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 similar to 2000 days after explosion, reaching a luminosity limit L-x similar to 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 similar to 10(41) erg s(-1), suggesting that the luminous X-ray emission L-x similar to 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 (theta > 30 degrees), 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-circle dot, 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 <(M) over dot> < 2 x 10(-5) M-circle dot 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.