Binary Observations with the VERITAS Gamma-Ray Observatory

Binary Observations with VERITAS

Gernot Maier for the VERITAS Collaboration Gamma-ray Binaries

Microquasar Pulsar wind - stellar disk Pulsar wind - stellar wind Mirabel(Science 2012)

Mirabel

Mirabel 2012 Mirabel 2012 Szostec & Dubus (2011) clumpy winds, transient accretion disks, disk/jet precession, quiescence/flaring periods, …

goal to understand acceleration processes, environment, pulsar wind and jet properties, dynamical changes

| VERITAS Binary Observations | Gernot Maier 2 VERITAS

> array of four 12 m Imaging Atmospheric Cherenkov Telescopes located in southern Arizona > energy range: 85 GeV to >30 TeV > field of view of 3.5o > angular resolution ~0.08o at 1 TeV > point source sensitivity (5σ detection): 1% Crab in < 25 h (10% in 25 min)

| VERITAS Binary Observations | Gernot Maier 3 VERITAS Binary Program - HMXB

orbital type period type of observation exposure reference

regular since 2006 ApJ 2008, 2009, 2011, LS I +61 303 Be+NS/BH 26.5 d 220 h (10-30 h/season) 2013, 2016

regular since 2006 ApJ 2009, 2014, in prep HESS J0632+057 B0pe+NS/BH 315 d 260 h (10-30 h/season) (ICRC 2019)

PSR J2032+4127/ archival; around Be+NS/BH ~50 y 180 h ApJ 2018 MT91 213 periastron

LS 5039 06.5V+NS/BH 3.9 d 8 h in preparation

1A 0535+262 O+NS 111 d during giant outburst 24 h ApJ 2011

4U 0115+634 B0.2Ve+NS 24.3 d during giant outburst 5.5 h ApJ 2016

Be/X-ray Binary Be+NS/HB - filler program (~130 h) in preparation discover program

Cygnus X-1 O9.7Iab + BH 5.6 d Cygnus survey 15 h ApJ 2018, ICRC 2009 Wolf Rayet + FoV of TeV Cygnus X-3 4.8 h 44 h ApJ 2013, ApJ 2018 BH? 2032+4130

| VERITAS Binary Observations | Gernot Maier 4 VERITAS Binary Program - LMXB, others

orbital type period type of observation exposure reference

V 404 Cyg K+BH 6.47 d during giant outburst 4 h ApJ 2016

| VERITAS Binary Observations | Gernot Maier 5 VERITAS Binary Program - LMXB, others

orbital type period type of observation exposure reference

V 404 Cyg K+BH 6.47 d during giant outburst 4 h ApJ 2016

10MΘ star+NS/ during hard X-ray MAXI J1820+070 ? 12.2 h ICRC 2019 BH outburst HMXBs & LMXBs survey of Cygnus - - 2-6 h ApJ 2018 in Cygnus region region Nova in a V407 Cygni outburst (LAT) 5 h ApJ 2012 symbiotic binary ToO SGRs+AXPs - ICRC 2009 Magnetars (GRB pipeline) TO (radio quiet/HE G+MSP 4.8 h 25 h ApJ 2016 PSR J1023+0038 flare) Presentations of VERITAS results at this workshop: • Overview - common aspects of LS I +61303, HESS J0632+-57 • HESS J0632+057: with H.E.S.S./MAGIC —> Daniela • HESS J0632+057: with NuSTAR —> Raul • PSR J2032+4127/MT91 213: with MAGIC —> Alicia • MAXJ J1820+070: with H.E.S.S./MAGIC —> Jean-Pierre

| VERITAS Binary Observations | Gernot Maier 5 516 LS I +61 303 ARAGONAHESSET AL. J0632+057 Vol.PSR698 J2032+4127/ 3. OBSERVATIONS AND RADIAL VELOCITY MEASUREMENTS OF LS 5039 MT91 213 Spectra of LS 5039 were taken at the CTIO 1.5 m telescope > betweenB0pe2007 starAugust (Mand 2008= 16April Min sΘervice) mode. We used > Be star (10-15 MΘ) + grating 47 in the second order, a 200 µm slit, the BG39 filter>, andBe star (15 MΘ) + compact object the+L oralcompact1K CCD detector object. Spectra (2-3were wa velength-calibratedneutron star at using He–Ar comparison lamp spectra generally taken before (2-3 MΘ) at 1.6 kpc andMafterΘ) eachat 1.1-1.7exposure. The kpcobserv ed wavelength region was1.4-1.7 kpc therefore about 4050–4700 Å, with 2500 < R < 3150 across > 26.5 day modulation > the315chip. d orbital period in > associated with For each night that we had service time available in fall across entire 2007,X-rayswe obtained four to six spectra, each with an exposuregamma-ray source time of 30 minutes. During the spring of 2008, we obtained electromagnetic > twupdatedo spectra each orbitalnight of observ solutionations, each of 22 minutesTeV 2032+4130 duration. Thus we obtained a total of 98 blue spectra of LS 5039. spectrum The(Moritaniimages were zero-corrected, et al 2018)flat-fielded, and wavelength-> orbital period ~50 y calibrated onto a log wavelength scale using standard procedures Figure 2. Radial1667velocity daycurve of Lsuper-orbitalS I +61 303. Periastron corresponds to very weak GeV (Ho et al 2017) φ(TG) >0.275 and is marked as a dotted line in this plot. The points plotted > in IRAF, and all spectra were interpolated onto a common as open=diamondsmodulationare from Grundstrom etinal. (radio,2007), crosses X-are from Casares heliocentricdetectionwavelength grid. The spectra were rectified to a et al. (2005a), and filled circles are from this work. unit continuum using line-free regions. > periastron approach in ray, GeV/TeV Since the signal-to-noise ratio was somewhat low, we chose to coadd pairs of consecutive spectra from each night. The total2017 elapsed time during two consecutive observations is only one hour, about 1% of the orbital period, so coadding the spectra does not significantly affect the measured Vr. On two nights we collected an odd number of spectra, and in these cases the last spectrum of each set was examined individually. Therefore, we had 50 new spectra from which to obtain Vr measurements and improve the orbital elements. The spectra from 2007 August 29, were taken near the time of inferior conjunction and thus showed the least variation in Vr, so we chose to average these six spectra to produce a reference spectrum. This reference spectrum is plotted in Figure 4. Five + lines were examined in each spectrum: Hγ , Hδ, He ii λλ4200, 4542, and He i λ4471. The spectra also recorded the strong He ii λ4686 line, but a bad column on the chip interfered with Aragona et al measuring reliable Vr from this line. We performed a cross- (ApJ 2009) correlation between each spectrum and the reference spectrum to obtain its relative Vr, and then we used the mean Vr from a parabolic fit of the line cores in the reference spectrum to find its absolute Vr. | VERITAS Binary Observations | Gernot Maier The period of the system was obtained using the dis- 6 crete Fourier transform and CLEAN deconvolution program of Roberts et al. (1987) (written in IDL7 by A. W. Fullerton). The Figure 3. Orbital geometry of LS I +61 303, looking down on the orbital plane, showing the relative orbits (r/a) of the optical star (12.5 M ; Casares et al. Vr from our observations were combined with the mean values 2005a) and its compact companion of unknown mass. The relati⊙ ve orbit of the from all lines measured by McSwain et al. (2001), McSwain compact object is shown as a solid line, while the Be star’s relative orbit depends et al. (2004), and Casares et al. (2005b). The Vr measurements greatly on the mass of the companion. The dashed line indicates the Be star’s of Casares et al. (2005b) indicate a value of γ that is sys- orbit assuming a 4 M black hole, while the dotted line assumes a 1.4 M 1 neutron star. The rele⊙vant phases of periastron, apastron, and conjunctions⊙ tematically higher than our data sets by 7.0 km s− , so we are marked along the orbit of the compact companion. The center of mass subtracted this value from their measurements. No significant is indicated with a cross, and the thin solid line is the orbital major axis. difference was found between the Vr data presented here and past measurements obtained by our group. We used all of the available Vr with the CLEAN algorithm, which found a strong our Vr measurements provide excellent coverage of the orbit peak at P 3.9060263 d (which was improved slightly with the with no large gaps in orbital phase, and the errors in our fit later orbital=fit), nearly identical to the period found by Casares are slightly lower than those of Grundstrom et al. (2007) and et al. (2005b). Our group has previously found P 4.1 d (Mc- significantly lower than those of Casares et al. (2005a). We also Swain et al. 2001) and P 4.4 d (McSwain et =al. 2004) for = emphasize that our final orbital solution relies upon the fixed LS 5039, due to the very high scatter in its Vr curve, which P from Gregory (2002), but we found very similar values for has lead to considerable confusion about the correct orbital pe- each orbital element when we allowed P to vary. We found riod of this system. We note that our period search also resulted P 26.4982 .0076 d using the fitting program of Morbey & in P 3.906 d when we excluded the data of Casares et al. = ± Brosterhus (1974) with the combined Vr data, which is not an = improvement over Gregory (2002). 7 IDL is a registered trademark of Research Systems, Inc. very rough illustration! Orbits to scale

PSR B1259-63

TeV 2032+4130

LS 5039 size of systems (0.1-30 AU) periastron distance (0.1-0.95) periods (days to 50 years) orbital and disc orientation, disk size disk LS I +61 303 HESS J0632+057 | VERITAS Binary Observations | Gernot Maier 7 LS I +61 303 - light curve vs orbital phase based on 2007-2016 observations

• detection throughout the orbits (except one bin) • ~3% quiescence flux • single emission maximum around apastron

| VERITAS Binary Observations | Gernot Maier 8 LS I +61 303 - light curve vs orbital phase based on 2007-2016 observations

Γ0.8-0.5= Γapastron= 2.81±0.16 2.63±0.06

• detection throughout the orbits (except one bin) • ~3% quiescence flux • single emission maximum around apastron • no significant spectral variability detected

| VERITAS Binary Observations | Gernot Maier 8 Light curves and (missing?) spectral variability

HESS J0632+057 LS I +61 303

• Γ0.5-0.8 = 2.63±0.06 • Γ0.2-0.4 = 2.57±0.05 (near apastron) (first peak)

• Γ0.8-0.5 = 2.81±0.16 • Γ0.6-0.8 = 2.56±0.12 (second peak)

• Γ0.8-0.2 = 2.70±0.15

| VERITAS Binary Observations | Gernot Maier 9 LS I +61 303 - light curve vs super-orbital period Ahnen et al 2916: VERITAS data 2007-2013

| VERITAS Binary Observations | Gernot Maier 10 LS I +61 303 - light curve vs super-orbital period Ahnen et al 2916: VERITAS data 2007-2013 2014-2015 2015-2016 2016-2017 2017-2018 2018-2019

| VERITAS Binary Observations | Gernot Maier 10 LS I +61 303 - light curve vs super-orbital period Ahnen et al 2916: VERITAS data 2007-2013

2014-2015 2015-2016 2016-2017 2014-2015 2015-2016 2016-2017 2017-2018 2018-2019

| VERITAS Binary Observations | Gernot Maier 10 LS I +61 303 2014/2015 - bright state or flare?

30% Crab flux: highest flux ever seen

very sharp flare profile (fall time 1-2 days)

highest energy photon ~10 TeV

• exceptional or missed due to the low coverage in gamma-ray observations? (VERITAS observed only ~10% of the orbits of LS I +61 303 in the past 10 years) • flares with time scales of a few hundred seconds are observed in X-rays (e.g. Smith et al 2009) • flare emission independent of canonical apastron emission?

| VERITAS Binary Observations | Gernot Maier 11 HESS J0632+057 - bright state or flare?

Jan / Feb 2018 Daily X- and Gamma-ray spectra

Preliminary Preliminary

flux decay time ~5 days

0.3 0.4 orbital phase

| VERITAS Binary Observations | Gernot Maier 12 HESS J0632+057 - regular or unusual flares?

Coverage per orbit - still limited despite large data set (18 orbits)

‘Outbursts’ possibly a repeating feature

Assuming an orbital period of 317.3 days Grey band: average Gamma-ray light curve (68% uncertainty band)

| VERITAS Binary Observations | Gernot Maier 13 Gamma-ray - X-ray Correlations

HESS J0632+057 LS I +61 303 X-Ray X-ray vs Gamma-ray

Kar 2018 (Thesis U of Utah) VERITAS 2019 (in prep)

HESS J0632+057 Gamma-Ray • both binaries indicate X-ray - TeV correlations • no GeV-TeV correlation detected in both binaries

| VERITAS Binary Observations | Gernot Maier 14 very rough illustration! Common Picture?

PSR B1259-63

TeV 2032+4130

HESS J0632+057 LS I +61 303 | VERITAS Binary Observations | Gernot Maier 15 Summary - VERITAS Binary Observations

• large and diverse data sets on binary observations • LS I +61 303 and HESS J0632+57: 2006-2019, more than 200 h • continue data taking for at least the next three years

• LS I +61 303: flare in 2014 clearly outside the expected if dependency on super-orbital period holds

• complex variability observed in LS I +61 303 and HESS J0632+057

• large multi-wavelength data sets available for the bright gamma-ray binaries should allow detailed modelling of the emission patterns

| VERITAS Binary Observations | Gernot Maier 16