PoS(HEASA2015)005 -LAT Fermi http://pos.sissa.it/ and Suzaku † ∗ [email protected] [email protected] Speaker. A footnote may follow. The nova-like variablewavelengths. AE Aquarii The iswhereas emission the a in nature radio, of unique thewavelengths optical system is emission still and towards that not higher clearly soft energies shows defined. such X-ray emission as has hard at been X-ray and almost exploredIn gamma-ray this extensively, all study a search for pulsed emission has been conducted utilizing data. The methodology and results from theshow analysis that will be the shown. possibility The resultscannot of from be the a excluded. analysis non-thermal component towards higher energies in AE Aquarii ∗ † Copyright owned by the author(s) under the terms of the Creative Commons c Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). P.J. Meintjes University of the Free State E-mail: 3rd Annual Conference on High Energy18-20 Astrophysics June in 2015 Southern Africa -HEASA2015, University of Johannesburg, Auckland Park, South Africa H.J. van Heerden Exploring the nature of AE Aquariienergies using at Sazuku higher and Fermi-LAT University of the Free State E-mail: PoS(HEASA2015)005 ], 5 [ keV 1 − 20 16 Suzaku Suzaku . . the WD 0 0 Einstein + − 9 and erg s . WD 1 TeV] sug- ], explaining . 50 0 I 10 H.J. van Heerden 33 > ] and X-ray emis- ], in addition with γ 10 8 7 ε [ × ]. A study to search

6 ]. The highly magne- . ], with the very strong ]. Correlations between 3 1 17 = , 13 , 12 2 , 48 M . 16 ˙ ΩΩ 12 0 , I ]. In 2012 a multi-wavelength ∼ the WD mass and R − . This large spin down power is 15 88 h [ 19 . 2 33 s, is spinning down at a rate of 9 − WD s ≈ = 16 was determined from the − orb keV or a power law with a photon index ]. The properties of the hard X-ray emis- spin 10 ˙ 26 47 with M 14 ΩΩ . . I 0 0 × 2 + − − ] can be seen in Figure 24 . -ray) emission. 3 12 g cm 2 ASCA, XMM-Newton, Chandra, Swift γ − ] for a WD mass of 50 6 = 10 data [ 2 ) and gamma-ray (MAGIC) telescopes was conducted 10 keV. P × / ∼ 2 ˙ P γ Swift ε π ≈ 2 Suzaku − 2 WD R = ˙ Ω WD , resulting in a spin-down luminosity of ], which has a spin period of P ]. The fitted multi-thermal components at temperatures of 2 1 4 and 2 M . − 12 1 0 ]. The MAGIC telescope was utilised during follow-up studies, but again . The spin-down luminosity − 2 s s G) [ − ≈ 18 6 -ray, there is still substantial uncertainty as to whether AE Aquarii is an emitter 14 γ 19 s I − 10 . g cm 0 50 10 ∼ keV as well as the excess above the extrapolated hard X-ray emission data, that was 10 1 = for the 2005 and 2006 × 14 13 . . 33 = 0 0 63 62 64 . . P . − + 0 0 ]. The secondary is a K2-K5 type evolved , with the primary and secondary com- ]. Subsequent studies utilised data from 10keV), such as sharp pulse profiles, could best be described through non-thermal emission 50 / 5 ]. No significant detections for steady TeV as well as variable (33.08 and 16.54 s pulsed) 1 + − ], and could act as a reservoir that drives non-thermal particle acceleration [ π 53 9 11 ≥ . = 2 21 The first observational studies conducted at Very High Energies (VHE) [ The system has been extensively studied, and the emission mechanisms for the radio, optical The X-ray emission has been studied since the discovery of the WD spin pulsations in AE Aqaurii is a unique nova-like magnetic cataclysmic system. It consists 12 . 10keV) component has been fitted with a multi-thermal model [ , 120 times greater than the inferred accretion luminosities derived from UV [ = spin 20 ≤ ˙ of 1 [ campaign using optical, UV, X-ray ( explained by either a third thermal component of 54 33 s pulsations used to updatesion the ( WD spin ephemeris [ from accelerated particles, as proposed fromthe a fit pulsations of in a the power-law model soft [ data X-ray were emission also and found the [ lowerand 0 hard X-ray emission (10-25 keV) for TeV emission using theepisodic Whipple emission 10 [ m telescope foundno no evidence of evidence any for steady any TeV steady, gamma-ray pulsed emission or was found [ of pulsed radiation at energies above where I radius, with the 0.2 factor extrapolated from [ sion [ data [ to detect, define and model the( soft and hard X-ray emission components. The soft X-ray emission and soft X-ray components are wellIn and spite clearly of defined in a terms number ofas of the hard studies currently X-ray into proposed and models. the nature of possible emission towards higher energies, such ponents orbiting the centre of mass of the system at a P of a fast rotatingmechanism driving white the dwarf in-falling (WD) matterblobs from primary [ the star secondary that star away is in in the the form of ejector interacting state with a propeller Exploring the nature of AE Aquarii at higher energies using Sazuku and Fermi-LAT 1. Introduction tized WD (B Ω the radio synchrotron and possible high energy ( gested possible optical-like VHE gamma-ray pulsed emission [ P moment of inertia I ∼ PoS(HEASA2015)005 -ray γ ], only AGILE http: 12 and H.J. van Heerden Fermi above 250 GeV and 1 data from 2005 (left) and − s 2 − cm Suzaku 12 − 10 × 39 . . -LAT in the search for and characterisation of 3 Fermi and Suzaku above 1 TeV for a power-law spectrum with a slope of -2.6 resulted from 1 − ]. Fortunately the advent of space-based telescopes such as s 2 21 − Space Telescope was launched on 10 July 2005 into a low (LEO) , cm 20 observed AE Aquarii on three separate occasions during October of 2005, 2006 and XIS and HXD data analysis 13 − Background subtracted X-ray spectra of AE Aquarii from Suzaku 10 ]. × ]. 12 The This study utilised data from Suzaku 22 Suzaku 401 . the 2009 dataset (ID 404001010), which had an on-source observation length of 294159 s, was the campaign [ non-thermal emission in AE Aquarii atin higher [ energies. It is a continuation of the study presented 2. at 550 km altitude.sitive It between has 0.2-12 two primary keVgies instruments, and of the the 10-600 soft keV. hard X-ray Additional X-ray instrument information (XIS) detector on that the (HXD) is telescope that sen- and is mission sensitive is between available at ener- TeV emission were found. Upper-limit values of 6 2009. As the 2005 and 2006 datasets were already previously analysed and discussed [ 2006 (right). Indicated are theilluminated soft (red) thermal emission instruments, spectra as forindicates the well the XIS PIN as front non the illuminated X-ray (black)from HXD background and [ and PIN back the spectra expected cosmic (blue). X-ray background The respectively. Adopted light and dark green curves 7 increased the amount of dataemission available from to this utilise enigmatic in source. the search for steady, pulsed or episodic //heasarc.gsfc.nasa.gov/docs/suzaku/ Figure 1: Exploring the nature of AE Aquarii at higher energies using Sazuku and Fermi-LAT PoS(HEASA2015)005 for the FI 30 − for the BI data. H.J. van Heerden 10 . 75 3 × − 10 261 . × 337 . http://heasarc.gsfc. value of 1.25, and a fit to the BI data for the FI data and F-statistic of 70.043 for the BI data. However, the proposed 2 39 49 χ − − 10 10 × × value of 1.242. A F-test comparison between the 4 2 008 337 . . χ value of 1.519, and a fit to the BI data with a p-value of 2 . with a reduced χ 2 7 − 10 value of 1.466. An F-test comparison between the new proposed × 2 with a reduced χ 6 171 . − with a reduced 10 22 × − 24 . 10 × XIS spectra for the FI (blue) and BI (black) data with proposed 2-Mekal models for the FI with a reduced . for the FI data and F-statistic of 111.796 and p-value of 1 678 16 . 67 − Suzaku − 10 10 × × An additional Mekal component was therefore added. It resulted in a fit to the FI data with a An additional Bremsstrahlung component was tested and subsequently improved the fit to the For the soft X-ray emission the cleaned xis0 and xis3 (front illuminated (FI) sensors), as well 214 06 . . data and F-statistic of 130.454 and p-value of 1 model and the null model resulted in F-statistic of 73.606 and p-value of 2 3 model again showed an unacceptable fit below 1.5 keV as can be seen in Figure p-value of 2 Figure 2: and BI spectra represented by the pink and red curves receptively. FI data with a p-value of 3 An F-test between the newsulted proposed in a model F-statistic of and 98.373 the and p-value 3-Mekal of model 2 (null model for this test) re- Exploring the nature of AE Aquarii at higher energies using Sazuku and Fermi-LAT used for this study. Spectral analysisusing of the "XSELECT" XIS (Version data 2.4c) as wellsion and as 6.15.1) "XSpec" the software HXD package (Version PIN available 12.8.2) data fromnasa.gov/ were the available performed HEASARC in site the at Heasoft (Ver- as the xis1 (back illuminatedspectra (BI) were sensor) extracted and data saved were along used.model with files. the The The latest source xis0 calibration and as database xis3 (CALDB) well datamodels response were as was and combined sky based for background a upon total the FItested. spectrum. previously The mentioned An selection studies. of initial spectral Multi-thermal nullbelow Mekal model 1.5 models keV 2 was as component can first Mekal be model seen in was Figure tested, but did not show a good fit with a p-value of 4 new proposed model and the null7 model (2-Mekal) resulted in F-statistic of 93.804 and p-value of PoS(HEASA2015)005 1 − s 2 − erg cm 11 H.J. van Heerden − . 1 10 − s × 2 6 . − erg cm 12 − 10 × 5 value of 1.58. The fitted model was then used to 2 . The fitted model was then used to determine a flux χ . The PIN spectrum and fitted model can be seen in 4 1 − s 2 − erg cm for the BI data. The final accepted Multi-Mekal + Bremmsstrahlung 11 with a reduced − 28 6 − 10 − 10 × 10 1 × . × XIS spectra for the FI (blue) and BI (black) data with proposed mutli-Mekal + 2 . 071 XIS spectra for the FI (blue) and BI (black) data with proposed 3-Mekal models for the FI . Suzaku Suzaku . The model determined flux values for the soft X-ray emission (XIS) and hard X-ray 5 For the hard X-ray emission the RAW uncleaned PIN data was chosen, to make use of the ever determine flux values for the PIN data between energies of 14-40 keV of 1 improving instrument response and galacticFor background the model fit files of available thein from final a the extracted p-value CALDB. PIN of spectrum, 2 a simple power law was chosen. The fit resulted Bremsstrahlung models for the FI and BI spectra represented by the pink and red curves receptively. and 40-96 keV of 2 Figure 4: Figure Figure 3: and BI spectra represented by the pink and red curves receptively. and p-value of 1 model fitted spectra can bevalue seen for in the XIS Figure data between energies of 0.4-5.0 keV of 8 Exploring the nature of AE Aquarii at higher energies using Sazuku and Fermi-LAT PoS(HEASA2015)005 http: http:// H.J. van Heerden ] a more in depth analysis 22 50 6 Energy (keV) -LAT data as mentioned in [ ). Fermi . 10 ) and the Fermi Science Support Center at HEASARC ( 20 ], Fermi ASI (Agenzia Speziala Italiana) Science Data Center ( for a false colour map of the binned likelihood analysis. The indicated

6 23

10 10 10

−3 −4 −5

keV s counts

−1 −1 HXD-PIN spectrum with proposed power-law model represented by the black curve. The -LAT data analysis Suzaku Based on the binned as well as unbinned likelihood analysis results for the total energy range, The Fermi Gamma-ray Space Telescope was launched on 11 June 2008 into a LEO at 550 Since the previous analysis of Fermi no statistically significant detection was made(ROI). of Refer AE to Aquarii Figure within the selected region of interest was performed on the availabledures data used sets, and as results well obtained. as100 MeV more The and thorough selected 300 testing data GeV, as of included wellframe the Pass as 239557417 subsets relevant 7 - of proce- datasets the END for data (MET). in energiesconjunction Analysis terms with between was of the different performed python energy LATAnalysisScripts using v0.2.0 bins, and Fermi for Heasoft Science the v6.15.1. time Tools v9r32p5 in regions in yellow is relevant detected sources from the 2nd Fermi Catalogue. The regions in white 3. km. The primarybetween instrument 20 is MeV the -whole Large gamma-ray 300 emission Area GeV. sky The Telescope everysion 3 (LAT) telescope is hours. that is available Additional is from predominantly information [ sensitive in on to the survey telescope energies mode and mis- and covers the error bars are statistical in nature. Figure 5: //fermi.asdc.asi.it/ fermi.gsfc.nasa.gov/ssc/ Exploring the nature of AE Aquarii at higher energies using Sazuku and Fermi-LAT emission (PIN) spectra were thendiagram also for AE included Aquarii, in Figure an updated spectral energy distribution (SED) PoS(HEASA2015)005 ). ], 7 17 , 16 , -LAT data, 15 H.J. van Heerden Fermi 7 1 2 69 ). 7 3 62

4 Zone 1 Zone as recommended for 55 5

Hz), considering the very long baseline Zone 4 Zone σ 9 − 6 49 10 × 94 42 7

.

Zone 3 Zone AE Aqr AE 35 11

28 Zone 2 Zone 13 21 ] that the WD in AE Aquarii could possibly behave like a spun-up 13 15 levels, with a very strong QPO-like feature (16.507 s) next to it (Figure 14 σ 9 . and 4 σ Hz) times the Fourier resolution (5 5 − Likelihood analysis map for the region centred on AE Aquarii. Indicated in yellow are relevant 10 × Based on the likelihood analysis, a different methodology was undertaken in the form of peri- A power peak (16.5398 s) that corresponds within error with the first harmonic was found 97 . although QPO-like features close to thesewas periods used were with also the found. following Therefore(2 parameters: the "gptsearch" A tool Rayleigh analysistime. was The done number with of a trailsThe step were resultant size set power of spectrum, to with 5000 2000 the aroundwas noise 40 examined level for mHz set any to at power 4 cover at the the frequencies specified 10-70 WD mHz. frequencies (Figure pulsar, as well as earlier reports of possible GeV and TeV emission at these periods [ Figure 6: odogram analysis of the dataset to determine if(33.08 any s) pulsed modulation and at first or close (16.54 towas s) the based fundamental harmonics upon were visible a within report the [ data. The argument for the search between the 3 Fermi detected sources from theAquarii 2nd as Fermi well Catalogue. as selected Also test indicated zones in used white during are the the testing selected of ROI the of analysis methodology. AE Exploring the nature of AE Aquarii at higher energies using Sazuku and Fermi-LAT were used in the following analysis procedures,indicated. with The the test ROI of zones AE was Aquarii selectedwell and to as selected cover test distances a zones from range the ofthe target gamma-ray analysis ROI sky methodology. to background All broaden densities of the as these sampleerror region box population sizes as used were defined during set for the at the testing 2 2nd of degrees, Fermi to Catalogue. specify the size of the PoS(HEASA2015)005 8 . No similar 6 H.J. van Heerden in distribution through the σ 4 > flux and selected values from previ- Histogram of the Rayleigh Z distribution Suzaku Figure 8: for AE Aquarii, between energies300 of GeV. 250 MeV and 8 . 9 , a low level peak is visible within the noise structure for the 9 versus the Rayleigh statistic Z was plotted. As can be seen from Figure -LAT it will be within the noise level. The occurrence of this peak through (Pr) spectrum centred on ) 10 dZ / Fermi dN ( 10 -LAT upper-limits, along with determined Rayleigh -Log , and determining the distribution of those peaks through the different energy bins, any Fermi σ -LAT and the determined upper-limit values for AE Aquarii, is due to the cumulative effect As can be seen from Figure With no statistical likelihood source detection, for determination of flux values, made within From these results it is concluded that if any viable low level modulation from AE Aquarii is Figure 7: the first harmonic (indicated by redthe dashed WD line) spin for period forgies AE of Aquarii, 250 MeV between and ener- 300 GeV. region centred on AE Aquarii.the To same test analysis the methodology was validity applied of to the the technique four used test zones and indicated the in results Figure obtained, the Pass-7 LAT data based ondence level the were determined recommended for techniques, the energy upper-limit binsThese considered, values for at inclusion the into a 95% SED for confi- AE Aquarii. structure was found for any ofcating the that test the zones between proposed the low test levelthe frequencies power data of is analysed. 10-70 not mHz, due thus to indi- the analysis methodology, but is inherent to ous studies were then included into acurves SED for for selected AE instruments. Aquarii. Also TheFermi included difference were between sensitivity response the 2- instrument response curve for the power spectrum values correspond to white noise. detectable with the Exploring the nature of AE Aquarii at higher energies using Sazuku and Fermi-LAT To consider the noise versus signal distributiontogram of of the log power peaks of the resultant spectrum, a his- different energy bins was therefore tested.the This different was selected accomplished by energy producing1-100 bins, power spectra GeV i.e. for and 250-500 1-300 MeV,than GeV. 500-750 By 4 sampling Mev, 750-1000 possible MeV, signalpossible 1-10 peaks, consistent GeV, low i.e. level modulation all couldwhite peaks be noise identified. at will powers This have is greater alow based random on level distribution the modulation through assumption will that the bedifferent different energy stable energy bins. and bins, Refer have while to an Figure a consistent occurrence of PoS(HEASA2015)005 H.J. van Heerden 10 keV under certain condi- > γ ε . for selected energy bins for AE Aquarii. The 10 σ 9 A magnetic propeller in the cataclysmic variable AE (1997) 436. spectral analysis that indicates a possible Bremsstrahlung 286 ) observed at the first harmonic of the WD spin period, shows s Suzaku 5 used. This means that for the calculation of the sensitivity 02323 . 0 ∼ ± 5386 . , Monthly Notices of the RAS Sampled Rayleigh peaks with power above . A renewed effort is therefore called for studies utilising newer and more sensitive VHE instru- Based on the results from the ments, such as CTA, in conjunction withAE multi-wavelength Aquarii analysis could techniques, to be resolve an whether emitter of pulsed emission at energies component in conjunction with a power lawcharged spectrum, particles the possibility that exists can for a below population level accelerated of power to (16 free higher energies.that the This possibility result, of non-thermal along high with energy the emission in possible AE Aquarii cannot totally be excluded. References [1] Wynn, G. A. and King, A. R. and Horne, K., tions. 4. Final discussions and conclusion fundamental frequency and first harmonic of the current model WD spin period is indicatedfrom in red. the dataset length of curve the longer the datasetthus used, lowering the the more lower counts limit isis for available then to detectable applicable refine energy to the for upper-limitis sensitivity energy the available, model ranges, Fermi-LAT which and instrument. i.e. increases the the The likelihoodenergy longer opposite range. of the a Any dataset positive emission length detection, from the the thussensitivity more source, curve increasing counts and if the the detectable, upper-limit upper-limits. would then Refer be to somewhere Figure between the Figure 9: Exploring the nature of AE Aquarii at higher energies using Sazuku and Fermi-LAT PoS(HEASA2015)005 Suzaku , (1980) L133. 1e+028 H.J. van Heerden 240 (1990) 155. HESS Burst(Jun 93) II Flare(Jul 89) − CTA 20 Rays (Durham) , Monthly Notices of MAGIC Rays (Potchefstroom) − −  1e+026  VHE Fermi upper limits MAGIC upper limits TeV (1995) 649. Burst(Oct 90) Flare(Oct 93) (1990) 775. 275 AGILE 1e+024 FERMI 90 1e+022 (1994) 313. , Astrophysical Journal (2005) 573 (1997) 319. 2 433 360 1e+020 Ray − X (1991) 290. Terada et al. (2007,2008) 2009 X-ray spectra of cataclysmic variables from the − − 10 1e+018 Frequency (Hz) 382 Suzaku Suzaku On the location of the oscillations in AE Aquarii A study of the absorption lines from the donor star in the , Monthly Notices of the RAS , New Astronomy 1e+016 UV On the moments of inertia and radii of the white dwarfs and Spectral energy distribution of AE Aquarii. Spectral energy Opt 5 − K3 , Astrophysical Journal The diamagnetic blob propeller in AE Aquarii and non-thermal radio po 1e+014 bb IR (1993) L39. , Monthly Notices of the RAS , Astrophysical Journal Supplement Series ] and the University of Durham VHE gamma-ray telescope at Narrabi, N.S.W., 1e+012 410 15 A discovery of a brake on the white dwarf in AE Aquarii. , Astrophysical Journal The ultraviolet pulsations of the cataclysmic variable AE Aquarii as observed 33 second X-ray pulsations in AE Aquarii. RADIO Evidence for particle acceleration in a magnetized white dwarf from radio and , Contributions of the Astronomical Observatory Skalnate Pleso The characteristics of the cool component of the cataclysmic binary AE Aquarii 1e+010 (1994) 577. 267 ] respectively. 1e+008 015 016 017 006 007 008 009 010 011 012 013 014 − − − − − − − − − − − − Updated SED for AE Aquarii, including newly calculated flux and upper-limit values for

17

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-LAT data. The sensitivity curves for selected instruments are indicated, i.e. AGILE (1 year),

 F .s (erg.cm )

1 − 2 − Einstein Observatory with the Hubble Space Telescope Astrophysical Journal gamma-ray observations polytropic the RAS exotic cataclysmic variable AE Aquarii. derived from its HIPPARCOS . to mid-infrared emisiion. Fermi [9] Eracleous, M. and Halpern, J. and Patterson, J., [8] Eracleous, M. et al., [10] de Jager, O. C., and Fermi (2 years), MAGIC-IIincluded (50 for the hours), Potchefstroom and HESS DurhamMk (50 I groups Cherenkov were hours) telescope for [ and experiments conducted CTA using (Theoretical the 50 Nooigedacht hours). The values [7] Welsh, W.F. and Horne, K. and Gomer, R., [6] Andronov, I. L. and Yavorskij, Y. B., Australia [ [2] Welsh, W.F. and Horne, K. and Gomer, R., Figure 10: [3] Friedjung, M., [5] de Jager, O. C. et al., [11] Patterson, J. et al., Exploring the nature of AE Aquarii at higher energies using Sazuku and Fermi-LAT [4] Meintjes, P. J. & Venter, L. A., PoS(HEASA2015)005 , , 4 (2006) , 369 (1998) 203. 9 H.J. van Heerden , Astroparticle Physics , Proceedings of the 30th , Astroparticle Physics , Monthly Notices of the RAS (1994) 292. 11 , 33rd International Cosmic Ray Conference (2013) 434 (2014) 8. -ray emission from AE Aquarii in a multiwavelength γ (1992) 325. (2008) 387. (2008) 715. -ray emission from AE Aquarii coincident with high optical 568 2 γ 60 Fermi-LAT analysis and upper-limit calculations for AE Aquarii 401 (2012) 1557. 421 X-ray characteristics and the spectral energy distribution of AE Aquarii. (2009) 1071. A burst of pulsed VHE gamma rays from AE Aquarii. 697 Search for TeV The large area telescope on the Fermi Gamma-ray space telescope. , Astrophysical Journal AE Aquarii: An emitter of pulsed TeV Gamma rays resempling optical emission Simultaneous optical and TeV gamma-ray observations of the cataclysmic A search for TeV emission from AE Aquarii. MAGIC search for VHE (2015) 111. Suzaku discovery of hard X-ray pulsations from the rotating magnetized white dwarf, The white dwarf in AE Aqr brakes harder. Observation of AE Aquarii with the MAGIC telescope. 86 , Astrophysical Journal , Publications of the ASJ , Astronomy and Astrophysics Mem. S.A.It. context. Astrophysical Journal AE Aquarii. 1983. during flares. (1995) 99. International Cosmic Ray Conference and X-ray states with the MAGIC[icrc2013-0397]. telescopes. variable AE Aquarii. Monthly Notices of the RAS [22] van Heerden, H.J. and Meintjes, P.J., [23] Atwood, W. B. et al., [15] Meintjes, P. J. et al., [18] Lang, M. J. et al., [21] Aleksié, J. et al., Exploring the nature of AE Aquarii at higher energies using Sazuku and Fermi-LAT [12] Terada, Y. et al., [13] Oruru, B. & Meintjes, P. J., [16] Meintjes, P. J. et al., [17] Chadwick, P. M. et al., [19] Sidro, N. et al., [20] López-Coto, R. et al., [14] Mauche, C. W.,