V. Simon , G. Pizzichini , R. HudecV. Simon , G. Pizzichini , R. Hudec

The optical long-term activity The optical long-term activity of the high-energy sources: of the high-energy sources: Perspectives for ESA GaiaPerspectives for ESA Gaia

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11 Astronomical Institute, The Czech Academy of Sciences, Astronomical Institute, The Czech Academy of Sciences, 25165 Ondrejov, Czech Republic25165 Ondrejov, Czech Republic

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2 Czech Technical University in Prague, FEE, Prague, Czech Republic

1,21,2 1,21,233

3 INAF/IASF Bologna, via Gobetti 101, 40129 Bologna, Italy

Talk: 12Talk: 12thth INTEGRAL/BART Workshop, 20-24 April 2015, INTEGRAL/BART Workshop, 20-24 April 2015, Karlovy Vary, Czech RepublicKarlovy Vary, Czech Republic

22Source: Source: WikipediaWikipedia

ESA Gaia satelliteESA Gaia satellite

Light path of telescope 1

Primary mirror 1

A space observatory designed for astrometry A space observatory designed for astrometry Limiting magnitude: ~ 20 (400-100 nanometers)Limiting magnitude: ~ 20 (400-100 nanometers) The satellite can be used also as a monitor The satellite can be used also as a monitor (brightnesses and ultra-low-dispersion (brightnesses and ultra-low-dispersion spectra)spectra) About 80 observations of a given field About 80 observations of a given field

The color indices are determined from the magnitudes of an objectThe color indices are determined from the magnitudes of an objectmeasured in the individual filters (e.g. measured in the individual filters (e.g. U – BU – B, , B – VB – V, , V – RV – R, , R – IR – I).).

important information on the spectral energy distributionimportant information on the spectral energy distribution

magnitudes and color indices can be determined even from magnitudes and color indices can be determined even from ultra-low-dispersion spectra obtained by ESA Gaiaultra-low-dispersion spectra obtained by ESA Gaia

Photometric filters in astrophysicsPhotometric filters in astrophysics

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Why to use color indices in analysis of optical counterparts of Why to use color indices in analysis of optical counterparts of high energy sources? high energy sources? It is It is a powerfula powerful and sensitive approach which and sensitive approach which helphelpss us to: us to:

investigate spectral energy distribution and its changes by using investigate spectral energy distribution and its changes by using photometric filters – even very faint objects can be studiedphotometric filters – even very faint objects can be studied

search for search for the the common common properties properties of the of the sources of a given kind (e.g. sources of a given kind (e.g. various types of binary X-ray sources, optical afterglows of GRBs…)various types of binary X-ray sources, optical afterglows of GRBs…)

search for search for the the relations among colorsrelations among colors and and luminositie luminosities of a given object s of a given object or a kind of objectsor a kind of objects

constrain the constrain the extinction in extinction in the medium the medium between the observer and the between the observer and the source (and also extinction inside the source)source (and also extinction inside the source)

resolution among the individual radiation mechanisms (e.g. synchrotron resolution among the individual radiation mechanisms (e.g. synchrotron radiation, cyclotron radiation, thermal emission)radiation, cyclotron radiation, thermal emission)

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OOptical afterglows ptical afterglows (OAs) (OAs) of of gamma-ray bursts gamma-ray bursts ((GRBsGRBs))

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Data from BATSE onboard Compton GRO satellite

A very large range of profiles and durations of the bursts

The gamma-ray light curves and positions of GRBsThe gamma-ray light curves and positions of GRBs

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Galactic coordinates

GRBs are uniformly distributed in the sky. They are not concentrated either toward the Galactic center or toward the Galactic plane.

Distribution of the positions of GRBs in the sky

IInitial stage of a nitial stage of a GRBGRB. The core of the star has . The core of the star has collapsed. A black hole collapsed. A black hole has formed within the has formed within the starstar (it (it launches a jet of launches a jet of matter)matter)..(Credit: NASA / SkyWorks Digital)(Credit: NASA / SkyWorks Digital)

Zhang et al. (2006)

Long GRBs Long GRBs Core collapse of a massive starCore collapse of a massive star

Short GRBsShort GRBs Merging compact objects in a binary (e.g. NS+NS)Merging compact objects in a binary (e.g. NS+NS)

Relativistic jet is the dominant source of Relativistic jet is the dominant source of radiation from gamma-ray to the infrared radiation from gamma-ray to the infrared (and radio) spectral region.(and radio) spectral region.

Intensity of this emission depends on Intensity of this emission depends on the inclination angle (the jet has to point the inclination angle (the jet has to point toward the observer to be seen).toward the observer to be seen).

A A black black hole hole is is embedded by a embedded by a torus of infalling torus of infalling matter. matter. AA jet of jet of this matterthis matter is launchedis launched..

Which kinds of objects give rise to GRBs?Which kinds of objects give rise to GRBs?

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All observations are in the All observations are in the RR band (red light) and their time is in the observer frame. band (red light) and their time is in the observer frame.Zhang et al. (2006)

Brightness of most OAs already falls when Brightness of most OAs already falls when they are discovered in the optical band. they are discovered in the optical band.

(typically, a power-law decay is dominant) (typically, a power-law decay is dominant)

Luminosity proportional to Luminosity proportional to tt -a-a

OA lasts much OA lasts much longer than GRB longer than GRB (days versus seconds (days versus seconds or minutes)or minutes)

Relativistic jet is the dominant source of radiation from gamma-Relativistic jet is the dominant source of radiation from gamma-ray to the infrared (and radio) spectral regions.ray to the infrared (and radio) spectral regions.Intensity depends on the inclination angle (the jet has to point toward the observer).Intensity depends on the inclination angle (the jet has to point toward the observer).

Typical light curves of optical afterglows (OAs) of GRBsTypical light curves of optical afterglows (OAs) of GRBs

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Limiting brightness Limiting brightness of Gaia dataof Gaia data

The color index changed only very little – it is therefore possible to combine the The color index changed only very little – it is therefore possible to combine the data data of the individual OAs obtained in different of the individual OAs obtained in different t–Tt–T00

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GRB 080319BGRB 080319B

Extreme change of the Extreme change of the optical brightness of the optical brightness of the OA in the initial phase: OA in the initial phase: a decline by 7.9 mag a decline by 7.9 mag during 4.6 hours after during 4.6 hours after the GRB trigger the GRB trigger

Typical time evolution of the color index of OATypical time evolution of the color index of OA

Pre-Pre-Swift Swift ensemble of GRBsensemble of GRBs

Ensemble of OAs (Ensemble of OAs (t - Tt - T0 0 << 10 10 dd) in the observer frame ) in the observer frame (corrected for the Galactic (corrected for the Galactic reddening)reddening)

OAs with redshift OAs with redshift zz < 3.5 < 3.5 form a very narrow belt form a very narrow belt with negligible variations with negligible variations with timewith time

OAs of the OAs of the SwiftSwift GRBs are GRBs are mapped in earlier phases mapped in earlier phases than beforethan before

25 GRBs inside the belt25 GRBs inside the belt

OAs of GRBs observed by OAs of GRBs observed by SwiftSwift

10 GRBs inside the belt10 GRBs inside the belt

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Time evolution of the color indices of OAsTime evolution of the color indices of OAs

Simon et al. (2013)Simon et al. (2013)

OAs of GRBs OAs of GRBs observed by observed by SwiftSwift

Ensemble for the Ensemble for the centroid: 9 GRBscentroid: 9 GRBs

CentroidCentroid

Ensemble of OAsEnsemble of OAs ((t-Tt-T0 0 < 10 < 10 ddays) ays) (redshift (redshift z z < 3.5) in < 3.5) in the observer frame the observer frame (corrected for the (corrected for the Galactic reddening)Galactic reddening)

Color-color diagrams of OAs in the observer frameColor-color diagrams of OAs in the observer frame

1111Simon et al. (2013)Simon et al. (2013)

Vectors: rVectors: representative reddening epresentative reddening outside our Galaxy: outside our Galaxy: EEB-VB-V == 0.50.5 mag mag

DData corrected for ata corrected for the the reddeningreddening and and lightlight contribution contribution of of the the host galaxy. host galaxy.

Separation Separation ofof the the colors colors appropriate appropriate to to the the early early OAOA and SNand SN 2006aj is clear 2006aj is clear for for UVW2UVW2 -- BB,, UVW1UVW1 -- UU, , UVMUVM2 2 -- U UVW1VW1. .

BB band light curve band light curve

Color Color indicesindices

Early OAEarly OA

UVOT/UVOT/SwiftSwift data data

GRB 060218/GRB 060218/SN 2006ajSN 2006aj

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SN 2006ajSN 2006aj

Simon et al. (2010)Simon et al. (2010)

OOptical afterglowptical afterglows s (OAs) (OAs) can can be be detected detected as the NEW objects as the NEW objects with with untriggered untriggered GGaia observations aia observations even several days after the even several days after the appropriate appropriate GRB. GRB.

CColor indices of olor indices of OAs OAs – – a powerfula powerful approach to the study approach to the study of such of such eevents:vents:

Many OAs Many OAs display display specific color indices with negligible time specific color indices with negligible time eevolutionvolution during the decline of brightness. Thisduring the decline of brightness. This helps helps distinguish distinguish them them from from other kinds of other kinds of tr transients ansients by photometric by photometric observations observations using using several several color filterscolor filters even without available detection of gamma-rayseven without available detection of gamma-rays. . This finding will also be helpful for their observation with ESA Gaia.This finding will also be helpful for their observation with ESA Gaia.

A A search for search for the the common properties of common properties of OAs is possible.OAs is possible.

Optical afterglows – perspectives for ESA Gaia (I)Optical afterglows – perspectives for ESA Gaia (I)

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CoConstrainnstraininging the properties of the local interstellar medium of GRBs the properties of the local interstellar medium of GRBs

Resolving among the individual radiation mechanisms (e.g. Resolving among the individual radiation mechanisms (e.g. synchrotron radiation versus supernova – important for synchrotron radiation versus supernova – important for investigation of the GRB-supernova relation)investigation of the GRB-supernova relation)

Searching for Searching for orphan afterglowsorphan afterglows (GRBs without detected gamma-rays (GRBs without detected gamma-rays (e.g. the jet is not pointing directly to the observer, Lorentz factor is (e.g. the jet is not pointing directly to the observer, Lorentz factor is too small…), but the optical emission may still be observed) too small…), but the optical emission may still be observed) > a matter of debate> a matter of debate – events predicted by theories, but only – events predicted by theories, but only long-term deep monitoring of the sky can resolve between long-term deep monitoring of the sky can resolve between the theories. the theories.

Optical afterglows – perspectives for ESA Gaia (II)Optical afterglows – perspectives for ESA Gaia (II)

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Binary X-ray sourcesBinary X-ray sources

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Stream impact Stream impact onto diskonto disk

Mass streamMass stream

Compact objectCompact object

Accretion diskAccretion disk

Donor – thermal (optical, IR)Donor – thermal (optical, IR)

Compact object (white dwarf, Compact object (white dwarf, neutron star, black hole)neutron star, black hole)

Structure and emission regionsStructure and emission regions

Accretion disk – thermal Accretion disk – thermal radiation (UV, optical, IR)radiation (UV, optical, IR)

Jets – synchrotron (radio)Jets – synchrotron (radio)

Accretion Accretion columncolumn

Crossing Crossing Alfven radiusAlfven radius

WDWD

Donor – thermal radiation Donor – thermal radiation (optical, IR)(optical, IR)

Synchrotron emission (e.g. from Synchrotron emission (e.g. from the vicinity of the donor) (radio)the vicinity of the donor) (radio)

Accretion column – cyclotron Accretion column – cyclotron (optical , IR) (optical , IR)

Accretion shock near the magnetic Accretion shock near the magnetic pole(s) of the WD – bremsstrahlung pole(s) of the WD – bremsstrahlung (hard X-rays) (hard X-rays)

Heated surface of the WD – thermal Heated surface of the WD – thermal (soft X-rays, far UV, UV)(soft X-rays, far UV, UV)

PolarsPolars Disk accretionDisk accretion

Close vicinity of the compact object Close vicinity of the compact object CVs: bremsstrahlung (X-rays) CVs: bremsstrahlung (X-rays) XBs: Comptonizing cloud (inverseXBs: Comptonizing cloud (inverse Compton process – hard X-rays) Compton process – hard X-rays)

DonorDonor

DonorDonor

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Changes of mass transfer rate dChanges of mass transfer rate dm/m/ddt t from donor onto the compact from donor onto the compact object object (timescale: days, weeks, months, years)(timescale: days, weeks, months, years)

Thermal instability of the accretion disk Thermal instability of the accretion disk (timescale: days, weeks, (timescale: days, weeks, months)months)

Hydrogen burning on the white dwarf (in CVs)Hydrogen burning on the white dwarf (in CVs) :: Episodic: Episodic: – – classical nova explosion classical nova explosion (timescale: weeks, months)(timescale: weeks, months) – – recurrent novae recurrent novae (timescale: weeks, months)(timescale: weeks, months) Steady-state:Steady-state: – – supersoft X-ray sources supersoft X-ray sources (timescale: days, weeks, months)(timescale: days, weeks, months)

Mechanisms for the long-term activity of binary Mechanisms for the long-term activity of binary X-ray sourcesX-ray sources

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Simulation using AFOEV data

Activity in non-magnetic CVsActivity in non-magnetic CVs

Sequence (from top to bottom):Sequence (from top to bottom):

Large - amplitude, isolated Large - amplitude, isolated outburstsoutbursts

Numerous outbursts with Numerous outbursts with short intervals in betweenshort intervals in between

Dominant small fluctuations Dominant small fluctuations in the high statein the high state