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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
  1. Fermi GRB 230603A: Global MASTER-Net observations report
  2. Fermi trigger No 707039690: Global MASTER-Net observations report
  3. GRB 230506B: Chandra localization of the X-ray afterglow
  4. ZTF and GIT Observations of the Candidate Optical Afterglow AT2023jxk
  5. GRB 230606A: Swift-BAT refined analysis
  6. GRB 230606A: Gaoyazi/GOT optical upper limit
  7. GRB 230606A: Fermi GBM Observation
  8. GRB 230606A: BOOTES-5/JGT optical upper limit
  9. LIGO/Virgo/KAGRA S230602ap: Zwicky Transient Facility observations
  10. GRB 230606A: Swift-XRT refined Analysis
  11. GRB 230604A: GRBAlpha detection
  12. GRB 230606A: Swift/UVOT Upper Limits
  13. LIGO/Virgo S230606z: Global MASTER-Net observations report
  14. GRB 230606A: Enhanced Swift-XRT position
  15. LIGO/Virgo S230606d: Global MASTER-Net observations report
  16. LIGO/Virgo/KAGRA S230606d: Identification of a GW compact binary merger candidate
  17. GRB 230606A: Swift detection of a burst
  18. Fermi-LAT gamma-ray observations of IceCube-230603A
  19. LIGO/Virgo/KAGRA S230605o: Updated Sky localization
  20. IceCube-230603A: Upper limits from a search for additional neutrino events in IceCube
  21. LIGO/Virgo/KAGRA S230601bf: Updated Sky localization
  22. Super-Kamiokande: Neutrino search for SN2023ixf
  23. GRB 230604A: AstroSat CZTI detection of a short GRB
  24. LIGO/Virgo/KAGRA S230605o: Identification of a GW compact binary merger candidate
  25. LIGO/Virgo S230605o: Global MASTER-Net observations report
  26. LIGO/Virgo S230604z: Global MASTER-Net observations report
  27. IceCube-230603A - IceCube observation of a high-energy neutrino candidate track-like event
  28. GRB 230603A: Fermi GBM Final Real-time Localization
  29. LIGO/Virgo S230603aa: Global MASTER-Net observations report
  30. LIGO/Virgo S230602ap: Global MASTER-Net observations report
  31. LIGO/Virgo/KAGRA S230518h: Upper limits from a two-week IceCube neutrino search
  32. GRB 230521A: VZLUSAT-2 detection
  33. GRB 230522A: GRBAlpha and VZLUSAT-2 joint detection
  34. LIGO/Virgo S230601bf: Global MASTER-Net observations report
  35. LIGO/Virgo/KAGRA S230601bf: Identification of a GW compact binary merger candidate
  36. LIGO/Virgo S230531f: Global MASTER-Net observations report
  37. GRB 230525A: CALET Gamma-Ray Burst Monitor detection
  38. LIGO/Virgo/KAGRA S230529ay: Zwicky Transient Facility observations
  39. LIGO/Virgo/KAGRA S230528a: Zwicky Transient Facility observations
  40. LIGO/Virgo/KAGRA S230527ch: Zwicky Transient Facility observations
  41. LIGO/Virgo/KAGRA S230529ay: Upper limits from CALET observations.
  42. LIGO/Virgo/KAGRA S230529ay: AstroSat CZTI non-detection and upper limits
  43. LIGO/Virgo S230529ay: Global MASTER-Net observations report
  44. LIGO/Virgo/KAGRA S230529ay: upper limits from AGILE/MCAL
  45. LIGO/Virgo/KAGRA S230529ay: Coverage and upper limits from MAXI/GSC observations
  46. LIGO/Virgo/KAGRA S230529ay: Upper limits from Fermi-GBM Observations
  47. LIGO/Virgo/KAGRA S230529ay: Updated Sky localization and EM Bright Classification
  48. LIGO/Virgo/KAGRA S230529ay: No counterpart candidates in INTEGRAL SPI-ACS prompt observation
  49. LIGO/Virgo/KAGRA S230529ay: Identification of a GW compact binary merger candidate
  50. LIGO/Virgo S230529p: Global MASTER-Net observations report
  51. GRB 230529A: Fermi GBM Final Real-time Localization
  52. Alert from the HAWC Burst Monitor HAWC-230527A
  53. LIGO/Virgo S230525a: Global MASTER-Net observations report
  54. LIGO/Virgo/KAGRA S230518h: Updated Sky localization
  55. LIGO/Virgo/KAGRA S230520ae: Updated Sky localization
  56. Fermi-LAT gamma-ray observations of IceCube-230524A
  57. LIGO/Virgo/KAGRA S230518h: Upper limits from Glowbug gamma-ray observations
  58. GRB 230510A: Swift-BAT refined analysis
  59. GRB 230525A: Fermi GBM Detection
  60. LIGO/Virgo/KAGRA S230518h: TESS observations of the localization region
  61. GRB 230525A: Fermi GBM Final Localization
  62. IceCube-230524A: Upper limits from a search for additional neutrino events in IceCube
  63. GRB 230523B: GRBAlpha detection
  64. GRB 230524A: Fermi GBM Observation
  65. IceCube Alert 230524.47: Global MASTER-Net observations report
  66. LIGO/Virgo/KAGRA S230518h: No transient candidates in CALET observations
  67. LIGO/Virgo/KAGRA S230524x: Retraction of GW compact binary merger candidate
  68. IceCube-230524A - IceCube observation of a high-energy neutrino candidate track-like event
  69. GRB 230524B: AstroSat CZTI detection
  70. GRB 230524A: AstroSat CZTI detection
  71. GRB 230524A: AGILE detection
  72. Fermi trigger No 706610076: Global MASTER-Net observations report
  73. LIGO/Virgo S230524b: Global MASTER-Net observations report
  74. GRB 230524A: Fermi GBM Final Real-time Localization
  75. Fermi trigger No 706599831: Global MASTER-Net observations report
  76. Fermi trigger No 706536788: Global MASTER-Net observations report
  77. LIGO/Virgo/KAGRA S230521k: MASTER new OT discovery
  78. GRB 230523B: Name correction from GCN Circular 33859
  79. GRB 230523A: Swift/BAT-GUANO detection of a short hard burst
  80. LIGO/Virgo/KAGRA S230521k: Additional candidates from Zwicky Transient Facility
  81. Fermi Gamma-ray Burst Monitor trigger 706536788/230523509 is not a GRB
  82. GRB 230523A: Fermi GBM Final Real-time Localization
  83. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-230523A
  84. LIGO/Virgo S230522n: Global MASTER-Net observations report
  85. LIGO/Virgo S230522a: Global MASTER-Net observations report
  86. LIGO/Virgo/KAGRA S230522n: Upper limits from IceCube neutrino search
  87. LIGO/Virgo/KAGRA S230518h: Swift/UVOT Upper Limits for MeerLICHT candidates: AT2023ixg and AT2023iyb
  88. LIGO/Virgo/KAGRA S230522a: 2 counterpart neutrino candidates from IceCube neutrino searches
  89. LIGO/Virgo S230521k: Global MASTER-Net observations report
  90. # LIGO/Virgo/KAGRA S230521k: Zwicky Transient Facility observations
  91. GRB 230518B: VZLUSAT-2 detection
  92. Fermi Gamma-ray Burst Monitor trigger 706338208/230521211 is not a GRB
  93. LIGO/Virgo S230520ae: Global MASTER-Net observations report
  94. Fermi trigger No 706328428: Global MASTER-Net observations report
  95. IPN triangulation of GRB 230518A (short)
  96. Fermi trigger No 706331483: Global MASTER-Net observations report
  97. Fermi trigger No 706317104: Global MASTER-Net observations report
  98. GRB 230520A: CALET Gamma-Ray Burst Monitor detection
  99. GRB 230521A: Fermi GBM Final Real-time Localization
  100. LIGO/Virgo/KAGRA S230520ae: Identification of a GW compact binary merger candidate: End-to-End Test
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