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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').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. GRB 250327A: Swift detection of a burst
  2. GRB 250327A: Fermi GBM Final Real-time Localization
  3. Fermi trigger No 764700395: Global MASTER-Net observations report
  4. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  5. Konus-Wind detection of GRB 250322A (short)
  6. IPN triangulation of GRB 250322B
  7. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  8. EP250321a: Mondy AZT-33IK Continued Optical Observations
  9. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  10. GRB 250322A: third epoch of NOT optical observations
  11. GRB 250322A: Swift-BAT refined analysis
  12. The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source
  13. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  14. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  15. GRB 250322A: further NOT optical observations
  16. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  17. GRB 250322A: Swift/UVOT Upper Limits
  18. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  19. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  20. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  21. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  22. GRB 250321B: Swift-XRT observations
  23. GRB 250322A: Swift-XRT refined Analysis
  24. EP250321a: TNOT Observation of Optical Counterpart
  25. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  26. GRB 250322A: Gemini-North redshift of candidate host galaxy
  27. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  28. SVOM/sb25032302: SVOM detection of a long X-ray transient
  29. GRB 250322A: AstroSat CZTI detection of a short burst
  30. GRB 250322B: AstroSat CZTI detection of a bright long burst
  31. GRB250322A: STEP/T80S optical limits
  32. GRB 250322A: Gemini-South optical observations
  33. GRB 250322A: VLT optical observations
  34. GRB 250322A: VLT near-infrared observations
  35. FRB 250316A: DDOTI Continued Optical Observations
  36. GRB 250322A: NOT optical upper limits
  37. GRB 250322A: Enhanced Swift-XRT position
  38. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  39. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  40. GRB 250322A: MASTER optical observation
  41. EP250321a: Liverpool Telescope optical follow-up
  42. EP250321a: Mondy AZT-33IK Optical Observations
  43. GRB 250322A: Swift detection of a short burst
  44. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  45. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  46. EP250321a: KAIT optical observations
  47. EP250321A: COLIBRÍ Continuing Optical Observations
  48. GRB 250225B: GECAM-A detection
  49. GRB 250312A: GECAM-A detection
  50. GRB 250321B: Swift ToO observations
  51. EP250321a: WFST optical observations
  52. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  53. GRB 250321C: Fermi GBM Final Real-time Localization
  54. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  55. GRB 250320B: Fermi GBM Observation
  56. EP250321a: Xinglong 216 decaying optical observations
  57. GRB 250321A: Swift-BAT refined analysis
  58. GRB 250321A: Swift-XRT refined Analysis
  59. GRB 250320B: Fermi-LAT detection
  60. GRB 250321B: SVOM detection of a sub-threshold transient event
  61. EP250321a: SVOM/VT optical observation
  62. EP 250321A: Optical counterpart detection by LCO.
  63. EP250321a: Kinder optical follow-up observations
  64. GRB 250321A: Swift/UVOT Upper Limits
  65. GRB 250320B: SVOM/GRM observation of a long burst
  66. EP250321a: LCO optical counterpart detection
  67. EP250321a: Swift-XRT detection of an X-ray source
  68. EP250321A: COLIBRÍ Optical Observations
  69. EP250321a: VLT/X-shooter redshift z = 4.368
  70. GRB 250320B: AstroSat CZTI detection
  71. EP250321a: REM optical/NIR afterglow detection
  72. Fermi GRB 250320B: Global MASTER-Net observations report
  73. EP250321a: BOOTES-5/JGT optical afterglow detection
  74. EP250321a: TRT optical counterpart detection
  75. EP250321a: Global MASTER-Net observations report
  76. Swift GRB 250321A: Global MASTER-Net observations report
  77. Fermi GRB 250321A: Global MASTER-Net observations report
  78. EP250321a: Einstein Probe detection of an X-ray transient
  79. GRB 250321A: GOTO optical upper limits
  80. GRB 250321A: Swift-XRT localisation
  81. GRB 250314A: Keck/NIRC2 J-band upper limit
  82. EP250226a/GRB 250226A: KAIT optical observations
  83. GRB 250321A: Fermi GBM Observation
  84. GRB 250321A: Swift detection of a burst
  85. GRB 250321A: Fermi GBM Final Real-time Localization
  86. GRB 250320B: Fermi GBM Final Real-time Localization
  87. GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
  88. GRB 250317B: Mondy AZT-33IK Continued Optical Observations
  89. GRB 250320A: Fermi GBM Final Real-time Localization
  90. Fermi GRB 250319B: Global MASTER-Net observations report
  91. FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
  92. GRB 250313A: GRBAlpha detection
  93. LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
  94. GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
  95. GRB 250319B: Fermi GBM Final Localization
  96. GRB 250319A: Fermi GBM Final Localization
  97. GRB 250317D: EIRSAT-1 GMOD Detection
  98. LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
  99. GRB 250314A: ATCA radio upper limits
  100. EP250302a: VLA observations

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