1. V. Simon, G. Pizzichini, R. Hudec The optical long-term activity of the high-energy sources: Perspectives for ESA Gaia v 1 Astronomical Institute, The Czech Academy of Sciences, 25165 Ondrejov, Czech Republic 25165 Ondrejov, Czech Republic v 2 Czech Technical University in Prague, FEE, Prague, Czech Republic 1,21,23 3 INAF/IASF Bologna, via Gobetti 101, 40129 Bologna, Italy Talk: 12 th INTEGRAL/BART Workshop, 20-24 April 2015, Karlovy Vary, Czech Republic

2. 2 Source: Wikipedia ESA Gaia satellite Light path of telescope 1 Primary mirror 1  A space observatory designed for astrometry  Limiting magnitude: ~ 20 (400-100 nanometers)  The satellite can be used also as a monitor (brightnesses and ultra-low-dispersion spectra) (brightnesses and ultra-low-dispersion spectra)  About 80 observations of a given field

3. The color indices are determined from the magnitudes of an object measured in the individual filters (e.g. U – B, B – V, V – R, R – I ).  important information on the spectral energy distribution  magnitudes and color indices can be determined even from ultra-low-dispersion spectra obtained by ESA Gaia ultra-low-dispersion spectra obtained by ESA Gaia Photometric filters in astrophysics 3

4. Why to use color indices in analysis of optical counterparts of high energy sources? It is a powerful and sensitive approach which helps us to:  investigate spectral energy distribution and its changes by using photometric filters – even very faint objects can be studied photometric filters – even very faint objects can be studied  search for the common properties of the 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 the relations among colors and luminosities of a given object or a kind of objects or a kind of objects  constrain the extinction in the medium 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 radiation, cyclotron radiation, thermal emission) radiation, cyclotron radiation, thermal emission) 4

5. Optical afterglows (OAs) of gamma-ray bursts of gamma-ray bursts (GRBs) (GRBs) 5

6. 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 GRBs 6 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

7. Initial stage of a GRB. The core of the star has collapsed. A black hole has formed within the star (it launches a jet of matter). (Credit: NASA / SkyWorks Digital) Zhang et al. (2006) Long GRBs Core collapse of a massive star Short GRBs Merging compact objects in a binary (e.g. NS+NS) Relativistic jet is the dominant source of radiation from gamma-ray to the infrared (and radio) spectral region. Intensity of this emission depends on the inclination angle (the jet has to point toward the observer to be seen). A black hole is embedded by a torus of infalling matter. A jet of this matter is launched. Which kinds of objects give rise to GRBs? 7

8. All observations are in the R band (red light) and their time is in the observer frame. Zhang et al. (2006) Brightness of most OAs already falls when they are discovered in the optical band. (typically, a power-law decay is dominant) Luminosity proportional to t -a OA lasts much longer than GRB (days versus seconds or minutes) Relativistic jet is the dominant source of radiation from gamma- ray to the infrared (and radio) spectral regions. Intensity depends on the inclination angle (the jet has to point toward the observer). Typical light curves of optical afterglows (OAs) of GRBs 8 Limiting brightness of Gaia data of Gaia data

9. The color index changed only very little – it is therefore possible to combine the data The color index changed only very little – it is therefore possible to combine the data of the individual OAs obtained in different t–T 0 of the individual OAs obtained in different t–T 0 9 GRB 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 OA

10. Pre- Swift ensemble of GRBs Ensemble of OAs ( t - T 0 < Ensemble of OAs ( t - T 0 < 10 d) in the observer frame 10 d) in the observer frame (corrected for the Galactic (corrected for the Galactic reddening) reddening) OAs with redshift z < 3.5 OAs with redshift z < 3.5 form a very narrow belt form a very narrow belt with negligible variations with negligible variations with time with time OAs of the Swift GRBs are OAs of the Swift GRBs are mapped in earlier phases mapped in earlier phases than before than before 25 GRBs inside the belt OAs of GRBs observed by Swift 10 GRBs inside the belt 10 Time evolution of the color indices of OAs Simon et al. (2013)

11. OAs of GRBs observed by Swift Ensemble for the centroid: 9 GRBs Centroid Ensemble of OAs Ensemble of OAs ( t-T 0 < 10 days) ( t-T 0 < 10 days) (redshift z < 3.5) in (redshift z < 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 frame 11 Simon et al. (2013)  Vectors: representative reddening outside our Galaxy: E B-V = 0.5 mag E B-V = 0.5 mag

12. Data corrected for the reddening and light contribution of the host galaxy. Separation of the colors appropriate to the early OA and SN 2006aj is clear for UVW2 - B, UVW1 - U, UVM2 - UVW1. B band light curve Color Colorindices Early OA UVOT/Swift data GRB 060218/ SN 2006aj 12 Simon et al. (2010)

13.  Optical afterglows (OAs) can be detected as the NEW objects with untriggered Gaia observations even several days after the appropriate untriggered Gaia observations even several days after the appropriate GRB. GRB. Color indices of OAs – a powerful approach to the study of such events:  Many OAs display specific color indices with negligible time evolution during the decline of brightness. This helps distinguish them from during the decline of brightness. This helps distinguish them from other kinds of transients by photometric observations using several other kinds of transients by photometric observations using several color filters even without available detection of gamma-rays. color filters even 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 search for the common properties of OAs is possible. Optical afterglows – perspectives for ESA Gaia (I) 13

14.  Constraining the properties of the local interstellar medium of GRBs  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 orphan afterglows (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 – events predicted by theories, but only > a matter of debate – 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) 14

15. Binary X-ray sources 15

16. Stream impact onto disk onto disk Mass stream Compact object Accretion 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 regions Structure and emission regions Accretion disk – thermal Accretion disk – thermal radiation (UV, optical, IR) radiation (UV, optical, IR) Jets – synchrotron (radio) Jets – synchrotron (radio) Accretion column column Crossing Crossing Alfven radius WD 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) Polars Polars Disk accretion Disk accretion Close vicinity of the compact object Close vicinity of the compact object CVs: bremsstrahlung (X-rays) CVs: bremsstrahlung (X-rays) XBs: Comptonizing cloud (inverse XBs: Comptonizing cloud (inverse Compton process – hard X-rays) Compton process – hard X-rays) Donor Donor 16

17.  Changes of mass transfer rate d m/ d t from donor onto the compact object (timescale: days, weeks, months, years) object (timescale: days, weeks, months, years)  Thermal instability of the accretion disk (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 (timescale: weeks, months) – classical nova explosion (timescale: weeks, months) – recurrent novae (timescale: weeks, months) – recurrent novae (timescale: weeks, months) Steady-state: Steady-state: – supersoft X-ray sources (timescale: days, weeks, months) – supersoft X-ray sources (timescale: days, weeks, months) Mechanisms for the long-term activity of binary X-ray sources 17

18. Simulation using AFOEV data Activity in non-magnetic CVs Sequence (from top to bottom):  Large - amplitude, isolated outbursts outbursts  Numerous outbursts with short intervals in between short intervals in between  Dominant small fluctuations in the high state in the high state Increase of mass transfer rate d m /d t Thermally unstable disk Thermally stable disk (most time) Data source: AFOEV Systematics of the long- term activity of cataclysmic variables (CVs) 18

19. Novalike and VY Scl type systems Approximated sampling of the Gaia data Daily means Segment of Z Cam dwarf nova without standstills Dwarf novae of Z Cam type Dwarf novae of U Gem type – frequent outbursts Dwarf novae of U Gem type – rare outbursts Observations from the AFOEV database (daily means) (segment of 4 years) We approximate the Gaia sampling by the data separated by ~20 days. The number of the data ~ the number of obs. by ESA Gaia. - description of the properties of the light curve almost independent of sampling Statistical distributions of brightness in the long-term light curves of CVs – separation into subtypes Histograms of brightness in the long-term activity of CVs 19

20.  Profiles of the light curvescataclysmic variables (CVs) will be  Profiles of the light curves of cataclysmic variables (CVs) will be significantly affected by the sampling of the Gaia data. significantly affected by the sampling of the Gaia data.  The individual outbursts in dwarf novae are expected to be covered by only a few Gaia data points – no or very limited information on by only a few Gaia data points – no or very limited information on the profile of a given outburst (a the profile of a given outburst (also difficult to determine the type of CV from the profile of the light curve itself).  We find that the statistical distribution of brightness (in magnitudes) and its parameters (the standard deviation, skewness, excess) are and its parameters (the standard deviation, skewness, excess) are only slightly distorted by the sampling of the Gaia data (even if the only slightly distorted by the sampling of the Gaia data (even if the profile of the individual outbursts and/or high/low states are affected profile of the individual outbursts and/or high/low states are affected by the sampling). by the sampling). Perspectives for investigation of CVs with ESA Gaia (I): 20

21. Outburst in dwarf nova Hack & la Dous (1993) Dwarf novae in quiescence Dwarf novae in outburst Color-color diagrams of ensemble of CVs Color indices of cataclysmic variables (CVs) 21

22. Long-term activity of the intermediate polar Simon (2014) 16 V1223 Sgr Sept 11, 1966; JD 2 439 380 "Normal" level Sept 14, 1966; JD 2 439 383 Moment of the peak Moment of the peak brightness (outburst) Outburst on Bambergphotographicplates 22

23. Relation of the optical and X-ray intensity in a series of outbursts Maitra & Charles (2008 Maitra & Charles (2008) Simultaneous observations of the outburst in the optical and X-ray bands: duration of outburst in various bands and X- ray/optical ratio may differ substantially Optical Aql X-1 (soft X-ray transient) Optical X-ray Optical X-ray X-ray 23

24. Inactive state Sonneberg photographic data (one plate per night) Sonneberg photographic data (one plate per night) Data folded with the orbital period of 40.8 hours Remarkably different profile of the low-state orbital modulation with respect to that of the active state Simon et al. (2002) Inactive state Long-lasting active state Simon et al. (2002) Hudec &Wenzel (1976) Active state Inactivestate Perspectives for Gaia: Large changes of the orbital modulation Large changes of the orbital modulation and the responsible physical processes and the responsible physical processes can be studied even using sampled data can be studied even using sampled data Separation of the time intervals of the Separation of the time intervals of the different states of the long-term activity different states of the long-term activity is possible and will be helpful is possible and will be helpful Her X-1 (Low-mass X-ray binary) 24

25. Differences in the B-mag histograms: Explanation: variations in the mass accretion rate and the relatively short time period typically covered by optical observations McNamara McNamara et al. (2003) et al. (2003) Activity of persistent X-ray sources Hudec (1981) Russell et al. (2010) Long-term light curve in blue light. Annular means from archival photographic plates. - composition of rapid and long-term activity 25 4U 1957+11 Optical X-ray

26. Comparison of several measurements from several epochs will reveal Comparison of several measurements from several epochs will reveal that the object is variable (active). that the object is variable (active).  Transients in the expected coverage by Gaia data: - Newly identified source near the peak magnitude of outburst - Newly identified source near the peak magnitude of outburst - Declining branch is expected to be covered by multiple observations - Declining branch is expected to be covered by multiple observations - Even systems which have not been observed to undergo outburst - Even systems which have not been observed to undergo outburst can be identified in Gaia data as variable objects e.g. by their can be identified in Gaia data as variable objects e.g. by their orbital modulation orbital modulation  Persistent sources: - Fluctuations of brightness on the timescale of days - Fluctuations of brightness on the timescale of days - Amplitude of long-term variations: ~1 mag (~ 2.5 in intensities) - Amplitude of long-term variations: ~1 mag (~ 2.5 in intensities) - Orbital modulation - Orbital modulation How to pick up LMXB from several heavily sampled Gaia data points X-ray binaries in Gaia data 26

27. Acknowledgements: Acknowledgements: This study was supported by grants 13-394643 and 13-33324S provided by the Grant Agency of the Czech Republic. Full references on each OA are given in J. Greiner's Web page http://pwww.mpe.mpg.de/~jcg/grbgen.html. This research has made use of the observations provided by the ASM/RXTE team (Levine et al., 1996, ApJ, 469, L33). It also used the observations from the AAVSO International database (Massachusetts, USA (e.g. Henden 2013)) and the AFOEV database operated in Strasbourg, France. I thank the variable star observers worldwide whose observations contributed to this analysis.I also thank Prof. Petr Harmanec for providing contributed to this analysis. I also thank Prof. Petr Harmanec for providing me with the code HEC13. The Fortran source version, compiled version and brief instructions how to use the program can be obtained at http: //astro.troja.mff.cuni.cz/ftp/hec/HEC13/ 27