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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 250328A: SVOM detection of a burst
  2. FRB 20250316A: FTW optical observations
  3. LIGO/Virgo/KAGRA S250328ae: NED Galaxies in the 4-Update Localization Volume
  4. EP250302a: SPI-ACS/INTEGRAL Upper Limit
  5. GRB 250327B: CrAO and SAO RAS Optical Observations
  6. GRB 250327B: OHP/T193 spectroscopic observations and redshift confirmation
  7. GRB 250327B: further optical observations by LCOGT
  8. EP250315a: Pan-STARRS r and i-band imaging and photometry
  9. GRB 250327b: Liverpool Telescope optical observations
  10. GRB 250322A: GRANDMA/TNOT optical upper limits
  11. LIGO/Virgo/KAGRA S250328ae: Updated Sky localization
  12. GRB 250327A: SVOM/VT upper limits on the XRT position
  13. LIGO/Virgo/KAGRA S250328ae: Identification of a GW compact binary merger candidate
  14. GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  15. GRB 250327B: Las Cumbres optical counterpart detection
  16. GRB 250327B: Swift-XRT detection of the X-ray afterglow
  17. GRB 250327B: 1.6m Mephisto optical observations
  18. GRB 250327B: NOT spectroscopic redshift z = 3.035
  19. GRB 250327A: Swift-XRT refined Analysis
  20. GRB 250327B: GOTO optical counterpart detection
  21. GRB 250327B: SVOM/VT optically bright counterpart
  22. GRB 250327B: SAO RAS optical candidate
  23. GRB 250327B: SVOM detection of a burst
  24. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  25. FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
  26. GRB 250327A: J-band observations with WINTER
  27. GRB 250327A: SVOM/VT optical candidate
  28. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  29. GRB 250327A: Fermi GBM observation
  30. Fermi GRB 250327A: Global MASTER-Net observations report
  31. Swift GRB 250327A: Global MASTER-Net observations report
  32. GRB 250327A: DDOTI Optical Observations
  33. GRB 250327A: COLIBRÍ optical upper limit
  34. GRB 250327A: Swift detection of a burst
  35. GRB 250327A: Fermi GBM Final Real-time Localization
  36. Fermi trigger No 764700395: Global MASTER-Net observations report
  37. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  38. Konus-Wind detection of GRB 250322A (short)
  39. IPN triangulation of GRB 250322B
  40. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  41. EP250321a: Mondy AZT-33IK Continued Optical Observations
  42. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  43. GRB 250322A: third epoch of NOT optical observations
  44. GRB 250322A: Swift-BAT refined analysis
  45. The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source
  46. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  47. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  48. GRB 250322A: further NOT optical observations
  49. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  50. GRB 250322A: Swift/UVOT Upper Limits
  51. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  52. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  53. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  54. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  55. GRB 250321B: Swift-XRT observations
  56. GRB 250322A: Swift-XRT refined Analysis
  57. EP250321a: TNOT Observation of Optical Counterpart
  58. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  59. GRB 250322A: Gemini-North redshift of candidate host galaxy
  60. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  61. SVOM/sb25032302: SVOM detection of a long X-ray transient
  62. GRB 250322A: AstroSat CZTI detection of a short burst
  63. GRB 250322B: AstroSat CZTI detection of a bright long burst
  64. GRB250322A: STEP/T80S optical limits
  65. GRB 250322A: Gemini-South optical observations
  66. GRB 250322A: VLT optical observations
  67. GRB 250322A: VLT near-infrared observations
  68. FRB 250316A: DDOTI Continued Optical Observations
  69. GRB 250322A: NOT optical upper limits
  70. GRB 250322A: Enhanced Swift-XRT position
  71. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  72. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  73. GRB 250322A: MASTER optical observation
  74. EP250321a: Liverpool Telescope optical follow-up
  75. EP250321a: Mondy AZT-33IK Optical Observations
  76. GRB 250322A: Swift detection of a short burst
  77. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  78. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  79. EP250321a: KAIT optical observations
  80. EP250321A: COLIBRÍ Continuing Optical Observations
  81. GRB 250225B: GECAM-A detection
  82. GRB 250312A: GECAM-A detection
  83. GRB 250321B: Swift ToO observations
  84. EP250321a: WFST optical observations
  85. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  86. GRB 250321C: Fermi GBM Final Real-time Localization
  87. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  88. GRB 250320B: Fermi GBM Observation
  89. EP250321a: Xinglong 216 decaying optical observations
  90. GRB 250321A: Swift-BAT refined analysis
  91. GRB 250321A: Swift-XRT refined Analysis
  92. GRB 250320B: Fermi-LAT detection
  93. GRB 250321B: SVOM detection of a sub-threshold transient event
  94. EP250321a: SVOM/VT optical observation
  95. EP 250321A: Optical counterpart detection by LCO.
  96. EP250321a: Kinder optical follow-up observations
  97. GRB 250321A: Swift/UVOT Upper Limits
  98. GRB 250320B: SVOM/GRM observation of a long burst
  99. EP250321a: LCO optical counterpart detection
  100. EP250321a: Swift-XRT detection of an X-ray source

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