Results from a Systematic Survey of X-Ray Emission from Hydrogen-poor Superluminous SNe

We present the results from a sensitive X-ray survey of 26 nearby hydrogen-poor superluminous supernovae (SLSNe-I) with Swift, Chandra, and XMM. This data set constrains the SLSN evolution from a few days until ~2000 days after explosion, reaching a luminosity limit L x ~ 10^(40) erg s^(−1) and revealing the presence of significant X-ray emission possibly associated with PTF 12dam. No SLSN-I is detected above L_x ~ 10^(41) erg s^(-1), suggesting that the luminous X-ray emission L_x ~ 10^(45) erg s^(−1) associated with SCP 60F6 is not common among SLSNe-I. We constrain the presence of off-axis gamma-ray burst (GRB) jets, ionization breakouts from magnetar engines and the density in the sub-parsec environments of SLSNe-I through inverse Compton emission. The deepest limits rule out the weakest uncollimated GRB outflows, suggesting that if the similarity of SLSNe-I with GRB/SNe extends to their fastest ejecta, then SLSNe-I are either powered by energetic jets pointed far away from our line of sight (θ > 30°), or harbor failed jets that do not successfully break through the stellar envelope. Furthermore, if a magnetar central engine is responsible for the exceptional luminosity of SLSNe-I, our X-ray analysis favors large magnetic fields B > 2 x 10^(14) G and ejecta masses M_(ej) > 3 M_⊙, in agreement with optical/UV studies. Finally, we constrain the pre-explosion mass-loss rate of stellar progenitors of SLSNe-I. For PTF 12dam we infer Ṁ < 2 x 10^(-5) M_⊙ yr^(-1), suggesting that the SN shock interaction with an extended circumstellar medium is unlikely to supply the main source of energy powering the optical transient and that some SLSN-I progenitors end their lives as compact stars surrounded by a low-density medium similar to long GRBs and type Ib/c SNe.