57 day (Fekel et al. 2000)• MWD = 1.37 (0.13) Msun (Stanishev et al. 2004)• Eruptions in 1866, 1946, Prec ~80 year

• Optically very bright: peaks of 2 mag and 3 mag, respectively• Closest known recurrent-symbiotic nova, D = 0.91 +/0.02 kpc (Schaefer 2022)• Earlier predictions by Luna+20 and others• All other known recurrent-symbiotic novae have exploded
during Fermi-era (V745 Sco 2014, V3890 Sgr 2019, RS Oph
2021; also symbiotic V407 Cyg 2010)• 3x closer than RS Oph; naively scale by distance =>~10x brighter?
• Other symbiotic binary systems: Neutron star GX 1+4/
V2116 Oph; Black hole V404 Cyg
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Predicted eruption date:~2024.2 (as shown)to 2026.8.
Data shown up to epoch 2022.8.
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Gamma-ray Novae: Questions• Are all novae GeV gamma-ray sources ?
• Yes, with reliable distances, majority of novae within ~4 kpc detected; subset of Bulge novae (D ~ 8 kpc).

• Symbiotics (and recurrents) as keystone systems ?
• Hadronic emission has outsized role in RS Oph, and likely other symbiotics.
• Expect outburst of T CrB (D~0.9 kpc), in 2020’s, with prompt ~MeV (<1 day). Additional outbursts fromother known systems (RS Oph 203X?)• Role of future VHE observations, particularly with the Cherenkov Telescope Array?
• Provide useful constraints on the maximum energy of accelerate particles.

T. Cheung VGGRS 2023

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Summary• New source classes to be discovered still.
• Supernovae at GeV and TeV energies.
• Transitional milli-second pulsars at TeV energies.

• Next nova detection to come soon?
• T Coronae Borealis• More sensitive instruments to come soon at TeV energies• Cherenkov Telescope Array (CTA)

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Thank you very much for your attention!

Back up

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Relative numbers

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Mechanism of emission of tMSP

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Number of Type IIn ccSNe• Frequency: a few objects within 10 years of CTA

ICRC SATELLITE 2023 - D. HADASCHGALACTIC TRANSIENTS[Cold & Hjorth 2023]• Bright transient survey (BTS) Zwicky Transient Facility
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Search at GeV energies• Systematic search for γ-ray emission in Fermi-LAT data
• 100 MeV to 300 GeV from the ensemble of 147 SNe Type IIn exploding in a dense CSM [Fermi-LAT Coll. 2015].
• No candidate found -> limits on the ratio of γ-ray and optical luminosity: exclude ratio >0.1

• 55,880 candidates from Open Supernova Catalog with a variable-size sliding-time-window analysis[Prokhorov et al. 2023].
• 4.0σ evidence for γ-ray emission from transient sources occurring in the directions of 2 SN candidates.
• Transient γ-ray signal tentatively associated with SN iPTF14hls by Yuan et al. (2018), but quasar in FoV.
• Search by Xi et al. 2020: fading GeV gamma ray source spatial coincidence with SN 2004dj (chancecoincidence 0.2%)• -> γ-ray emission arising from the supernova ejecta interacting with surrounding high-density shell, which
decelerates the ejecta and converts ∼1% of the SN kinetic energy to relativistic protons.

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Core-collapsed SNe searches

H.E.S.S. Coll. 2019• Non-detection -> environment before
outburst was not dense enough.
• Constraints on progenitor’s mass loss
rates [Dwarkadas 2013]

R. Simoni

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68• While it is plausible that all novae host internal shocks and emit gamma-rays, the rate of
gamma-ray detected novae (∼ 1 yr−1) is only a small fraction of the optical discovery rate (∼ 5 −10 yr−1). The Fermi detections tend to be of relatively nearby novae (∼ 2 − 5 kpc) and of
marginal significance (Supplemental Table 1 and Supplemental Figure 1), suggesting that many
novae go undetected due to the limited flux sensitivity of Fermi-LAT.

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Late-time LAT emission in nearby novae

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Correlated light curves in brightest LAT novae

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Fermi-LAT GeV Novae: 2008 - 2023

T. Cheung VGGRS 2023

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Fermi-LAT GeV Novae: 2008 - 2023
• V549 Vel 2017 is fainter both optically (V = 9.1, D~2-5 kpc) and in gamma rays, and is one of theleast luminous gamma-ray novae [Li et al. 2020]• RS Ophiuchi: First Nova detected at TeV
energies• T CrB 202X?: Stay tuned.

T. Cheung VGGRS 2023

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