arXiv subjects

Kim L. Page

Publications and source records attributed to Kim L. Page.

At least 19 recordsLinked to original sources

arXiv2026

Shocks in the Symbiotic Recurrent Nova V3890 Sgr: VLBI Radio Imaging and Fermi GeV Gamma-Rays

We present very long baseline interferometric (VLBI) radio imaging and Fermi/LAT GeV $γ$-ray observations of the 2019 eruption of the symbiotic recurrent nova V3890 Sgr.The VLBI imaging spans 8 -- 51 days after eruption, synchronous with the detected $γ$-rays. VLBI imaging shows the eruption starts out asymmetric on day 8 with an eastern component brighter than a western component. By day 32 the blast is rather circularly symmetric, and on day 49, the nova shell is brighter along the north--south axis. This morphological evolution is explained by interaction with circumstellar material (CSM) comprised of a spherical wind plus an over-density in the orbital plane. Comparing radio images to optical line widths gives an expansion parallax distance of 6.8 kpc. In the first 32 days or eruption, VLBI images capture $>$80 per cent of the integrated flux (as measured by the VLA), implying that synchrotron emission dominates. A second peak in the VLA light curve is explained by an image on day 48 that reveals the nova shell surrounded by a diffuse halo, powered by synchrotron emission from particles that have diffused upstream of the shock. The $γ$-rays appear around optical maximum and remain detectable for 23 days; marginally significant $γ$-rays reappear around day 60, concurrent with the second radio peak. Modelling indicates radio and $γ$-ray emission arise in distinct shock regions: $γ$-rays from dense CSM in the orbital plane, radio from the more spherical CSM component. X-ray observations constrain the spherical CSM density, which is higher than in other symbiotic recurrent novae. Assuming equipartition, we estimate the fraction of the post-shock pressure in magnetic fields, $ε_B = 3 \times 10^{-4} - 2 \times 10^{-3}$.

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arXiv2025

Multiple outflows and delayed ejections revealed by early imaging of novae

Novae are thermonuclear eruptions on accreting white dwarfs in interacting binaries. Although most of the accreted envelope is expelled, the mechanism -- impulsive ejection, multiple outflows or prolonged winds, or a common-envelope interaction -- remains uncertain. GeV $γ$-ray detections from $>20$ Galactic novae establish these eruptions as nearby laboratories for shock physics and particle acceleration, underscoring the need to determine how novae eject their envelopes. Here we report on near-infrared interferometry, supported with multiwavelength observations, of two $γ$-ray detected novae. The images of the very fast 2021 nova V1674~Her, taken just 2--3 days after discovery, reveal the presence of two perpendicular outflows. The interaction between these outflows likely drives the observed $γ$-ray emission. Conversely, the images of the very slow 2021 nova V1405~Cas suggest a delay in the ejection of the bulk of the accreted envelope of more than 50 days after the start of eruption, as the nova slowly rises to visible peak and during which the envelope engulfed the system in a common envelope phase. These unprecedented images offer direct observational evidence that the mechanisms driving mass ejection from the surfaces of accreting white dwarfs are not as simple as previously thought, revealing multiple outflows and delayed ejections.

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arXiv2025

Prompt Periodicity in the GRB 211211A Precursor: Black-hole or magnetar engine?

The merger origin long GRB 211211A was a class (re-)defining event. A precursor was identified with a $\sim 1$ s separation from the main burst, as well as a claimed candidate quasi-periodic oscillation (QPO) with a frequency $\sim20$ Hz. Here, we explore the implications of the precursor, assuming the quasi-periodicity is real. The precursor variability timescale requires relativistic motion with a Lorentz factor $Γ\gtrsim80$, and implies an engine driven jetted outflow. The declining amplitude of the consecutive pulses requires an episodic engine with an `on/off' cycle consistent with the QPO. For a black-hole central engine, the QPO can have its origin in Lense-Thirring precession of the inner disk at $\sim6-9$ $r_g$ (gravitational radii) for a mass $M_\bullet\leq4.5$ $M_{\odot}$, and $\lesssim 7$ $r_g$ for $M_\bullet>4.5$ $M_{\odot}$ and dimensionless spin $χ\sim 0.3 - 0.9$. Alternatively, at a disk density of $\sim10^{8 - 12}$ g cm$^{-3}$, the required magnetic field strength for a QPO via magnetohydrodynamic effects will be on the order $B\sim10^{12 - 14}$ G. If the central engine is a short lived magnetar or hypermassive neutron star, then a low-frequency QPO can be produced via instabilities within the disk at a radius of $\sim20 - 70$ km, for a disk density $\sim10^{9 - 12}$ g cm$^{-3}$ and magnetic field $\gtrsim10^{13 - 14}$ G. The QPO cannot be coupled to the neutron star spin, as the co-rotation radius is beyond the scale of the disk. Neither engine can be ruled out -- however, we favour an origin for the precursor candidate QPO as early jet-disk coupling for a neutron star -- black hole merger remnant with mass $M_\bullet>4.5$ $M_{\odot}$.

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arXiv2025

Simultaneous multi-wavelength observations of the repeating fast radio burst FRB 20190520B with Swift and FAST

Among several dozen known repeating Fast radio bursts (FRBs), those precisely localized offer the best opportunities to explore their multi-wavelength counterparts, which are key to uncovering their origins. Here we report our X-ray, ultraviolet (UV), and optical observations with the $Swift$ satellite of the repeating FRB 20190520B, in coordination with simultaneous radio observations with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Our aim was to detect potentially associated multi-wavelength bursts and identify any persistent multi-wavelength counterpart to the associated persistent radio source (PRS). While a total of 10 radio bursts were detected by FAST during the $Swift$ observations, we detected no X-ray, UV, or optical bursts in accompany with the radio bursts. We obtained the energy upper limits ($3σ$) on any multi-wavelength bursts as follows: $5.03 \times 10^{47}$ erg in the hard X-ray band (15--150 keV), $7.98 \times 10^{45}$ erg in the soft X-ray band (0.3--10 keV), and $4.51 \times 10^{44}$ erg in the U band (3465Å), respectively. The energy ratio between soft X-ray (0.3--10 keV) and radio emission of the bursts is constrained as $<6\times10^{7}$, and the ratio between optical (U band) and radio as $<1.19\times10^{6}$. We detect no multi-wavelength counterpart to the PRS. The 3$σ$ luminosity upper limits are 1.04$\times10^{47}$ (15--150 keV), 8.81$\times10^{42}$ (0.3--10 keV), 9.26$\times10^{42}$ (UVW1), and 2.54$\times10^{42}$ erg s$^{-1}$ (U), respectively. We show that the PRS is much more radio loud than representative pulsar wind nebulae, supernova remnants, extended jets of Galactic X-ray binaries, and ultraluminous X-ray sources, suggestive of boosted radio emission of the PRS.

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arXiv2024

Millinovae: A New Class of Transient Supersoft X-ray Sources without a Classical Nova Eruption

Some accreting binary systems containing a white dwarf (such as classical novae or persistent supersoft sources) are seen to emit low-energy X-rays with temperatures of ~10^6 K and luminosities exceeding 10^35 erg/s. These X-rays are thought to originate from nuclear burning on the white dwarf surface, either caused by a thermonuclear runaway (classical novae) or a high mass-accretion rate that sustains steady nuclear burning (persistent sources). The discovery of transient supersoft X-rays from ASASSN-16oh challenged these ideas, as no clear signatures of mass ejection indicative of a classical nova eruption were detected, and the origin of these X-rays remains controversial. It was unclear whether this star was one of a kind or representative of a larger, as yet undiscovered, group. Here, we present the discovery of 29 stars located in the direction of the Magellanic Clouds exhibiting long-duration, symmetrical optical outbursts similar to that seen in ASASSN-16oh. We observed one of these objects during an optical outburst and found it to be emitting transient supersoft X-rays, while no signatures of mass ejection (indicative of a classical nova eruption) were detected. We therefore propose that these objects form a homogeneous group of transient supersoft X-ray sources, which we dub ``millinovae'' because their optical luminosities are approximately a thousand times fainter than those of ordinary classical novae.

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arXiv2023

Astronomy as a Field: A Guide for Aspiring Astrophysicists

This book was created as part of the SIRIUS B VERGE program to orient students to astrophysics as a broad field. The 2023-2024 VERGE program and the printing of this book is funded by the Women and Girls in Astronomy Program via the International Astronomical Union's North American Regional Office of Astronomy for Development and the Heising-Simons Foundation; as a result, this document is written by women in astronomy for girls who are looking to pursue the field. However, given its universal nature, the material covered in this guide is useful for anyone interested in pursuing astrophysics professionally.

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arXiv2023

A two-component clumpy model for the shell evolution of classical novae: the case of V5668 Sgr

The shell of the classical nova V5668 Sgr was resolved by ALMA at the frequency of 230 GHz 927 days after eruption, showing that most of the continuum bremsstrahlung emission originates in clumps with diameter smaller than $10^{15}$ cm. Using VLA radio observations, obtained between days 2 and 1744 after eruption, at frequencies between 1 and 35 GHz, we modeled the nova spectra, assuming first that the shell is formed by a fixed number of identical clumps, and afterwards with the clumps having a power law distribution of sizes, and were able to obtain the clump's physical parameters (radius, density and temperature). We found that the density of the clumps decreases linearly with the increase of the shell's volume, which is compatible with the existence of a second media, hotter and thinner, in pressure equilibrium with the clumps. We show that this thinner media could be responsible for the emission of the hard X-rays observed at the early times of the nova eruption, and that the clump's temperature evolution follows that of the super-soft X-ray luminosity. We propose that the clumps were formed in the radiative shock produced by the collision of the fast wind of the white dwarf after eruption, with the slower velocity of the thermonuclear ejecta. From the total mass of the clumps, the observed expansion velocity and thermonuclear explosion models, we obtained an approximate value of 1.25 M$_{\odot}$ for the mass of the white dwarf, a central temperature of $10^7$ K and an accretion rate from the secondary star of $10^{-9}-10^{-8}$ M$_{\odot}$ y$^{-1}$.

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arXiv2023

The Luminosity Phase Space of Galactic and Extragalactic X-ray Transients Out to Intermediate Redshifts

We present a detailed compilation and analysis of the X-ray phase space of low- to intermediate-redshift ($ 0\le z \le 1$) transients that consolidates observed light curves (and theory where necessary) for a large variety of classes of transient/variable phenomena in the 0.3--10 keV energy band. We include gamma-ray burst afterglows, supernovae, supernova shock breakouts and shocks interacting with the environment, tidal disruption events and active galactic nuclei, fast blue optical transients, cataclysmic variables, magnetar flares/outbursts and fast radio bursts, cool stellar flares, X-ray binary outbursts, and ultraluminous X-ray sources. Our overarching goal is to offer a comprehensive resource for the examination of these ephemeral events, extending the X-ray duration-luminosity phase space (DLPS) to show luminosity evolution. We use existing observations (both targeted and serendipitous) to characterize the behavior of various transient/variable populations. Contextualizing transient signals in the larger DLPS serves two primary purposes: to identify areas of interest (i.e., regions in the parameter space where one would expect detections, but in which observations have historically been lacking) and to provide initial qualitative guidance in classifying newly discovered transient signals. We find that while the most luminous (largely extragalactic) and least luminous (largely Galactic) part of the phase space is well-populated at $t > 0.1$ days, intermediate luminosity phenomena (L$_x = 10^{34} - 10^{42}$ erg s$^{-1}$) represent a gap in the phase space. We thus identify L$_x = 10^{34} - 10^{42}$ erg s$^{-1}$ and $t = 10^{-4} - 0.1$ days as a key discovery phase space in transient X-ray astronomy.

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arXiv2023

GRB 221009A: Discovery of an Exceptionally Rare Nearby and Energetic Gamma-Ray Burst

We report the discovery of the unusually bright long-duration gamma-ray burst (GRB), GRB 221009A, as observed by the Neil Gehrels Swift Observatory (Swift), Monitor of All-sky X-ray Image (MAXI), and Neutron Star Interior Composition Explorer Mission (NICER). This energetic GRB was located relatively nearby (z = 0.151), allowing for sustained observations of the afterglow. The large X-ray luminosity and low Galactic latitude (b = 4.3 degrees) make GRB 221009A a powerful probe of dust in the Milky Way. Using echo tomography we map the line-of-sight dust distribution and find evidence for significant column densities at large distances (~> 10kpc). We present analysis of the light curves and spectra at X-ray and UV/optical wavelengths, and find that the X-ray afterglow of GRB 221009A is more than an order of magnitude brighter at T0 + 4.5 ks than any previous GRB observed by Swift. In its rest frame GRB 221009A is at the high end of the afterglow luminosity distribution, but not uniquely so. In a simulation of randomly generated bursts, only 1 in 10^4 long GRBs were as energetic as GRB 221009A; such a large E_gamma,iso implies a narrow jet structure, but the afterglow light curve is inconsistent with simple top-hat jet models. Using the sample of Swift GRBs with redshifts, we estimate that GRBs as energetic and nearby as GRB 221009A occur at a rate of ~<1 per 1000 yr - making this a truly remarkable opportunity unlikely to be repeated in our lifetime.

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arXiv2022

The first nova eruption in a novalike variable: YZ Ret as seen in X-rays and gamma-rays

Peaking at 3.7 mag on 2020 July 11, YZ Ret was the second-brightest nova of the decade. The nova's moderate proximity (2.7 kpc from Gaia) provided an opportunity to explore its multi-wavelength properties in great detail. Here we report on YZ Ret as part of a long-term project to identify the physical mechanisms responsible for high-energy emission in classical novae. We use simultaneous Fermi/LAT and NuSTAR observations complemented by XMM-Newton X-ray grating spectroscopy to probe the physical parameters of the shocked ejecta and the nova-hosting white dwarf. The XMM-Newton observations revealed a super-soft X-ray emission which is dominated by emission lines of CV, CVI, NVI, NVII, and OVIII rather than a blackbody-like continuum, suggesting CO-composition of the white dwarf in a high-inclination binary system. Fermi/LAT detected YZ Ret for 15 days with the gamma-ray spectrum best described by a power law with an exponential cut-off at 1.9 +/-0.6 GeV. In stark contrast with theoretical predictions and in keeping with previous NuSTAR observations of Fermi-detected classical novae (V5855 Sgr and V906 Car), the 3.5-78 keV X-ray emission is found to be two orders of magnitude fainter than the GeV emission. The X-ray emission observed by NuSTAR is consistent with a single-temperature thermal plasma. We detect no non-thermal tail of the GeV emission expected to extend down to the NuSTAR band. NuSTAR observations continue to challenge theories of high-energy emission from shocks in novae.

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arXiv2021

Optical and near-infrared spectroscopy of Nova V2891 Cygni: evidence for shock-induced dust formation

We present multi-epoch optical and near-infrared observations of the highly reddened, \pion{Fe}{ii} class slow nova V2891 Cygni. The observations span 15 months since its discovery. The initial rapid brightening from quiescence, and the presence of a $\sim$35 day long pre-maximum halt, is well documented. The evidence that the current outburst of V2891 Cyg has undergone several distinct episodes of mass ejection is seen through time-varying P Cygni profiles of the O\,{\sc i} 7773\,$Å$ line. A highlight is the occurrence of a dust formation event centred around $\sim$+273d, which coincides with a phase of coronal line emission. The dust mass is found to be $\sim0.83-1.25 \times 10^{-10} M_{\odot}$. There is strong evidence to suggest that the coronal lines are created by shock heating rather than by photoionization. The simultaneous occurrence of the dust and coronal lines (with varying velocity shifts) supports the possibility that dust formation is shock-induced. Such a route for dust formation has not previously been seen in a nova, although the mechanism has been proposed for dust formation in some core-collapse supernovae. Analysis of the coronal lines indicates a gas mass and temperature of 8.35--8.42$\times10^{-7}$ M$_\odot$ and $\sim(4.8-9.1)\times10^{5}$~K respectively, and an overabundance of aluminium and silicon. A Case B analysis of the hydrogen lines yields a mass of the ionized gas of ($8.60\pm1.73)\times10^{-5}$ M$_{\odot}$. The reddening and distance to the nova are estimated to be $E(B-V)$ = 2.21$\pm$0.15 and $d$ = 5.50 kpc respectively.

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arXiv2021

The Remarkable Spin-down and Ultra-fast Outflows of the Highly-Pulsed Supersoft Source of Nova Hercules 2021

Nova Her 2021 (V1674 Her), which erupted on 2021 June 12, reached naked-eye brightness and has been detected from radio to $γ$-rays. An extremely fast optical decline of 2 magnitudes in 1.2 days and strong Ne lines imply a high-mass white dwarf. The optical pre-outburst detection of a 501.42s oscillation suggests a magnetic white dwarf. This is the first time that an oscillation of this magnitude has been detected in a classical nova prior to outburst. We report X-ray outburst observations from {\it Swift} and {\it Chandra} which uniquely show: (1) a very strong modulation of super-soft X-rays at a different period from reported optical periods; (2) strong pulse profile variations and the possible presence of period variations of the order of 0.1-0.3s; and (3) rich grating spectra that vary with modulation phase and show P Cygni-type emission lines with two dominant blue-shifted absorption components at $\sim 3000$ and 9000 km s$^{-1}$ indicating expansion velocities up to 11000 km s$^{-1}$. X-ray oscillations most likely arise from inhomogeneous photospheric emission related to the magnetic field. Period differences between reported pre- and post-outburst optical observations, if not due to other period drift mechanisms, suggest a large ejected mass for such a fast nova, in the range $2\times 10^{-5}$-$2\times 10^{-4} M_\odot$. A difference between the period found in the {\it Chandra} data and a reported contemporaneous post-outburst optical period, as well as the presence of period drifts, could be due to weakly non-rigid photospheric rotation.

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arXiv2020

Surveying the X-ray Behavior of Novae as They Emit $γ$-rays

The detection of GeV $γ$-ray emission from Galactic novae by $Fermi$-LAT has become routine since 2010, and is generally associated with shocks internal to the nova ejecta. These shocks are also expected to heat plasma to $\sim 10^7$ K, resulting in detectable X-ray emission. In this paper, we investigate 13 $γ$-ray emitting novae observed with the Neil Gehrels $Swift$ Observatory, searching for 1-10 keV X-ray emission concurrent with $γ$-ray detections. We also analyze $γ$-ray observations of novae V407 Lup (2016) and V357 Mus (2018). We find that most novae do eventually show X-ray evidence of hot shocked plasma, but not until the $γ$-rays have faded below detectability. We suggest that the delayed rise of the X-ray emission is due to large absorbing columns and/or X-ray suppression by corrugated shock fronts. The only nova in our sample with a concurrent X-ray/$γ$-ray detection is also the only embedded nova (V407 Cyg). This exception supports a scenario where novae with giant companions produce shocks with external circumbinary material and are characterized by lower density environments, in comparison with novae with dwarf companions where shocks occur internal to the dense ejecta.

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arXiv2020

X-ray Spectroscopy of the gamma-ray Brightest Nova V906 Car (ASASSN-18fv)

Shocks in gamma-ray emitting classical novae are expected to produce bright thermal and non-thermal X-rays. We test this prediction with simultaneous NuSTAR and Fermi/LAT observations of nova V906 Car, which exhibited the brightest GeV gamma-ray emission to date. The nova is detected in hard X-rays while it is still gamma-ray bright, but contrary to simple theoretical expectations, the detected 3.5-78 keV emission of V906 Car is much weaker than the simultaneously observed >100 MeV emission. No non-thermal X-ray emission is detected, and our deep limits imply that the gamma-rays are likely hadronic. After correcting for substantial absorption (N_H ~ 2 x 10^23 cm^-2), the thermal X-ray luminosity (from a 9 keV optically-thin plasma) is just ~2% of the gamma-ray luminosity. We consider possible explanations for the low thermal X-ray luminosity, including the X-rays being suppressed by corrugated, radiative shock fronts or the X-rays from the gamma-ray producing shock are hidden behind an even larger absorbing column (N_H >10^25 cm^-2). Adding XMM-Newton and Swift/XRT observations to our analysis, we find that the evolution of the intrinsic X-ray absorption requires the nova shell to be expelled 24 days after the outburst onset. The X-ray spectra show that the ejecta are enhanced in nitrogen and oxygen, and the nova occurred on the surface of a CO-type white dwarf. We see no indication of a distinct super-soft phase in the X-ray lightcurve, which, after considering the absorption effects, may point to a low mass of the white dwarf hosting the nova.

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arXiv2020

Chandra High Energy Transmission Gratings Spectra of V3890 Sgr

The recurrent nova (RN) V3890 Sgr was observed during the 7th day after the onset of its most recent outburst, with the Chandra ACIS-S camera and High Energy Transmission Gratings (HETG). A rich emission line spectrum was detected, due to transitions of Fe-L and K-shell ions ranging from neon to iron. The measured absorbed flux is $\approx 10^{-10}$ erg cm$^{-2}$ s$^{-1}$ in the 1.4-15 Angstrom range (0.77-8.86 keV). The line profiles are asymmetric, blue-shifted and skewed towards the blue side, as if the ejecta moving towards us are less absorbed than the receding ones. The full width at half maximum of most emission lines is 1000-1200 km s$^{-1}$, with some extended blue wings. The spectrum is thermal and consistent with a plasma in collisional ionization equilibrium with column density 1.3 $\times 10^{22}$ cm$^{-2}$ and at least two components at temperatures of about 1 keV and 4 keV, possibly a forward and a reverse shock, or regions with differently mixed ejecta and red giant wind. The spectrum is remarkably similar to the symbiotic RNe V745 Sco and RS Oph, but we cannot distinguish whether the shocks occurred at a distance of few AU from the red giant, or near the giant's photosphere, in a high density medium containing only a small mass. The ratios of the flux in lines of aluminum, magnesium and neon relative to the flux in lines of silicon and iron probably indicate a carbon-oxygen white dwarf (CO WD).

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arXiv2020

Direct evidence for shock-powered optical emission in a nova

Classical novae are thermonuclear explosions that occur on the surfaces of white dwarf stars in interacting binary systems (Bode & Evans 2008). It has long been thought that the luminosity of classical novae is powered by continued nuclear burning on the surface of the white dwarf after the initial runaway (Gallaher & Starrfield 1978). However, recent observations of GeV $γ$-rays from classical novae have hinted that shocks internal to the nova ejecta may dominate the nova emission. Shocks have also been suggested to power the luminosity of events as diverse as stellar mergers (Metzger & Pejcha 2017), supernovae (Moriya et al. 2018), and tidal disruption events (Roth et al. 2016), but observational confirmation has been lacking. Here we report simultaneous space-based optical and $γ$-ray observations of the 2018 nova V906 Carinae (ASASSN-18fv), revealing a remarkable series of distinct correlated flares in both bands. The optical and $γ$-ray flares occur simultaneously, implying a common origin in shocks. During the flares, the nova luminosity doubles, implying that the bulk of the luminosity is shock-powered. Furthermore, we detect concurrent but weak X-ray emission from deeply embedded shocks, confirming that the shock power does not appear in the X-ray band and supporting its emergence at longer wavelengths. Our data, spanning the spectrum from radio to $γ$-ray, provide direct evidence that shocks can power substantial luminosity in classical novae and other optical transients.

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arXiv2019

Swift spectra of AT2018cow: A White Dwarf Tidal Disruption Event?

The bright transient AT2018cow has been unlike any other known type of transient. Its high brightness, rapid rise and decay and initially nearly featureless spectrum are unprecedented and difficult to explain using models for similar burst sources. We present evidence for faint gamma-ray emission continuing for at least 8 days, and featureless spectra in the ultraviolet bands -- both unusual for eruptive sources. The X-ray variability of the source has a burst-like character. The UV-optical spectrum does not show any CNO line but is well described by a blackbody. We demonstrate that a model invoking the tidal disruption of a 0.1 - 0.4 Msun Helium White Dwarf (WD) by a 100,000 to one million solar mass Black Hole (BH) located in the outskirts of galaxy Z~137-068 could provide an explanation for most of the characteristics shown in the multi-wavelength observations. A blackbody-like emission is emitted from an opaque photosphere, formed by the debris of the WD disruption. Broad features showing up in the optical/infrared spectra in the early stage are probably velocity broadened lines produced in a transient high-velocity outward moving cocoon. The asymmetric optical/infrared lines that appeared at a later stage are emission from an atmospheric layer when it detached from thermal equilibrium with the photosphere, which undergoes more rapid cooling. The photosphere shrinks when its temperature drops, and the subsequent infall of the atmosphere produced asymmetric line profiles. Additionally, a non-thermal jet might be present, emitting X-rays in the 10-150 keV band.

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arXiv2016

IACHEC Cross-Calibration of Chandra, NuSTAR, Swift, Suzaku, and XMM-Newton with 3C 273 and PKS 2155-304

On behalf of the International Astronomical Consortium for High Energy Calibration (IACHEC), we present results from the cross-calibration campaigns in 2012 on 3C 273 and in 2013 on PKS 2155-304 between the then active X-ray observatories Chandra, NuSTAR, Suzaku, Swift and XMM-Newton. We compare measured fluxes between instrument pairs in two energy bands, 1-5 keV and 3-7 keV and calculate an average cross-normalization constant for each energy range. We review known cross-calibration features and provide a series of tables and figures to be used for evaluating cross-normalization constants obtained from other observations with the above mentioned observatories.

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